ON THE ASSAY OF CORTICOTROPHIN: COMPARISON OF THE PLASMA CORTICOSTEROID AND ADRENAL ASCORBIC ACID RESPONSE

Abstract

A new subcutaneous assay method for corticotrophin using the level of free plasma corticosteroids in hypophysectomized rats as the response is described. A critical evaluation of the results compared with those of the adrenal ascorbic acid depletion assay method is given. It was found, that the plasma corticoid method has about the same precision (λ = 0.25) as the adrenal ascorbic acid depletion method, but that the former is about five times more sensitive. It is possible to apply a cross-over design to the plasma corticoid method, which increases the assay efficiency to about 250 per cent of non-cross-over assays. From simultaneous measurements of adrenal ascorbic acid concentration and plasma corticoid levels and subsequent calculation of their correlation coefficients it appeared, that the mechanism of ascorbic acid depletion is quantitatively not closely linked to that of adrenal corticoid output in the individual rat. On the basis of its advantages from the theoretical points of view (higher specificity) and for practical reasons, it is proposed to replace the adrenal ascorbic acid depletion method by the plasma corticoid method for pharmacopeial corticotrophin assays.