Effects of venous pressure elevation on myogenic vasoconstrictive responses to static and dynamic arterial pressures.

In order to establish the nature of the stretch-evoked dynamic properties of vascular smooth muscle in arterioles, we have examined the static and dynamic effects of both arterial pulse pressure and elevated venous pressure on the resistance vessels (arteries and arterioles) in an intestinal mesenteric preparation derived from dogs. The dynamic myogenic response to stretch stimuli was directly related to both the frequency of arterial pulse pressure (1-20 c/min) and the level of venous pressure (0-45 mmHg). Under elevated venous pressure (20 mmHg), the mean arterial flow decreased with an increase in the frequency of arterial pulse pressure. The arteriolar vascular tone (namely, vascular resistance) was seen to be enhanced. We found that elevated venous pressure promotes active constriction (9-53%) of arteriolar smooth muscle (myogenic mechanism). The elevation of venous pressure also caused a rhythmic constriction (vasomotion) in the site of both vein and artery, which was completely abolished by an alpha-blocker (phentolamine). The results suggest that during venous pressure elevation a very pronounced myogenic constriction in terminal arterioles is caused by either a local neural reflex or a propagated myogenic response in the arteriolar network.