Green Tea Extract (CUMC6335), not Epigallocatechin Gallate, Cause Vascular Relaxation in Rabbits

The aim of the present study was to examine whether green tea extract (CUMC6335) affects the blood pressure and the isolated aortic contractility of the rabbit in comparison with one of the most powerful active catechins, epigallocatechin gallate (EGCG). The phenylephrine $(1-10\;{\mu}M)-induced$ contractile responses were greatly inhibited in the presence of CUMC6335 (0.3-1.2 mg/ml). Also, high potassium (56 mM)-induced contractile responses were depressed in high concentration (0.6-1.2 mg/ml), but not affected in low concentration CUMC6335 (0.3 mg/ml). However, epigallocatechin gallate $(EGCG,\;4-12\;{\mu}g/ml)$ did not affect the contractile responses evoked by phenylephrine and high $K^+$. The infusion of CUMC6335 with a rate of 20 mg/kg/30 min made a significant reduction in pressor responses induced by intravenous norepinephrine. However, EGCG (1 mg/kg/30 min) did not affect them. Collectively, these results obtained from the present study suggest that intravenous CUMC6335 causes depressor action in the anesthetized rat at least partly through the blockade of adrenergic ${\alpha}_1-receptors$. CUMC6335 also causes the relaxation in the isolated aortic strips of the rabbit partly via the blockade of adrenergic ${\alpha}_1-receptors$, in addition to the unknown direct mechanism. It seems that there is no species difference in the vascular effect between the rat and the rabbit.