Effect of insulin upon the cellular character of rat adipose tissue

The effect of insulin upon the lipid content, and the number and size of fat cells in the epididymal, retroperitoneal, and subcutaneous adipose tissue of a large number of rats were examined. Insulin administration began either in early life (birth, 1, or 3 wk of age) or during adulthood (age 10 wk). At different times during growth, groups of treated and control animals were killed and the size and number of fat cells in each of the three adipose depots were determined. Insulin-treated animals gained weight at an increased rate and had fatter epididymal, retroperitoneal, and subcutaneous adipose depots than untreated controls. In each site the expanded adipose tissue was accompanied by an increase in the lipid content per cell (cell size), but in no case was there an increase in the number of adipose cells. This was the case regardless of whether insulin treatment was initiated before weaning (birth, 1 wk of age), at weaning (3 wk), or post weaning (10 wk) and irrespective of the duration of the insulin treatment.