The hypotensive effect of 2-(5-chloro-2-phenoxyanilino)-2-imidazoline (FR35447)

The hypotensive effect of FR35447 was comparable to that of prazosin and was more potent than that of hydralazine, but its duration of action was shorter. Repeated administration of FR35447 or prazosin to hypertensive rats for 5 consecutive days induced no significant difference in the intensity or duration of the hypotensive effect. In contrast, marked tachyphylaxis to hydralazine or phentolamine was observed. FR35447 as well as prazosin induced only a transient increase in cardiac output in anesthetized dogs, whereas hydralazine induced a longlasting increase. This difference may contribute to no development of tolerance to FR35447 or prazosin. FR35447 decreased the pressor response to noradrenaline, but not that to angiotensin II or vasopressin in pithed rats, which indicates that FR35447 is an alpha-adrenoceptor antagonist. FR35447 has some selectivity for alpha 2-adrenoceptors, but the selectivity was far less than that of yohimbine. Since FR35447 induced only slight hypotension following intracerebroventricular injection in anesthetized cats, the hypotensive effect of the drug does not appear to be mediated through the central nervous system. Whereas prazosin induced a dose-dependent increase in blood glucose in rats, FR35447 showed no significant effect.