A Comparison Between the Vascular Responses to Adrenaline and Noradrenaline in Individual Skeletal Muscles of the Cat

Abstract

The effects of intra-arterially and intravenously administered adrenaline and noradrenaline on the venous outflow from individual muscles in the hind limbs of cats under chloralose anaesthesia were studied. The various responses to these amines were shown to depend on the dose administered, the route of injection, the general arterial blood pressure and the vasomotor tone in the muscle. They did not vary with the type of muscle studied. When the vasomotor tone was high, intra-arterially administered adrenaline caused vasodilatation, vasoconstriction or a compound response according to the dose administered. Intra-arterially administered noradrenaline caused only vasoconstriction. However, both intravenously administered adrenaline and noradrenaline in small doses caused vasodilatation in skeletal muscles, the former being the more potent. That this effect depended on intact nervous connections was confirmed in cross-circulation experiments in which the muscle of one cat was perfused entirely by blood from a donor cat. When the vasomotor tone in the muscle was low, either naturally or as a result of acute denervation, it was difficult to produce any dilatation with adrenaline, and noradrenaline always caused vasoconstriction. Under these conditions, the increase in blood flow produced by the intravenous administration of the amines was shown, by means of a blood pressure stabiliser, to be a passive effect caused by the rise in blood pressure forcing more blood through the muscles.