A new classification of β-adrenoceptor blocking drugs

Partial agonist activity of celiprolol, a cardioselective beta-antagonist

The beta-antagonistic effects of celiprolol were assessed in isolated guinea-pig preparations. The pA2 values obtained were 7.84 +/- 0.07, 7.79 +/- 0.06 and 6.45 +/- 0.11 against the positive chronotropic and inotropic effects in the atria and relaxant effects in the trachea induced by isoproterenol, respectively, indicating that celiprolol is a cardioselective beta-antagonist. Celiprolol produced slight positive chronotropic and inotropic effects in atrial preparations and a uniquely strong relaxant effect in tracheal preparations. All these effects were attenuated by pretreatment with 10(-6) M atenolol or 10(-6) M propranolol. In pithed rats, celiprolol produced pressor responses at doses lower than 0.03 mg/kg and hypotensive responses at doses higher than 0.3 mg/kg. It produced sustained increases in heart rate in all doses applied. These effects were attenuated by pretreatment with 1 mg/kg of propranolol. The pressor response might be taken to be a reflection of an increase in cardiac function mediated by cardiac beta 1-receptor stimulation, while the hypotension may be ascribed mainly to stimulation of beta 2-adrenoceptors in the vascular system. It is concluded that celiprolol exerts a uniquely strong partial agonist activity at beta 2-adrenoceptors.

An analysis of blood pressure effects of nipradilol and prizidilol in normotensive and spontaneously hypertensive rats

Nipradilol and prizidilol are beta-adrenoceptor blocking drugs with vasodilator action. These drugs lowered blood pressure (BP) in spontaneously hypertensive (SHR) rats acutely (24 hr) and subacutely (3 weeks) at doses of 10 and 20 mg/kg per day, p.o., respectively. Nipradilol decreased plasma renin concentration in acute and subacute studies, whereas it was unchanged with prizidilol treatment. Paradoxical effects of these drugs on BP were analyzed further: BP determined indirectly at the tail was slightly higher in SHR rats than the control, whereas BP determined directly through an aortic cannula without anesthesia, restraint, or prewarming was lower. We found that the discrepancy between BP values determined directly and indirectly was due to the increase in BP by prewarming stress during the determination by the tail cuff method.