Pre- and postcapillary resistances in cat mesentery

Abstract

The hemodynamic behavior of the isolated autoperfused intestinal loop (including mesenteric segment) of the cat was studied in terms of inflow and outflow pressures ( BP and VP), arteriolar and venular pressures ( P a and P v ), and blood flow ( Q). The regional vascular resistance [ RR = (BP − VP) Q ] was subdivided into a precapillary resistance [ P r R = (BP − P a) Q ], capillary resistance [ CR = (P a − P v) Q ], and postcapillary resistance [ P s R = (P v − VP) Q ]. With normal perfusion pressure it was found that: P r R = 68%, P s R = 20.5% and CR = 11.5%. Two different responses were noted when perfusion pressure was lowered to 20mm Hg. In the first group, precapillary resistance fell significantly, whereas postcapillary resistance did not change. In the second group, the regional resistance increased due to the increase in precapillary resistance and a significantly greater increase in postcapillary resistance. The regulatory mechanism in the first group is based on local readjustment of the precapillary vasculature with no participation of postcapillary vessels. The second group of responses appears to be related to completely dilated vessels, where regulation is achieved by increasing postcapillary resistance in an attempt to maintain the capillary pressure and homeostatic balance.