title: LH-RH binding to purified pituitary plasma membranes: absence of adenylate cyclase activation.
abstract: Purified bovine pituitary plasma membranes possess two specific LH-RH binding sites. The high affinity site (2.5 X 10(9) l/mol) has low capacity (9 X 10(-15) mol/mg membrane protein) while the low affinity site 6.1 X 10(5) l/mol) has a much higher capacity (1.1 X 10(-10) mol/mg). Specific LH-RH binding to plasma membranes is increased 8.5-fold during purification from homogenate whilst adenylate cyclase activity is enriched 7--8-fold. Distribution of specific LH-RH binding to sucrose density gradient interface fractions parallels that of adenylate cyclase activity. Mg2+ and Ca2+ inhibit specific [125I]LH-RH binding at micromolar concentrations. Synthetic LH-RH, up to 250 microgram/ml, failed to stimulate adenylase cyclase activity of the purified bovine membranes. Using a crude 10,800 g rat pituitary membrane preparation, LH-RH similarly failed to activate adenylate cyclase even in the presence of guanyl nucleotides. These data confirm the presence of LH-RH receptor sites on pituitary plasma membranes and suggest that LH-RH-induced gonadotrophin release may be mediated by mechanisms other than activation of adenylate cyclase.
mesh_terms: D000262:Adenylyl Cyclases / Q000378:metabolism*; D002118:Calcium / Q000494:pharmacology; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D004789:Enzyme Activation; D007987:Gonadotropin-Releasing Hormone / Q000378:metabolism* / Q000494:pharmacology; D007700:Kinetics; D008274:Magnesium / Q000494:pharmacology; D010902:Pituitary Gland / Q000378:metabolism*; D011956:Receptors, Cell Surface / Q000378:metabolism*; D013973:Thyrotropin-Releasing Hormone / Q000494:pharmacology
chemical_list: D011956:Receptors, Cell Surface; D007987:Gonadotropin-Releasing Hormone; D013973:Thyrotropin-Releasing Hormone; D000262:Adenylyl Cyclases; D008274:Magnesium; D002118:Calcium