Role of the Pituitary in Restitution of Blood Volume after Hemorrhage*

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Abstract
Blood volume restitution after hemorrhage depends upon restoration of plasma protein from the interstitium. This fluid shift is induced by hyperosmolality, which is mediated in part by increased cortisol; but infusion of cortisol, in the absence of hemorrhage, does not change plasma osmolality. To test the possibility that pituitary hormones may be implicated in both blood volume and plasma protein restitution, intactsplenectomized, adrenalectomized-splenectomized, and hypophysectomized-splenectomized dogs, anesthetized with pentobarbital, were hemorrhaged (7.5 ml/kg), and restitution of blood volume and plasma protein, osmolality, cortisol, and arterial pressure were determined. The adrenalectomized dogs were infused with cortisol either at a basal rate or at a high rate. The hypophysectomized dogs were infused only with cortisol (high rate) alone or with an infusion of saline. Adrenalectomized dogs infused with cortisol at a basal rate showed a decrease in osmolality and no restitution of blood volume or plasma protein at 24 h. Hypophysectomized dogs infused only with cortisol showed no change in osmolality and an attenuated restitution of blood volume and plasma protein. Hypophysectomized dogs infused with both cortisol and saline showed no change in osmolality but showed accelerated and complete restitution of blood volume and plasma protein. Linear relations were found between plasma protein restitution and blood volume restitution, and between hyperosmolality and plasma protein restitution. The results indicate that increased cortisol, an additional adrenal factor, and a pituitary factor are required for restitution of blood volume and plasma protein after hemorrhage and suggest that their effects are mediated through hyperosmolality.