The Relative Potency of Adrenal Corticoids by the Thymus Involution Method

Abstract

An adrenal corticoid which has an α-ketolic grouping at C17, a ketone or β-hydroxyl at C11, a ketone at C3, and a double bond in the 4,5 position is able to involute the thymus gland of the weanling rat. The thymolytic activity of an 11-oxycorticosteroid is increased approximately 3 to 3.5 times by the addition of an α-hydroxyl at C17. The ability of a 17-hydroxycorticosteroid to cause thymic atrophy is enhanced 1.2 times by acetylation at C21, 1.5 times by replacement of a ketone at C11 with β-hydroxyl group, 4 to 5 times by the formation of a 1,2 double bond, and 8 to 10 times by the introduction of a fluorine atom in the α position at C9. The potency of Δ1-11-oxycorticosteroids relative to naturally occurring corticoids is significantly greater when the steroids are injected in an aqueous medium than when they are given in corn oil. The relative activities of adrenal corticoids as determined by the thymus involution method do not differ significantly from those obtained by other glucocorticoid bio-assays.

Comparison of Potency Estimates for Glucocorticoids Using Two Thymolytic Assay Procedures

“…Although the order of activity for the steroids evaluated by different assay methods compared favorably, the quantitative values did not agree. Greater agreement was observed between Stephenson's (3,4,15) values and those recorded from the 5day multiple injection assay than potency estimates from the 48-hour single injection method. Discrepancies between potency ratios were most pronounced for steroids possessing a 16~,17a-acetonide function.…”

“…Earlier work(3) has shown that injection medium in-fluences the relative potency of some corticosteroid analogs. Perhaps use of corn oil as steroid vehicle by Stephenson (3,4,15) and carboxymethylcellulose vehicle by present authors has contributed to the disparity in steroid ketal potencies.…”

“…Since the classical work by Ingle( 1), and Wells and Kendall(2), involution of the thymus gland has been used as a criterion of glucocorticoid activity (3,4,5). Experimentation has shown that the relative potency of a steroid varies with injection vehicle( 3), route of administration and animal species (5).…”

“…The thymolytic potencies of 11 steroids previously reported ( 3,4,15) assayed in intact female rats receiving multiple injections over 48 hours, were compared with potency values derived from the presently described thymus assays (Table 111). Although the order of activity for the steroids evaluated by different assay methods compared favorably, the quantitative values did not agree.…”

Improved Cryofixation Applicable to Freeze Etching

“…In investigations of solutions or colloidal systems, cryoprotectants are of no use at all. Therefore, several attempts have been made to increase the speed of freezing, which is known to improve the quality of a cryofixed electron-microscopic specimen (3,(6)(7)(8)(9) To overcome this difficulty, a spray-freezing method was developed, which can be applied to freeze-etching.Since this "spray-freeze-etch" method has previously been described only in a short note (11), the details of the procedure are given in this paper. …”