Cholesterol metabolism was studied in jejunal mucosa of the rat with special emphasis on cholesterol synthesis of villous cells, the site of intestinal lipid absorption. The type of diet and nutritional state clearly affected the cholesterologenesis of villous cells. Consequently, the incorporation of 14C-acetate into nonsaponifiable lipids (NSL; includes squalene and sterols) decreased in the following order of magnitude: 1) fat-free diet supplemented with safflower oil (FFD-SO), 2) FFD alone, 3) standard rat chow, 4) 1% cholesterol in FFD-S(, 5) total fast. Both the cholesterol feeding and the fast increased the total cholesterol concentrations in the villous cells, but the concentrations were unaffected by the other diets. In rats fed FFD-SO diet the cholesterol synthesis was significantly higher in the villous than in the crypt cells, although the cellular cholesterol concentrations were similar. The hepatic cholesterol synthesis from 14C-acetate was low in rats fed FFD-SO as compared with chow diet, whereas the incorporation of 14C-acetate into hepatic fatty acids and the incorporation of 3H-mevalonate into NSL were not affected by the diet. 5% cholestyramine had no significant effect on the cholesterol synthesis or cholesterol concentrations of the villous cells during high (FFD-SO diet) or low cholesterol synthesis (chow or cholesterol feeding). FFD-SO increased serum total cholesterol compared with chow diet and total fast, whereas cholestyramine and cholesterol feeding had no effect. Intraperitoneal administration of the hypocholesterolemic agent, 4-aminopyrazolopyrimidine, to fasting rats decreased markedly crypt cell cholesterol and increased cholesterol synthesis in the crypt cells and in the villous cells.(ABSTRACT TRUNCATED AT 250 WORDS)