Blood Progesterone and Pregnenolone Levels During Phenobarbital (PB) Block of PMS-induced Ovulation in Immature Rats1

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

“…Animals treated with PB show reduced amounts of progesterone and higher amounts of pregnenolone in the blood (Meyer et al, 1971). Injection of pregnenolone did not cause ovulation in these PB-treated animals while small amounts of progesterone overcame PB-block of ovulation ( .…”

“…In the animals treated with PB, increased pregnenolone and decreased progesterone were found (Meyer et al, 1971;Norman & Greenwald, 1971;Karavolas et al, 1972). In animals treated with PB, the conversion of pregnen¬ olone to progesterone is inhibited and the optimal ratio of oestrogen : pro¬ gesterone for ovulation is not attained.…”

“…An injection of progesterone did restore ovulation, but injection of pregnenolone acetate in doses up to 4 mg did not restore ovulation in these rats. Meyer, Karavolas, Klausing & Norgard (1971) reported that rats treated with PB and primed with PMSG showed a decrease in plasma progesterone levels and an increase in the levels of pregnenolone, suggesting that PB inhibits the conversion of pregnenolone to progesterone. These findings were sup¬ ported and extended by the work of Karavolas, Gupta & Meyer (1972).…”

Studies on the Mode of Action of Sodium Pentobarbital in Blocking Ovulation in Rats

“…The different results obtained by Hagino (1969) and Meyer et al (1971) could be due to slight differences in the experimental design. We therefore decided to distinguish between the central and peripheral sites of action of PB by studying the effects of intracerebrally administered PB on ovulation in the experimental model used by Meyer et al (1971), i.e. immature rats primed with PMSG and given a single injection of progesterone to evoke an ovulatory response.…”

“…Cross & Dyer (1971) reported reduced unit activity of hypothalamic neurons following intravenous injection of subanaesthetic doses of sodium methohexitone (Brietal: Eli Lilly Co. Ltd) but response to urethane was variable. Using a somewhat different experimental design involving progesterone-induced ovulation, a direct action of PB on the ovary has been implicated in inhibition of ovulation by this drug (Meyer, Karavolas, Klausing & Norgard, 1971;Karavolas, Gupta & Meyer, 1972). These authors have proposed that PB inhibits ovulation by markedly altering the secretory patterns of progestagens from the ovary.…”