Intestinal absorption and metabolism of 9-cis-beta-carotene in vivo: biosynthesis of 9-cis-retinoic acid.

This study was done to examine the intestinal absorption and cleavage of 9-cis-beta-carotene in vivo. A micellar solution, containing either no addition or 10 mumol of 9-cis- or all-trans-beta-carotene, was perfused for 2 h through the upper portion of the small intestine of ferrets. The effluent of a mesenteric lymph duct cannulation was collected, as well as intestinal mucosa scrapings, a portal blood sample, and a liver biopsy, both before and after perfusion. Carotenoids and retinoids were measured by reverse-phase, high performance liquid chromatography. 9-Cis- and all-trans-beta-carotene were transported equally well into mesenteric lymph, although the intestinal concentration of the corresponding isomer was tenfold higher after perfusion of the 9-cis- isomer than after perfusion of all-trans-beta-carotene. Regardless of which isomer was used, perfusion of beta-carotene resulted in the biosynthesis of similar amounts of retinoic acid in portal blood, liver, and intestine. However, after the perfusion of all-trans-beta-carotene, all the retinoic acid formed was in the all-trans- form, whereas the perfusion of 9-cis-beta-carotene resulted in the biosynthesis of about 50% of the total retinoic acid as the 9-cis-isomer. We conclude that in the in vivo ferret model, 9-cis-beta-carotene has a good bioavailability and is a precursor of 9-cis-retinoic acid.