The metabolic clearance rate of progesterone in males and ovariectomized females.

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Abstract
A method has been presented for the estimation of the metabolic clearance rate (MCR) of progesterone by single injection and continuous infusion from plasma and whole blood. A comparison of the single injection and continuous infusion methods of measuring MCR in males and ovariectomized patients has been studied. The MCR measured by single injection (MCRR) is approximatelyfequivalent to MCR measured by continuous infusion (MCRr) in both groups of subjects. However, the continuous infusion method is considered more accurate and practical. The plasma MCRR for 6 males is 2450 [plus or minus] 437 (SE) L/day with a coefficient of variation of 43%. The calculated total volume of distribution is 27 to 39 L. The plasma MCRR for 3 ovariectomized females is 2428 [plus or minus] 322 (SE) L/day with a coefficient of variation of 23%. The plasma MCRr for 10 males is 2080 [plus or minus] 137 (SE) L/day with a coefficient of variation of 21%. The plasma MCRr for 11 ovariectomized females is 2l73 [plus or minus] 175 (SE) L/day with a coefficient of variation of 27%. There is no difference between males and ovariectomized females in the rate of clearance of progesterone from the plasma. The blood MCRr for 5 males is 3691 [plus or minus] 119 L/day; the plasma/blood ratio is 1.7 [plus or minus] 0.2 (SE) with a mean hematocrit of 44%, which indicates that there is no appreciable progesterone in the red cells. The rapid disappearance of progesterone has been shown to be a result of metabolism rather than distribution into a large volume. In the presence of high hepatic extraction, progesterone is metabolized appreciably by the extrasplanchnic circulation. The measured MCR values lead to calculated plasma production rates in the male that are much less than the corresponding urinary production rates. The discrepancy is less in ovariectomized females.