Hormonal effects on triacylglycerol secretion of rat liver

The influence of epinephrine, norepinephrine, insulin, and prednisolone on the triacylglycerol (TG) secretion rate of rat liver was determined in vivo under different nutritional conditions (non-fasting, 10 and 16 h fasting, respectively). It was possible to estimate the triacylglycerol secretion rate by the Triton method without regard to fasting intervals. The subcutaneous administration of hormones was followed in all cases by changes of lipid parameters. Variations of secretion rate were found only by applications of norepinephrine, insulin, and prednisolone. Frequently, but not always, a change of free fatty acid (FFA) concentration in serum, that means a change of FFA mobilization in adipose tissue, was accompanied by an alteration of the TG secretion rate and in some cases by a change of TG concentration in serum in the same direction. We suggest that under these conditions the hormonal effect on TG secretion is realized by influence on the mobilization of FFA in adipose tissue. If the enhancement of FFA in serum is not followed by an increase of TG secretion, the elevated FFA influx into the liver is possibly used for oxidation or synthesis of phospholipids too. The role of nutritional factors was especially seen in 16 h fasting animals in which no rise of TG secretion rate was observed in spite of high FFA levels. In some cases reduced serum TG concentrations were observed without preceeding decreases of TG secretion rate out of the liver. Probably this effect is caused by increased clearance of serum TG.