Pharmacological properties of the stereoisomers of prizidilol: their use in analysis of reflex tachycardia and blood pressure control in normotensive cats, rats, and dogs

Prizidilol, a combined vasodilator/beta-adrenoceptor antagonist, has two optical isomers. The pharmacological activities of these isomers have been established and heart rate/blood pressure responses to both isomers have been determined. Both the R and S isomers elicited similar blood pressure lowering and vasodilator activity in anaesthetised normotensive rats. S-Prizidilol was a substantially more potent beta-adrenoceptor antagonist in vitro and in vivo than R-prizidilol. Neither optical isomer showed any specificity for either beta 1- or beta 2-adrenoceptors. In conscious rats both isomers lowered blood pressure similarly with only marginal differences in heart rate. In conscious cats the importance of increased sympathetic drive in reflex tachycardia was emphasised by the incidence of tachycardia after R-prizidilol but not after S-prizidilol when administered at equieffective blood pressure lowering doses. In conscious dogs both isomers caused tachycardia although S-prizidilol tended to cause the greater fall in blood pressure.