Plasma concentration of steroid hormones after intravenous infusion of testosterone in castrated male transsexuals.

Ten male transsexuals who had surgical operations for sex-reassignment at least three months previously were given intravenous infusion of 2.4 mg (7 subjects) or 12 mg (3 subjects) testosterone over a period of seven hours. In both groups, plasma levels of testosterone and oestradiol measured by radioimmunoassay were significantly elevated one hour after the start of the infusion and remained raised throughout the infusion period. With the lower rate of infusion, plasma levels of testosterone rose from 0.6 ng/ml to 7.4 ng/ml, oestradiol from 16.2 pg/ml to 22.4 pg/ml while levels of androstenedione remained unchanged. When 12 mg testosterone was infused, the level of this hormone was elevated from 0.5 ng/ml to 29.6 ng/ml, while oestradiol increased from 16.5 pg/ml to 45.0 pg/ml. These results indicate that when physiological doses of testosterone are infused, conversion to oestradiol contributes to approximately 13.5% of total circulating oestradiol in men.