“…The pharmacokinetics of propranolol were compared with those of the f51-adrenoceptor selective blocker SL 75212 which has similar physicochemical characteristics (Davies & Turner, 1979) but which, unlike propranolol, undergoes little 'first-pass' loss (F = 80%, Bianchetti, Gomeni, Kilborn, Morselli, Taylor & Warrington, 1979 (dl-3-[2-(3-t-butylamino-2-hydroxypropoxy)phenyl]-6-hydrazinopyridazine) is a new compound which has been shown to combine ,B-adrenoceptor blockade with hydralazine-like vasodilatation both in animals (Taylor, Roe & Slater, 1979) and in man (Collier & Pitcher, 1980). In the present study the P-adrenoceptor blocking activity in six normal subjects of a single oral dose of 200 mg SK & F 92657 was assessed and compared to that of placebo and that of propranolol 40 mg, by measuring heart rate and blood pressure responses to intravenous infusions of isoprenaline at intervals up to 7 h after drug administration.…”