Effect of prostaglandin F-2 alpha on plasma levels of progesterone and pregnenolone in the hysterectomized guinea-pig.

Repeated injections of PGF-2 alpha were given to hysterectomized guinea-pigs. Within 12 h after the first injection, plasma progesterone levels were significantly reduced (P less than 0.001) and declined to less than 1 ng/ml by the 4th day after the end of PGF-2 alpha treatment. A decline in plasma levels of pregnenolone paralleled that of progesterone. PGF-2 alpha treatment did not affect the metabolic clearance rate of [3H]pregnenolone, but the converions of [3H]pregnenolone to [3H]progesterone was reduced by about 50%.