Myogenic Nature of Increase in Intestinal Vascular Resistance with Venous Pressure Elevation

Abstract

These studies attempted to distinguish between the various intrinsic mechanisms which might be responsible for the increase in vascular resistance seen in the intestine with venous pressure elevation (the venous-arteriolar response). Intra-arterial infusion of procaine did not block the response, indicating that a local reflex is not involved. However, the resistance increase was greatly modified during infusion of a smooth muscle relaxant (papaverine). Cyanide and ischemia were more effective than papaverine, resistance remaining unchanged as venous pressure was elevated. The tone of the intestinal wall was not increased with venous pressure elevation. In preparations perfused with an oil-kerosene mixture, resistance decreased as venous pressure was elevated, although intravascular and extravascular fluid accumulation was quantitatively the same as in the blood-perfused control. It is concluded that the venous-arteriolar response is not dependent upon neural mechanisms, nor is it due to purely physical factors. It is suggested that elevation of venous pressure causes sufficient increase of arteriolar pressure to induce a myogenic response of the resistance vessels.