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Intestinal Absorption of Biotin in the Rat^1,2,

Clinical Nutrition Research Unit and Section of Gastroenterology, Department of Medicine, The University of Chicago, 5841 South Maryland Avenue, Box 400, Chicago, IL 60637

We examined the absorption of biotin using the in vivo intestinal loop technique. Jejunal segments from male rats were filled with solutions containing [³H]biotin and [¹⁴C]inulin in Krebs-Ringer phosphate buffer, pH 6.5. Absorption was determined on the basis of luminal tritium disappearance after correction for inulin recovery. At biotin concentrations of 0.1 and 5.0 µM, luminal biotin disappearance was linear for at least 10 min. At biotin concentrations ranging from 2.3 nM to 75 µM, 10–28% of the administered dose was absorbed in 10 min. The concentration dependence of luminal biotin disappearance is consistent with the presence of both saturable and nonsaturable (linear) components of biotin uptake, with estimated K_m = 9.6 µM and J_max = 75.2 pmol/(2.5 cm loop · min). The rate constant for nonsaturable uptake is 3.1 pmol/(2.5 cm loop · min · µM). We conclude that at biotin concentrations less than 5 µM, biotin absorption proceeds largely by the saturable process, whereas at concentrations above 25 µM, nonsaturable uptake predominates. Additional studies demonstrated significantly less biotin uptake in the ileum than in the jejunum, a finding in agreement with previous in vitro studies.

KEY WORDS: • biotin • intestinal absorption • rat

¹ This study was supported by US Public Health Service grants AM26678 and AM15351.

² Presented in part at the Federation of American Societies for Experimental Biology meeting in Anaheim, California, in April 1985. Bowman, B. B., Selhub, J. & Rosenberg, I. H. (1985) In vivo studies of intestinal biotin absorption in the rat. Fed. Proc. 44, 1547, (abs. 6647).

³ To whom reprint requests should be sent.

Manuscript received 20 September 1985. Revision accepted 18 February 1986.

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