Cardiovascular and flux relationships in canine ileum

Abstract

Blood flow and pressure in denerved ileum of anesthetized dogs were altered by occlusion of the mesenteric artery or vein or by infusion of intraarterial sodium nitroprusside (0.015-1.5 mg/min). Unidirectional Na and H2O fluxes were measured and absorptive site blood flow was estimated from the clearance of tritiated H2O. Net Na and H2O absorptions were reduced by mesenteric venous or arterial occlusion. Net secretion occurred with mesenteric venous occlusion. Nitroprusside reduced net absorption only at an infusion rate of 0.15 mg/min. The absorptive Na and H2O fluxes were reduced by both mesenteric venous or arterial occlusion, with venous occlusion being more effective. Nitroprusside reduced the absorptive Na flux at an infusion rate of 0.15 mg/min but not the absorptive H2O flux. The secretory flux of Na was increased by mesenteric venous occlusion but reduced by arterial occlusion and not changed by nitroprusside infusion. The secretory H2O flux was decreased by moderate degrees of mesenteric venous occlusion but was unchanged at greater levels. Arterial occlusion decreased secretory H2O fluxes. Nitroprossude infusion increased secretory H2O fluxes at an infusion rate of 0.015 mg/min. The absorptive and secretory Na and H2O fluxes were significantly correlated with absorptive site blood flow plus estimated capillary pressure. Absorptive site blood flow was primarly responsible for changes in absorptive fluxes and estimated capillary pressure for changes in secretory fluxes. Absorptive site blood flow affected the secretory and absorptive fluxes of H2O more equally than the Na fluxes. Apparently absorptive site blood flow affected H2O fluxes primarily by altering diffusional exhange but affected the Na fluxes primarily by O2 delivery. Capillary pressure primarily affected the secretory fluxes through effects on ultrafiltration.