Lipoprotein lipase and metabolic activities in incubated bovine adipose tissue explants: effects of insulin, dexamethasone, and fetal bovine serum.

An in vitro system was used to study the regulation of lipoprotein lipase (LPL) activity in bovine adipose tissue. The utilization of two energetic and lipogenic substrates, acetate and glucose, and the activity of glucose-6-phosphate dehydrogenase (G6PDH), an enzyme involved in de novo lipogenesis, were also studied. Nine nonlactating, nonpregnant Holstein cows were given limited amounts of feed for 10 d, then they were overfed for 3 to 5 wk. Samples of perirenal adipose tissue were incubated for 24 or 48 h. Insulin (2 mU/mL) increased (P < .001) daily glucose and acetate utilization and attenuated (P < .001) the loss of G6PDH activity detected after 1 or 2 d of incubation. Dexamethasone (DEX, 10 nM) added to the insulin-supplemented medium decreased (P < .02) glucose utilization, but it did not change acetate utilization or G6PDH activity. A higher concentration of DEX (100 nM) potentiated (P < .004) the ability of insulin to attenuate the decrease in G6PDH activity without changing substrate utilization. Under basal conditions, LPL activity was decreased by approximately 66% after 2 d of incubation. The decline in LPL activity was attenuated by insulin addition (P < .02) and was further attenuated (P < .004) by 100 nM of DEX. The addition of 10% fetal bovine serum alone to the medium had no effect on LPL activity, and fetal bovine serum decreased this activity when it was added to the insulin-supplemented medium.

[Effect of food intake on variations in different plasma constituents at the end of gestation and the start of lactation]. / Influence de la prise alimentaire sur les variations de différents constituants plasmatiques chez la vache en fin de gestation et en début de lactation.

Four dairy cows received a diet mainly constituted of a mixture of 60% maize silage and 40% concentrate, within four weeks before and six weeks after calving. During this period, blood samples were taken from the jugular vein, twice a week, before and two hours after the morning meal. Five plasmatic components were analyzed: glucose, non-esterified fatty acids, beta-hydroxybutyrate, acetate and urea. Prandial variations depend on the physiological stage: the post-feeding decrease in concentration of non-esterified fatty acids is very slight during late pregnancy and important during early lactation; concentration of beta-hydroxybutyrate post-feeding increases during late pregnancy, but not during early lactation. These results are discussed with variations of energy balance and feeding level. The correlations between different plasma components are often higher before feeding than after, especially between non-esterified fatty acids and beta-hydroxybutyrate. The concentration of non-esterified fatty acids is highly correlated with energy balance, except during the last ten days before calving.

Duodenal rapeseed oil infusion in early and midlactation cows. 5. Milk fatty acids and adipose tissue lipogenic activities.

Lipogenic activities of perirenal adipose tissue were investigated in early (wk 3) and midlactation (wk 19 to 26) cows that received a duodenal rapeseed oil infusion (1.0 to 1.1 kg/d). In midlactation, oil infusion resulted in a decreased rate of fatty acid synthesis from acetate and a decreased rate of the activities of fatty acid synthetase and glucose-6-phosphate dehydrogenase, whereas lipoprotein lipase activity tended to increase. The rate of glucose incorporation into glyceride-glycerol and the activities of glycerol-3-phosphate dehydrogenase and malic enzyme were not significantly affected. Fatty acid C14:0 content of perirenal adipose tissue was decreased, and fatty acid C18:2 and C18:3 contents were increased in oil-infused cows. In early lactation, rates of acetate incorporation into fatty acids and activities of fatty acid synthetase and lipoprotein lipase were very low. Activities of glucose-6-phosphate dehydrogenase and glycerol-3-phosphate dehydrogenase were lower in the early than in the midlactation trial. Oil infusion did not change the measured parameters. In both trials, percentages and yields of milk fatty acids C18:1, C18:2, and C18:3 were increased, whereas those of C14:0 and C16:0 were decreased by oil. Calculated transfer rates of absorbed fatty acid C18:2 from oil to milk fat were 16 to 26%. Results suggested that oil fatty acids affected adipose and mammary de novo lipogenesis in a direct way without affecting fatty acid esterification in adipose tissue or total fat secretion in mammary tissue.

Messenger RNAs encoding lipoprotein lipase, fatty acid synthase and hormone-sensitive lipase in the adipose tissue of underfed-refed ewes and cows.

The mechanisms involved in the nutritional regulation of genes encoding lipogenic (lipoprotein lipase (LPL) and fatty acid synthase (FAS)) and lipolytic (hormone-sensitive lipase (HSL)) enzymes were investigated by comparing the levels of the corresponding mRNAs in the adipose tissue (AT) of underfed or underfed-refed ewes and cows. Refeeding sharply increased LPL and FAS activities (19-25- and 6-8-fold, respectively) and moderately increased (2-4 fold) the activities of glucose-6-phosphate dehydrogenase (G6PDH), malic enzyme (ME) and glycerol-3-phosphate dehydrogenase (G3PDH). Northern blot analysis revealed three LPL transcripts and a single FAS transcript in cow and ewe AT. A single HSL mRNA was detected in cow AT and two transcripts in ewe AT. Refeeding sharply increased LPL and FAS mRNA levels, while restriction slightly increased (cows) or had no effect (ewes) on the HSL mRNA levels. This suggests that nutritional factors regulate sharply the expression of LPL and FAS genes by pretranslational mechanisms, but less clearly that of HSL gene.