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ABSTRACT: This work was aimed to determine whether isometric contraction in Wistar rat aorta is related to the phosphatidylinositol 3-kinase (PI3K)/Akt-dependent activation of endothelial nitric oxide synthase (eNOS). Basically, we hypothesized that additional increases in active tone occur after the pharmacological inhibition of a transduction pathway involved in NO synthesis or action. In intact aortic rings contracted with phenylephrine or high K(+), the cumulative administration of the PI3K inhibitor, LY294002, elicited significant decreases--but not supplementary increases--in tone. In endothelium-intact tissues, on the other hand, the Akt1/2 kinase inhibitor did not alter phenylephrine- and K(+)-induced isometric contractions. The PI3K inhibitor wortmannin (1 × 10(-7) m) produced a significant supplementary contraction only in endothelium-intact aortic rings precontracted with phenylephrine. Higher concentrations of this inhibitor produced relaxations of phenylephrine and high K(+)-constricted endothelium-intact and endothelium-denuded aortic rings. LY294002 and wortmannin did not cause any potentiating effect on phenylephrine- and angiotensin II-induced concentration-dependent contractile responses in endothelium-intact tissues. In intact aortic rings contracted with phenylephrine or high K(+), the addition of the NOS inhibitor, L-NAME, or the guanylyl cyclase inhibitor, ODQ, further augmented tone in a concentration-dependent manner, and these supplementary contractions were significantly reduced by endothelium removal. Taken together, our data suggest that the PI3K/Akt pathway is not counteracting aortic isometric contractions by activation of the eNOS. It appears, on the other hand, that the smooth muscle PI3K can stimulate contraction without activation of the protein kinase Akt in response to GPCR agonists and high K(+).
Fundamental and Clinical Pharmacology 06/2011; 25(3):313-22. · 1.80 Impact Factor
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ABSTRACT: In experiments in vivo, we studied whether the endothelial dysfunction induced by nitric oxide (NO) synthesis inhibition is simultaneously or sequentially manifested as a reduced level of endothelium-dependent agonist-induced vasodilatation, an increased responsiveness to vasoconstrictors, and hypertension. Vascular responses to acetylcholine, phenylephrine, and angiotensin II were measured in pithed rats after acute intravenous injection (100 mg/kg) and short-term oral administration of N(G) -nitro-L-arginine methyl ester (L-NAME; 60 mg/kg per day) for 1 and 3 days (L-NAME(1d) and L-NAME(3d), respectively). Pithed rats were chosen because drug-induced cardiovascular responses reflect only peripheral effects. Parallel experiments examined mean arterial pressure (MAP) values in anesthetized rats. After short-term L-NAME(1d) and L-NAME(3d) treatments, the MAP was significantly elevated in anesthetized but not pithed rats. Acute intravenous administration of L-NAME elevated MAP in pithed rats. Intravenous infusion of phenylephrine was used to compensate for the pressor response induced by L-NAME in pithed animals. The maximum decrease and duration of the hypotensive responses to acetylcholine were unaltered by the acute and both short-term L-NAME treatments in pithed rats. These treatments, on the other hand, increased phenylephrine- and angiotensin II-induced pressor responses in pithed animals. In isolated aortic rings prepared from pithed rats treated acutely and short-term with L-NAME, acetylcholine-induced relaxations were inhibited. Thus, the inhibition of NO-dependent vasodilator tone after acute intravenous injection and short-term oral L-NAME administration may be associated with vascular smooth muscle hyper-responsiveness to pressor agonists and hypertension, whereas the hypotensive responses to acetylcholine could not be associated with the L-NAME-induced endothelial dysfunction in pithed rats.
Fundamental and Clinical Pharmacology 06/2011; 25(3):333-42. · 1.80 Impact Factor
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ABSTRACT: We tested whether heterologous receptor desensitization induced by activation of AT1 receptors may explain the purported relaxation produced by angiotensin II in normal rat aorta. Also, the role for AT2 receptors in the promotion of vasodilation was studied. In endothelium-intact and endothelium-denuded aortic rings, angiotensin II elicited biphasic contractions, which were significantly depressed when repeated in each tissue. Angiotensin II produced biphasic responses on phenylephrine preconstricted endothelium-intact and endothelium-denuded tissues, without reducing precontractile tone. These responses were abolished in the presence of the AT1 receptor antagonist losartan, but no relaxing responses to angiotensin II were uncovered. PD123319 did not influence angiotensin II responses in endothelium-intact tissues precontracted with phenylephrine; thus, under AT2 receptors blockade the contractile effects of angiotensin II were not overexposed. In conclusion, angiotensin II-induced biphasic responses can be attributed to AT1 receptors activation and rapid desensitization with time. Desensitization proved to be homologous in nature, since precontractile tone induced by phenylephrine was not depressed by angiotensin II (i.e., angiotensin II did not induce heterologous α1-adrenergic receptors desensitization). We found no functional evidence of the participation of AT2 receptors in angiotensin II elicited biphasic contractions. Angiotensin II does not exert relaxant effects in normal rat aorta.
