Abstract
The effects of SGB-483, a newly-synthesized hypotensive agent, on the blood pressure were studied in unanesthetized and anesthetized rats. SGB-483 produced a significant hypotensive action in the conscious SHR and renal hypertensive (clipping) rats, and it caused reversal of the pressor response to adrenaline in the anesthetized Wistar-Imamichi rats, SHR, and clipping rats. In an isolated guinea pig aorta preparation, SGB-483 competitively inhibited the contractile response to phenylephrine with a pA2 value of 7.64±0.08. In pithed rats that were pretreated with β-adrenoceptor blocker, the pressor effect of adrenaline (1 μg/kg) was not completely blocked by either prazosin (1 mg/kg), an al-selective blocker, or yohimbine (1 mg/kg), an α2-selective blocker. SGB-483 (1 mg/kg) had no effects on the prazosin-resistant part of the pressor effect of adrenaline, but significantly inhibited the yohimbine-resistant part. Clonidine-induced reversal of the tachycardia induced in the pithed rat by cardiac sympathetic nerve stimulation was unaffected by SGB-483, indicating that SGB-483 is a selective antagonist of the α1-adrenoceptor.
