The influence of prostaglandin F-2 on pregnenolone metabolism by the autotransplated ovary of the ewe

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Abstract
Eight ewes each with an autotransplanted ovary received infusions of 3H-labeled pregnenolone (41 .mu.Ci/h) for 8 h into the artery supplying the ovary, together with prostaglandin (PG) F2.alpha. (30 .mu.g/h) for 3 h beginning 2 h after the start of the pregnenolone infusion. All animals exhibited estrus 2-3 days after the start of the experiment. During the PGF-2.alpha. infusion blood flow through the ovaries was increased by 13%, but subsequently returned to pre-infusion levels. Secretion rates of endogenous progesterone and 20.alpha.-hydroxypregn-4-en-3-one dropped rapidly 5 h after the PGF-2.alpha. infusion had started from values of 250 .mu.g/h and 25 .mu.g/h to values below 60 .mu.g/h and 8 .mu.g/h, respectively. At this time the conversion of radioactive pregnenolone to progesterone was reduced by 50% of its initial value, but the secretion of endogenous pregnenolone and the formation of radioactive metabolites other than progesterone were not diminished. In 4 control animals, which received pregnenolone only, no changes in ovarian blood flow, steroid secretion rates, or in the conversion of labeled pregnenolone were observed. These results suggest a possible involvement of PGF-2.alpha. in the regulation of progesterone biosynthesis by an action on the 3.beta.-hydroxysteroid oxidoreductase-.DELTA.5-4 isomerase enzyme system.