ASSAY OF ADRENOCORTICAL HORMONES ON THE THYMUS OF THE WEANLING RAT

Abstract

Involution of the thymus gland of intact weanling rats has been used as the criterion of the response to 11-oxycorticosteroids. Other substances known to cause thymus atrophy exhibited dosage–response relationships which differed significantly from those observed with 11-oxycorticosteroids. Thymus involution was produced at a faster rate and at smaller dose levels by adrenal corticoids than by any of the other steroid hormone preparations examined. The slope of the dosage–effect line obtained with an 11-oxycorticosteroid may be increased by using (a) adrenalectomized rats, (b) female rats, and (c) vegetable oil as the injection medium. The error term of the assay may be reduced by (a) using littermates in each treatment group, (b) maintaining the weight range within dosage groups as small as possible, and (c) equalizing the total weight of the rats in each dosage group at the start of the assay. The standard error of the potency ratio was usually less than ± 15% when 40 intact female rats of the Wistar strain, 21–23 days old, were employed in a two-dose assay design. This method provided estimates of potency of commercial adrenal cortical extracts which did not differ significantly from those obtained by a procedure using deposition of reducing substances in the liver of adrenalectomized male rats as the criterion of the response. The chief advantages of the thymus involution method are: (a) intact rats may be employed and (b) chemical analyses of tissues are not required.