Abstract
As a succeeding work of our previous investigation, where preovulatory changes of steroidogenesis of the rabbit follicles was studied, steroid hormone formation in vitro by developing corpora lutea isolated from the rabbit has been investigated in the present communication. Five to eight developing corpora lutea following the rupture of preovulatory follicles were isolated from rabbit ovaries under stereomicroscope at the 15th, 18th, 24th, 48th, 72th and 96th hour after intravenous injection of 100IU/kg of human chorionic gonadotropin (hCG) and incubated with 100μCi of acetate-1-14C in Krebs-Ringer bicarbonate buffer at 37°C for 3 hours under an atmosphere of 95% oxygen plus 5% carbon dioxide. Each incubation was terminated by freezing quickly and stored at - 20°C until twenty to thirty-one corpora lutea had been collected for each time period before commencement of analysis. Incorporations of radioactive acetate into pregnenolone, 17α-hydroxypregnenolone, progesterone, 17α-hydroxyprogesterone, 20a-hydroxyprogesterone, dehydroepiandrosterone, androstenedione, testosterone, estrone and estradiol-17β were analysed by the reverse dilution technique with recrystallization to constant specific activity and expressed as dpm per 20 corpora lutea after correction for analytical losses.
The overall incorporation into the ten steroids remained at the minimal rate observed just prior to ovulation until the 15th hour, began to increase by the 18th hour, and increased constantly toward completion of corpus luteum formation. A comparable quantitative change was found with 14C incorporation into C21 steroids. However, incorporation into C19 steroids elevated temporarily between the 18th and 48th hours with drastic decrease by the 72 hour.
Incorporation into C18 steroids showed a transient rise at the 18th hour, followed by a gradual decrease to nil by the 72th hour after hCG injection.
Progesterone was the most prominent product formed from acetate-14C at each point of time in the course of corpus luteum formation. The other major steroidal products varied in the interval between follicle rupture and completion of corpora lutea; i.e. 17α-hydroxy-progesterone and 20α-hydroxyprogesterone at the 15th hour, 17α-hydroxyprogesterone and androstenedione at the 18th hour, 17α-hydroxyprogesterone and 20α-hydroxyprogesterone at the 24th and 48th hours, pregnenolone and 20α-hydroxyprogesterone at the 72th and 96th hours. Distribution patterns of radioactivity among the individual steroids achieved a complete accordance by the 96th hour with that of corpus luteum of pregnant rabbits as previously reported.
It was thus pointed out that marked qualitative as well as quantitative changes in steroidogenesis of developing corpora lutea occurred during the process of corpus luteum formation.
