ANTIDIURETIC HORMONE IN THE SERUM OR PLASMA OF RATS1

Abstract

THE recent reports of Birnie and his colleagues were the first describing the antidiuretic action of serum of normal or adrenalectomized rats (Birnie et al., 1949 and 1950). Their results suggested that antidiuretic hormone of neurohypophysial origin can be detected in rather high concentration in rat serum especially after adrenalectomy. Subsequently, Dicker and Ginsburg (1950) concluded that heparinized plasma of rats lacks the antidiuretic substance which can be detected in serum. Their report implied that the antidiuretic substance is an artifact of the clotting process. It seemed important to reinvestigate various aspects of these findings. Does circulating blood in the normal rat contain antidiuretic hormone in relatively enormous concentrations represented by approximately 0.75 milli-unit of Pitressin per ml. of serum? Can a more reliable estimate of the amount of antidiuretic substance in serum be made than is possible if assays are performed by intraperitoneal or subcutaneous injection into rats? Is the concentration markedly increased following adrenalectomy