Effects of homocysteine and puerarin on coronary vasomotor responses

by Yeung, King-yin

(Uncorrected OCR) Abstract of thesis entitled

Effects of homocysteine and puerarin on coronary

vasomotor responses Submitted by Dennis King Yin Yeung

for the degree of Master of Philosophy at The University of Hong Kong

in August 2003

The present study addresses the vascular effects of short-term exposure to

homocysteine and puerarin in porcine coronary artery rings. In some

experiments, the endothelium of porcine coronary artery ring was disrupted by

perfusion of Triton-X100 (0.5 %) for 30 seconds. Changes in isometric tension

force were measured in organ baths.

Vascular responses to

endothelium-dependent relaxing agents, bradykinin and the calcium ionophore

A23187, endothelium-independent relaxing agents, sodium nitroprusside and

cromakalim, also to contracting agents potassium chloride (KCI),

5-hydroxytryptamine, the thromboxane A2 analogue U46619 and endothelin-1

were investigated in the presence and/or absence of homocysteine and puerarin.

An elevated level of homocysteine represents a strong and independent risk

factor for many cardiovascular diseases. The vascular endothelium has been

shown to be the initial target of homocysteine. In the present study,

endothelium-dependent relaxation to bradykinin and A23187, but not

endothelium-independent relaxation to sodium nitroprusside was attenuated by homocysteine (1 mM and 5 mM). This impairment of endothelium-dependent

relaxation by homocysteine was more profound with increasing exposure time.

The vasoconstrictions to the receptor-mediated agents, 5-hydroxytryptamine, U46619 and endothelin-1, but not to the depolarising agent KCI, were appreciably inhibited after incubation with homocysteine (1 mM) for 30 minutes. In summary,

homocysteine exerts inhibitory actions on both vasodilation and vasoconstriction

regardless of the signaling pathway. These inhibitions, however, demonstrate the dependency of exposure time.

Radix Puerariae, is a Chinese medicinal herb that is widely used in China for the

management of cardiovascular disorders. The major bioactive isoflavonoid

derivative isolated from this herb is puerarin, which has been demonstrated to contribute to the cardioprotective role of Radix Puerariae through the promotion of

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vasodilation and inhibition of vasoconstriction. Therefore, the focus of my study

was to elucidate the intracellular mechanisms responsible for the vascular actions

of puerarin. At a concentration with no direct vascular effects (10M ), puerarin significantly reduced vasoconstrictions to 5-hydroxytryptamine and endothelin-1, without affecting the responses to KCI, following short-term exposure (30 minutes). Short-term exposure to puerarin (10M ) also resulted in significant potentiation of the vasodilation by the endothelium-independent agents, cromakalim and sodium nitroprusside. Endothelium-dependent relaxation to bradykinin and A23187 were unaffected by puerarin. The potentiating actions of puerarin persisted following the inhibition of nitric oxide synthase with L-NAME and in endothelium-disrupted porcine coronary arterial rings. While cyclic AMP analogue 8-bromo-cyclic AMP and the protein kinase A activator Sp-cyclic AMPS mimicked the enhancement of endothelium-independent relaxation by puerarin however, the cyclic GMP analogue 8-bromo-cyclic GMP had no effect on

relaxation to sodium nitroprusside and cromakalim. Furthermore, the cyclic

AMP-dependent protein kinase A inhibitor Rp-cyclic AMPS, but not the cyclic GMP antagonist Rp-8-bromo-cyclic GMPS, effectively reversed the enhancing

actions of puerarin on vasodilation to sodium nitroprusside. Taken together,

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these data indicate that puerarin can acutely modulate vasoconstriction and vasodilation in porcine coronary arteries. The present findings also suggest that the beneficial effect of puerarin on endothelium-dependent relaxation is mediated via cyclic AMP-dependent cascade and possibly Gs protein.

Word count = 482

Signed .

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