β-adrenoreceptor blocking and antihypertensive activity of PP-24, a newly synthesized aryloxypropanolamine derivative

PP-24 is a newly synthesized putative beta-adrenoceptor antagonist. The objective of the study was to the evaluate beta-adrenoceptor blocking activity of PP-24 on isolated rat preparations: right atria, uterus and colon. Effects on the rat ECG and renal hypertension (induced by left renal artery ligation) were also investigated. Treatment with PP-24 Q and 10 mg kg(-1)) for 7 days in rats with renal hypertension significantly reduced the mean atrial blood pressure. Single i.v. injections of isoprenaline (0.3, 1 and 3 mu g kg(-1)) alone in normal anaesthetized rat caused hypotension and tachycardia, while PP-24 alone produced dose-dependent falls in mean aterial pressure and bradycardia. Pretreatment of anaesthetized rats with test compounds significantly blocked the hypotension response but not the tachycardia induced by isoprenaline (0.3, 1 and 3 mu g kg(-1)). The pA(2) of PP-24 to beta(1)-, beta(2)- and beta(3)-adrenoceptors was 7.72 +/- 0.082, 7.40 +/- 0.082 and 6.39 +/- 0.16, respectively. The beta(1)/beta(2) selectivity ratio was 2.08, compared with 1.27 for propranolol and 39.17 for atenolol. It is concluded that PP-24 possesses beta-adrenoceptor blockade activity but with non-specific affinity for beta(1)- and beta(2)-adrenoceptor subtypes. The rank order of potency of the antagonists for beta(1)-adrenoceptors was atenolol > PP-24 > propranolol. The anti hypertensive activity of PP-24 in rats with renal hypertension appears to be due to blockade of beta-adrenoceptors.