title: Influence of pregnancy on G-protein coupling to adenylate cyclase activation in guinea-pig myometrium.
abstract: The regulatory factors controlling uterine activity during pregnancy remain unclear in many species. Since myometrial relaxants raise intracellular cyclic AMP, modulation of signalling pathways coupling cell-surface receptors to adenylate cyclase activation could be an important site for control. To assess the functional activity of the stimulatory GTP-binding protein Gs we have measured adenylate cyclase activation by GTP, its non-hydrolysable analogue guanosine 5'-(beta-gamma-imido)triphosphate (Gpp(NH)p), fluoride, forskolin and manganese in a 50,000 g membrane fraction prepared from the myometrium of non-pregnant, mid-pregnant (30-32 days) and late-pregnant (62-66 days) guinea-pigs (full term 67 +/- 2 days). While forskolin- and manganese-dependent enzyme activation was unaltered by pregnancy, maximal stimulation by Gpp(NH)p and fluoride was enhanced by up to 200%. Recovery of adenylate cyclase activity in the 50,000 g fraction was essentially constant at 20-24% of the total activity throughout pregnancy, and thus cannot explain the increases observed. Since guanine nucleotides and fluoride stimulate adenylate cyclase through activating Gs, and forskolin and manganese act at the level of the catalytic unit, these data are consistent with a pregnancy-related increase in Gs functional coupling while adenylate cyclase activity is unaltered. These observations suggest a physiological regulation of myometrial Gs activity during pregnancy which could facilitate hormonal stimulation of adenylate cyclase and contribute to uterine quiescence by increasing uterine sensitivity to relaxants.
authors: Laboratory of Cellular and Developmental Physiology, University of Oxford, John Radcliffe Hospital, Headington.
authors: S J
authors: SJ
authors: Arkinstall
authors: C T
authors: CT
authors: Jones
mesh_terms: D000262:Adenylyl Cyclases / Q000378:metabolism*; D000818:Animals; D002712:Chlorides; D005576:Colforsin / Q000494:pharmacology; D004789:Enzyme Activation / Q000187:drug effects; D005260:Female; D019204:GTP-Binding Proteins / Q000378:metabolism*; D006165:Guanylyl Imidodiphosphate / Q000494:pharmacology; D006168:Guinea Pigs; D008345:Manganese / Q000494:pharmacology; D017895:Manganese Compounds; D009215:Myometrium / Q000187:drug effects / Q000378:metabolism*; D011247:Pregnancy / Q000378:metabolism*; D012969:Sodium Fluoride / Q000494:pharmacology
chemical_list: D002712:Chlorides; D017895:Manganese Compounds; D005576:Colforsin; D006165:Guanylyl Imidodiphosphate; D008345:Manganese; D012969:Sodium Fluoride; D019204:GTP-Binding Proteins; D000262:Adenylyl Cyclases; C025340:manganese chloride