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Effects of exercise on platelet and aortic functions in aged rats
Abstract
To assess age- and exercise-related changes in platelet aggregation, we measured the magnitude of platelet aggregation with a four-channel aggregometer, plasma and aortic polyunsaturated fatty acids by gas chromatography and related prostanoids with a reagent kit in young and aged non-exercised and in aged exercised rats.
Platelet aggregation in platelet-rich plasma induced by ADP (5 microm) in the primary wave increased with age. In the non-exercised groups, the basal levels of thromboxane B2 in platelet-rich plasma increased in aged rats compared with young rats. In aged exercised rats, the basal levels of 6-keto-prostaglandin F1alpha in platelet-rich plasma were stimulated and those of thromboxane B2 were depressed, compared with non-exercised aged rats. The plasma levels of eicosapentaenoic acid and docosahexaenoic acid increased with age. Only aortic eicosapentaenoic acid in the aged group increased by exercise. In the aged non-exercised and exercised groups, the aortic, but not the plasma, levels of eicosapentaenoic acid correlated inversely with the basal levels of thromboxane B2 in platelet-rich plasma (r = -0.53, P < 0.05) and associated negatively with the magnitudes of platelet aggregation induced by ADP (5 microm) (r = -0.47, P < 0.05).
These findings suggest that exercise in aged rats increases aortic eicosapentaenoic acid concentrations, which in turn depress the basal levels of thromboxane, B2 in platelet-rich plasma to modulate platelet aggregation.
... Increased lean muscle Decreased triglycerides Lopez et al. 1975 Berg et al. 1997 Decreased cholesterol Decreased blood pressure Evenwel and Struyker-Boudier 1979; Overton et al. 1988 Paffenbarger et al. 1991 Decreased inflammation Kalani et al. 2006 Adamopoulos et al. 2001 Decreased platelet aggregation Tanaka et al. 2003 Rauramaa et al. 1986 Antidepressant Greenwood et al. 2003 Dimeo et al. 2001 168 Appl. Physiol. ...
Every rodent experiment is based on important parameters concerning the levels of caloric intake and physical activity. In many cases, these decisions are not made consciously, but are based on traditional models. For experimental models directed at the study of caloric intake and activity, the selection of parameters is usually aimed at modeling human conditions, the ultimate goal of which is to gain insight into the pathophysiology of the disease process in man. In each model, it is important to understand the influence of diet, exercise, and genetic background on physiology and the development of disease states. Along the continuum of energy intake from caloric restriction to high-fat feeding, and of energy output from total inactivity to forced exercise, a number of models are used to study different disease states. In this paper, we will evaluate the influence of the quantity and composition of diet and exercise in several animal models, and will discuss how each model can be applied to various human conditions. This review will be limited to traditional models using the rat as the experimental animal, and although it is not an exhaustive list, the models presented are those most commonly represented in the literature. We will also review the mechanisms by which each affects rat physiology, and will compare these to the analogous mechanisms in the modeled human disease state. We hope that the information presented here will help researchers make choices among the available models and will encourage discussion on the interpretation and extrapolation of results obtained from traditional and novel rodent experiments on diet, exercise, and chronic disease.
Objective: To observe the effect, of training on the content of plasma 6-keto-PGF1α and the TXB 2, and the PGI 2/TXA 2 balance in spontaneously hypertensive rats(SHR). Method: Male SHR are randomly divided into the control group and swimming exercises group. After 10 weeks of training, plasma TXB 2, 6-keto-PGF1α content and resting blood pressure level were measured. Result: Resting blood pressure level of exercise group obviously descended, plasma 6-keto-PGF1α, 6-keto-PGF1α/TXB 2 ascended obviously as compared with that of control group. Conclusion: Proper training can descend the resting blood pressure level of SHR, and obtain better balance between PGI 2 and TXA 2 to prevent developing of hypertension and thrombosis.
The purpose of this study was to measure the influence of 6 wk of omega 3 (600 mg EPA and 400 mg DHA per day) supplementation alone or in association with an antioxidant (30 mg vitamin E, 60 mg vitamin C and 6 mg β carotene per day) on resting and exercise-induced alteration in oxidation, antioxidant status and lipids in judoists (n = 37). Subjects were randomly assigned to three groups: placebo, omega 3, or omega 3 and antioxidant. Blood samples were collected in preexercise and postexercise conditions (judo-training session), both before and after the supplementation period. The following parameters were analyzed: α-tocopherol, retinol, lag phase , maximum rate of oxidation (Rmax), maximum amount of conjugated dienes (CDmax), nitric oxide (NO), malondialdehyde (MDA), lipoperoxides (LOOH) concentrations, salivary glutathione peroxidase activity, and the lipid profile. Dietary data were collected using a 7-day dietary record. A significant interaction effect between supplementation and time (p < .01) on triglycerides was noted at rest and after exercise, with resting values significantly lower in the omega 3 group after supplementation than in the placebo group. Significant interaction effects between supplementation and time (p < .05) on resting MDA, LOOH concentrations and Rmax were found, with elevated values in the omega 3 group after supplementation and no change in the placebo group's levels. The authors observed a significantly greater NO and lipid peroxidation (MDA, Rmax, CDmax, LOOH) increase with exercise in the omega 3 group than with placebo. The addition of antioxidants did not prevent the formation of oxidation products at rest. On the contrary, it seems that the combination of antioxidants added to the omega 3 supplements led to a decrease in LOOH, CDmax, Rmax and MDA concentrations after a judo training session. With the addition of antioxidants, the retinol and α-tocopherol significantly increased at rest and after the training session.
Cultured endothelial cells derived from human umbilical veins or bovine aorta produce a potent inhibitor of platelet aggregation. The inhibitor is synthesized from sodium arachidonate or or prostaglandin endoperoxides by a microsomal enzyme system. Tranylcypromine, a specific antagonist of prostacyclin synthetase, suppresses production of the inhibitor by endothelial cells. The inhibitor, which is ether extractable, has been identified using a two-step thin-layer radiochromatographic procedure and a synthetic prostaglandin I2 standard. With this procedure, we have shown that human and bovine endothelial cells convert sodium [3H]arachidonate to radiolabeled prostaglandin I2 and 6-keto-prostaglandin F1alpha, as wellas prostaglandin E2. Thus, endothelial cells may be non-thrombogenic in vivo because they synthesize and release prostaglandin I2, a potent inhibitor of platelet aggregation.
