BRADYKININ AND VASOPRESSIN ACTIVATE PHOSPHOLIPASE-D IN RAT LEYDIG-CELLS BY A PROTEIN KINASE-C-DEPENDENT MECHANISM

In the present study we report that bradykinin stimulated phospholipase D activity in rat Leydig cells. Bradykinin added for 8 min stimulated choline formation in a dose-dependent manner and, in the presence of ethanol, bradykinin (100 nmol/l) stimulated transphosphatidylation by phospholipase D resulting in the formation of phosphatidylethanol. This stimulation was abolished after down-regulation of protein kinase C by long-term pretreatment for 22 h with phorbol 12-myristate 13-acetate (PMA). The stimulation of phospholipase D by the simultaneous addition for 8 min of maximum concentrations of PMA and vasopressin (AVP), PMA and bradykinin, or AVP and bradykinin produced no additive phosphatidylethanol or choline response, suggesting that AVP, bradykinin and PMA stimulated phospholipase D-catalysed phosphatidylcholine hydrolysis by a similar protein kinase C-dependent mechanism. Furthermore, LH (10 ng/ml), insulin (500 nmol/l, GH (100 ng/ml), interleukin-1beta (5 U/ml) and platelet-activating factor (200 nmol/l) were found not to activate phospholipase D, whereas the Ca2+ ionophore A23187 (10 mumol/l) stimulated phosphatidylethanol formation, suggesting that Ca2+ might be a regulator of phospholipase D in Leydig cells.