Co-occurrence of immunoreactive corticotropin-like and alpha-melanotropin-like material in pituitary cells: differences between young and adult rats.
We examined to which extent adrenocorticotropin (ACTH)-like substances are cleavable into alpha-melanotropin (MSH)-like material by application of exogenous enzymes on pituitary sections prior to immunocytochemical stainings. In pro-opiomelanocortin (POMC) cells of the anterior lobe from developing rats (1 to 21 postnatal days) at least one of two cells contained alpha-MSH-like immunoreactivity besides ACTH-like immunostaining. Pretreatment of these tissue sections with tryptic enzymes enhanced remarkably alpha-MSH-like immunostaining. In contrast, alpha-MSH-like immunoreactivity was almost not detectable in anterior lobes from adult rats, also after treatment with enzymes. After adrenalectomy (ax) POMC cells in anterior lobes behaved similarly: a few days after the operation almost all ACTH cells contained also alpha-MSH immunostaining, whereas after more than two weeks alpha-MSH immunostaining was nearly absent, also after application of enzymes. In contrast to rats, in young and adult guinea pig pituitaries all ACTH-like immunoreactivity was prevented by treatment with tryptic enzymes. These observations are consistent with the assumption that occurrence of ACTH- and alpha-MSH-like substances in rat pituitaries is regulated by a protection mechanism against proteolytic cleavage in the ACTH sequence which appears with delay in differentiating and maturing cells.
D000324:Adrenocorticotropic Hormone / Q000032:analysis*; D000375:Aging; D000818:Animals; D000831:Animals, Newborn; D005260:Female; D005333:Fetus; D006168:Guinea Pigs; D009074:Melanocyte-Stimulating Hormones / Q000032:analysis*; D010902:Pituitary Gland / Q000196:embryology / Q000254:growth & development*; D010903:Pituitary Gland, Anterior / Q000254:growth & development; D010908:Pituitary Hormones, Anterior / Q000032:analysis*; D011247:Pregnancy; D011333:Pro-Opiomelanocortin; D011498:Protein Precursors / Q000032:analysis*; D011863:Radioimmunoassay; D051381:Rats; D011919:Rats, Inbred Strains
D010908:Pituitary Hormones, Anterior; D011498:Protein Precursors; D011333:Pro-Opiomelanocortin; D000324:Adrenocorticotropic Hormone; D009074:Melanocyte-Stimulating Hormones