Adipose tissue cellularity: effect on insulin and thyroxine.

The influence of insulin and thyroxine on the cellularity of adipose tissue in the rat epididymal fat pad has been studied. Incorporation of (3H) thymidine into the DNA of fat cells and stroma was measured together with fat cell size and number in rats pre-treated with either one of these hormones. There was an increase in fat pad weight in insulin treated rats which was due to 'lipid filling' of existing adipocytes and not increased proliferation of new fat cells. Thyroxine treated rats showed a decrease in fat pad weight caused by a decrease in size of individual fat cells. Cell number remained unaffected by either treatment.