K.W. Chiu

The Chinese University of Hong Kong, Hong Kong, Hong Kong

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Publications (51)90.26 Total impact

  • P.K.T. Pang · J J Shan · K W Chiu
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    ABSTRACT: Tetramethylpyrazine (TMP) is a compound purified from a medicinal plant Ligusticum wallichii Franch. Its effects on in vivo blood pressure, in vitro vascular contractility, and intracellular calcium regulation in rats were examined in the present study to see if it was a possible calcium antagonist in the vascular tissue. Data showed that TMP was hypotensive and had a direct vascular effect. It not only blocked the entry of extracellular calcium through calcium channels but also inhibited the release of intracellular stored calcium in the vascular smooth muscle cell. It was a true calcium antagonist.
    Planta Medica 11/1996; 62(5):431-5. DOI:10.1055/s-2006-957933 · 2.15 Impact Factor
  • K. W. Chiu · A. H. W. Lam · P. K. T. Pang
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    ABSTRACT: The straw mushroom Volvariella volvacea is one of the common edible mushrooms in Hong Kong and is widely cultivated in Southeast Asian countries. It has been reported to produce a hypotensive response in animals including humans. An aqueous extract of the mushroom (SME) was prepared and given through intravenous injections to normotensive rats. The blood pressure changes produced by SME alone or in the presence of various drugs were studied. The effects of SME on the kidney function of water-loaded rats and on isolated tissue preparations of the tail artery and right atrium were examined. An i.v. injection of SME produced a hypotensive effect in rats with an ED50 of 25 mg dry weight/kg body weight. This hypotensive effect of SME was attenuated or blunted in the presence of hexamethonium, phentolamine, pyrilamine and cimetidine suggesting the involvement of the α-adrenergic component of the autonomic system and/or histamineergic stimulation. SME did not increase urinary excretion nor sodium diuresis. It produced positive chronotropic and inotropic effects on isolated right atria and induced contraction of isolated tail artery strips. This latter contractile response was inhibited by antagonists of serotonin and α-adrenoceptor, ketanserin and phentolamine respectively. Partial purification using dialysis and liquid chromatography revealed that the hypotensive active substances had molecular masses between 8000 and 12000 dalton. These substances were heat stable and resistant to trypsin digestion. In view of the similarity in blood pressure and cardiovascular response, SME might contain serotonin-like substances.
    Phytotherapy Research 03/1995; 9(2):93 - 99. DOI:10.1002/ptr.2650090203 · 2.66 Impact Factor
  • K.W. Chiu · K.Y. Lam
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    ABSTRACT: The plasma thyroid hormones (TH) in the snake, Elaphe taeniura, were studied using RIA. Samples of plasma were obtained from untreated snakes in March, May and September as weU as thyroidectomized snakes in May. Scale biopsies were taken from each snake in order to see if there were any correlations of plasma T3 and T4 levels and epidermal changes during the sloughing cycle. Plasma samples were also taken from another snake species Ptyas korros and a chelonia sp. Clemmys mutica for comparison. Data showed that the plasma T3 and T4 levels of these reptilian species were very low (less than 1 nmol/1) and there were extensive individual variations (from below detection to 0.910 nmol/1). There were seasonal variations in these levels in E. taeniura. One week after thyroidectomy, the plasma levels of T3 and T4 could not be detected, suggesting that the thyroid gland is the only source of thyroid hormones in the snake. There was no correlation between mean plasma T3 and T4 levels during the resting and renewal phase. The extreme low level of plasma T4 preceding, and its absence following thyroidectomy which always precipitates, the renewal phase provide circumstantial support to the inhibitory role of TH on epidermal proliferation/differentiation in sloughing.
