Abstract
Changes in rat ovarian 20α-OH-SDH3 and G-6-PDH activities as well as their intraglandular distribution during pregnancy, at parturition and during lactation have been determined concurrently with measurements of the peripheral blood and uterine tissue levels of progesterone and 20α-OH-P. In addition, effects of gonadotrophic hormones, hypophysectomy, placental dislocation and hysterectomy on the regulation of these enzyme activities have been examined. 20α-OH-SDH activity and 20α-OH-P concentrations decreased during early pregnancy as progesterone concentrations rose to a peak. At midgestation, day 7–12, a second rise in plasma progesterone occurred accompanied by an increase in 20α-OH-P. No increase in 20α-OH-SDH was evident at this time. Between days 19 and 21 progesterone levels dropped sharply coincident with a rapid rise in ovarian 20α-OH-SDH and peripheral 20α-OH-P concentration. A high positive correlation existed between plasma 20α-OH-P concentrations and ovarian 20α-OH-SDH activities. Uterine and placental steroid concentrations reflected the fluctuations seen in plasma steroid levels; however, progesterone, not 20α-OH-P, appeared to be preferentially accumulated in uterine tissue. Involuting corpora lutea present during early pregnancy gave an intense histochemical reaction for both 20α-OH-SDH and G-6-PDH, but only G-6-PDH was present in corpora lutea of pregnancy, thecal cells and interstitial tissue. At midpregnancy G-6-PDH distribution was unaltered except for its disappearance from involuting corpora lutea. 20α-OH-SDH was not detectable histochemically during midgestation. On day 19 20α-OH-SDH activity developed in small loci distributed randomly in some corpora lutea of pregnancy and became uniformly distributed within all corpora by day 21. Enzyme activity increased logarithmically during this period. Hypophysectomy did not alter the rate of enzyme increase, but delayed the time of initiation about 4 hr. Luteinizing hormones (LH and HCG) administered at midpregnancy as well as total placental dislocation and hysterectomy increase 20α-OH-SDH and G-6-PDH activities. LtH administration following hysterectomy inhibited the increases in enzyme activity. Ovarian 20α-OH-SDH in suckling mothers was only 50% of that in mothers deprived of their litters. It is concluded that progesterone catabolism to 20α-OH-P constitutes a normal regulatory mechanism for reducing the progestational potency of rat ovarian secretions during pregnancy, that ovarian 20α-OH-SDH and G-6-PDH activities are under gonadotrophic hormone regulation, and that increased 20α-OH-SDH activity provides an index of the luteolytic process. (Endocrinology82: 844, 1968)
Published Version
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