An unstable [t1/2 at 37 degrees = 32 +/- 2 (SD) sec] intermediate, thromboxane A2, was detected in the conversion of prostaglandin G2 into 8-(1-hydroxy-3-oxopropyl)-9,12L-dihydroxy-5,10-heptadecadienoic acid (thromboxane B2) in platelets. The intermediate was trapped by addition of methanol, ethanol, or sodium azide to suspensions of washed human platelets incubated for 30 sec with arachidonic acid or prostaglandin G2. The structures of the resulting derivatives demonstrated that the intermediate possessed an oxane ring as in thromboxane B2 but lacked its hemiacetal hydroxyl group. Additional experiments using 18O2 or [2H8]arachidonic acid in the formation of thromboxane B2 and CH3O2H for the trapping of thromboxane A2, together with information on the t1/2 of the intermediate, indicated the presence of an oxetane structure in thromboxane A2. Incubation of arachidonic acid or prostaglandin G2 with washed platelets led to formation of an unstable factor that induced irreversible platelet aggregation and caused release of [14C]serotonin from platelets that had been incubated with [14C]serotonin. The properties and the mode of formation of this factor indicated that it was identical with thromboxane A2. Furthermore, evidence is presented that the more unstable and major component of rabbit aorta contracting substance (RCS) formed in platelets and guinea pig lung is also thromboxane A2.
Conventional techniques for the determination of fatty acid composition of lipids require solvent extraction, purification, hydrolysis, and derivatization procedures that are both lengthy and cumbersome. A 1-hr direct transesterification procedure carried out in methanol-benzene 4:1 with acetyl chloride circumvented all these steps and was applicable for analysis of both simple (triglycerides) and complex lipids (cholesteryl esters, phospholipids, and sphingomyelin). Recoveries (greater than 95%) of standards unaffected by the presence of 5% water and 200 mg of silica suggested that the technique could be used for the quantitative analysis of total fatty acids as well as of fatty acids in classes of lipids separated on silica from biological samples. When compared to the Folch procedure, the technique led to a 20.1% increase in total fatty acids for plasma, 3.9% for feces, 7.4% for bile, and 9.7% for rat liver. We therefore conclude that this one-step direct transesterification procedure is superior to currently used methods, not only because of its simplicity and speed, but also because of its added precision.
To study the effects of physical exercise on biochemical risk factors for ischaemic heart disease 31 healthy middle aged men undertook regular physical exercise for two months and 29 served as controls in a randomised trial. In the men taking regular exercise serum cholesterol concentrations increased 26% more in the high density lipoprotein subfraction two (HDL2) and decreased 31% more in the subfraction three (HDL3) and 9% more in the low density lipoprotein fraction than in the control group. A tendency towards increased plasma 6-keto-prostaglandin F1 alpha concentration and decreased serum thromboxane B2 concentration was found during the period of regular exercise, but prostaglandin E2 concentrations remained unchanged. The increase in plasma 6-keto-prostaglandin F1 alpha concentration was associated with an increase in serum HDL2 cholesterol concentration in the group taking regular exercise. Our data suggest that mild regular physical exercise favourably influences cholesterol distribution in serum lipoproteins in healthy middle aged men and may have beneficial effects on circulating metabolites of arachidonic acid.
The antithrombotic effect of long-term aerobic exercise was studied in rat cerebral blood vessels using an argon (Ar) laser-induced thrombosis technique. Rats were subjected to treadmill exercise at 70% VO2max for 2 and 4 months. The number of laser irradiations required to form an occlusive thrombus in the exercise group was significantly increased compared to that of the control group after 2- and 4-month training periods. Fibrinolytic activity increased just after exercise but there was no significant difference between the exercise and the control group in the resting state after a period of exercising conditioning. The results demonstrated that long-term aerobic exercise decreased the thrombotic tendency in rat cerebral vessels and suggested that such exercise might have a protective effect on these blood vessels.
In a study of the relationship between thrombocytopenia and increased vascular fragility, changes in the endothelium of capillaries and postcapillary venules of the tongue were examined by electron microscopy. Adult male albino rabbits (4 kg) were maintained thrombocytopenic (platelets less than 20,000/cu mm) up to 24 hr by one to three injections of guinea pig antirabbit platelet serum. Within 6 hr the normal projections and folds of the lumenal surface of the endothelial surface were largely effaced. In addition, the endothelium became thinner. In places, pores and membranous diaphragms were observed. Endothelial junctions appeared normal. Identical findings were observed if rabbits were made thrombocytopenic by administration of intraperitoneal busulfan. Intravenously administered Thorotrast was observed in endothelial cells and in the extravascular spaces within 3 min after injection into thrombocytopenic animals, while it was seen only intravascularly in control rabbits. With the spontaneous restoration of circulating platelets, the endothelium reverted to normal.
During the 1960s it was observed that certain long-chain saturated or unsaturated fatty acids induced aggregation of washed human platelets, but the physiological significance of this phenomenon was questioned [44].
The vascular endothelium and, especially, the pulmonary endothelium play the important metabolic role in activation (e.g., angiotensin I) and inactivation (e.g., bradykinin, 5-hydroxytryptamine, catecholamines, nucleotides) of circulating hormones and autacoids [120]. Apart from its metabolic function the endothelium also acts as a generator of two powerful mediators: prostacyclin [34, 84] and endothelium-derived relaxing factor (EDRF) [29]. In contrast with “classical” mediators prostacyclin (t 1/2 = approx 4 min) [12, 34] and EDRF (t 1/2 = approx 6 s) [16, 32] are highly labile. Prostacyclin is one of the products of cyclo-oxygenation of arachidonic acid, while the chemical structure of EDRF remains unknown. Both these mediators are released from the endothelium by similar stimuli, including agonists of muscarinic and serotonin receptors, thrombin, bradykinin and calcium ionophore A 23 187 [36]. Lipid peroxides and oxygen free radicals are the decisive factors in either suppression of the generation or termination of the action of these mediators [34, 37, 121].
Six men (X = 27.3 yr) ran at 60%, 70% and 80% of maximal oxygen consumption on separate days for 30 minutes to determine exercise intensity effects on 6-keto-PGF1α, TXB2, and 6-keto-PGF1α/TXB2 ratios. At rest, 6-keto-PGF1α was 384 ± 68.3 pg/ml; TXB2 was 147 ± 55.6 pg/ml; and the 6-keto-PGF1α/TXB2 ratio was 4.63 ± 1.3. After exercise at 60%, 70%, and 80% TXB2 increased to 523.2 ± 117.5, 611.7 ± 155.4∗ and 643.8 ± 121.7∗ pg/ml, respectively (∗p < .05). Post-exercise ratios tended to be inversely related to exercise intensity; however, no statistically significant differences were found between these values. These data suggest that exercise-induced increases in TXB2 may be related to intensity.
