Adrenocorticotrophin-related peptides in adult and foetal sheep pituitary glands.

Differences in foetal and adult adrenal function may be due to qualitative as well as quantitative changes in the pituitary corticotrophic stimulus. Pituitary glands from adult and foetal sheep were freshly dissected and stored at -70 degrees C until extracted at pH 1.5. The extracts were subjected to chromatography on Sephadex G-100 superfine and fractions were assayed by multiple radioimmunoassays directed against the NH2- and CO2H-terminal sequences of ACTH and lipotrophin (LPH). Peaks corresponding to beta-melanocyte-stimulating hormone (beta-MSH), beta-LHP, gamma-LPH, beta-endorphin and ACTH were identified, with little or no evidence for the presence of alpha-MSH and corticotrophin-like intermediate lobe peptide. Three peaks of large molecular weight material, A. B and C, were identified and their relative proportions shown to be considerably greater in the foetus than in the adult. The immunoassay profile of peaks A and B suggested that they were 'stem hormones' which could give rise to a family of biologically active peptides. Since the 'family tree' which they engender varies according to the stage of development, it is proposed that the changes in the 'trophic family' may explain the different adrenal responses of the foetal and adult sheep.