    Comparative Biochemistry and Physiology Part A Physiology 01/1994; 107(1-107):107-112. DOI:10.1016/0300-9629(94)90281-X · 2.17 Impact Factor
  • K W Chiu · Y C Lee · P.K.T. Pang
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    ABSTRACT: Cardiovascular and renal actions of hydrins and arginine vasotocin (AVT) in frogs (Rana tigrina and Rana catesbeiana) were examined in view of their relationships as precursor/prohormone-hormones in the anuran amphibian. In vitro hydrins and AVT respectively vasorelaxed and vasoconstricted KCl-preconstricted femoral artery in R. tigrina. AVT also produced dose-dependent contractions on untreated preparations; hydrins had no effect on these preparations. Both the hydrins and AVT were positively inotropic and chronotropic, with AVT being more potent. In vivo hydrins and AVT were anti-diuretic except at high doses, when AVT became diuretic. The hydrins and AVT were vasodepressor and pressor, respectively, in R. catesbeiana. These data suggest that the addition of one to three amino acids onto the AVT molecule reverses the contractile response in the vascular smooth muscle. With this dissociation of the vascular effect from that of the renal, the hydrins might play a physiological role in water balance of frogs.
    General and Comparative Endocrinology 08/1993; 91(1):1-7. DOI:10.1006/gcen.1993.1098 · 2.47 Impact Factor
  • C. C. Wong · K. Y. Lam · K. W. Chiu
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    ABSTRACT: The extrathyroidal conversion of thyroxine to triiodothyronine in the snake, Elaphe taeniura, has been determined in vitro. The liver, kidney and pancreas are important organs showing significant 5-deiodinase activity. The pancreas has a higher conversion rate (18.53.58 pmolmin-1mg protein-1) than other vertebrate tissues that have been studied. The 5-deiodinase activity is dependent on substrate (thyroxine) concentration, cofactor, i.e. dithioerythritol concentration, temperature, duration of incubation and pH. It is sensitive to iopanoic acid, propylthiouracil, salicylate and propranolol. It is also indicative that the 5-deiodinase activity increased and decreased, respectively, in snakes with experimentally induced hyper- and hypo-thyroidism. These characteristics suggest that snake 5-deiodinase is similar to that of mammals, probably of type I category.
    Journal of Comparative Physiology B 05/1993; 163(3):212-218. DOI:10.1007/BF00261667 · 2.62 Impact Factor
  • K.W. Chiu · Y.C. Lee
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    ABSTRACT: 1. The cardiac responses of isolated frog (Rana tigrina) atria to peptide hormones were studied.2. Calcitonin gene-related peptide (CGRP), arginine vasotocin (AVT), bovine parathyroid hormone fragment (bPTH-(1–34)) and oxytocin (OXY) produced dose-related positive chronotropic and inotropic responses; atrial natriuretic peptide (ANP) was negative chronotropic and inotropic; cholecystokinin (CCK), vasoactive intestinal peptide (VIP) were without effects.3. The dose-related responses under bPTH-(1–34) stimulation but not CGRP or AVT were attenuated in the presence of ANP (300 ng/ml, ≈0.98 × 10−7 M). As expected ANP decreased the basal AR and AT responses of the isolated atria and the inhibitory effects were dose-dependent.4. As shown previously, propranolol blocked the atrial tension stimulated by bPTH (1–34) but did not alter the cardiac responses to CGRP and AVT.5. In the presence of β-adrenergic blocker (propranolol 10−7M) or ANP (10−7M), the AR and AT changes under ISO stimulation in the frog were also decreased.6. These cardiac changes suggest the cardiac inhibitory effects of ANP are related to β-adrenoceptor activity and ANP might be a β antagonist.
