Comparison and Effects of Natural and Synthetic Glucose Tolerance Factor in Normal and Genetically Diabetic Mice

Abstract

Glucose tolerance factor (GTF) is thought to be volatile in the dry state at certain temperatures. This property allowed us to measure the stable and the volatile chromium contents of three brewer's yeast GTF preparations and to investigate the possible relationship between the volatile chromium content and its biologic activity. Two forms of chromium were found in brewer's yeast extracts by flameless atomic absorption spectroscopy using two different methods of sample preparation. Three brewer's yeast GTF preparations were found to contain total Cr concentrations ranging from 0.40 to 0.81 μg. per milligram dry weight and volatile Cr concentrations ranging from 0.02 to 0.39 μg. per milligram dry weight. The biologic response obtained with each GTF preparation was linearly related to the concentration of volatile chromium present. These observations suggest that the volatile chromium fraction in brewer's yeast is biologically important, whereas the active component of these yeast preparations is probably a precursor of GTF. The metabolic effects of synthetic chromium-nicotinic add-ammo acid complexes and a brewer's yeast GTF preparation were compared in normal and genetically diabetic mice. The synthetic preparations mimicked the effects of brewer's yeast GTF by lowering plasma glucose and triglyceride concentrations, although at different time courses. In addition, biologically active synthetic complexes have been synthesized and may contain no volatile chromium. Synthetic complexes of chromium-nicotinic acid-amino acids lowered blood glucose by only IS to 20 per cent in normal mice as against a 36 per cent reduction with brewer's yeast GTF. Further, a synthetic product produced a significant reduction in the elevated plasma concentrations of glucose and triglycerides in genetically diabetic mice (18 and 26 per cent, respectively). This is in contrast to the 29 per cent reduction in plasma glucose and a 56 per cent reduction in plasma triglycerides produced by GTF prepared from brewer's yeast. These findings suggest that the synthetic factors are similar to, but not identical with, the active GTF fraction extracted from brewer's yeast.