Effect of trivalent chromium complexes on glucose uptake by epididymal fat tissue of rats.

The glucose tolerance factor is a dietary agent required in rats for maintenance of normal removal rates of glucose from the blood (2). Recently, we have identified trivalent chromium as the active ingredient (3). GTFl is present in natural diets, for instance table scraps or McCollum’s wheat-casein diet, whereas To&a yeast diets, casein-sucrose diets, and even commercial laboratory chows were found to be GTF-deficient (4). Trivalent chromium thus appears to be a physiological dietary agent, in very small amounts essential for normal utilization of glucose. Certain, but not all, trivalent chromium complexes prevent the development of the impaired glucose tolerance on GTF-deficient diets; they also cure the fully developed defect overnight with a single stomach-tubed dose of 20 pg of chromium per 100 g of weight. In the intact animal, intravenous glucose tolerance is affected by many regulatory mechanisms. It is known that peripheral tissue is the main site of glucose disappearance, whereas the liver plays only a minor role (5). Conversion into fat appears to be a major metabolic pathway for the excess sugar. In order to define the site of action of GTF more closely, glucose uptake was measured with epididymal fat tissue from rats on GTFdeficient and GTF-supplemented diets, and a study was made of the effect in vitro of trivalent chromium complexes on the incorporation of glucose into fat. It was found that minute levels of GTF-active chromium compounds under appropriate conditions greatly enhance the activity of this system.