Influence of Fimasartan (a Novel AT₁Receptor Blocker) on Catecholamine Release in the Adrenal Medulla of Spontaneously Hypertensive Rats

Abstract

The aim of this study was to determine whether fimasartan, a newly developed AT1 receptor blocker, can affect the CA release in the isolated perfused model of the adrenal medulla of spontaneously hypertensive rats (SHRs). Fimasartan (5~50 µM) perfused into an adrenal vein for 90 min produced dose- and time-dependently inhibited the CA secretory responses evoked by ACh (5.32 mM), high K+ (56 mM, a direct membrane depolarizer), DMPP (100 µM) and McN-A-343 (100 µM). Fimasartan failed to affect basal CA output. Furthermore, in adrenal glands loaded with fimasartan (15 µM), the CA secretory responses evoked by Bay-K-8644 (10 µM, an activator of L-type Ca2+ channels), cyclopiazonic acid (10 µM, an inhibitor of cytoplasmic Ca2+-ATPase), and veratridine (100 µM, an activator of Na+ channels) as well as by angiotensin II (Ang II, 100 nM), were markedly inhibited. In simultaneous presence of fimasartan (15 µM) and L-NAME (30 µM, an inhibitor of NO synthase), the CA secretory responses evoked by ACh, high K+, DMPP, Ang II, Bay-K-8644, and veratridine was not affected in comparison of data obtained from treatment with fimasartan (15 µM) alone. Also there was no difference in NO release between before and after treatment with fimasartan (15 µM). Collectively, these experimental results suggest that fimasartan inhibits the CA secretion evoked by Ang II, and cholinergic stimulation (both nicotininc and muscarinic receptors) as well as by membrane depolarization from the rat adrenal medulla. It seems that this inhibitory effect of fimasartan may be mediated by blocking the influx of both Na+ and Ca2+ through their ion channels into the rat adrenomedullary chromaffin cells as well as by inhibiting the Ca2+ release from the cytoplasmic calcium store, which is relevant to AT1 receptor blockade without NO release.

Pharmacological Profiles of a Highly Potent and Long-Acting Angiotensin II Receptor Antagonist, Fimasartan, in Rats and Dogs after Oral Administration

“…Co., Ltd., Seoul, Republic of Korea) was approved by the Korea Food and Drug Administration (KFDA) in 2010 for the treatment of essential hypertension. Several nonclinical and clinical studies have been conducted on fimasartan, for example, (1) clinical studies have been undertaken on its efficacy and safety in large populations 8,9) and interactions with other concomitant drugs [10][11][12] and (2) nonclinical studies have investigated the mechanistics underlying its other pharmacological activities, such as, its inhibitory effect on catecholamine secretion, 13) its cardioprotective effect, which was attributed to the prevention of mitochondrial damage, 14) its anti-atherosclerotic effect, 15) and its anti-inflammatory potential.…”