Biphasic Generation of Diacylglycerol by Angiotensin and Phorbol Ester in Bovine Adrenal Chromaffin Cells

Stimulation of angiotensin receptors in bovine adrenal medullary cells with Sar¹-angiotensin II increased diacylglycerol levels in a biphasic fashion. An initial peak occured at 3 min and an increase was observed again at 60 min and even at 18 hrs. Phorbol 12-myristate 13-acetate produced a similar pattern of increase in diacylglycerol levels. Both the angiotensin analog and the phorbol ester also increased the release of [³H]choline into the culture medium from prelabelled cells. The long-term diacylglycerol production could be derived from phosphatidylcholine rather than from the phosphoinositides. The latter may be the source of the angiotensin stimulated initial production of diacylglycerol and activation of PKC. Activated PKC then turns on the continuous production of DAG which maintains PKC in an active state for long periods of time in the presence of the peptide.