title: Gonadotropin releasing hormone stimulates the formation of inositol phosphates in rat anterior pituitary tissue.
abstract: The production of inositol phosphates in response to gonadotropin releasing hormone (GnRH) was studied in rat anterior pituitary tissue preincubated with [3H]inositol. Prelabelled paired hemipituitaries from prepubertal female rats were incubated in the presence or absence of GnRH in medium containing 10 mM-Li+ X Li+, which inhibits myo-inositol-1-phosphatase, greatly amplified the stimulation of inositol phosphate production by GnRH (10(-7) M) to 159, 198 and 313% of paired control values for inositol 1-phosphate, inositol bisphosphate and inositol trisphosphate respectively after 20 min. The percentage distribution of [3H]inositol within the phosphoinositides was 91.3, 6.3 and 2.4 for phosphatidylinositol, phosphatidylinositol 4-phosphate and phosphatidylinositol 4,5-bisphosphate respectively and was unaffected by GnRH. The stimulation of inositol trisphosphate production by GnRH was evident after 5 min incubation, was dose-dependent with a half-maximal effect around 11 nM, and was not inhibited by removal of extracellular Ca2+. Elevation of cytosolic Ca2+ by membrane depolarization with 50 mM-K+ had no significant effect on inositol phosphate production. These findings are consistent with the hypothesis that GnRH action in the anterior pituitary involves the hydrolysis of phosphatidylinositol 4,5-bisphosphate. The resulting elevation of inositol trisphosphate may in turn lead to intracellular Ca2+ mobilization and subsequent stimulation of gonadotropin secretion.
authors.forename: M P
authors.initials: MP
authors.lastname: Schrey
mesh_terms: D000818:Animals; D002118:Calcium / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D005260:Female; D066298:In Vitro Techniques; D007295:Inositol Phosphates / Q000378:metabolism*; D008094:Lithium / Q000494:pharmacology; D010716:Phosphatidylinositols / Q000378:metabolism; D010903:Pituitary Gland, Anterior / Q000187:drug effects / Q000378:metabolism*; D010906:Pituitary Hormone-Releasing Hormones / Q000494:pharmacology*; D051381:Rats; D011917:Rats, Inbred Lew; D013268:Stimulation, Chemical; D013403:Sugar Phosphates / Q000378:metabolism*; D013997:Time Factors
chemical_list: D007295:Inositol Phosphates; D010716:Phosphatidylinositols; D010906:Pituitary Hormone-Releasing Hormones; D013403:Sugar Phosphates; D008094:Lithium; D002118:Calcium