Young exercised rats with a diminished weight gain had a decrease in high density lipoprotein (HDL) cholesterol and phospholipid levels in the plasma and augmented free cholesterol and phosphatide in the aorta. When the weight gain in the trained rats paralleled the gain in non-exercised animals, the values of these lipids were not altered. The levels of aortic free cholesterol in the non-exercised and exercised groups were inversely associated with concentrations of HDL-cholesterol, but were not related to the activities of lecithin cholesterol acyltransferase. In addition, the total cholesterol and phospholipid contents in the aorta negatively correlated with HDL-cholesterol concentrations. We propose that in young exercised rats with a diminished weight gain, the removal of aortic lipids is hampered due to a reduction in HDL-cholesterol.
Bleeding time was determined before (BTo) and after ingestion of 1 (BT1), 3.5 (BT3.5) and 25 (BT25) mg acetyl-salicylic acid (ASA)/kg in 50 men and 20 women of varying age. It was found that BT falls with age in men maybe due to a reduction in PGI2/TXA2 ratio. The changes in bleeding time could be abolished by ASA ingestion. The index Ia = (BT25-BTo)/BT25 increased with age in both men and women. While all age groups increased bleeding time upon administration of a small dose of aspirin only in the younger age groups did the bleeding time thereafter fall significantly, when the dose was increased to 25 mg/kg.
The influence of age on platelet lipid peroxide (LPO), platelet membrane fluidity and the composition of fatty acid was investigated in female Wistar rats widely ranging in age from 14 to 720 days old. LPO levels were significantly higher (p < 0.05) in the platelets of upper age groups than in those of lower age groups, showing a significantly positive correlation with age (r = 0.84, p < 0.0001). Membrane fluidity, assessed by 1,6-diphenyl-1,3,5-hexatriene (DPH) fluorescence polarization, was significantly reduced with age. The composition of fatty acid demonstrated an age-related elevation (p < 0.05) in the unsaturation index. The rises in the LPO levels revealed a significantly positive correlation with DPH-polarization (r = 0.73, p < 0.0001). Thus our results suggested that the age-related deterioration of platelet membrane fluidity, despite a significant elevation in the unsaturation index, was due to the age-related higher basal levels of LPO in platelets.
In human platelet-rich plasma (PRP) eicosapentaenoic acid (EPA) inhibited platelet aggregation induced by a stable analogue of PGH2 (U46619), arachidonic acid, collagen or ADP. EPA was more potent than oleic, linoleic, α-linolenic or γ-linolenic acids. In aspirin-treated platelets, aggregation induced by U46619 was inhibited to a similar extent by arachidonic acid or by EPA over a range of concentrations of 0.05–0.3 mM. EPA incubated with PRP did not induce the generation of a thromboxane (TXA)-like activity; indeed it prevented the formation of TXA2 induced by arachidonic acid or by collagen. The anti-aggregatory activity of EPA was not influenced by inhibitors of cyclo-oxygenase and lipoxygenase. The anti-aggregatory action of EPA may be caused by a rapid occupancy by EPA of TXA2/PGH2 “receptors” on platelet membrane as well as by a slower displacement of arachidonic acid from platelet phospholipids by chemically unchanged molecules of EPA.Not all samples of PRP were irreversibly aggregated by PGH2, but in those that were, PGH3 also induced an immediate dose-dependent but reversible aggregation. After a 4 min incubation of non-aggregating doses of PGH2 or PGH3 (100–300 nM) with PRP a stable anti-aggregatory compound was detected. The inhibitory activity produced from PGH3 was apparently more potent (ca 10 times) than that obtained from PGH2. The anti-aggregating compounds were identified by TLC and GLC-MS as PGD2 and PGD3. The apparent difference of potency between PGD2 and PGD3 was attributed to the concurrent production of PGE2 and PGE3. PGE2 prevented the inhibitory effect of PGD2 whereas PGE3 did not affect the activity of PGD3.It is concluded that one of the reasons for the low incidence of myocardial infarction in Eskimos could be that the pro-aggregatory arachidonic acid is replaced in their phospholipids by the anti-aggregatory EPA.
Studies from our laboratory have suggested a role for ferrous iron in the metabolism of arachidonic acid and demonstrated that inhibitors of prostaglandin synthesis exert their effect by complexing with the heme group of cyclooxygenase. Docosahexaenoic acid (DHA) is a potent competitive inhibitor of arachidonic acid metabolism by sheep vesicular gland prostaglandin synthetase. In this study we have evaluated the effect of exogenously added DHA on platelet function and arachidonic acid metabolism. DHA at 150 μM concentration inhibited aggregation of platelets to 450 μM arachidonic acid. At this concentration DHA also inhibited the second wave of the platelet response to the action of agonists such as epinephrine, adenosine diphosphate and thrombin. Inhibition induced by this fatty acid could be overcome by the agonists at higher concentrations. DHA inhibited the conversion of labeled arachidonic acid to thromboxane by intact, washed platelet suspensions. However, platelets in plasma incubated first with DHA then washed and stirred with labeled arachidonate generated as much thromboxane as control platelets. These results suggest that the polyenoic acids, if released in sufficient quantities in the vicinity of cyclooxygenase, could effectively compete for the heme site and inhibit the conversion of arachidonic acid.
Plasma β-thromboglobulin (βTG) was measured by radioimmunoassay in 219 healthy subjects age range (12–103), arbitrarily dividied into 3 groups: 127 young, 35 middle aged and 57 old. In 73 of the subjects, plasma platelet factor 4 (PF4) level was also determined by RIA. Plasma βTG (mean 33.9ng/ml), range 3–95) and PF4 (mean 15.2 ng/ml, range 6.62–50) levels increased with age with a significant difference between the mean plasma level of the 3 groups. In addition there was a significant sex difference in old females compared to old males. A significant correlation between the 2 proteins was found in each of the 3 groups of subjects and in the whole group suggesting that both proteins are released in vivo from the same pool and presumably at the same rate. Our results indicate that in vivo platelet activation and “release reaction” is significantly enhanced in old and middle aged subjects compared to young suggesting abnormal hemostatic mechanisms in these individuals. This enhanced platelet activity may reflect a prethrombotic state.
