Adenylate cyclase agonist properties of CGP-12177A in brown fat: evidence for atypical beta-adrenergic receptors.
Thermogenesis in brown adipose tissue (BAT) is stimulated by catecholamine activation of adenylate cyclase through the beta-adrenergic receptor. Recently it was reported that the beta-adrenergic antagonist CGP-12177A stimulates oxygen consumption in BAT. To investigate the mechanism of action of CGP-12177A in BAT, we assessed the inhibitory and stimulatory affects of CGP-12177A on the adenylate cyclase system in myocardial and BAT membranes from rats. CGP-1277A inhibited isoproterenol-stimulated adenylate cyclase activity in a dose-dependent manner, with an inhibitory constant (Ki) of 1.94 +/- 0.18 microM in BAT and 0.49 +/- 0.11 microM in the heart. However, in the absence of isoproterenol, CGP-12177A stimulated adenylate cyclase in BAT with two components of activation, and half-maximal stimulation occurred at 1 microM and 1.5 mM. In contrast, CGP-12177A did not stimulate adenylate cyclase activity in heart membranes. Propranolol inhibited the isoproterenol-stimulated activity with a potency that was one log less in BAT compared with heart. Propranolol fully blocked the high-affinity component but only weakly blocked the low-affinity component of CGP-12177A-stimulated activity in BAT. Pindolol was also less potent in BAT but inhibited the CGP-12177A-stimulated activity in a manner similar to the inhibition of the isoproterenol-stimulated activity, suggesting the CGP-12177A activation was beta-receptor mediated. Binding curves of [125I]iodocyanopindolol ([125I]ICYP) in competition with CGP-12177A demonstrated a shift to lower affinity in the presence of beta,gamma-imidoguanosine 5'-triphosphate, indicating that CGP-12177A has agonist properties with respect to the [125I]ICYP binding site.(ABSTRACT TRUNCATED AT 250 WORDS)
Scarpace
P J
PJ
Geriatric Research, Education and Clinical Center, Department of Veterans Affairs Medical Center, Gainesville, Florida 32608.
Matheny
M
M
D000262:Adenylyl Cyclases / Q000378:metabolism*; D002001:Adipose Tissue, Brown / Q000187:drug effects / Q000201:enzymology / Q000502:physiology*; D000319:Adrenergic beta-Antagonists / Q000494:pharmacology*; D000818:Animals; D001667:Binding, Competitive; D002462:Cell Membrane / Q000378:metabolism; D004789:Enzyme Activation; D005260:Female; D006165:Guanylyl Imidodiphosphate / Q000494:pharmacology; D007545:Isoproterenol / Q000494:pharmacology; D007700:Kinetics; D009206:Myocardium / Q000378:metabolism; D011412:Propanolamines / Q000494:pharmacology*; D051381:Rats; D011916:Rats, Inbred F344; D011943:Receptors, Adrenergic, beta / Q000187:drug effects / Q000502:physiology*
D000319:Adrenergic beta-Antagonists; D011412:Propanolamines; D011943:Receptors, Adrenergic, beta; D006165:Guanylyl Imidodiphosphate; D000262:Adenylyl Cyclases; D007545:Isoproterenol; C033394:CGP 12177