ONTOGENY OF HEPATIC SN-1,2-DIACYLGLYCEROL CONTENT AND PROTEIN-KINASE-C ACTIVITY IN THE NEONATAL RAT - LACK OF CONCORDANCE

Altered activity of protein kinase C has commonly been related to acti vator-induced changes in cellular sn-1,2-diacylglycerol (1,2-DAG) conc entration. In neonatal liver 1,2-DAG can be synthesized by the develop mentally expressed monoacylglycerol acyltransferase (MGAT) activity (E C 2.3.1.22). Rat liver homogenates were examined on selected days afte r birth to determine whether the high MGAT activity present in neonata l rat liver was associated with high 1,2-DAG concentrations and altere d protein kinase C activity and location. Although MGAT specific activ ity peaked between days 5 and 12, 1,2-DAG concentrations declined 63% between days 1 and 10, and the activity and membrane location of prote in kinase C activity remained unchanged. Liver triacylglycerol content changed little during this time period, but the phospholipid and cera mide content of liver increased about 60 and 100%, respectively. Thus, changes in cell membrane 1,2-DAG content may not always be associated with changes in protein kinase C activity because multiple factors (i ncluding 1,2-DAG, fatty acids, and sphingosine) modulate the activity of this enzyme. Glycerolipid synthesis is likely to be the primary fat e of the 1,2-DAG synthesized by the monoacylglycerol pathway.