Increased sensitivity of fat cell adenylate cyclase to stimulatory agonists during fasting is not related to impaired inhibitory coupling system.
In rat adipocytes, inhibition of the forskolin-stimulated cyclic AMP response by nicotinic acid and N6-phenylisopropyladenosine was unaltered by a 72 h fasting. Under assay conditions favouring inhibition, basal and forskolin-stimulated adenylate cyclase responses to inhibition by GTP and nicotinic acid were also unimpaired by fasting. Under the same conditions, however, low GTP concentrations elicited a clear activatory effect in membranes from fasted but not from fed rats. Fasting failed to alter the incorporation of [32P]ADP ribose into the alpha i-subunit of Ni and the attenuation of nicotinic acid inhibitory action that are both induced by pertussis toxin. These results, demonstrating unimpaired inhibitory control of adenylate cyclase in starved rat adipocytes, suggest that the permissive effect of fasting on the action of stimulatory receptor agonists in fat cells reflects a specific increase in the activity of the adenylate cyclase stimulatory coupling system.
D037361:Adenylate Cyclase Toxin; D000262:Adenylyl Cyclases / Q000378:metabolism*; D000273:Adipose Tissue / Q000201:enzymology*; D000818:Animals; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000378:metabolism; D005215:Fasting; D019204:GTP-Binding Proteins / Q000494:pharmacology; D006160:Guanosine Triphosphate / Q000494:pharmacology; D008297:Male; D009525:Niacin / Q000494:pharmacology; D037342:Pertussis Toxin; D010660:Phenylisopropyladenosine / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D013997:Time Factors; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
D037361:Adenylate Cyclase Toxin; D010566:Virulence Factors, Bordetella; D005576:Colforsin; D009525:Niacin; D010660:Phenylisopropyladenosine; D006160:Guanosine Triphosphate; D000242:Cyclic AMP; D037342:Pertussis Toxin; D019204:GTP-Binding Proteins; D000262:Adenylyl Cyclases