Cyclic adenosine 3',5'-monophosphate in rat cerebral cortical slices: effects of methoxamine and clonidine.
In incubated slices of cerebral cortex from Sprague-Dawley rats, methoxamine and clonidine have no effect on basal levels of cyclic AMP. Methoxamine effectively inhibits the noradrenaline-stimulated formation of cyclic AMP. The inhibitory constant for methoxamine was 12.6 mumol/l. In the presence of 100 mumol/l adenosine, methoxamine does not inhibit the activity of noradrenaline, but is capable to activate alpha-adrenergic receptors leading to enhanced formation of cyclic AMP. The mechanism by which adenosine alters adrenergic receptors to become methoxamine-sensitive is not known. Clonidine inhibits the effect of noradrenaline alone or in combination with adenosine on the cyclic-AMP-generating system. It does not, as reported earlier, enhance the activity of submaximal concentrations of the beta-adrenergic agonist isoproterenol. These data do not support the concept of adrenergic receptors which require both, alpha- and beta-stimulation for maximal activation of adenylate cyclase.
D000241:Adenosine / Q000494:pharmacology; D000818:Animals; D002540:Cerebral Cortex / Q000378:metabolism*; D003000:Clonidine / Q000494:pharmacology*; D000242:Cyclic AMP / Q000096:biosynthesis / Q000378:metabolism*; D007545:Isoproterenol / Q000494:pharmacology; D008297:Male; D008729:Methoxamine / Q000494:pharmacology*; D009638:Norepinephrine / Q000494:pharmacology; D010646:Phentolamine / Q000494:pharmacology; D011433:Propranolol / Q000494:pharmacology; D051381:Rats
D011433:Propranolol; D000242:Cyclic AMP; D008729:Methoxamine; D000241:Adenosine; D007545:Isoproterenol; D003000:Clonidine; D009638:Norepinephrine; D010646:Phentolamine