Effect of ascorbic acid on the intestinal absorption of bile salts and metabolism of cholesterol in guinea pigs.

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Abstract
The major bile acid and its salt were identified as chenodeoxycholic acid and its taurine conjugate, respectively. The critical micelle concentration (cmc) value of sodium chenodeoxycholate was about 0.9 mM suggesting approximately the same order as reported on others with di-hydroxy groups. Added ascorbic acid did not exert any effect on the cmc value. Sodium taurochenodeoxycholate was favorably absorbed from the ileum portion of guinea pigs, and the absorption there appeared to obey a type of saturation kinetics as was demonstrated with other bile salts. Ascorbic acid inhibited the absorption significantly and especially in the lower concentration region of sodium taurochenodeoxycholate than its cmc, where the percent inhibition was approximately 30-35. Double reciprocal treatment did not indicate any feasibility of competitive inhibition for the system of taurochenodeoxycholate and ascorbic acid. This effect of ascorbic acid could be explained neither by a change in physicochemical properties of the bile salt nor the direct action on intestinal mucosa, based on the results of cmc and additional pre-treatment tests, but may be rather discussed by some participation in the hydrolysis and/or dehydroxylation of that salt occurring in the intestinal tissues other than mucosal membrane. I.p. administration of this vitamin and its dehydro form for 4 days enhanced the biliary amount of total chenodeoxycholate by about 60% of the control. Both in situ and in vitro experiments supported the in vivo results, so this metabolic aspect may be recognized as one of the physiological functions of ascorbic acid which was reported to lower serum cholesterol, in addition to suppressive effect on the ileal absorption of taurochenodeoxycholate.