Prostacyclin (PGX) strikingly increases cyclic AMP concentrations in human platelets. Prostacyclin is approximately 10 times more active than PGD2, 30 times more active than PGE1 and more than 1000 times more active than its stable end product, 6-oxo-PGF1alpha. These results correlate well with the anti-aggregating activity of prostacyclin, compared with PGE1 and PGD2.
This article has no abstract; the first 100 words appear below.
PROSTAGLANDINS are potent vasoactive agents with a wide variety of other actions that depend on the species and organ tested and the prostaglandin used. They are synthesized from 20-carbon polyunsaturated fatty acids containing three, four or five double bonds. These fatty acids are present in the phospholipids of the cell membranes of all mammalian tissues. The main precursor of prostaglandins in man is eicosatetraenoic or arachidonic acid (four double bonds), which gives rise to the prostaglandins (PG's) containing two double bonds (PGE2, PGF2α, PGD2, prostacyclin and thromboxane A2). PGE2 and PGF . . .
Source Information
From the Department of Prostaglandin Research, Wellcome Research Laboratories, Langley Court, Beckenham, Kent BR3 3BS, U.K., where reprint requests should be addressed to Dr. Moncada.
PROSTACYCLIN (PGI2) is generated by vascular walls from arachidonic acid or prostaglandin endoperoxides1. It is the most potent inhibitor of platelet aggregation so far described, and acts by increasing cyclic AMP in the platelets2,3, presumably through adenyl cyclase stimulation. The enzyme which synthesises prostacyclin is concentrated in the endothelial lining of the vessels4; clearly, platelets could be prevented from clumping onto the walls of healthy vessels by the generation of prostacyclin5. Unlike prostaglandin E2 or F 2α, prostacyclin is not inactivated as it passes through the pulmonary circulation6,7, and in dog lungs, in vivo, prostacyclin is the major metabolite generated during an infusion of arachidonic acid 8. In the preceding paper, Gryglewski et al.9 conclude that prostacyclin is continuously generated by and released from cat lungs in vivo. We report here that we have confirmed this conclusion in a different species (rabbits) by the use of an antiserum which cross-reacts with prostacyclin and neutralises its anti-aggregating activity10. This antiserum (PGI2 antiserum) was raised in rabbits using a stable analogue of prostacyclin, 5,6-dihydro-prostacyclin (PGI1), as the hapten, conjugated to bovine serum albumin10.
VASCULAR walls generate from prostaglandin endoperoxides or arachidonic acid an anti-aggregatory and a vasodilator substance, prostacyclin (PGI2)1,2. Several prostaglandins are rapidly inactivated as they traverse the pulmonary circulation3 but prostacyclin passes through unchanged4,5. We report here that prostacyclin is continuously generated by the lungs in vivo or in vitro. Clearly, such an endocrine-like function of the lungs could play an important part in the natural resistance of the organism against intra-arterial thrombosis.
Microsomes prepared from rabbit or pig aortas transformed endoperoxides (PGG2 or PGH2) to an unstable substance (PGX) that inhibited human platelet aggregation. PGX was 30 times more potent in this respect than prostaglandin E1. PGX contracted some gastrointestinal smooth muscle and relaxed certain isolated blood vessels. Prostaglandin endoperoxides cause platelet aggregation possibly through the generation by platelets of thromboxane A2. Generation of PGX by vessel walls could be the biochemical mechanism underlying their unique ability to resist platelet adhesion. A balance between formation of anti- and pro-aggregatory substances by enzymes could also contribute to the maintenance of the integrity of vascular endothelium and explain the mechanism of formation of intra-arterial thrombi in certain physiopathological conditions.
Prostaglandin (PG) endoperoxides (PGG2 and PGH2) contract arterial smooth muscle and cause platelet aggregation. Microsomes from pig aorta, pig mesenteric arteries, rabbit aorta and rat stomach fundus enzymically transform PG endoperoxides to an unstable product (PGX) which relaxes arterial strips and prevents platelet aggregation. Microsomes from rat stomach corpus, rat liver, rabbit lungs, rabbit spleen, rabbit brain, rabbit kidney medulla, ram seminal vesicles as well as particulate fractions of rat skin homogenates transform PG endoperoxides to PGE- and PGF- rather than to PGX-like activity. PGX differs from the products of enzymic transformation of prostaglandin endoperoxides so far identified, including PGE2, F2alpha, D2, thromboxane A2 and their metabolites. PGX is less active in contracting rat fundic strip, chick rectum, guinea pig ileum and guinea pig trachea than are PGG2 and PGH2. PGX does not contract the rat colon. PGX is unstable in aqueous solution and its antiaggregating activity disappears within 0.25 min on boiling or within 10 min at 37degrees C. As an inhibitor of human platelet aggregation induced in vitro by arachidonic acid PGX was 30 times more potent than PGE1. The enzymic formation of PGX is inhibited by 15-hydroperoxy arachidonic acid (IC50 = 0.48 mug/ml), by spontaneously oxidised arachidonic acid (IC 50 less than 100 mug/ml) and by tranylcypromine (IC50 = 160 mug/ml). We conclude that a balance between formation by arterial walls of PGX which prevents platelet aggregation and release by blood platelets of prostaglandin endoperoxides which induce aggregation is of the utmost importance for the control of thrombus formation in vessels.
MALES stand at risk in many pathological states1, especially cardiovascular disease, in which there is a statistically significant higher mortality in men than women2. We have described3 a sex difference in platelet responsivity in rats and guinea pigs where platelets from males were significantly more sensitive to aggregating stimuli than those from females. Increased platelet responsiveness has been detected in humans,in thromboembolic disease4 and after acute myocardial infarction5. Indeed, the principal post mortem finding in subjects who died suddenly is occlusion in the pulmonary circulation due to platelet aggregation6. We have suggested3 that platelet sensitivity is mediated by the androgenic steroids and that androgens contribute to the incidence of thrombotic disease.