Vascular Pharmacology 11/2010; 54(1-2):29-35. · 1.99 Impact Factor
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ABSTRACT: In this work, the possibility that isometric contraction activates endothelial nitric oxide synthase (eNOS) in a calcium/calmodulin (Ca2+/CaM)-dependent manner was examined in rat thoracic aorta. Step-wise stable contractile responses (precontractions) to phenylephrine were obtained in endothelium-intact and endothelium-denuded aortic rings. The subsequent addition of the NO synthase inhibitor, N(G)nitro-l-arginine methyl ester (l-NAME), or the soluble guanylyl cyclase inhibitor, ODQ, further augmented precontractions in a concentration-dependent manner. The amplitude of l-NAME- and ODQ-induced increases in tone were dependent on the level of precontraction; the maximal increments for l-NAME and ODQ were observed in arteries precontracted with phenylephrine at 67% of its maximal effect. Likewise, in endothelium-intact non-contracted arteries, l-NAME and ODQ induced small but significant increases in tone. Neither l-NAME nor ODQ had any effect in endothelium-denuded preparations. In endothelium-intact aortic rings precontracted with high K+ solutions, l-NAME also elicited supplementary contractions dependent on precontraction level. The CaM antagonist, calmidazolium, inhibited in a concentration-dependent, noncompetitive, manner the effects of l-NAME on the tone of endothelium-intact phenylephrine-precontracted aortic rings. These results suggest that isometric contraction increases the activity of eNOS by means of the Ca2+/CaM complex in rat aorta.
Vascular Pharmacology 09/2008; 50(1-2):14-9. · 1.99 Impact Factor
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ABSTRACT: The objective of this study was to re-examine whether the effect of the nitric oxide synthesis inhibitor, N(G)-nitro-L-arginine methyl ester (L-NAME), on blood pressure depends on peripheral vascular tone. The effects of L-NAME (10 mg/kg, i.v.) on diastolic blood pressure (DBP), systolic blood pressure (SBP), pulse pressure (PP) and heart rate (HR) were studied in pithed rats. Sal-pithed rats received 0.9% NaCl, 10 microl/kg/min. Vascular tone was step-wise increased with 3, 10 and 30 microg/kg/min intravenous phenylephrine infusion (LPhe-pithed, MPhe-pithed and HPhe-pithed rats respectively). L-NAME elicited vasopressor responses in all the animals studied. L-NAME increases in SBP and DBP in Sal-pithed rats were significantly smaller than the ones obtained in phenylephrine infused rats. The increases in DBP elicited by L-NAME were greater in LPhe-pithed rats compared with those of MPhe-pithed and HPhe-pithed rats (i.e. the step-wise rises in DBP obtained with phenylephrine were inversely related to the increases in DBP produced by L-NAME); however, the increases in SBP were similar between these experimental groups. The PP increased during L-NAME-induced pressor responses in phenylephrine-infused rats. l-NAME increases in PP showed the following order: Sal-pithed < LPhe-pithed < MPhe-pithed < or = HPhe-pithed rats. HR was not modified by L-NAME. In conclusion, the vasopressor responses produced by L-NAME in pithed rats are influenced by the pre-existing vasomotor tone in complex form. We did not find a simple positive correlation between the vascular tone or level of arterial pressure, and the magnitude of the diastolic and systolic pressor responses elicited by L-NAME. Interestingly, the increase in PP induced by l-NAME was greater in accordance with the increasing value of baseline arterial pressure. NO synthesis inhibition in the arterial endothelium may possibly explain the increase in PP caused by L-NAME, as resulting from the reduction in proximal conduit artery compliance.
Fundamental and Clinical Pharmacology 02/2008; 22(1):45-52. · 1.80 Impact Factor
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ABSTRACT: In rat aorta, the presence of functional alpha(2)-adrenoceptors (alpha(2)-AR) was investigated in ring preparations preconstricted with alpha(1)-adrenergic and non- alpha(1)-adrenergic agonists. Particularly, the hypothetical interference of alpha(2)-AR agonists with alpha(1)-AR-mediated vasoconstriction was evaluated. Relaxant and contractile responses to alpha(2)-AR agonists were obtained. In endothelium-intact and endothelium-denuded aortic rings preconstricted with phenylephrine (1 x 10(-6) m), the imidazoline derivatives, clonidine and UK14304, induced relaxations with similar order of potencies (-log EC(50)) and maxima relaxant effects respectively. Pretreatment with the NO synthase inhibitor, N(G)-nitro-L-arginine methyl ester (L-NAME) had no effect on the relaxant responses to clonidine and UK14304. In phenylephrine-constricted rings with endothelium, relaxations to clonidine and UK 14304 were not antagonized by the selective alpha(2)-AR antagonist, rauwolscine (< or =1 x 10(-6) m). Clonidine and UK 14304 induced only contractions on endothelium-intact and endothelium-denuded aortic rings contracted with prostaglandin F(2alpha) (3 x 10(-7) m). Moreover, clonidine and UK 14304-induced relaxation of endothelium-denuded arteries precontracted with methoxamine but not with serotonin. Finally, the concentration-contraction curves to clonidine and UK 14304 in endothelium-denuded aortic rings were significantly shifted to the right by the alpha(1D)-AR selective antagonist, BMY 7378, and rauwolscine. The pA(2) and pK(B) values for BMY 7378 and rauwolscine, respectively, against endothelium-independent actions of clonidine and UK 14304 were characteristic of an effect on the alpha(1D)-AR. The other selective alpha(2)-AR agonist tested BHT 933 (an azepine derivative), lacks considerable relaxant and contractile effects in rat aorta. The results provide no evidence for the presence of functional alpha(2)-AR in rat aorta. Respectively, the relaxant and contractile effects of the imidazoline derivatives, clonidine and UK 14304, may be due to an adjustable (in relation to the agonist-dependent active state of the alpha(1)-AR), inhibitory and excitatory, interaction with alpha(1)-ARs.
