Dietary fat saturation affects glucose metabolism without affecting insulin receptor number and affinity in...

The effects of dietary fat source on epididymal fat cell insulin receptor binding and affinity and on glucose transport and use by genetically diabetic rats were studied. Male BHE rats were fed 6% fat/64% sucrose diets. The fat consisted of 1% corn oil plus 5% beef tallow, menhaden oil or corn oil. Glucose tolerance was assessed at 100, 300 and 600 d of age. At 100 d of age the fat pads were excised, isolated adipocytes prepared and insulin receptor number, receptor affinity, 3-O-methyl glucose uptake and glucose use determined. Insulin receptor number and binding affinity were not affected by dietary fat type. The transport and subsequent use of glucose were greater in fat cells from rats fed beef tallow compared with those from rats fed corn oil or menhaden oil. All three groups exhibited a deterioration in glucose tolerance with age. Although we observed greater glucose transport, oxidation and conversion to fatty acids in beef tallow-fed rats, we saw no differences in these measurements between cells from corn or menhaden oil-fed rats. Thus, we conclude that the effects of these dietary lipids are attributable to effects of saturated fatty acids on intracellular events rather than on the insulin receptor per se, and that the type of unsaturated fatty acid [(n-3) vs. (n-6)] is of little importance to the regulation of glucose metabolism by isolated adipocytes.