In a study of the relationship between thrombocytopenia and increased vascular fragility, changes in the endothelium of capillaries and postcapillary venules of the tongue were examined by electron microscopy. Adult male albino rabbits (4 kg) were maintained thrombocytopenic (platelets less than 20,000/cu mm) up to 24 hr by one to three injections of guinea pig antirabbit platelet serum. Within 6 hr the normal projections and folds of the lumenal surface of the endothelial surface were largely effaced. In addition, the endothelium became thinner. In places, pores and membranous diaphragms were observed. Endothelial junctions appeared normal. Identical findings were observed if rabbits were made thrombocytopenic by administration of intraperitoneal busulfan. Intravenously administered Thorotrast was observed in endothelial cells and in the extravascular spaces within 3 min after injection into thrombocytopenic animals, while it was seen only intravascularly in control rabbits. With the spontaneous restoration of circulating platelets, the endothelium reverted to normal.
Six men (X = 27.3 yr) ran at 60%, 70% and 80% of maximal oxygen consumption on separate days for 30 minutes to determine exercise intensity effects on 6-keto-PGF1 alpha, TXB2, and 6-keto-PGF1 alpha/TXB2 ratios. At rest, 6-keto-PGF1 alpha was 384 +/- 68.3 pg/ml; TXB2 was 147 +/- 55.6 pg/ml; and the 6-keto-PGF1 alpha/TXB2 ratio was 4.63 +/- 1.3. After exercise at 60%, 70%, and 80% TXB2 increased to 523.2 +/- 117.5, 611.7 +/- 155.4*, and 643.8 +/- 121.7* pg/ml, respectively (*p less than .05). Post-exercise ratios tended to be inversely related to exercise intensity; however, no statistically significant differences were found between these values. These data suggest that exercise-induced increases in TXB2 may be related to intensity.
The body can adjust to a variety of stressors (physical activity, environmental, emotional, etc.) that are known to disrupt normal homeostatic conditions. Specific metabolic and physiological adaptations are required for both acute and chronic stimuli. The sympathoadrenal system is essential for such adjustments as they control and regulate a number of key bodily functions. In response to an acute bout of exercise, both central and peripheral alterations are elicited. The extent of these responses is dependent upon exercise intensity, duration, and tissue specificity. Further, endurance training results in adaptations that are tissue specific and enhance the ability for the maintenance of exercise energetics. While a number of markers are frequently used to assess the involvement of the sympathoadrenal response (plasma and tissue norepinephrine and epinephrine levels), it is important to examine more specific variables such as rates of turnover, synthesis and removal, and activity of key enzymes related to catecholamine metabolism.
To investigate the functional alteration of human aortic endothelial cells with aging, prostacyclin synthesis was qualitatively and quantitatively examined. The endothelial cells of human aortas and umbilical veins or inferior vena cavae were immunohistochemically examined and found positive for prostacyclin, but the intensity of aortic endothelial cells from older subjects was low. In addition to the endothelial cells, smooth muscle cells in the thickened intima, not the media, of the aorta were also immunoreactive. Endothelial cells were successfully cultured from human aortas obtained from infants through aged subjects and were subdivided into three groups: young, middle, and old. Prostacyclin synthesis by endothelial cells from all types of blood vessels was extremely great at the primary culture, but decreased abruptly in the following subcultures. Among the aortic endothelial cells, the young group synthesized the largest amount of prostacyclin in a conventional culture condition, with synthesis progressively decreasing in the older groups. The in vitro prostacyclin biosynthesis was supported by the qualitative analysis on the tissue sections. These results indicate that prostacyclin synthesis of the aortic endothelial cells decreases with age, but intimal smooth muscle cells potentially have a back-up mechanism and substitute this synthesis to some extent. The decreased synthesis of prostacyclin with age may play an important role in the development and advancement of thrombosis and atherosclerosis.
Some investigators have speculated that a decrease in prostacyclin production observed during ageing of endothelial cells is caused by an increase in intracellular lipid peroxide. We checked this speculation using an in vitro model to study the ageing of human vascular endothelial cells. For this purpose we determined the levels of intracellular lipid peroxide of endothelial cells at various culture ages, and found that the level of intracellular lipid peroxidation did not increase during in vitro ageing. Amounts of intracellular lipid peroxide also differed depending on the growth phase, the addition of heparin and the strain of endothelial cells, but the cells producing prostacyclin at a low level did not necessarily contain larger amounts of intracellular lipid peroxide. Therefore, we postulate that the age-related decrease in prostacyclin production is not due to an increase in the amount of intracellular lipid peroxide as a function of age.
The effects of exercise and exercise conditioning on blood platelet function were investigated in six healthy individuals who had not engaged in regular exercise for at least 1 yr prior to the study. The subjects (three men and three women) had a mean age of 28 (range 23-32) and participated in a supervised program of treadmill exercise. Subjects exercised for 20 min, three times weekly, for 12 wk at 70-80% of estimated maximum heart rate. Samples for platelet counts, platelet aggregation, and plasma beta-thromboglobulin (beta-TG) were obtained prior to training and after 6 and 12 wk of training. All subjects responded with an increase in aerobic capacity during training. Resting mean systolic and diastolic blood pressures decreased after training (P less than 0.05). Platelet counts increased after exercise, and the increment in week 12 exceeded that in the 1st wk by 57%. Platelet aggregation studies in platelet rich plasma (PRP) showed an increase in slope after exercise (week 1, P less than 0.05) which decreased with training (week 1 vs week 12, P less than 0.01). Aggregation studies utilizing impedance aggregometry in diluted native whole blood showed an acceleration of both spontaneous aggregation (P less than 0.01 weeks 6 and 12) and aggregation using epinephrine as an agonist (P less than 0.05) following exercise. Plasma beta-TG levels did not increase significantly after exercise; however, resting concentrations of beta-TG decreased with training (P less than 0.03).(ABSTRACT TRUNCATED AT 250 WORDS)
Blood platelet activity increases with advancing age. This study was designed to determine if changes in a key signal-transducing mechanism in the platelet, phosphoinositide turnover, are associated with the enhanced platelet activity seen in aging.
Platelets were harvested from a total of 40 healthy, non-obese, 22- to 62-year-old individuals, free of any clinical evidence of atherosclerotic vascular disease, and having normal serum laboratory lipid levels. Studies of platelet activity included measurement of in vitro platelet aggregation and plasma beta-thromboglobulin (beta-TBG), a marker of in vivo platelet secretion. Basal and thrombin-stimulated phosphoinositide turnover was measured following [32P]-orthophosphate incorporation into the various phospholipids, isolation of the phosphoinositides and phosphatidic acid by thin-layer chromatography and autoradiography, and quantification by liquid scintillation spectroscopy of these radiolabeled phospholipids.
