LH biosynthesis and secretion in rat anterior pituitary cell cultures: stimulation of LH glycosylation and secretion by GNRH and an agonistic analogue and blockade by an antagonistic analogue.

In rat anterior pituitary cell cultures GnRH (1nM) stimulated a pro-e increase in LH release into the medium from 1 to 8 h of incubation, while cellular LH showed a corresponding decrease. GnRH (1nM) neither modified the uptake nor the incorporation of [3H]-glucosamine and [3H]-proline into total protein. The incorporation of ["HI-proline into cellular LH also was unaffected by GnRH. In contrast, GnRH stimulated a 3 to 4-fold increase in [3H]-glucosamine incorporation into cellular LH. The agonistic analogue, [des G~YNH,~~]-LHRH ethylamide, mimicked the GnRH effects and was 5 to 6 times more potent than GnRH. The antagonistic analogue, [D-Phe*, D-Phe6]-LHRH blocked the GnRH-stimulated effects. These results suggest that GnRH and agonistic analogues may preferentially regulate turnover or synthesis of the carbohydrate moiety of LH. It has been demonstrated that both natural and synthetic GnRH preparations stimulate the release of gonadotropins from rat pituitaries in vivo and -in vitro (l-7). Further studies revealed that GnRH increases the accumulation -___ of total radioimmunoassayable LH (8-lo), suggesting the possibility that it may regulate, not only the release but also the synthesis of LH. Currently there are reports in favor (11-14) and against (15, 16) the involvement of GnRH in protein synthesis in the rat anterior pituitary. The present studies have attempted to resolve these conflicting results by investigating the direct effects of GnRH and peptide analogues in a rat anterior pituitary cell culture system.