[Effect of LHRH on the synthesis and phosphorylation of proteins in gonadotropic cells]

Protein secretion by cultured pituitary cells from 14 day-old female rats was estimated using [35S]-méthionine incorporation, electrophoresis and autoradiography. Stimulation by LHRH promoted biosynthesis and fast release of a protein of apparent molecular weight 87,000 daltons and pI 4.6. Gonadotrophs enriched by centrifugal elutriation were particularly rich in this polypeptide which was thus called GP-87 (Gonadotrope polypeptide). Cells were then cultured with [32P]-orthophosphate and proteins were analyzed. Our first results tend to show that GP-87 is phosphorylated, at least in the cells. We suggest that this specific protein, the secretion of which is correlated with LH release, participates to the response mechanisms of gonadotrope cells stimulated by LHRH.