Site of Action of Cocaine on the Perfused Artery

Abstract

THE histochemical investigation of tissue sections containing arteries using the fluorescence technique indicates that the noradrenergic structures are superimposed on the outer surface of the smooth muscle layer¹. Applying the same technique to the central artery of the rabbit ear, we have found that catecholamine-like fluorescence occurs only in the layer immediately outside the circular smooth muscle, between this muscle and the adventitia. The fluorescence appears as a series of discrete bead-like structures uniformly distributed around the perimeter of the smooth muscle layer as shown in Fig. 1. The histological observations drew our attention to the possibility that uptake of noradrenaline by the artery was restricted to sites at the outer perimeter of the smooth muscle layer and, if so, the action of drugs such as cocaine which inhibit uptake of noradrenaline and sensitize the arterial wall to its action may be influenced by the particular surface of the artery to which the noradrenaline is applied. The following experiment shows that this is the case.