Comparison of green tea extract and epigallocatechin gallate on blood pressure and contractile responses of vascular smooth muscle of Rats
2003
Lim, Dong -Yoon | Lee, Eun Sook | Park, Hyeon -Gyoon | Kim, Byeong -Cheol | Hong, Soon -Pyo | Lee, Eun -Bang
The present study was conducted to investigate the effects of green tea extract (GTE) on arte-rial blood pressure and contractile responses of isolated aortic strips of the normotensive rats and to establish the mechanism of action. The phenylephrine (10~ᵖ⁶~10~ᵖ⁵M)-induced contrac-tile responses were greatly inhibited in the presence of GTE (0.3–1.2 mg/mL) in a dose-depen-dent fashion. Also, high potassium (3.5x10-ᵖ²~5.6x1CTᵖ² M)-induced contractile responses were depressed in the presence of 0.6–1.2 mg/mL of GTE, but not affected in low concentration of GTE (0.3 mg/mL). However, epigallocatechin gallate (EGCG, 4–12 ug/mL) did not affect the contractile responses evoked by phenylephrine and high Kᵖ⁺. GTE (5–20 mg/kg) given into a femoral vein of the normotensive rat produced a dose-dependent depressor response, which is transient. Interestingly, the infusion of a moderate dose of GTE (10 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 demonstrate that intravenous GTE causes a dose-dependent depressor action in the anesthetized rat at least partly through the blockade of adrenergic α₁-receptors. GTE also causes the relaxation in the isolated aortic strips of the rat via the blockade of adrenergic α₁-receptors, in addition to the unknown direct mechanism. It seems that there is a big differ-ence in the vascular effect between GTE and EGCG.
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