TIME TRENDS OF PLASMA-LIPIDS AND ENZYMES SYNTHESIZING HEPATIC TRIACYLGLYCEROL DURING POSTPARTUM DEVELOPMENT OF FATTY LIVER IN DAIRY-COWS

We studied development of fatty liver in high producing dairy cows wit h free access to feed during the dry period and thus showed the combin ed effects of parturition and prepartum overfeeding. Postpartum liver triacylglycerol concentrations at 1 wk postpartum, as measured in live r biopsies, had increased more than 6-fold, which was preceded or acco mpanied by an increase in plasma NEFA concentrations. Concentrations o f hepatic phospholipid changed only slightly. The amounts of total lip ids in serum, very low density lipoproteins, and high density lipoprot eins significantly decreased by .5 wk after parturition, and concentra tions of high density lipoproteins rose steadily. The pattern was simi lar for concentrations of total cholesterol and phospholipid in serum. Total lipid concentrations in low density lipoproteins were not alter ed after parturition. The activity of microsomal phosphatidate phospho hydrolase in the liver showed a transient increase at .5 wk after calv ing, but activity of microsomal glycerolphosphate acyltransferase rema ined relatively constant. The activities of diacylglycerol acyltransfe rase had increased about twice at 1 wk after calving and remained at t his high level until at least 4 wk after parturition. The rise in acti vity of diacylglycerol acyltransferase was probably a response to the extra influx of fatty acids to channel them into triacylglycerol. Acti vities of microsomal cholinephosphate cytidylyltransferase initially i ncreased after calving and then decreased slightly. Activities of hepa tic choline kinase had increased after calving. This study indicates t hat hepatic triacylglycerol accumulates because of the increased hepat ic uptake of NEFA and the simultaneous increase in activity of diacylg lycerol acyltransferase.