Mean plasma concentration, metabolic clearance and basal plasma production rates of testosterone in normal young men and women using a constant infusion procedure: effect of time of day and plasma concentration on the metabolic clearance rate of testosterone.

Abstract

ABSTRACT Plasma specimens were obtained from 2 normal men and 2 normal women at 90-min intervals (16 specimens) during a 24-hr period, pooled and analyzed for testosterone using a double isotope derivative method. The data were compared to those obtained in individual plasma specimens taken at approximately 4-hr intervals. The plasma testosterone level found in the pool of the 16 specimens in each subject was considered a close approximation of the daily mean. The plasma testosterone levels of the pool in the men were 22.0 and 21.8% lower than the respective values seen at 9 am. Thus, the use of a morning plasma level of testosterone for the calculation of a mean daily plasma production rate of the steroid in men would introduce a significant error. Since the mean of the 9 am, 5 pm and 10 pm specimens was considerably closer to the daily mean (pool), it has been used as a reasonable compromise to the true mean. In contrast to the males, the female subjects failed to show any significant diurnal variation ...