    Comparative Biochemistry and Physiology Part C Comparative Pharmacology 11/1992; 103(3-103):483-487. DOI:10.1016/0742-8413(92)90169-8
  • K. W. Chiu · Y. C. Lee · K. H. Yung
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    ABSTRACT: The cardiovascular activity of the aqueous (A) and 30% MeOH (B) fractions of an ethanol extract of the daffodil bulbs (Narcissus tazetta) was examined using in vivo and in vitro preparations of normotensive rats and in the presence/absence of various blockers: α, β-adrenergic, cholinergic, ganglionic, histaminergic, enzyme converson inhibitor, calcium channel. These fractions (A and B) produced similar dose-dependent hypotensive responses in the anesthetized animals. The responses induced by fraction B might be mediated via adrenergic and cholinergic receptor activation. In isolated atrial preparations, fraction A increased the atrial rate (+ ve chronotropism) but not the atrial tension (inotropism). Fraction B, however, produced negative chronotropic but positive inotropic responses. Fraction B had no effect on the untreated tail vascular smooth muscle but increased the tension on AVP-preconstricted helical strips. It is suggested that the daffodil bulb contains cardiovascular active substances, the sum total of the effects produced accounts for the hypotensive action. It is further shown that these substances are distinct from those of well-documented antimitotic narciclasine.
    Phytotherapy Research 09/1992; 6(5):231 - 236. DOI:10.1002/ptr.2650060502 · 2.66 Impact Factor
  • L W Kline · T Kaneko · K W Chiu · P.K.T. Pang
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    ABSTRACT: The presence of a calcitonin gene-related peptide (CGRP)-like material was demonstrated in the gallbladder of the bullfrog, Rana catesbeiana, using immunocytochemistry and confirmed by radioimmunoassay. An intense immunocytochemical reaction was observed in nerves located in the smooth muscle layers and associated with blood vessels. No immunoreactive nerve fibers were associated with ganglia, nor were immunoreactive cell bodies observed. Radioimmunoassay showed that 25.03 +/- 2.5 pmol/g tissue of CGRP-like material was present. In vitro tension studies using gallbladder strips showed that CGRP exerted an inhibitory effect on both acetylcholine- and cholecystokinin octapeptide-induced tension but had no effect on KCl-, norepinephrine-, or cerulein-induced tension. CGRP may act directly on the gallbladder smooth muscle to inhibit contraction.
    General and Comparative Endocrinology 08/1992; 87(1):14-9. DOI:10.1016/0016-6480(92)90144-9 · 2.47 Impact Factor
  • K.W. Chiu · Y.C. Lee · Y.M. Yau · P.K.T. Pang
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    ABSTRACT: 1. Calcitonin gene-related peptide (CGRP) produced dose-related positive chronotropic and inotropic responses in isolated atria of a newt, Triturus sp. and a frog, Rana tigrina. It was apparent that CGRP was stimulatory on the heart of the amphibian species. 2. In the frog, these dose-related responses were attenuated in the presence of a CGRP antagonist (hCGRP 3 x 10(-8) M). This was indicative of the presence of cardiac CGRP receptors. 3. In the presence of beta-adrenergic (propranolol 10(-6) M) and calcium channel (verapamil 10(-8) M, but not nifedipine 10(-8) M) blocker, the basal AR in the frog were decreased. AR induced by CGRP were increased however. 4. The maximal AR and AT responses of the isolated atria to CGRP were not affected by the presence of propranolol. 5. In the presence of calcium channel blockers (verapamil and nifedipine), the maximal AT response was attenuated. These changes suggest the cardiac effects of CGRP are related to calcium mobilization.
    Comparative Biochemistry and Physiology Part C Comparative Pharmacology and Toxicology 07/1992; 102(2):315-8. DOI:10.1016/0742-8413(92)90117-P
  • K.W. Chiu · Y.C. Lee · P.K.T. Pang
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    ABSTRACT: The effects of parathyroid hormone (PTH) analogues on isolated rat tail arteries and frog arteries and heart were examined. Synthetic bovine PTH fragment 1 to 34 [bPTH-(1-34)], porcine PTH-(1-34), [Ala1] pPTH-(1-34), and [Nle8] pPTH-(1-34) were tested for vasorelaxant activity on helical strips of the rat tail artery and the frog iliac and femoral artery, preconstricted with arginine vasopressin or arginine vasotocin in the rat and the frog, respectively. For cardiac activity, PTH analogues were administered to isolated frog atria, and atrial rate and atrial tension (AT) were measured. The N-terminal amino acid alanine appears to be pivotal for vasorelaxant activity of PTH molecules on the rat tail artery strips. Data from the frog preparations supported the finding in the rat, although the iliac and femoral arterial preparations differed in their responses. The N-terminal serine in pPTH-(1-34), compared with the other PTH analogues, appeared to be responsible for different cardiac responses, being negatively chronotropic and without effect on AT.
