Sex difference in the influence of obesity on the retention of a tracer of 3H-estradiol.

Overview

The influence of obesity on the retention of a tracer of 3H-estradiol was studied in 15 nonobese premenopausal women, 15 obese premenopausal women (49%-274% above desirable weight), and 27 young men ranging in weight from 5% below to 330% above a desirable weight. The women showed a clear-cut inverse linear correlation between the 72 hr excretion of radioactivity and the percent deviation from desirable weight over the entire weight range examined (y equals 66 minus 0.10x, r equals -0.59, P less than 0.005); the average excretion in the 6 most obese women (145%-272% above desirable weight) was 45 plus or minus 11 (SD)%, significantly lower than the values of 65 plus or minus 12% in 15 nonobese women (P less than 0.025). The obese men showed no correlation whatever between excretion of radioactivity and relative body weight; the average excretion of the 6 most obese men was 55 plus or minus 7, not significantly different from the value of 56 plus or minus 12 in nonobese men. This sex difference makes untenable the hypothesis previously proposed by others that retention of estradiol tracers is obese women (men were not studied ) is due to simple solubility of estrogens in fat. Various alternative possibilities to explain the present data are discussed and it is concluded that a possibility worth examining is that the adipose tissue of women contains specific estrogen binding protein (? receptor) while the adipose tissue of men does not.