Mechanisms of pressure-induced myogenic activation of cerebral and renal arteries: role of the endothelium.

Control of blood flow is mediated by a variety of metabolic, neurogenic, myogenic and other mechanisms. The basic response of the myogenic mechanisms is a mechanical stimulus that activates vascular muscle via a sensor within the vessel wall. We studied the way in which increases in transmural pressure within the physiological range can activate cerebral and renal vascular muscle by depolarizing the muscle cell membrane. These membrane electrical effects depend on the external calcium concentration [( Ca2+]o) and on the presence of an intact vascular endothelium. Bioassay experiments have shown that an elevation in pressure releases a vasoactive product(s) from endothelial cells, which mediates the pressure-dependent membrane depolarization in these vessels. These responses may affect the autoregulation of blood flow in that vessels become smaller as pressures increase between 60 and 160 mmHg.