    General and Comparative Endocrinology 07/1992; 86(3):506-10. DOI:10.1016/0016-6480(92)90075-U · 2.47 Impact Factor
  • K.W. Chiu · Y.C. Lee
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    ABSTRACT: 1.1.|Cardiac adrenoceptors in a snake, Ptyas korros, and a newt, Triturus sp. were examined in winter months using isolated atrial preparations maintained at 6°C. Treatments included stimulation of the isolated atria with selective α and β adrenergic agonists (phenylephrine and isoproterenol respectively) in the presence or absence of a β antagonist (propranolol).2.2.|In the snake, both phenylephrine (PHE) and isoproterenol (ISO) produced dose dependent increases in atrial rate (AR) and tension (AT). However, the increases produced under PHE occurred at relatively high doses. Propranolol blunted these effects. These data suggest that β adrenoceptors are the predominant post-synaptic adrenoceptors in snake atria.3.3.|In the newt, ISO produced dose dependent increases in AR and AT, viz. positive chronotropic and inotropic, but PHE was positive inotropic and had no effect on AR. These increases produced by ISO and PHE were abolished with propranolol.4.4.|Data from the present study therefore showed no indication that α adrenoceptors are important, if indeed present, at the low temperature environment as reported in the frog.
    Journal of Thermal Biology 05/1991; 16(3-16):141-144. DOI:10.1016/0306-4565(91)90035-Z · 1.51 Impact Factor
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    O. L. Shum · K. W. Chiu
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    ABSTRACT: The cardiovascular action of Solanum melongena extract (SME) was investigated using in vivo and in vitro preparations. SME produced dose-dependent hypotensive responses in normotensive albino rats. The duration of response was also dose dependent. In pharmacological antagonist studies, the hypotensive action of SME was proved not to be mediated through the autonomic ganglion, the -adrenoceptor or the histaminergic receptor. SME worked via the β-adrenoceptor and cholinergic (muscarinic) receptor inducing the hypotensive response. A dose-related attenuation of hypotension with increasing dosages of the β-adrenoceptor blocker, propranolol, and the cholinergic receptor blocker, atropine was observed. In vitro studies indicated that the vasorelaxing and negative inotropic effect of SME might be implicated in the hypotensive response. The activities of the β-adrenergic and acetylcholine receptors mediated by SME in turn promoted vasodilation of the resistant vessels and a reduction in cardiac activity respectively. It is also possible that the hypotensive effect of SME could be accounted for by its influence on the activity of the renin-angiotensin system, since a significant difference of the hypotensive response of SME was obtained with captopril. Furthermore, SME induced diuresis in water-loaded rats which might also account for the hypotensive effect observed. SME could be a very potent hypotensive agent.
    Phytotherapy Research 04/1991; 5(2):76 - 81. DOI:10.1002/ptr.2650050208 · 2.66 Impact Factor
  • K.W. Chiu · T.Y. Chung · P.K.T. Pang
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    ABSTRACT: 1. The cardiovascular effects of bovine parathyroid hormone fragment [bPTH-(1-34)] and isoproterenol (ISO) on frog (Rana tigrina) isolated atria and helical strips of blood vessels were examined since PTH produces a beta-adrenergic-like effect in the mammal. 2. Data showed that both bPTH-(1-34) and ISO were vasorelaxant in KCl and arginine vasoctocin (AVT) preconstricted dorsal aorta, iliac and femoral arteries. 3. They both relaxed extracellular calcium-dependent contrations. 4. There was no additive nor synergistic effect between them in AVT preconstricted strips. 5. Both bPTH-(1-34) and ISO were positively inotropic but differed in their chronotropic effects, being negative and positive. 6. In the tiger frog, bPTH-(1-34) shows beta-adrenergic like contractile responses in both the cardiac and vascular smooth muscle as in the mammal, but not in the heart rate.
