RESPONSES OF BLOOD CAPILLARIES TO ACUTE HEMORRHAGE IN THE RAT

Abstract

Rats anesthetized with Na pento-barbital were subjected to acute hemorrhage while observations were made on the circulation in the mesoappendix and in the skin of the hind foot. Vasoconstriction always ap-pears earlier in the skin, is more pronounced and is of longer duration than in the mesoappendix. Hemorrhage accentuates the vasomotion of the peripheral muscular vessels and results in the development of a hyper-reactive response to mechan- ical and chemical stimuli. These compensatory reactions persist into the terminal stages of circulatory failure. In the mesoappendix the flow from the arterioles tends to bypass the capillary bed. When the flow into the capillary bed fails, the blood, shunted across to the venules, reverses its direction and flows backward into the capillaries where it stagnates. It is to be inferred that the circulatory failure is due not so much to a deterioration of the intrinsic properties of the capillary bed as to the lack of propulsive force from the lowered blood pressure.