Comparative effects of RX 781094, mianserin, yohimbine, rauwolscine and prazosin in reversing clonidine inhibition of MIX-stimulated lipolysis in hamster isolated white fat cells.

Different alpha-adrenergic receptor antagonists: RX 781094, yohimbine and rauwolscine (selective alpha 2-adrenergic antagonists); mianserin (tetracyclic anti-depressant, antagonist at alpha 2-presynaptic autoreceptors) and prazosin (selective alpha 1-adrenergic antagonist) were used at concentrations ranging from 10(-7) to 10(-4) M, to reverse clonidine inhibition of MIX-stimulated lipolysis in the hamster fat cell. In this adipose tissue (like human but unlike rat) there co-exist prolipolytic beta-adrenoceptors and antilipolytic alpha-adrenoceptors. Although no effects were observed with prazosin, RX 781094 was ten times more potent than yohimbine or its isomer rauwolscine in reversing clonidine inhibition of the MIX-stimulated lipolysis. Mianserin was an effective blocker only from a concentration of 10(-4) M, consistent with its relative lack of specificity for alpha 2-adrenoceptors cited elsewhere. Overall these results confirm the utility of this model for testing compounds presumed to act at alpha 2-adrenoceptors.