    Comparative Biochemistry and Physiology Part C Comparative Pharmacology and Toxicology 02/1991; 100(3):547-52. DOI:10.1016/0742-8413(91)90038-U
  • K. W. Chiu · Y. C. Lee
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    ABSTRACT: The cardiac effects of neurohypophysial hormones in the Japanese eel, Anguilla japonica (Temminck and Schlegel), were studied in isolated atrial preparations at room temperatures of 17–20C, 25–28C, or 28C. Arginine vasotocin (AVT), oxytocin (OXY), mesotocin (MSN), and isotocin (ISN) produced dose-related positive chronotropic and inotropic responses. Arginine vasopressin (AVP) was not effective. The effects of ISN on the atrial rate and tension were not affected in the presence of phentolamine or propranolol, which are and adrenergic antagonists, respectively. The activity of the eel heart and the effects of neurohypophysial hormones are temperature-dependent. The functional significance of these cardiac effects of neurohypophysial hormones is not known.
    Journal of Comparative Physiology B 05/1990; 160(2):213-216. DOI:10.1007/BF00300956 · 2.62 Impact Factor
  • K W Chiu · Y.C. Lee · P.K.T. Pang
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    ABSTRACT: The cardiac effects of neurohypophysial hormones (NH) in the frog, Rana tigrina, and in the snake, Ptyas mucosa, were studied in isolated atrial preparations. Arginine vasopressin (AVP), vasotocin (AVT), isotocin (ISN), mesotocin (MSN), and oxytocin (OXY) produced dose-related positive chronotropic and inotropic responses in the frog atria. AVT was the most potent. In the snake, AVP, AVT, MSN, and OXY produced dose-related positive inotropic but not chronotropic changes. OXY was the most potent. Data indicate that there is a direct action of NH on the heart in both animals, the atrial rate and tension responses to NH are not coupled, and judging by the efficacy, AVT and OXY might be the natural NH in the frog and snake, respectively, which may account for the high concentrations required of other NH to be cardiac stimulating.
    General and Comparative Endocrinology 05/1990; 78(1):150-4. DOI:10.1016/0016-6480(90)90055-Q · 2.47 Impact Factor
  • K.W. Chiu · Y.C. Lee · P.K.T. Pang
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    ABSTRACT: The vasorelaxant effect of atrial natriuretic peptide (ANP) in two species of frogs, Rana catesbeiana and R. tigrina, were studied in vitro. Isolated arterial strips were prepared from the aortic loop, dorsal aorta, iliac, and femoral arteries in the frog. These were stimulated to contract with KCl, norepinephrine, or arginine vasotocin. When maximal contraction was attained, ANP was added to assess if it could relax the strips. Data show that ANP is vasorelaxant in these preparations. The sensitivity of these tissues depends on the contractile agents, e.g., KCl-stimulated preparations from R. catesbeiana did not respond to ANP. Data also suggest that ANP action elicited in the frog vascular tissue is due to an inhibitory effect on the mobilization of the intracellular calcium store and/or calcium influx from extracellular space to initiate contraction.
