Changes in Plasma Levels of 17-Hydroxycorticosteroids During the Intravenous Administration of Adrenocorticotropin (Acth). Iv. Response to Prolonged Infusions of Small Amounts of Acth*

Continuous intravenous infusions of ACTH at rates of 0.8 to 1.4 i.u. per twenty-four hours maintained the plasma concentration of free 17-hydroxy-corticosteroids above the maximal levels attained spontaneously during a diurnal variation. No diurnal variation of the plasma level of free 17-hydroxycorticosteroids was observed during these sustained elevations produced by infusions of ACTH at rates greater than 0.8 i.u. per day. In males the maximal plasma 17-hydroxycorticosteroid levels can probably be achieved during the normal diurnal variation by the secretion of ACTH at a rate of less than 4 i.u. per day for a period of less than four hours. Continuous infusion of very small amounts of ACTH increased the capacity of the adrenal to produce 17-hydroxycorticosteroids, whether or not increased steroid secretion resulted from the initial infusion.