title: Enkephalin-mediated inhibition of forskolin-stimulated rabbit luteal adenylyl cyclase activity.
abstract: Forskolin at 25-100 microM elicited 10- to 15-fold stimulation of rabbit luteal adenylyl cyclase activity in the absence of guanine nucleotides. Addition of saturating concentrations of GTP or guanyl-5'-yl imidodiphosphate [GMP-P(NH)P] inhibited forskolin stimulation by 15-25% and 35-45%, respectively, in Na+-free media. The further addition of 8 microM [D-Ala2, Met5] enkephalin amide (Da-ENK) caused an additional 16-24% inhibition of activity in the presence of GTP plus forskolin, but did not alter enzymatic activity in the presence of forskolin alone or forskolin plus GMP-P(NH)P. Inhibition by guanine nucleotide alone or Da-ENK plus GTP was only observed in the presence of forskolin. Maximal inhibition by Da-ENK was observed at 25 microM forskolin. Da-ENK reduced the IC50 for GTP by 2.3-fold but did not alter the IC50 for GMP-P(NH)P. Addition of Na+ above 3 mM attenuated the inhibitory responses to GTP and GTP plus Da-ENK, but not to GMP-P(NH)P or GMP-P(NH)P plus Da-ENK. Above 100 mM, Na+ inhibited enzymatic activity in the presence of forskolin, forskolin plus GTP and forskolin plus GMP-P(NH)P in the absence and presence of Da-ENK. These findings suggest that the rabbit corpus luteum contains an inhibitory receptor for opiate peptides that couples to adenylyl cyclase.
mesh_terms: D000262:Adenylyl Cyclases / Q000378:metabolism*; D000818:Animals; D005576:Colforsin; D003338:Corpus Luteum / Q000187:drug effects / Q000201:enzymology*; D004224:Diterpenes / Q000494:pharmacology*; D004744:Enkephalin, Methionine / Q000031:analogs & derivatives* / Q000494:pharmacology; D005260:Female; D006160:Guanosine Triphosphate / Q000494:pharmacology; D006165:Guanylyl Imidodiphosphate / Q000494:pharmacology; D011817:Rabbits
chemical_list: D004224:Diterpenes; D005576:Colforsin; D006165:Guanylyl Imidodiphosphate; D004744:Enkephalin, Methionine; C022118:enkephalinamide-Met, Ala(2)-; D006160:Guanosine Triphosphate; D000262:Adenylyl Cyclases