LHRH-stimulated release of stored and newly synthesized gonadotrop polypeptide (GP-87) by cultured rat gonadotrophs.
Enriched gonadotrophs from rat pituitaries were used to analyze the kinetics of release in vitro of the Gonadotrop Polypeptide (GP-87) under LHRH stimulation. Proteins in cultured cells were labeled with [35S]methionine. Labeling of the intracellular GP-87 pool was effected during 16 hours prior to LHRH (10(-7) M) stimulation. Proteins were analyzed either by one-dimensional SDS-PAGE (Medium content) or by two-dimensional PAGE (Cell content). An apparent half-life (intracellular catabolism + release) of 31 h for GP-87 was estimated from control cells; it dropped to 2.5 h in stimulated cells due to intense release (26% after 1 h and about 80% after 8 h of stimulation). When cells were simultaneously labeled and stimulated, the newly synthesized species appeared in the medium after a lag phase of 30 minutes, time required for synthesis and full subsequent processing. From both series of experiments, it is concluded that the hypothalamic decapeptide promotes exocytosis of the newly synthesized GP-87 well before the endogenous GP-87 pool is exhausted. Furthermore, the release of another discrete protein (B2, Mr: 81 kDa) is also stimulated by LHRH. These proteins being co-released with LH could be part of the sorting and/or routing process of hormones towards exocytosis.
D000818:Animals; D002864:Chromogranins; D005260:Female; D007987:Gonadotropin-Releasing Hormone / Q000494:pharmacology*; D007700:Kinetics; D010903:Pituitary Gland, Anterior / Q000378:metabolism*; D011506:Proteins / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D013268:Stimulation, Chemical
D002864:Chromogranins; D011506:Proteins; D007987:Gonadotropin-Releasing Hormone