Adrenoceptor of the alpha2-subtype mediating inhibition of the human fat cell adenylate cyclase

Abstract. In an attempt to characterize the adenylate cyclase-coupled alpha-adrenoceptors of human fat cells the effects of various alpha-adrenergic agonists and antagonists were examined in the presence of 0.05 mmol/1 of propranolol.
The order of agonist potencies with respect to alpha-adrenergic inhibition was (—)-adrenaline > alpha-methyl-(-)-noradrenaline >> (—)-phenylephrine with half-maximal inhibition occurring at 2 μmol/1 of (-)-adrenaline and 7 μmol/l of alpha-methyl-(-)-noradrenaline respectively.
The inhibition of adenylate cyclase induced by 005 mmol/1 of (—)-adrenaline was reversed by the alpha-blocking agents yohimbine and prazosin, with the alphai-site-directed antagonist yohimbine being more than 100-times more potent than prazosin which is more active at alphai-sites.
The results show that the cyclase-coupled alpha-adrenoceptors of human fat cells, which probably represent the physiologically relevant target of antili-polytic catecholamine effects, display characteristic features of the alpha₂-adrenoceptor subtype.