Estimation of Blood Acth by means of a Cross-Circulation Technique ‡§

Since no direct chemical method is at present available for the quantitation of ACTH secretion, indirect indices have, of necessity, been employed. Although many physiological and biochemical changes are associated with an increased activity of the pituitary-adrenal system, only a few of these are applicable as a method for the detection of such activity. Up to the present time, the detection of the release of ACTH from the anterior pituitary has been carried out by one of two methods. The first is to observe the change in one of the indices of ACTH secretion in the animal to which an experimental procedure under study has been applied. For example, the decline in the adrenal ascorbic acid has been extensively employed as an index of ACTH secretion. However, in the intact animal, this only indicates that an increased discharge of ACTH has taken place, but gives no information as to the duration of the increased secretion of ACTH. This is because the increased activity of the adrenal cortex continues for a long time after a brief stimulus with ACTH,18 despite the fact that ACTH is inactivated with extreme rapidity.' The second, more quantitative, method for the determination of ACTH in blood, used by Sydnor and Sayers,' Gemzell,' Cooke,' Bornstein,' Parrott,6 9 10 and others, is to pool the blood of a large number of rats subjected to the same procedure. After suitable extraction and chemical manipulation, the concentrated material is injected into hypophysectomized rats, and the ACTH estimated by means of the decline in adrenal ascorbic acid according to the standard method of bioassay developed by Sayers, et al.' While this method can be employed to determine the blood ACTH at