Mechanisms of hypolipidemic action of nicotinic acid.

Abstract

The effects of NA treatment were investigated in 5 normolipidemic and 10 hyperlipidemic subjects. Nicotinic acid lowered the levels of plasma lipids in alt patients on normal American diets but had no effect on plasma lipids of patients on HCD. NA did not affect intestinal absorption of cholesterol. Its effects on cholesterol balance were variable. Its action on cholesterol synthesis was investigated in 11 patients by three additional methods, each one of which indicated that synthesis of cholesterol was markedly inhibited. NA did not reverse the increase in synthesis of cholesterol in patients on HCD but it did reverse the increase in synthesis caused by cholestyramine. Hypocholesterolemic effect of NA was associated with mobilization of tissue cholesterol and (as reported by us previously for clofibrate) the drug also reversed an apparent increase in tissue pools of cholesterol in a patient given cholestyramine. Nicotinic acid had no effect on the activity of plasma lecithin‐cholesterol acyltransferase. NA treatment was associated with a decrease in the turnover of plasma TG. The increase in the fractional turnover rate of plasma TG seen after NA treatment was perhaps secondary to the decrease in the levels of plasma TG. Such e.ffects were not observed in patients on HCD. The primary mechanism of hypolipidemic action of NA appears to be its antilipolytic action on adipose tissue. Its effects on hepatic metabolism of lipids are probably secondary to the reduction in the circulating pool of plasma free fauy acids.