Natural Occurrence and Biological Activity of Vitamin a Derivatives in Rat Bile

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Abstract
A study was made to determine the biological activity of retinoyl β-glucuronide, a major biliary excretion product of administered retinoic acid in the rat, to evaluate the significance of the biliary excretion of vitamin A derivatives under normal nutritional conditions, to analyze the rate of excretion of vitamin A derivative, and to determine the chemical nature of the excreted products. Retinoyl β-glucuronide has a biopotency 30 to 100% as great as all-trans retinol or as all-trans retinoic acid. A more accurate estimate cannot be given because of the unknown effect of the isolation procedure on the glucuronide's biopotency. Similarly, a nonpolar retinoate derivative in bile (fraction I), which presumably is methyl retinoate, has a biopotency 50 to 200% as great as all-trans retinoate by like criteria. The biliary secretion of vitamin A derivatives, presumably glucuronides, appears to be a normal physiological process, inasmuch as labeled compounds were secreted at the rate of about 0.3 µg/ml in the bile of vitamin A-depleted rats from 6 to 32 days after the administration of labeled retinol. Finally, the rate of excretion of labeled retinoic acid derivatives in the excreta closely paralleled the rate of their secretion into bile. Most of the radioactivity appeared in the feces, mainly as retinoic acid but with a lesser amount as the glucuronide. A labeled derivative, presumably the glucuronide, appeared earlier in the urine but in much smaller amounts.

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