Effects of prenalterol and its N-homoveratryl derivative in the anaesthetized cat.

Abstract

The in vivo activity of prenalterol (P), its N-homoveratryl derivative (Compound XI) and (−)-isoprenaline (ISO) have been assessed in vagotomized, chloralose anaesthetized cats. The three compounds produced the same maximal tachycardia, P and XI being 76 and 202 times less potent than ISO as agonists. P and XI had little effect on mean blood pressure. All doses used produced an atenolol-sensitive increase in systolic pressure. Reductions in diastolic pressure were obtained with doses that were supramaximal for cardiac effects. P and XI were inactive as vasodilators in the perfused hind-limb. Dilator responses to i. a. ISO in the hind-limb were antagonized by i. v. doses of P and XI which produced supramaximal effects on the heart. All three compounds produced a β-receptor mediated reduction in soleus muscle contractility. P and XI had intrinsic activities of approximately 0.8 and were 513 and 7956 times less potent than ISO respectively. Comparisons of results obtained in the heart and soleus muscle showed that P and XI had a 7 and 39-fold selectivity as cardiac stimulants respectively. Infusions of ISO, P and XI produced increases in heart rate, cardiac output and stroke volume and decreases in total peripheral resistance. None of the compounds displayed selective inotropic actions. ISO decreased mean blood pressure while small increases were obtained with P and XI. All the cardiovascular effects produced by P and XI were reversed following the injection of atenolol.