Influence of endothelium on noradrenaline-induced vasoconstriction in rabbit central ear artery.

The effects of removing the endothelium of the rabbit central ear artery on the response to noradrenaline have been examined in vitro. A 10 mm segment of this artery was cannulated and connected to a constant flow perfusion circuit; the endothelium of some arteries was first removed mechanically. Vasomotor activity was determined by measuring the pressure at the input to the artery. Scanning electron microscopy, light microscopy and functional test with acetylcholine on intact and rubbed arteries showed that the endothelium had been effectively removed in lesioned arteries and remained intact in control arteries throughout the experiment. Internal or external noradrenaline-induced a concentration-dependent constriction which was significantly greater in the rubbed arteries. In contrast, there was no significant difference in the pressure/flow curves of control and rubbed arteries whether preconstricted with K+ or not. We conclude that the endothelium in the rabbit isolated ear artery greatly influences the response to internal or external noradrenaline, and that this effect cannot be explained by changes in the physical characteristics of de-endothelialized arteries. The endothelium thus may play an inhibitory role in noradrenaline-induced vasoconstrictions.