Effect of 5 -Dihydroprogesterone, Pregn-5-Ene-3,20-Dione, Pregnenolone and Related Progestins on Ovulation in PMSG-Treated Immature Rats

Abstract

The facilitative effects of certain progestational steroids on ovulation were investigated by using 25-day-old female rats which had been treated on Day 22 with a non-ovulatory dose of PMSG (12 i.u.). Ovulation was caused by treatment with pregnenolone or progesterone on the morning of Day 24. The dose of pregnenolone required was higher than that of progesterone. Progesterone had this effect throughout the morning of Day 24, while prenenolone was only effective between 07.00 and 10.00 hours on Day 24. The two metabolites of progesterone in the hypothalamus and uterus, 5\g=a\-dihydroprogesterone and 3\ g=a\ \ x =r eq-\ hydroxy-5\m=infty\-pregnan-20-one, were also tested for their ability to cause ovulation. Although 5\g=a\-dihydroprogesteronepossessed this ability, a dose three to four times that of progesterone was required to produce a comparable effect. Doses of up to 1 \m=.\5 mg 3\g=a\-hydroxy-5\g=a\-pregnan-20-one were without effect. Neither 17\g=a\-hydroxypregnenolone nor 17\g=a\-hydroxyprogesterone had any effect in influencing ovulation.Pregn-5-ene-3,20-dione had a facilitative ability comparable to that of progesterone in doses of 0\m=.\25 mg or higher. The facilitative effect of progesterone decreased when it was injected earlier on Day 24 or during the evening of Day 23; no potentiating effect was obtained at 14.00 hours on Day 23. The results obtained with pregnenolone, progesterone and related steroids support the hypothesis that the inhibition of ovulation by phenobarbital may be due in part to its interference with the conversion of pregnenolone to pregn-5-ene-3,20-dione.

Induction of Ovulation by Pregn-5-Ene-3,20-Dione and Progesterone in Immature Rats Treated With PMSG and Phenobarbital

“…Our results support this hypothesis. This is noteworthy as pregnenolone does have a facilitative action on ovulation in immature rats given a nonovulatory dose of PMSG and no PB (Sridharan, Meyer & Karavolas, 1974).…”