THE EFFECT OF 'TRAINING' ON THE RELEASE OF CORTICOTROPHIN IN RESPONSE TO MINOR STRESSFUL PROCEDURES IN THE RAT

Abstract

The results of experiments on hypothalamo-pituitary-adrenal function in laboratory animals may often be difficult to interpret because simple procedures such as control injections sometimes constitute a sufficiently severe form of stress to result in marked pituitary adrenocorticotrophic activity. An effort was made, therefore, to find a simple training procedure, in rats, which might result in a control injection no longer being responsible for corticotrophin (ACTH) release as shown by plasma corticosterone and adrenal ascorbic acid changes. The following procedures were tried: (I) ten training injections (0·9% NaCl solution, s.c., 0·1 ml./100 g.); (II) one or two training injections; (III) daily handling for a week. Twenty-four hr. after the training procedure the rats received s.c. injections of 0·9% NaCl solution, 0·1 ml./100 g. Plasma corticosterone (Zenker & Bernstein, 1958) and adrenal ascorbic acid (Roe & Kuether, 1943) were measured ½ and 1 hr. later, respectively.