Phospholipase D mediated transphospatidylation as a possible new pathway of ethanol metabolism in isolated rat pancreatic acini.

Activation of pancreatic phospholipase D (PLD) has been previously observed in response to caerulein (Cae), phorbol myristate acetate and growth factors. Although PLD involvement has been postulated in pancreatic cell proliferation and differentiation, the physiological role of this enzyme in pancreatic cells still remains unclear. In the presence of ethanol, PLD catalysed transphosphatidylation reaction, forming phosphatidylethanol (PEt). This study was thus undertaken to determine the involvement of PLD in ethanol metabolism in isolated pancreatic acini and to show the potential physiological consequences of transphosphatidylation. Dispersed pancreatic acini prelabelled with 3H myristic acid were incubated with 500 pM Cae in the presence or absence of different concentrations of ethanol, and labelled phosphatidylethanol (3H PEt) production or phosphatidic acid (3H PA) accumulation were measured. The production of PEt after Cae stimulation in pancreatic acini was significant from 0.5% up to 4% of ethanol in the medium and was not dependent on increasing concentration of ethanol. Prolonged up to 2 h stimulation with Cae in the presence of 1% ethanol did not increase PEt production which was almost stable since 5 min of stimulation. In the presence of different concentrations of ethanol (1-4%), the significant inhibition of PA accumulation was obtained after Cae stimulation, similar to inhibition with a specific PLD inhibitor--wortmannin. These data indicate that Cae activated PLD in the presence of ethanol caused PEt production in pancreatic acini. During formation of PEt in pancreatic acinar cells significant and parallel inhibition of PA accumulation was observed. This indicates the relation of PLD activation in isolated pancreatic acini to ethanol metabolism. Ethanol can act as an inhibitor of PLD activity. Since PA, a product of PLD, is known as a second messenger probably involved in cell proliferation and differentiation, this may suggest a potentially new mechanism for pancreatic tissue injury after ethanol ingestion.