Adrenocorticotropic Hormone Released by Pituitary Cells from Ovine Fetuses and Lambs

Abstract

The proportions of different molecular weight forms of adrenocorticotropic hormone (ACTH) present in pituitary extracts, cultured pituitary cell extracts and cell-derived incubation media from fetal and postnatal sheep have been determined. When pituitary extracts, cell extracts, and incubation media were subjected to gel filtration on Sephadex G50 fine, three forms of ACTH were always observed. 'Big' ACTH eluted in the void volume of the column; 'intermediate' ACTH eluted between 'big' ACTH and human ACTH, and 'little' ACTH eluted in the same fractions as human ACTH. High amounts of 'big' and 'intermediate' ACTH were observed in extracts of cultured pituitary cells from both fetuses and newborn lambs, whereas very few 'little' ACTH was found. Conversely, in incubation media, the predominant form of ACTH was always 'little' ACTH. The relative proportion of these three forms of ACTH were rather similar in pituitary extracts and in cell-derived incubation media from newborn lambs. However, for fetuses the proportions of 'big' and 'intermediate' ACTH were higher, whereas that of 'little' ACTH was lower in pituitary extracts than in cell-derived incubation media. Neither corticotropin-releasing factor (oCRF) nor arginine vasopressin (AVP), separately or in combination, was able to modify the relative proportion of the three forms of ACTH released by pituitary cells from newborns. Conversely, for fetal cells, the proportion of 'little' ACTH released in the medium was higher in the presence of oCRF and/or AVP than under control conditions. The proportion of 'little' ACTH released by pituitary cells in the absence of stimulating factor increased linearly between 63 days of gestation and 150 days postpartum.(ABSTRACT TRUNCATED AT 250 WORDS)