There was a positive correlation with age for both adenosine diphosphate (ADP)-induced aggregation (1.25 microM, r = 0.464, p less than 0.001; 2.5 microM, r = 0.386, p less than 0.05) and plasma beta-TBG (r = 0.381, p less than 0.055). There was a time-dependent increase of [32P]orthophosphate (32Pi) incorporation into platelet phosphatidylinositol 4,5-bisphosphate (PIP2) and phosphatidylinositol 4-phosphate (PIP), and isotopic equilibrium was reached by 120 minutes at 37 degrees C. A positive correlation was found between age and basal 32P-PIP2 (r = 0.640, p less than 0.001) and 32P-PIP (r = 0.676, p less than 0.0005). Basal 32Pi incorporation into PIP2 correlated positively with in vitro aggregation (1.25 microM ADP, r = 0.795, p less than 0.0001; 2.5 microM ADP, r = 0.755, p less than 0.0005) as did 32Pi incorporation into PIP (1.25 microM ADP, r = 0.815, p less than 0.0001; 2.5 microM ADP, r = 0.795, p less than 0.0001). There was also a positive correlation between plasma beta-TBG levels and basal 32P-PIP2 (r = 0.768, p less than 0.005) and 32P-PIP (r = 0.505, p less than 0.066). Finally, increasing age correlated with thrombin (4 U/mL)-stimulated 32P-PIP2 hydrolysis (r = 0.694, p less than 0.01) and phosphatidic acid formation (r = 0.556, p less than 0.05).
Dietary supplementation with cod-liver oil significantly augments endothelium-dependent relaxations in porcine coronary arteries. The present study was designed to examine the effect of dietary administration of omega 3 polyunsaturated fatty acids (mainly eicosapentaenoic acid, the major component of fish oil) on endothelium-dependent relaxations in porcine coronary arteries. Male Yorkshire pigs were maintained 4 wk on a regular diet with or without supplementation with purified eicosapentaenoic acid (3.5 g/day) and docosahexaenoic acid (1.5 g/day). Endothelium-dependent relaxations were examined in vitro. In rings from the treated group, endothelium-dependent relaxations were augmented in response to bradykinin, serotonin, and ADP, but not to the calcium ionophore A23187. These augmentations were not altered by indomethacin but were significantly inhibited by methylene blue, an inhibitor of guanylate cyclase. In the treated group, endothelium-dependent relaxations to aggregating platelets also were significantly augmented; platelet-induced contractions of quiescent rings were inhibited more by the presence of the endothelium than in arteries from the control group. Bioassay experiments demonstrated that the release of endothelium-derived relaxing factor(s) by bradykinin and relaxations of the vascular smooth muscle to the factor(s) were greater in arteries from the treated group. These observations indicate that dietary omega 3 polyunsaturated fatty acids augment receptor-operated endothelium-dependent relaxations, partly due to the augmented release of endothelium-derived relaxing factor(s) and partly due to the augmented relaxation of the vascular smooth muscle to the factor(s).
Large coronary artery calibres are regulated by humoral factors (autacoids) released from the endothelial cell lining. Several
hormones, transmitters and platelet-derived products like serotonin and ATP or acetylcholine, noradrenaline, and histamine,
stimulate such an autacoid release and thus an endothelium-mediated dilation in addition to their direct constrictor effect
on the vasculature. Another mechanical stimulus is the flow-induced shear stress acting as viscous drag upon the endothelial
surface along with the pulsatile stretching of the endothelial lining, which causes, in a moment to moment fashion, a continuous
adjustment of coronary calibres. With endothelial function impaired or absent as in atheromatosis or after balloon catheter
denudation this adjustment is compromised. Thus unbalanced constrictor effects may become effective especially in the presence
of a simultaneously reduced platelet antiaggregation.
The administration of carbachol to rabbits to stimulate the release of endothelium derived relaxing factor (EDRF) results in inhibition of platelet aggregation and elevation of platelet cyclic GMP content. These effects are reversed by simultaneous administration of the EDRF inhibitors methylene blue or haemoglobin. The data provide the first direct biochemical evidence of in vivo EDRF activity.
Platelet functions were investigated in sixteen old (78-94 years) and eight young (25-35 years) subjects. Whole blood platelet aggregation induced by collagen was higher in the elderly. Similarly, aggregation of platelet rich plasma and plasma-free platelets induced by various agents was increased but the collagen-induced release of ATP was reduced. In agreement with the enhanced platelet aggregability, the increase of thromboxane formation (under thrombin stimulation) was also noted in platelets from elderly people. To further assess platelet and vascular function in vivo, we measured the excretion of urinary TXB2, 2,3-dinor TXB2, 6-keto-PGF1 alpha and 2,3-dinor-6-keto-PGF1 alpha. The four metabolites were all increased in the elder population. In addition, a significant reduction of platelet vitamin E was observed in the elderly people, although the plasma content was normal. These results indicate numerous modifications of platelet behaviour with aging. They include the increased platelet susceptibility to aggregation, and the depletion of ATP granule content, which could reflect an activation in vivo in agreement with the enhanced urinary excretion of thromboxane and prostacyclin metabolites. We hypothesize that platelet hyperactivity associated with the enhanced oxygenated metabolism of arachidonic acid could be linked to vitamin E depletion. These changes may reveal a prethrombotic state in the elderly population.
It has been postulated that platelet function plays an important role in the initiation of atherosclerosis. Currently there are no definitive data on the longer-term effects of regular physical exercise on platelet function in humans. We assessed the influence of regular moderate-intensity physical exercise (brisk walking to slow jogging) on platelet aggregation in a population-based sample of middle-aged, overweight, mildly hypertensive men in eastern Finland. In this controlled study, we evaluated the net effect of exercise on platelet aggregation by studying changes in optical density and ATP release in platelet-rich plasma. A significant inhibition of secondary platelet aggregation from 27% to 36% was observed in the men taking regular exercise. These findings give new insight into the possible protective effects of exercise against the risk of ischemic heart disease.
Endothelial cell functions, such as arachidonic acid metabolism, may be modulated by membrane stresses induced by blood flow.
The production of prostacyclin by primary human endothelial cell cultures subjected to pulsatile and steady flow shear stress
was measured. The onset of flow led to a sudden increase in prostacyclin production, which decreased to a steady rate within
several minutes. The steady-state production rate of cells subjected to pulsatile shear stress was more than twice that of
cells exposed to steady shear stress and 16 times greater than that of cells in stationary culture.
