The Effect of Trivalent Chromium on Galactose Entrv

Trivalent chromium, recently identified as the active ingredient of the glucose tolerance factor, appears to be a dietary agent required for maintenance of normal glucose tolerance in the rat. The element, applied in the form of certain coordination complexes, prevents impairment of removal rates of intravenously injected glucose in rats on rations deficient in glucose tolerance factor, and it cures the fully developed defect overnight with one dose of approximately 20 pg per 100 g of body weight administered by stomach tube (1). In epididymal fat tissue of glucose tolerance factor-deficient rats, 0.001 to 0.1 pg of chromium per 2 ml of medium and approximately 100 mg of tissue in vitro increase glucose uptake and incorporation of glucose carbon into fat by up to 94% (2). The presence of insulin was found to be an indispensable requirement for this effect. Response to chromium supplementation was obtained with 0.1 and 1.0 milliunit per flask. Furthermore, in experiments studying the incorporation of carbon 14 into lipids, the greatest effect of chromium was observed with glucose as substrate and in the presence of insulin. The effect diminished when acetate-Cl4 was used in the presence of unlabeled glucose and insulin, and it became insignificant when either glucose or insulin was omitted from the system. These observations suggested a site of action of chromium close to that of insulin. The experiments reported here were designed to measure the effect of the element of the entry mechanism for sugar into the cell, and by the use of this system under well controlled chromium-free conditions, to determine the possible interdependence of insulin and chromium in their effect on entry rates. n-Galactose was used as a substrate; this sugar is poorly metabolized by peripheral tissue but its entry is regulated by insulin (3).