VERY SMALL FAT-CELL POPULATIONS DETERMINED BY A MODIFIED OSMIUM TETROXIDE-UREA METHOD

To facilitate investigations on very small fat cell (VSFC) populations in adipose tissue, an alternate method of preparing fat tissue samples was explored. The osmium tetroxide-8 M urea method, modified by addition of a 95% ethanol step in tissue processing, centrifugation between steps, and final resuspension in 55% glycerol in 0.01% Triton-saline, was compared with the collagenase method for determination of VSFC populations in Fischer 344 [rat] epididymal and Sprague-Dawley [rat] retroperitoneal adipose depots. For each method and in both depots, the average histogram of 300 adipocyte diameters, measured by microscopy, was bimodal with the nadir between 30 and 40 .mu.m diameter. The average histogram of fat cells <35 .mu.m in diameter showed a separate population of VSFC existed in each depot. The modified osmium-urea method gave better results and was easier to perform than the collagenase method. New questions concerning a role for the natural existence of a VSFC population in the adipose depot are raised.