Cystine Deficiency and Cholesterol Metabolism in Primates

• A deficiency of sulfur amino acids impairs sterol metabolism in several species.' The present work with primate species was directed at an explanation of this phenomenon. The role of dietary cholesterol in the regulation of blood cholesterol has been best documented for the rat* In that rodent, synthesis of cholesterol is reduced by the administration of dietary cholesterol. Gould et al. showed in the dog also that the presence of dietary cholesterol reduced the synthesis of cholesterol. This effect of feeding cholesterol is more readily demonstrated in vitro with liver preparations than in the whole animal. The influence of exogenous cholesterol on sterol metabolism, known as the "feed back regulation" of cholesterol level, has been extrapolated freely to the human situation. Thus it has been argued that restriction of dietary cholesterol is of little practical importance in regulating the level of serum cholesterol in human beings because of the compensating effect of changing rate of synthesis.