The effect of nicotinic acid on the metabolism of the plasma lipoproteins of rhesus monkeys

Abstract

The effect of nicotinic acid was investigated in Rhesus monkeys. Subcutaneous injections of nicotinic acid lower the plasma very low density lipoprotein (VLDL) and low density lipoprotein (LDL) concentrations, but have no effect on plasma high density lipoprotein (HDL) concentration. The fall in VLDL and LDL concentration is not accompanied by any change in the lipid or protein composition of either lipoprotein. Analysis by Sephadex gel chromatography and polyacrylamide-gel electrophoresis showed that the proteins of monkey VLDL and LDL are qualitatively similar to those of human VLDL and LDL, although there are differences in the proportions of the various proteins present in the two lipoproteins of the two species. Subcutaneous injections of nicotinic acid diminish the maximum incorporation of 14C from [ 14C]threonine into VLDL and LDL apoproteins, but have no effect on incorporation into albumin or HDL apoprotein. Peak incorporations into the apo-B and apo-C of VLDL are diminished to about equal extents by nicotinic acid. Comparison of the amount of 14C lost from apo-B of VLDL after the peak of incorporation, with that gained by apo-B of LDL during the same period, suggests that some of the circulating apo-B of LDL is derived from sources other than circulating VLDL.