title: Inhibition of thyrotropin-stimulated adenosine 3',5'-monophosphate formation in rat thyroid cells by an adenosine analog. Evidence that the inhibition is mediated by the putative inhibitory guanine nucleotide regulatory protein.
abstract: Addition of N6-(L-2-phenylisopropyl)-adenosine (PIA) to cultured FRTL-5 rat thyroid cells led to a concentration-dependent inhibition of TSH-stimulated cAMP formation. Half-maximal inhibition was attained with approximately 0.5 nM PIA. Forskolin and cholera toxin-stimulated cAMP production were also inhibited by PIA. 3-Isobutyl-methylxanthine inhibited the effect of PIA. These results are consistent with the presence of inhibitory adenosine receptors (Ri). Ri-sites were further demonstrated by the binding of 3H-cyclohexyl-adenosine to FRTL-5 plasma membranes. High (Kd = 0.50 +/- 0.07 nM) and low affinity (Kd = 5.95 +/- 2.33 nM) binding sites were observed. Pretreatment of FRTL-5 cells with pertussis, but not cholera, toxin effectively antagonized the inhibitory effects of PIA on cAMP production. ADP-ribosylation of FRTL-5 membranes with [32P]-NAD in the presence of cholera or pertussis toxin specifically labeled a 45,000 and 41,000 Mr species, respectively, which correspond to the alpha subunit of the stimulatory and inhibitory guanine nucleotide regulatory proteins. These results demonstrate that PIA inhibits TSH-stimulated cAMP production via Ri-sites on FRTL-5 thyroid cells. PIA appears to exert its inhibitory effects through the inhibitory guanine nucleotide regulatory protein.
mesh_terms: D000241:Adenosine / Q000031:analogs & derivatives* / Q000378:metabolism; D000818:Animals; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D002772:Cholera Toxin / Q000494:pharmacology; D000242:Cyclic AMP / Q000096:biosynthesis*; D019204:GTP-Binding Proteins / Q000378:metabolism*; D007700:Kinetics; D009243:NAD / Q000378:metabolism; D010660:Phenylisopropyladenosine / Q000494:pharmacology*; D051381:Rats; D011956:Receptors, Cell Surface / Q000378:metabolism; D011983:Receptors, Purinergic; D011989:Receptors, Thyrotropin; D013961:Thyroid Gland / Q000187:drug effects / Q000378:metabolism*; D013972:Thyrotropin / Q000378:metabolism / Q000494:pharmacology*
chemical_list: D011956:Receptors, Cell Surface; D011983:Receptors, Purinergic; D011989:Receptors, Thyrotropin; D009243:NAD; D010660:Phenylisopropyladenosine; C027513:N(6)-cyclohexyladenosine; D013972:Thyrotropin; D002772:Cholera Toxin; D000242:Cyclic AMP; D019204:GTP-Binding Proteins; D000241:Adenosine