Biosynthesis of delta-7-cholesten-3-beta-ol, delta-5,7-cholestadien-3-beta-ol, and delta-5-cholesten-3-beta-ol by guinea pig intestinal mucosa in vitro.

Methods were developed for the separation and determination of the various 27-carbon sterols of intestinal mucosa by means of thin-layer chromatography. Scrapings of the mucosa of the small intestine of guinea pig and rat were shown to incorporate isotope from (14)C-labeled acetate and mevalonate into sterols in vitro. For each substrate this activity was lowest in mucosa from the proximal third of the small intestine and greatest in mucosa from the more distal regions of the small intestine. The total 27-carbon sterol content of guinea pig mucosa varied only slightly along the length of the small intestine, but the concentration of cholesterol was highest distally. More than 95% of the radioactivity incorporated from acetate-2-(14)C into 27-carbon sterols by guinea pig mucosa in 4 hr was recovered as lathosterol and 7-dehydrocholesterol; less than 5% was in cholesterol. The specific activities of the 27-carbon sterols were consistent with the concept that synthesis proceeds from lathosterol to 7-dehydrocholesterol to cholesterol.