The biological activity of different molecular forms of ACTH on corticosterone production by perifused foetal rat adrenal glands in vitro

Abstract

Abstract. The responsiveness of perifused adrenal glands removed from rats at various stages of gestation to similar immunological quantities (2 ng) of 'big' (≅ 30 000 mol wt), 'intermediate' (≅ 13 000 mol wt) and 'little' (≅ 4500 mol wt) ACTH isolated by gel filtration chromatography from an acid extract of pituitary glands of 21 day-old rat foetuses was determined. This immunological quantity failed to induce a maximal response of the foetal adrenals. Cortisosterone was determined in the effluent perifusion by a radiocompetition assay. On days 17 and 19 of gestation, intermediate and little ACTH had, on a weight basis, the same corticosteroidogenic activity, but on day 21 the little was more potent than the intermediate form. The corticosterone release by these two forms of ACTH was log-dose dependent. The biological activity of big ACTH was very low on day 17, slightly increased until day 21 but remained significantly lower than that of intermediate and little forms. Big ACTH added to little ACTH in the perifusion medium did not modify the corticosteroidogenic activity of little ACTH on days 17, 19 and 21 of gestation.