Effect of Nicotinic Acid on the Incorporation of Radiocarbon

Xicotinie acid when fed to rats as O.S per cent of their diet caused an 83 per cent increase in radioactivity of liver eholesterol-digitonin precipitate. In vitro studies using rat liver slices indicated that nicotinic acid increased the incorporation of radiocarbon into cholesterol by 46 per cent. FOLLOWING the lead of Altschul,1 anumber of investigators have established that nicotinic acid depresses the serum cho-lesterol. A previous report2 indicated that inclusion of nieotinic acid in experimental diets fed to rabbits partially prevented the anticipated rise in serum cholesterol, pre-vented cholesterol deposition in the aorta and, to a lesser extent, cholesterol deposits in the liver. I t was emphasized that the mechanism whereby nicotinic acid altered serum and tissue cholesterol was unknown. It was pointed out, however, that the large number of methyl groups required for the excretion of nicotinic acid might alter cho-lesterol synthesis. The purpose of this study was to deter-mine: (1) the effect of nicotinic acid on the incorporation of sodium acetate 1-carbon14 into liver cholesterol * in the living organism, and (2) the effect of supplementary nicotinic acid on the incorporation of sodium acetate 1-carbon.14 into cholesterol in rat liver slices. METHODS Male rats of the Sprague-Dawley strain were fed a stock diet containing- 0.8 per cent nicotinic acid; an equal number of control animals were fed a stock diet. At the end of S days, the rats were injected intraperitoneally with sodium acetate 1-carbon " (6.0 ^ic/lOO Gm. body weight). At intervals of 30 min. to 4 hours following the injection the rats were killed by decapitation. The livers were removed and immediately homo-genized in chloroform (35 nil. ehloroforni/Gm. fresh liver tissue) by a Servall OmniinLxer for 3 min. at 14,500 r.p.m. The homogenates were filtered and the residue extracted with chloroform