Title: Progesterone and Estradiol Levels in Follicles and the <i>in vitro</i> Metabolism of Steroid Hormones by Hens during the Ovulatory Cycle
Abstract: Progesterone and estradiol contents and concentrations of the hierarchical follicles of the hen during the ovulatory cycle were measured with a radioimmunoassay. Progesterone content was always the highest in the largest follicle at 10, 4 and 1-0.3 hours before ovulation, and the value increased and reached a peak at 1-0.3 hours before ovulation, and rapidly decreased after the ovulation in the ruptured follicle. Estradiol content was the largest in the 3rd or 4th largest follicles during the ovulation cycles, and the lowest in the largest follicles among the large 6 follicles of the ovary. Amounts of in vitro release of either progesterone or estradiol from the hierarchical follicles of the ovary corresponded the hormone content of the corresponding follicles.[4-14C]-Labelled pregnenolone and progesterone were incubated with the homogenates of the largest and the 2nd largest follicles of hen ovary obtained at 10, 4 and 1-0.3 hours before ovulation and immediately after ovulation. The conversion of pregnenolone to progesterone (and other products) was always higher in the largest follicle than the 2nd largest follicle. The conversion of progesterone to 17α-hydroxyprogesterone (and other products) was always lower in the largest follicle than the 2nd largest follicle, and it decreased rapidly in the largest follicle at 1-0.3 hours before ovulation. Relatively higher combined activities of Δ5-steroid-3β-hydroxysteroid dehydrogenase and Δ5-Δ4 isomerase and significuntly lower activity of 17α-hydroxylase in the largest follicle at 1-0.3 hours before ovulation may account for the high concentration of progesterone in the follicle.