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A B S T R A C T Metabolic clearance rates of testosterone (MCRT) and androstenedione (MCRA) were determined twice during the same cycle in six normal women, using a constant infusion of testosterone-2H and androstenedione-"C. Nonlabeled steroids served as internal standards. Plasma concentrations of testosterone (iT) and androstenedione (iA) were measured, and the blood production of testosterone (PBT) and of androstenedione (PBA) were calculated. The interconversions of these two steroids were also estimated. Six ovariectomized women were studied in the same manner. For testosterone, the mean i in the normal women was not significantly different from that in the ovariectomized subjects, whereas the MCRT and PET were significantly lower in the ovariectomized subjects. For androstenedione, the mean MCRA values of the two groups of subjects were not different, whereas the iA and PBA in the normal women were about double those in the ovariectomized subjects. In comparing the follicular and luteal phases of the menstrual cycle in four of six subjects there was no difference in iT, MCRT, or PBT, whereas iA, MCRA, and PBA were increased in the luteal phase. In one ovariectomized woman infused with testosterone and androstenedione at physiologic levels, MCRT doubled but MCRA remained the same. After six wk on estrogen, the same subject did not show any change in MCRT after infusion of testosterone. It is suggested that MCRT depends on PBT and on plasma binding of testosterone which is partly estrogen dependent.

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