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Absorption of Inorganic, Trivalent Chromium from the Vascularly Perfused Rat Small Intestine^1,2,3,

St. Luke's-Roosevelt Hospital Center and The Institute of Human Nutrition Columbia University, College of Physicians and Surgeons New York, NY 10025

The absorption of inorganic, trivalent chromium (Cr) by the rat small intestine was investigated by quantifying three components of the absorptive process: 1) Cr uptake from a test meal, 2) Cr transport into the circulation and 3) Cr retention by the intestine. An in vitro, in situ double-perfusion technique was used in which the intestinal vasculature, from the superior mesenteric artery to the portal vein, and the intestinal lumen, from the duodenum to the ileum, were perfused simultaneously. The vasculature was perfused with a synthetic "plasma" (vascular perfusate) while the lumen was perfused with a nutrient-rich solution (intestinal perfusate) at concentrations of trivalent Cr of 0.2–20 µmol/l (10–1000 ppb). Dose-response curves, in which Cr transport, retention and uptake were plotted against the luminal Cr concentration, revealed that Cr absorption is a nonsaturable process. Regardless of the Cr concentration of the intestinal perfusate, 5.90 ± 0.33% (mean ± SEM) of the test dose was taken up from the meal, 5.52 ± 0.33% was transported into the vascular perfusate and 0.38 ± 0.03% was retained by the small intestine. Based on the criterion of saturability, it was concluded that inorganic, trivalent Cr is absorbed by the nonmediated process of passive diffusion in the small intestine of rats fed a Cr-adequate diet (1.44 µg Cr/g diet).

KEY WORDS: • inorganic, trivalent chromium • trace metal absorption • passive diffusion • small intestine • rat

¹ Supported by a United States Department of Agriculture Competitive Research Grant No. 59-2369-0-1-0517.

² Presented in part at the 70th Annual Meeting of the Federation of American Societies for Experimental Biology, St. Louis, MO, April 1986 [Fed. Proc. 45: 484 (abs. #1920).

³ This study is one of three studies that constituted the Ph.D. thesis of Hillary J. Dowling, "Trivalent chromium absorption in the vascularly perfused rat small intestine: its transport mechanism, and the effects of plasma proteins and dietary amino acids." The degree of Doctor of Philosophy was awarded in January, 1987 at Columbia University, New York City, NY.

Manuscript received 3 November 1988. Revision accepted 28 March 1989.