Comparison of green tea extract and epigallocatechin gallate on secretion of catecholamines from the rabbit adrenal medulla

The present study was designed to examine the effects of green tea extract (CUMC6335) and epigallocatechin gallate (EGCG) on secretion of catecholamines (CA) in the isolated perfused rabbit adrenal gland. In the presence of CUMC6335 (200 μg/mL) into an adrenal vein for 60 min, CA secretory responses evoked by ACh (5.32 mM), high K+ (56 mM), DMPP (100 μM for 2 min), and Bay-K-8644 (10 μM for 4 min) from the isolated perfused rabbit adrenal glands were greatly inhibited in a time-dependent fashion. However, EGCG (10 μg/mL) did not affect CA release evoked by ACh, high K+, and Bay-K-8644. CUMC6335 itself failed to affect basal catecholamine output. Taken together, these results demonstrate that CUMC6335 inhibits CA secretion evoked by stimulation of cholinergic nicotinic receptors, as well as the direct membrane depolarization from the isolated perfused rabbit adrenal gland. It is thought that this inhibitory effect of CUMC6335 may be due at least in part to the blocking action of the L-type dihydropyridine calcium channels in the rabbit adrenomedullary chromaffin cells, which is relevant to the cholinergic nicotinic blockade. It seems that there is a big difference in mode of action between CUMC6335 and EGCG.