Detection of Minute Amounts of Adrenocorticotropic Hormone by the Effect on Adrenal Venous Ascorbic Acid¹

Adrenal venous blood was collected from hypophysectomized plateaued female rats immediately following intravenous injection of ACTH. The ascorbic acid concentration of the adrenal venous blood, of systemic blood, and of the adrenal gland before and after administration of ACTH was estimated. The increase in adrenal venous ascorbic acid concentration during the period of cannulation (on the average, 9.0 min.) was related linearly to the log dose of ACTH over the range, 0.01 to 0.10 mu./lOO gm., with a standard deviation(s) of 2.12, a slope (b) of 20.0, and an index of precision (λ) of 0.106. A biological assay method based on this response was proposed for the assay of ACTH in blood. The absolute increase in adrenal venous ascorbic acid was significantly greater (P <.O5) than the loss in adrenal ascorbic acid during the period of cannulation, suggesting that ACTH had increased the rate of biosynthesis as well as the rate of secretion of adrenal ascorbic acid. A simplified technique for collection of adrenal venous blood employing an ordinary syringe and needle and applicable to young rats weighing as little as 150 gm. was developed. By this technique a marked increase in adrenal venous asorbic acid concentration was observed in blood samples collected for 60 sec, beginning 30 sec. after intravenous injection of 0.10 mu. of ACTH/100 gm.