The epidemiological characteristics of platelet aggregability were established in 958 participants in the Northwick Park Heart Study. The main analyses were based on the dose of adenosine diphosphate at which primary aggregation occurred at half its maximum velocity. Aggregability increased with age in both sexes, was greater in whites than blacks (particularly among men), and tended to decrease with the level of habitual alcohol consumption. Aggregability was, however, greater in women than men and in nonsmokers than smokers. There was no relation between aggregability on the one hand and obesity, current or past oral contraceptive use, menopausal state, or blood cholesterol and triglyceride concentrations on the other. Aggregability was somewhat, though not significantly, higher in men with a history of ischaemic heart disease and in those with electrocardiographic evidence of ischaemia than in those without. There was a strong association between the plasma fibrinogen concentration and aggregability. The widely held concept of platelet aggregability and its implications is probably an oversimplification. In the prevention of thrombosis it may be as useful to consider modifying external influences on platelet behaviour, such as plasma fibrinogen concentration or thrombin production, as it is to rely solely on platelet active agents.
The details of a radioimmunoassay capable of measuring as 5 pg of prostaglandin A, E, and F (PGA, PGE, and PGF) in human and rat plasma are described. Plasma samples are extracted (with 4000 cpm [(3)H] PGE(1) added for calculation of recovery) with an organic solvent system at an apparent pH of 5.8 and then chromatographed on silicic acid columns with increasing concentrations of methanol to separate PGA, PGE, and PGF. Each chromatographed sample is measured by radioimmunoassay, using the homologous antibody and tritiated marker. 40 normal individuals had mean plasma concentrations of PGA, PGE, and PGF of 1062+/-107 pg/ml, 385+/-30 pg/ml, and 141+/-15 pg/ml, respectively. Elevated PGE levels were measured in the plasma of patients with medullary carcinoma of the thyroid, carcinoid, and neuroblastoma. Treatment of rats with indomethacin decreased serum PGE levels by 67%. The radioimmunoassay appears to be of considerable experimental as well as clinical interest.
Some effects of marked thrombocytopenia have been studied in rabbits exposed to whole body irradiation with the ears shielded. In most animals marked thrombocytopenia was present 9–13 days after the irradiation. Lymph samples were obtained by draining a lymph vessel at the base of the ear. In 7 out of 11 rabbits a marked rise in the content of red cells in ear lymph occurred during thrombocytopenia. In the 4 other irradiated rabbits, which developed the same degree of thrombocytopenia, no such red cell increase in the ear lymph occurred. The reason for this is not known. Platelet production may have been resumed at an earlier stage in these 4 animals. The first few platelets produced at the end of the thrombocytopenic period were apparently consumed in repairing the endothelium. This notion is supported by the fact that in some of the 7 rabbits of the former group the erythrocyte-containing lymph was normalized one day before the number of circulating platelets started to rise. All rabbits showed a steady fall in body weight after irradiation. In the 7 rabbits with red cell increase in lymph, however, a moderate whole body weight gain could be observed at the time with marked thrombocytopenia. This suggests the existence of a slight degree of oedema during thrombocytopenia in these animals.
Separate mechanisms of action account for the effects of platelets on maintenance of vascular endothelium and on bleeding from mechanically injured vessels. Circulating platelets in excess of 50,000/mm3 are needed in thrombocytopenic dogs to consistently reduce their bleeding time to normal levels. Significant reduction of red cell diapedesis into the lymph, an index of endothelial damage, was observed following transfusions of small amounts of platelets in the same animal model whether or not the platelet count was increased. The known dependence of the bleeding time on “hemostatic plug” formation suggests that higher levels of circulating platelets are needed for its adequate formation, while small numbers of functional platelets may be needed to support the integrity of vascular endothelium. Since endothelial changes appear to account for initiating spontaneous bleeding and lack of hemostatic plug formation for its continuation, various programs of platelet replacement may be needed by thrombocytopenic individuals requiring prophylactic or therapeutic platelet transfusions.
In non-thermic conditions, platelets seem to ``nurture'' the micro-circulation in some way. This could obviously be valuable in the preservation of isolated organs.
1. Twelve healthy male subjects took a daily supplement of 20 ml of cod-liver oil for 6 weeks. This provided 1.8 g of eicosapentaenoic acid (20:5ω3) and 2.2 g of docosahexaenoic acid (22:6ω3). The effects of the supplement on blood lipids, haemostatic variables, bleeding time and plasma vitamin A and carotene were studied. In seven subjects platelet aggregation induced by adenosine 5′-pyrophosphate (ADP) was also studied.
2. The proportions of 20:5ω3 and 22: 6ω3 in platelet and erythrocyte phosphoglycerides were substantially increased by the supplement mainly at the expense of ω6 polyunsaturated fatty acids.
3. Mean plasma triglyceride concentrations were reduced and those of high-density-lipoprotein (HDL) cholesterol were increased by the supplement.
4. The mean bleeding time was significantly prolonged after 3 weeks of taking the supplement, but had returned to the presupplementation value 5 weeks after withdrawal of the supplement.
5. The maximum estimated response to platelet aggregation induced by ADP was increased by the supplement.
6. The mean levels of antithrombin III (immunological) and blood pressure were lower at the end of the period of supplementation and remained so 5 weeks after withdrawal of the supplement. No significant changes in other variables were noted.
The effects of highly purified eicosapentaenoic acid (97% pure) on the arachidonic acid cascade in isolated murine vascular cells and platelets were studied. The incorporation of eicosapentaenoic acid was not as active as that of arachidonic acid in platelets. The ratio of incorporation of eicosapentaenoic acid to arachidonic acid into platelet phospholipids was about 0.7. Analysis of the phospholipid fractions of platelets after labeling with 14C-eicosapentaenoic acid and 14C-arachidonic acid revealed that the incorporation of 14C-eicosapentaenoic acid into the fraction is significantly less than that of 14C-arachidonic acid, while the incorporation of both fatty acids into other phospholipid fractions was almost the same. On the other hand, no significant difference between either fatty acid in incorporation rate, kinetics or distribution in cellular phospholipids was found in cultured aortic smooth muscle cells. Following treatment with eicosapentaenoic acid, cells produced less prostacyclin from endogenous arachidonic acid than did control cells. This was not due to the decrease in fatty acid cyclooxygenase activity, but rather, due to the decrease in arachidonic acid content in cellular phospholipids. In addition, eicosapentaenoic acid was neither converted to prostaglandin I3 by the vascular cells nor to thromboxane A3 by platelets. Furthermore, similar results were also obtained by in vivo experiments in which rats were fed with eicosapentaenoic acid enriched diet.
