title: Thyroliberin receptor binding and adenylyl cyclase activation in cultured prolactin-producing rat pituitary tumor cells (GH cells).
abstract: A thyroliberin (TRH)-responsive particulate bound adenylyl cyclase is present in two rat anterior pituitary tumor cell strains (GH4C1 and GH3) which synthesize and secrete prolactin. At a given Mg2+ concentration, ATP and the guanyl nucleotides GTP and guanyl 5'-yl-imidodiphosphate (GMP-P(NH)P) caused a dose-dependent increase in adenylyl cyclase activity. The maximum response to thyroliberin occurred with ATP and GTP at concentrations above 0.30 mM and 2 microM, respectively. The maximal stimulatory effect of thyroliberin on adenylyl cyclase activity was 2-fold in the presence of GTP. GMP-P(NH)P increased the basal enzyme activity 4- to 10-fold over and above that of equimolar concentrations of GTP but supported poorly the TRH-induced response. Mg2+ caused a dose-dependent increase in the basal enzyme activity and reduced TRH and fluoride-induced responses. Also, Mn2+ and Co2+ stimulated the basal adenylyl cyclase activity while Zn2+, Ca2+, and Cu2+ inhibited the enzyme, and neither cations supported the TRH response. Half-maximal stimulation of the adenylyl cyclase by TRH and half-maximum binding of [3H]TRH to membranes at 35 degrees C were 102 and 56 nM, respectively. Pretreatment with TRH decreased the apparent Vmax of the enzyme and the maximal binding of [3H]TRH. Of 6 TRH analogs tested, only one was able to displace [3H]TRH from its receptor and to increase the adenylyl cyclase activity. We suggest that adenylyl cyclase activation is an early event in the stimulus secretion coupling between TRH and prolactin-producing GH cells.
mesh_terms: D000262:Adenylyl Cyclases / Q000378:metabolism*; D000818:Animals; D002460:Cell Line; D004305:Dose-Response Relationship, Drug; D004789:Enzyme Activation; D006160:Guanosine Triphosphate / Q000494:pharmacology; D006165:Guanylyl Imidodiphosphate / Q000494:pharmacology; D008274:Magnesium / Q000494:pharmacology; D008566:Membranes / Q000378:metabolism; D010911:Pituitary Neoplasms / Q000378:metabolism*; D011388:Prolactin / Q000378:metabolism*; D051381:Rats; D011956:Receptors, Cell Surface / Q000378:metabolism*; D018025:Receptors, Thyrotropin-Releasing Hormone; D013973:Thyrotropin-Releasing Hormone / Q000378:metabolism
chemical_list: D011956:Receptors, Cell Surface; D018025:Receptors, Thyrotropin-Releasing Hormone; D006165:Guanylyl Imidodiphosphate; D013973:Thyrotropin-Releasing Hormone; D006160:Guanosine Triphosphate; D011388:Prolactin; D000262:Adenylyl Cyclases; D008274:Magnesium