Blood flow, vascular resistance, and blood volume after hemorrhage in conscious adrenalectomized rat

Hemorrhage leads to cardiovascular collapse and death in adrenal-insufficient animals. To determine whether the cardiovascular collapse is due to vasodilation and/or failure to restore blood volume, we used radiolabeled microspheres and 125I-labeled albumin to measure blood flow and blood volume in conscious adrenalectomized (ADX) rats after 15 ml.kg-1.3 min-1 hemorrhage. In ADX rats, hemorrhage led to a greater fall than in sham rats in blood flow in the stomach, small intestines, cecum, colon, spleen, hepatic portal vein, kidney, testis, lung, thymus, bone, fat, forebrain, cerebellum, and brainstem. The greater fall in blood flow was caused by an increase in vascular resistance in these organs except brain and hepatic artery. Sham rats maintained or increased brain and hepatic artery blood flow after hemorrhage whereas flow decreased and remained depressed in ADX rats. ADX rats failed to restore blood volume, whereas sham rats completely restored blood flow by 2 h. We conclude that cardiovascular collapse in ADX rats does not result from vasodilatation but may result from a failure to restore blood volume. The failure to restore blood volume and the low blood flow to organs, especially brain and liver, may contribute to mortality in ADX rats after hemorrhage.