SIZE DISTRIBUTION OF ADIPOCYTES AND VARIATION IN ADIPOCYTE NUMBER IN LINES OF MICE SELECTED FOR HIGH OR LOW BODY-FAT

1. Adipocyte size and number were measured in epididymal fat pads from lines of mice selected for high or low body fat. 2. Epididymal fat pad weight at 10 weeks of age was 4-fold greater in the high fat than the low fat mice, accompanied by a 7-fold greater adipocyte volume but there was no difference in adipocyte number. Smaller differences in fatness and cell volume were observed at younger ages. 3. The high fat mice showed one or two populations of cells up to 5 weeks of age and at 7 weeks 3 days and 10 weeks showed two or more populations. In contrast, the low fat animals at all ages showed either one or two populations. 4. These findings imply that greater lipogenesis and cell filling, not cell proliferation, is the primary mechanism of increased fatness in these selected lines of mice.