The effects of dexamethasone on plasma free androgens during the normal menstrual cycle.

In order to evaluate the ovarian and adrenal contribution to peripheral plasma concentrations of total testosterone (TTe), indixes of the plasma concentrations of free testosterone (FTeI), free 17 beta-hydroxysteroid androgens (FHSI), and testosterone-binding globulin (TeBG) during the menstrual cycle, women were examined during three normal cycles and three other cycles under dexamethasone (0.5 mg., four times a day) suppression. All study cycles were apparently ovulatory. The mean TTe and FTeI during the midcycle period were significantly higher than during the early follicular (P less than 0.005) and the midluteal periods (P less than 0.01 and P less than 0.001, respectively). During the menstrual cycles under dexamethasone suppression only the difference in TTe and FTeI between the midcycle (37 +/- 12.4 (S.D.) ng. per 100 ml. and 10.5 +/- 4.0 (S.D.), respectively) and the midluteal (26.0 +/- 10.1 (S.D.) ng. per 100 ml and 7.2 +/- 3.2 (S.D.), respectively) periods was significant statistically (P less than 0.05). No significant differences in the mean levels of FHSI and TeBG between three periods within the cycle were noted in either the control or the dexamethasone-treated cycle. When each phase was compared, the mean levels of TTe, FTel, and FSHI were significantly lower in the dexamethasone-treated cycles than in the normal cycles. The data suggest that the level of TeBG is not perceptibly affected by physiologic fluctuation of estrogen levels during the menstrual cycle, and the FHSI levels are stable throughout the ovulatory cycle. Decrease in levels of TTe, FTeI, and FHSI during dexamethasone suppression seems to be due to reduction of androgen production as TeBG, a major determinant of the metabolic clearance rate of androgens, was not affected by dexamethasone.