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

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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.