CONTRACTILE ACTIONS OF RACEMIC AND D-PROPRANOLOL ON ISOLATED CANINE MESENTERIC AND CORONARY-ARTERIES

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  • 1 January 1982
    • journal article
    • research article
    • Vol. 220  (1) , 127-132
Abstract
Propranolol may exert a direct vasoconstrictor action which contributes to the increased systemic and regional vascular resistance observed after its acute administration. Helically cut strips of canine mesenteric and coronary arteries were exposed to cumulative concentrations of racemeic propranolol, d-propranolol, metoprolol and sotalol. Racemic and d-propranolol were equipotent in eliciting concentration-related increments in tension in the mesentric (3 .times. 10-6 -3 .times. 10-5 M) and coronary (3 .times. 10-7 -3 .times. 10-5 M) arterial strips. Metoprolol and sotalol did not cause contractions in concentrations up to 10-4 M. Phenoxybenzamine, 10-6 M, did not alter the contractile responses elicited by racemic and d-propranolol. Upon exposure of mesenteric strips to Ca-free media or 10-6 M verapamil, the contractile responses to propranolol (3 .times. 10-5 M) and KCl (30 mM) were markedly reduced (not significantly different); norepinephrine (10-6 M)-induced responses were inhibited to a significantly lesser degree. In coronary arteries exposed to Ca-free media or 10-6 M verapamil, the responses to propranolol, KCl and methoxamine (10-5 M) were all extensively decreased (not significantly different). Propranolol apparently exerted a direct contractile effect on canine mesenteric and coronary arteries, which is unrelated to its .beta. adrenergic blocking activity and is not mediated through action on .alpha. adrenergic receptors. The propranolol-induced contractions were apparently associated predominantly with an influx of Ca ion.