The metabolism of eicosapentaenoic acid (EPA) in cultured vascular smooth muscle cells isolated from human, rat, rabbit and miniature pig and bovine endothelial cells were studied. EPA was not able to be converted to any prostaglandins (PGs) in murine and porcine smooth muscle cells. However, in human and rabbit smooth muscle cells and bovine endothelial cells EPA was easily converted to delta 17-6-ketoPGF1 alpha, which is a stable metabolite of PGI3. Cyclooxygenase and 12-lipoxygenase activities in platelets isolated from human citrated blood were almost completely inhibited by EPA at the dose over 4 micrograms. But in platelets isolated from rat the inhibitory effects of EPA on arachidonic acid (AA) metabolism were much smaller than that in human platelets. In rat, EPA was not only being converted to no PGI3, but also being a blocker to PGI2 synthesis in vascular cells. Moreover, the rat EPA has much less activity in inhibiting thromboxane A2 (TXA2) synthesis in platelets. On the contrary, in human EPA was not only easily converted to PGI3 in vascular cells, but also blocking TXA2 synthesis in platelets. Thus, anti-aggregatory effects of EPA was positive in human and negative in rat perhaps due to species difference in sensitivity to EPA.
In order to evaluate the effects of aging on platelet alpha-adrenergic receptor function, we have examined the binding of [3H]dihydroergocryptine ( [3H]DHE), a nonselective alpha-adrenergic antagonist, to crude platelet membrane at 25 degrees C in 28 subjects of various ages (mean 48, range 21-77 years) and platelet aggregatory response to epinephrine in other 32 subjects of various ages (mean 51, range 27-82 years). The average values of the binding capacity and affinity for [3H]DHE showed 218 +/- 56 fmol/mg protein (mean +/- SD) and 1.80 +/- 0.20 nM, respectively. There was a significant correlation between the binding capacity for [3H]DHE and age (r = 0.654, p less than 0.001). On the contrary, no significant correlation was found between the binding affinity for [3H]DHE and age (r = 0.273, p greater than 0.1). Exaggerated aggregatory response to epinephrine with advancing age was also demonstrated in this study (r = 0.716, p less than 0.001). Thus, the demonstration of increased alpha-adrenergic receptor capacity in aging man offers a possible explanation for the observed age-associated hyperactivity of the platelets to epinephrine.
Obesity, diabetes, hyperlipidaemia and age are conditions predisposing to atheroscleorosis and arterial occlusion. Recently it has been claimed that increased synthesis of thromboxane A2 by platelets and decreased synthesis of prostacyclin (PGI2) by blood vessels play an important role. The “Zucker” rat, a genetically obese animal with hyperlipidaemia, hyperinsulinaemia and normoglycaemia was used to study platelet aggregation, thromboxane (TXB2) production and aortic PGI2 synthesis. Two age groups (6–8 months and 14–16 months old) and their homozygote lean controls were used. In the obese rats no increased aggregation was found with ADP, arachidonic acid and collagen. On the contrary platelets from young fatty rats were less sensitive to ADP than platelets from lean young animals. An increase in platelet sensitivity to aggregating agents with age was observed, especially in the obese rats. TXB2 measured in platelet rich plasma after exposure to ADP, arachidonic acid, arachidonic acid plus ADP and collagen was similar in the fatty and lean animals.Production of PGI2 from incubated aortic rings was lowest in young lean animals. No differences existed between the other groups of rats studied. Insulin added to aortic rings had no influence on PGI2 production. It is concluded that age rather than obesity, hyperlipidaemia or hyperinsulinaemia may cause platelet hyperresponsiveness to aggregating agents. Thromboxane and plateletaggregation do not closely correlate. PGI2 production is not reduced by metabolic alterations, thought to predispose to atherosclerosis.
It is demonstrated that feeding cod-liver oil to rats leads to a considerable reduction in the formation of platelet TxA2 and of vascular PGI2. No appreciable formation of TxA3 and PGI3 is observed, although arterial thrombosis is depressed and bleeding time is prolonged. These findings contradict the suggested role of prostaglandins of the 3-series in thromboregulation.
Platelets have been implicated in the development of atherosclerotic and thrombotic vascular diseases. Evaluation of platelet aggregation in relation to endogenously formed compounds which affect platelet function may provide information of clinical and pharmacological relevance. We describe a method in which thromboxane B2 (TXB2) formation was analyzed following stimulation of platelet-rich plasma (PRP) with ADP, 1-epinephrine, collagen, and arachidonic acid. In addition, we determined platelet sensitivity to prostacyclin following ADP- and collagen-induced platelet aggregation. The parameters under study were found to depend on the platelet count in PRP, on the type and dose of the aggregating agent used, and on the test time after blood sampling. By standardization of these variables, a reliable method was established which can be used in clinical and pharmacological trials.
Platelets play an important role in the pathogenesis of cardiovascular disease. It has also been noticed that regular exercise can reduce the risk of cardiovascular disease. This is the first study to demonstrate that endurance exercise training may suppress platelet adhesiveness and aggregation and that deconditioning may reverse the training effects. Healthy male sedentary subjects were randomly divided into control and training groups. The trained men were trained on a bicycle ergometer at about 60% of maximal oxygen consumption for 30 minutes per day, 5 days per week for 8 weeks, then deconditioned for 12 weeks. During the experimental period, blood samples of the trained subjects were collected before and immediately after a progressive exercise test every 4 weeks. The same experiments were applied to the controls at the beginning of this study and 8 weeks thereafter. A tapered parallel-plate chamber was used to assess platelet adhesiveness. Platelet aggregation induced by ADP was evaluated by the percentage of reduction in single platelet count. Our results showed that (1) platelet adhesiveness and aggregability were increased by short-term strenuous exercise in both control and trained groups, but the enhancement of platelet aggregability was decreased after exercise training in the trained subjects; (2) at rest and immediately after strenuous exercise, platelet adhesiveness and aggregability were decreased by training, whereas they were unchanged in the control group; and (3) deconditioning reversed the training effects on resting and postexercise platelet adhesiveness and aggregability back to the pretraining state. These results suggest that platelet adhesiveness and aggregability may be depressed by exercise training but be reversed back to the pretraining state after deconditioning.