Effects of plasma transferrin and albumin on the absorption of trivalent chromium

Abstract

Concentrations of transferrin and albumin were varied in the bloodstream to determine whether trivalent chromium absorption in the rat is affected by either of these putative chromium transport proteins. In a series of double perfusion experiments, the intestinal lumen was perfused with a standardized liquid test meal (intestinal perfusate) containing Cr 3+, with 51Cr 3+ as tracer. The vasculature which supplies the small intestine was perfused with a modified Kreb's-Ringer Bicarbonate solution, KRB, (vascular perfusate). The control KRB contained 5% human serum. Experimental KRB contained various concentrations of human serum, human apo-transferrin and bovine serum albumin. When plasma proteins were omitted from the vascular perfusate, both chromium uptake from the intestinal perfusate and chromium transport into the vascular perfusate decreased significantly (61 and 63 percent, respectively) from the control condition. Chromium uptake and transport returned to, but did not exceed, the control level when physiologic amounts of apo-transferrin and/or albumin were added. Chromium retention by the small intestine was unaffected by the plasma proteins. We conclude that the absorption of trivalent chromium is maximal when either transferrin or albumin is present in the circulation. However, only subphysiologic levels are necessary.