❙ABSTRACT❙ Background: The present study was attempted to compare enalapril, an angiotensin-converting enzyme inhibitor with losartan an angiotensin II (Ang II) receptor blocker in the inhibitory effects on the secretion of catecholamines (CA) from the perfused model of the rat adrenal gland. Methods: The adrenal gland was isolated and perfused with Krebs-bicarbonate. CA was measured directly by using the fluorospectrophotometer. Results: Both enalapril and losartan during perfusion into an

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... nal vein for 90 minutes inhibited the CA release evoked by acetylcholine (ACh), 1.1-dimethyl-4-phenyl piperazinium (DMPP, a selective N n agonist), high K + (a direct membrane-depolarizer), 3-(m-chloro-phenyl-carbamoyl-oxy-2-butynyltrimethyl ammonium (McN-A-343, a selective M 1 agonist), and Ang II in a time-dependent manner. Also, in the presence of enalapril or losartan, the CA release evoked by veratridine (an activator of voltage-dependent Na + channels), 6-dimethyl-3-nitro-4-(2-trifluoromethyl phenyl)-pyridine-5-carboxylate (BAY-K-8644, an L-type Ca -2+ channel activator), and cyclopiazonic acid (a cytoplasmic Ca 2+ -ATPase inhibitor) were significantly reduced. Based on the same concentration of enalapril and losartan, for the CA release evoked by ACh, high K + , DMPP, McN-A-343, Ang II, veratridine, BAY-K-8644, and cyclopiazonic acid, the following rank order of inhibitory potency was obtained: losartan > enalapril. In the simultaneous presence of enalapril and losartan, ACh-evoked CA secretion was more strongly inhibited compared with that of enalapril-or losartan-treated alone. Conclusions: Collectively, these results demonstrate that both enalapril and losartan inhibit the CA secretion evoked by activation of both cholinergic and Ang II type-1 receptors stimulation in the perfused rat adrenal medulla. When these two drugs were used in combination, their effects were enhanced, which may also be of clinical benefit. Based on concentration used in this study, the inhibitory effect of losartan on the CA secretion seems to be more potent than that of enalapril. (J Korean Soc Hypertens 2014;20(2):51-67)