In vitro metabolism of progestins. III. The metabolic clearance rate of medroxyprogesterone acetate in monkeys.

3H-medroxyprogesterone acetate (MPA) was synthesized by selective catalytic tritiation of the delta1-olefinic bond of 6alpha-methyl-17alpha-hydroxy-pregna-1,4-diene-3,20-dione acetate. The metabolic clearance rate of MPA (MCRMPA) was determined in 9 female Rhesus monkeys by the single injection technique. The blood MCRMPA was 201 +/- 19 L/day (42.2 +/- 4.0 L/day/kg) which was approximately the same as that reported for progesterone clearance in the monkey. We conclude that a greater biological activity of MPA compared to progesterone cannot be related to its prolonged retention in the blood. Although both MPA and amino-glutethimide alter the rate of steroid metabolism in some species, neither of these agents influences the metabolic clearance rate of 3H-MPA in the monkey.