SUBCELLULAR DISTRIBUTION AND ARTERIO-VENOUS DIFFERENCES OF SYNTHETIC 3H-β1–23-CORTICOTROPHIN-23-AMIDE-ACETATE IN THE ADRENAL OF RATS

Abstract

ABSTRACT Synthetic 3H-β1–23-corticotrophin-23-amide-acetate (3H-ACTH) was given as a single dose by means of a 95 s infusion into the thoracic aorta of hypophysectomized rats. Distribution of radioactivity was determined in adrenal subcellular fractions prepared by homogenization and differential centrifugation: 3, 12, 40 and 120 min after the start of the 3H-ACTH infusion. Radioactivity in nuclear fractions, given as a % of total adrenal CPM rose from 27 % (3 min) to 37 % (40 and 120 min, P < 0.0025). These results may indicate ACTH penetration through the outer cell membrane and interaction with adrenal nuclei. Microsomal radioactivity (18 %) at 3 min after the start of 3H-ACTH infusion appeared to be in excess of the contribution of this fraction to the total adrenal weight and decreased significantly with time (120 min: 3 %, P < 0.0005). These observations are discussed with regard to mechanisms of action of ACTH. When synthetic 3H-β1–23-corticotrophin-23-amide-acetate was infused into the thoracic aorta of rats, the differences in the radioactivity of the plasma from the aorta and from the adrenal vein were significantly higher (P < 0.0125) in hypophysectomized than in sham-operated rats, presumably indicating in the latter the saturation by endogenous ACTH of adrenal receptors for ACTH.