Turnover of hepatic and plasma triacylglycerol in sheep

Contributions of the intestine and liver to triacylglycerol (TG) formation from endogenous fatty acids were investigated in sheep. Cannulation and sampling of the intestinal lymph ducts and portal veins of two mature, nonpregnant ewes followed by an i.v. dose of 100 microCi of [14C]palmitate into a mesenteric cannula suggested intestinal contribution to endogenous TG production to be of no consequence. Turnover rates of TG within the plasma, hepatic microsomal and hepatic fat droplet compartments of four wethers averaged 20 +/- 8, 7.8 +/- 1.5 and 2.3 +/- .8 mg.h-1.kg body weight-1, respectively. A large, relatively inert pool of fat droplets with a slow turnover contained between 80 and 90% of the total hepatic TG. Hepatic TG concentration and turnover rates within the hepatic microsomal and fat droplet pools were inversely (r = -.86) and positively (r = .99) correlated, respectively, indicating that hepatic secretion of TG as lipoprotein was decreased as hepatic TG concentration increased. The model developed from these figures suggest that 40% of the plasma TG turnover is of endogenous origin and that this percentage value decreases when hepatic TG content is increased.