    General and Comparative Endocrinology 05/1990; 78(1):42-7. DOI:10.1016/0016-6480(90)90045-N · 2.47 Impact Factor
  • K.W. Chiu · Y.C. Lee · P.K.T. Pang
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    ABSTRACT: 1. The cardiac effects of the N-terminal (1-34) peptide fragment of bovine parathyroid hormone [bPTH-(1-34)] on isolated atria were examined in the frog, Rana tigrina. 2. bPTH-(1-34) produced dose-related inotropic response but no chronotropic response. This inotropic response varied at different times of the year. 3. The inotropic effect of bPTH-(1-34) was attenuated in the presence of verapamil and imidazole. 4. The mechanism of action of bPTH-(1-34) is probably a stimulation of calcium influx directly or indirectly via cAMP production.
    Comparative Biochemistry and Physiology Part C Comparative Pharmacology and Toxicology 02/1990; 95(2):197-9. DOI:10.1016/0742-8413(90)90103-G
  • C P Li · K H Yung · K W Chiu
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    ABSTRACT: Salvia miltiorrhiza cell culture extract (SCE) was shown to produce dose-dependent hypotensive response in normo-tensive rats. The mode of this hypotensive action was studied both in vivo and in vitro. This vasodepressor effect was not due to the presence of cations (potassium, calcium and magnesium) in the extract. In pharmacological antagonist studies, the hypotensive effect was shown not being mediated via the alpha-, beta-adrenoceptors, histamine receptors and autonomic ganglion; nor via direct vasodilation and diuresis. However, the vasodepressor effect was probably angiotensin- and/or bradykinin-related since captopril infusion potentiated the hypotensive effect of SCE. Furthermore, data indicated that the vasodepressor effect might be accounted for by the positive inotropic and negative chronotropic effects of SCE, the latter via its modulation of cholinergic activity.
    The American Journal of Chinese Medicine 02/1990; 18(3-4):157-66. DOI:10.1142/S0192415X90000204 · 2.76 Impact Factor
  • K W Chiu · J.Y. Chu
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    ABSTRACT: 1. Cardiac adrenergic receptors in a frog, Rana tigrina, were examined in winter and summer months using isolated atria preparation maintained at 24 degrees, 14 degrees and 6 degrees C. Treatments included an examination of the atrial responses to selective alpha and beta adrenergic agonists (phenylephrine and isoproterenol respectively) and antagonists (phentolamine and propranolol). 2. Basal atrial beating rates differed between summer and winter months and increased with temperature. 3. Phenylephrine produced dose-dependent increases in the atrial beating rate and tension in the winter frogs only at 6 degrees C. These increases were blunted by phentolamine. 4. Isoproterenol produced positive chronotropic effects of 14 degrees and 24 degrees C but not at 6 degrees C in both summer and winter frogs; these effects were abolished by propranolol. Further, at 6 degrees C, the contractile response of the atrial tissue to isoproterenol was very sensitive. 5. Data suggests that the alpha adrenoceptor might be physiologically important to the frog in the low temperature environment of the cold season, during which period the cardiac beta adrenergic activity would be minimal or even absent.
    Comparative Biochemistry and Physiology Part C Comparative Pharmacology and Toxicology 02/1989; 94(1):149-57. DOI:10.1016/0742-8413(89)90159-X
  • L.W. Kline · T Kaneko · K W Chiu · S Harvey · P.K.T. Pang
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    ABSTRACT: Calcitonin gene-related peptide (CGRP) was found using radioimmunoassay in the brain and spinal cord of the bullfrog, Rana catesbeiana. The brain extracts were found to contain 241.7 +/- 68.1 pg/mg tissue, and the spinal cord contained 1753.0 +/- 96.8 pg/mg tissue. An intense immunocytochemical reaction was observed in the dorsal spinal cord. Vascular studies using helical strips of the dorsal aorta, iliac artery, and femoral artery showed CGRP to exert a vasorelaxant effect which was most pronounced in the femoral artery and minimal in the aorta. As in the rat, CGRP was shown to exert its vasorelaxant effect by inhibiting the mobilization of intracellular calcium.
    General and Comparative Endocrinology 11/1988; 72(1):123-9. DOI:10.1016/0016-6480(88)90187-6 · 2.47 Impact Factor