Transcapillary fluid movements in sympathectomized intestine and skin during hemorrhagic hypotension

Net transcapilary fluid exchange in skin tissue (paw) and small intestine was observed during a 90 min period of hemorrhagic hypotension at 50 mm Hg in the cat. Reflex fluid transfer was prevented by regional sympathectomy and chi-adrenergic blockade. Early in hemorrhage, fluid absorption from the extravascular space occurred in both tissues, apparently caused by osmosis. The process was thus co-ordinated in time with a positive arterio-venous osmolar difference, in turn caused by a marked arterial hypersomolality. Experimetnal arterial hyperosomolality of similar magnitude, created by i.v. infusion of hypertonic glucose in non-bled animals, led to transcapillary fluid absorption in both intestine and skin and at rates similar to those in bleeding. Regional hypotsionen per se caused no fluid absorption. Later in hemorrhage (greater than 30 min), plasma fluid moved into the extravascular space both in skin and intestine, apparently due to a gradual increase of cappilary hydrostatic pressure. It is concluded that the arterial hypersomolality during bleeding can cause transcapillary fluid absorption in intestinal and skin tissues, as previously shown for skeletal muscle (Järhult 1973). The hemodynamic significance of this process for plasma volume regulation in hemorrhage is, however, much greater in skeletal muscle than in intestine and skin, mainly due to the much larger total mass of the muscle tissue.