Fundamental and Clinical Pharmacology 09/2006; 20(4):339-49. · 1.80 Impact Factor
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ABSTRACT: In this study, we aimed to elucidate whether the daily hypertensive dose of long-term N(G)-nitro-l-arginine methyl ester (l-NAME) treatment, could make a difference between endothelial and smooth muscle functions in rat thoracic aorta. We test the hypothesis that high-dose, long-term l-NAME treatment has a depressive effect on vascular smooth muscle contractile activity which is not related with nitric oxide (NO) synthesis inhibition. After 14 days of treatment, isometric tension and (45)Ca(2+) influx were measured in aortic tissues isolated from l-NAME(10) and l-NAME(100) hypertensive (10 and 100 mg/kg/day, systolic blood pressures 167 +/- 7 and 172 +/- 10 mmHg, respectively) and control normotensive rats (132 +/- 7 mmHg). In l-NAME(10)- and l-NAME(100)-treated rats, acetylcholine-induced relaxation in aortic rings was suppressed with no significant difference between the treatments. l-NAME(100) (but not l-NAME(10)) treatment, significantly inhibited contractile responses to phenylephrine, angiotensin II, and K(+) (80 mm) in endothelium-intact tissues. The effect of l-NAME(100) on phenylephrine-induced contractile responses was not observed after 3 days of treatment. In endothelium-denuded aortic tissues of l-NAME(100) (but not l-NAME(10))-treated rats, phenylephrine (1 x 10(-6) m)- and K(+) (80 mm)-induced contractions and (45)Ca(2+) influxes were significantly reduced. In Ca(2+)-free medium (0.1 mm EDTA), on the contrary, the transient contractions obtained by either phenylephrine (1 x 10(-6) m) or caffeine (1 x 10(-2) m), or the sustained contractions induced by 12-o-tetradecanoylphorbol-13-acetate (1 x 10(-6) m; a protein kinase C activator) in endothelium-denuded aortic rings, were not modified by both l-NAME treatments. These results indicate that in aortic rings from l-NAME hypertensive rats, low and high doses, long-term l-NAME administration may be associated with equivalent inhibition in NO-dependent vasodilator tone (corresponding to equivalent hypertension values); whereas only high-dose, long-term l-NAME administration produces an endothelium-independent decrease in vasocontrictor activity, at least partly explained by a reduction in extracellular Ca(2+) influx.
Fundamental and Clinical Pharmacology 01/2005; 18(6):669-77. · 1.80 Impact Factor
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ABSTRACT: Using endothelium-denuded rat aortic rings incubated in Ca2+ -free solution, we assessed the ability of testosterone to influence the contractile effect of phenylephrine, and the increase in resting tone (IRT) associated with Ca2+ ability to cross the plasma membrane. The addition of testosterone [10(-5)-10(-4) 5 min before phenylephrine [10(-6) M], inhibited both phenylephrine-induced contraction and IRT. These changes were not affected by cycloheximide (10(-5) M; a protein synthesis inhibitor of), flutamide (10(-5) M; an androgenic receptor antagonist), or by adding aminoglutethimide (10(-5) M; an aromatase inhibitor). Testosterone also blocked the contractile response to serotonin [10(-5) M] but not to caffeine [10(-2) M]. On the other hand, testosterone inhibited the contractile responses to cyclopiazonic acid (10(-6) M; a selective Ca2+ -ATPase inhibitor) or ryanodine (10(-5 M; an activator of sarcoplasmic reticulum Ca2+ -release channels) associated with capacitative Ca2+ influx through non-L-type Ca2+ channels. These data suggest that by acting on the cellular membrane, testosterone interferes with the signal transduction pathway of G(q-11) protein-coupled receptors, and inhibits capacitative Ca2+ influx through both L-type and non-L-type Ca2+ channels. These effects are non-genomic, non-mediated by the intracellular androgen receptor, and not due to the conversion of testosterone to estrogens.
Gaceta medica de Mexico 142(1):1-8. · 0.22 Impact Factor
