The effect of uptake by adrenergic nerve terminals on the sensitivity of arterial vessels to topically applied noradrenaline.

1. Direct observations were made of the rat mesenteric vasculature in vivo. They showed a gradual increase in the sensitivity to topically applied noradrenaline from the larger arteries to the precapillary arterioles which was paralleled by a gradual decrease in the density of the adrenergic innervation. 2. Both cocaine and chronic denervation increased the sensitivity to noradrenaline of the innervated arterial vessels, approximately in proportion to the density to their innervation. They did not affect the sensitivity of the non-innervated precapillary arterioles. 3. It is concluded that the sensitivity gradient to topically applied noradrenaline results mainly from the uptake of the applied catecholamine by the perivascular nerve terminals.