Synthesis of growth hormone, prolactin, and proopiomelanocortin by intact adult ovine pituitary tissue in vitro.

Synthesis of GH, PRL, and proopiomelanocortin (POMC) by the adult ovine pituitary was examined by culturing intact tissue explants in vitro and analyzing newly synthesized proteins by two-dimensional gel electrophoresis. Spots on autoradiographs of two-dimensional gels were identified by comigration with known standards, by analysis of tryptic peptides, or both. GH and PRL are the predominant proteins synthesized in the adult ovine pituitary, but their syntheses could not be detected in the neurointermediate lobe of the pituitary, the cerebral cortex, hypothalamus, mammillary body, or placenta. As quantified by cell-free translation in rabbit reticulocyte lysate, 14% of female ovine pituitary mRNA encodes pre-GH and 30% encodes pre-PRL. As determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, ovine pre-GH and pre-PRL have molecular weights of 24,500 and 26,000, respectively, indicating they contain leader peptides of 26-30 amino acids, as found in bovine, rat, and human pre-GH and pre-PRL. POMC, the precursor to corticotropin, endorphin, and other peptides, was synthesized primarily in the neurointermediate lobe of the pituitary, but synthesis was also detected in the anterior lobe. POMC synthesis was not detected in the hypothalamus, cerebral cortex, mammillary body, or placenta.