Role of solute in the early restitution of blood volume after hemorrhage.

We examined the putative roles of decreased capillary pressure and increased transcapillary osmolar gradient in mediation of the early restitution of blood volume after hemorrhage by comparing the degree of restitution of plasma volume and protein and comparing changes in capillary pressure and osmolality in awake dogs with those in dogs anesthetized with pentobarbital. Decreases in estimated capillary pressure and increases in plasma osmolality were greater in anesthetized than in awake dogs. However, early restitution of plasma volume and of protein was greater in awake animals. Analysis of the Starling forces indicated that interstitial hydrostatic pressure was greater in awake animals than in anesthetized animals, suggesting that interstitial volume increases more rapidly in awake animals. Selective venous sampling in anesthetized dogs indicated that the splanchnic and renal vascular beds release solute to the circulation following hemorrhage. However, rather than promoting the restitution of blood volume by production of a transcapillary osmolar gradient, the data suggest that the solute is delivered to the peripheral tissues, where it mediates the movement of water from cells to the interstitium more rapidly in awake than in anesthetized dogs. It thus appears that the early metabolic changes after hemorrhage, resulting in increased solute production, are important for the early restitution of blood volume and plasma protein.