LANDIS AWARD LECTURE - MYOGENIC RESPONSE AND MICROCIRCULATION

As the evidence for the myogenic response has become more substantial over the years, questions have been raised as to the underlying mechanism. On the one hand, it is well known that when smooth muscle is stretched it will respond by contracting. However, the behavior that is observed goes well beyond a simple transient response to stretch, because, in the steady state, the vessel is smaller with higher intravascular pressure. How can a vessel maintain the smaller diameter if the stimulus is stretch of the smooth muscle cells? Two ways are discussed. Sensitivity of the vessels to blood flow was observed. There may be an interaction between pressure-dependent and flow-dependent mechanisms such that the reaction of the pressure-dependent mechanism would be modulated somewhat by the flow sensitivity of the arteriole. If the myogenic mechanism were weak, it would be augmented, and, if it were strong, it would be attenuated by the flow-dependent mechanism. The 2 mechanisms may act in combination to give a reasonably constant flow through an organ, although the basic mechanism might be a myogenic response with the fine tuning, so to speak, carried out by the flow-dependent mechanism. Microscopic studies provide evidence in favor of the myogenic hypothesis.