K W Chiu

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

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Publications (32)47.25 Total impact

  • 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;
  • K W Chiu, Y C Lee, P K 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. · 2.82 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. · 2.02 Impact Factor
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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. · 2.82 Impact Factor
  • K W Chiu, Y C Lee, Y M Yau, P K 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.
  • K W Chiu, Y C Lee, P K 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. · 2.82 Impact Factor
  • K W Chiu, T Y Chung, P K 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.
  • 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. · 2.02 Impact Factor
  • K W Chiu, Y C Lee, P K 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. · 2.82 Impact Factor
  • K W Chiu, Y C Lee, P K 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. · 2.82 Impact Factor
  • K W Chiu, Y C Lee, P K 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.
  • 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.
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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. · 2.82 Impact Factor
  • C C Wong, J Y Chu, K W Chiu
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    ABSTRACT: 1. The uterine activity of rats treated neonatally with MSG was examined in vitro by measuring the contractile response of the tissue to hormone/chemical stimulation. 2. The uterine responses to ACh and ANG II remained unchanged following neonatal MSG treatment while those to PGF2 alpha were sensitized. 3. The responses to OT and 5-HT were characterized by a reduction of the maximal contractile force and the rate of change in tension increased and decreased compared with the control with OT and 5-HT respectively. 4. Data suggested that these changes on uterine contractility could be ascribed to various possible mechanisms of action of MSG.
    General Pharmacology 02/1988; 19(5):673-7.
  • K W Chiu, H Y Lim, P K Pang
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    ABSTRACT: 1. The cardiac effects of arginine vasotocin (AVT) on isolated atria were examined in three anuran and one urodele species. 2. AVT produced dose-related positive chronotropic and inotropic responses. 3. The responsiveness of the atrial tissue varied among species. 4. Both the basal atrial rate (AR) and tension (T) were attenuated in the presence of phentolamine and propranolol, alpha- and beta-adrenergic antagonists. Isoproterenol, a beta-adrenergic agonist, increased both AR and T, an effect which would be inhibited by propranolol. 5. The effects of AVT on both AR and T were not inhibited by alpha- and beta-adrenergic blockers, nor by verapamil and imidazole with the dosages used in the present study. 6. On the contrary, the effects of AVT on AR, but not T, was enhanced in the presence of both alpha- and beta-adrenergic blockers. 7. The mechanism of action of AVT on the amphibian atrium remains unknown.
    Comparative Biochemistry and Physiology Part C Comparative Pharmacology and Toxicology 02/1988; 89(2):147-51.
  • C.C. Wong, J.Y. Chu, K.W. Chiu
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    ABSTRACT: 1.1. The uterine activity of rats treated neonatally with MSG was examined in vitro by measuring the contractile response of the tissue to hormone/chemical stimulation.2.2. The uterine responses to ACh and ANG II remained unchanged following neonatal MSG treatment while those to PGF2α were sensitized.3.3. The responses to OT and 5-HT were characterized by a reduction of the maximal contractile force and the rate of change in tension increased and decreased compared with the control with OT and 5-HT respectively.4.4. Data suggested that these changes on uterine contractility could be ascribed to various possible mechanisms of action of MSG.
    General Pharmacology: The Vascular System. 01/1988;
  • C C Wong, K W Chiu
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    ABSTRACT: Putative triiodothyronine (T3) receptors have been detected in the nuclei of red blood cells (RBC) in a number of reptile species. The binding characteristics of T3 receptors in vitro were dissociation constant (Kd) 9.1 to 28.58, 36.8 and 40, and 11.12 and 11.36 pM, and binding capacity (Bmax) 0.12 to 0.37, 0.17 and 0.24, and 0.19 and 0.28 fmol per million cells in the rat snake (Ptyas korros), soft-shelled turtle (Trionyx sinensis), and tokay gecko (Gekko gecko), respectively. These data were obtained in all species using in vitro incubation of whole cell according to current receptor studies on living cells. With modified technique in subsequent experiments, these values of the binding characteristics were seemingly low. The discrepancy was ascribed to the assessment of "free" fraction of hormone which would be used in subsequent calculation.
    General and Comparative Endocrinology 07/1987; 66(3):434-40. · 2.82 Impact Factor
  • Integrative and Comparative Biology - INTEGR COMP BIOL. 01/1987; 27(1):121-131.
  • K W Chiu, V C Wong, M Y Chan, P K Pang
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    ABSTRACT: Three putative pressor systems, the alpha-adrenergic system (AS), the renin angiotensin system (RAS), and the arginine vasotocin system (AVT-S), were studied for their roles in blood pressure regulation and their possible interactions in the rat snake. Ptyas korros. Norepinephrine (NE), angiotensin I (ANG I), and arginine vasotocin (AVT) increased the mean arterial pressure (MAP) of the snake while administration of phentolamine, an alpha-adrenergic antagonist, and captopril, an ANG-converting enzyme inhibitor, but not KBIV24, an AVT antagonist, decreased the MAP. Treatment with any combination of two of these antagonists/inhibitor invariably decreased the MAP. Treatment with the agonist of the remaining third system invariably returned the MAP to normal or above. Phentolamine and KBIV24 attenuated the vasopressor effect of ANG I. Phentolamine and captopril enhanced the vasopressor effect of AVT. The pressor effect of NE was not altered by KBIV24 and captopril. It was concluded that there were at least two pressor systems (AS and RAS) regulating the basal MAP in the snake. There was also interaction among the three systems which could affect the MAP.
    General and Comparative Endocrinology 12/1986; 64(2):300-4. · 2.82 Impact Factor
  • B Y Ho, V C Wong, K W Chiu
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    ABSTRACT: The hindquarter of the rat snake, Ptyas korros, was isolated for perfusion study in order to investigate the mechanism of action of angiotensin (ANG) II. Both ANG II and norepinephrine (NE) produced concentration-dependent increases in perfusion pressure. [Sar1, Ile8] ANG II significantly attenuated the response to ANG II but not that of NE. Phentolamine significantly reduced the responses to both ANG II and NE, with much greater inhibition on NE than ANG II. These findings suggest the presence of ANG II receptors and alpha-adrenergic receptors in the hindquarter. Since tyramine did not exert any increase in perfusion pressure, the release of ANG II-stimulated catecholamines was probably not involved in the increase in perfusion pressure to ANG II in the present preparation. The partial attenuation of the response to ANG II by phentolamine, therefore, suggests that ANG II may act directly on both specific ANG II receptors and alpha-adrenergic receptors.
    General and Comparative Endocrinology 04/1986; 61(3):343-7. · 2.82 Impact Factor

Publication Stats

100 Citations
47.25 Total Impact Points

Institutions

  • 1975–1994
    • The Chinese University of Hong Kong
      • • Department of Biology
      • • Department of Physiology
      Hong Kong, Hong Kong
  • 1988–1992
    • University of Alberta
      • Department of Physiology
      Edmonton, Alberta, Canada
  • 1991
    • The University of Hong Kong
      • Department of Biology
      Hong Kong, Hong Kong