Control of ovarian follicular growth and maturation by the corpus luteum and the placenta during pregnancy in sheep

• Published in: Journal of reproduction & fertility Vol. 120; no. 1; pp. 151 - 158
• Main Authors: DRIANCOURT, M. A, FEVRE, J, MARTAL, J, AL-GUBORY, K. H
• Format: Journal Article
• Language: English
• Published: Cambridge Society for Reproduction and Fertility 01-09-2000; Journal of Reproduction and Fertility
• Subjects: Analysis of Variance; Animals; Aromatase - metabolism; Biological and medical sciences; Cesarean Section; Corpus Luteum - drug effects; Corpus Luteum - physiology; Culture Techniques; Dinoprost - pharmacology; Estradiol - metabolism; Estrus - metabolism; Female; Fundamental and applied biological sciences. Psychology; Gestational Age; Mother. Fetoplacental unit. Mammary gland. Milk; Ovarian Follicle - drug effects; Ovarian Follicle - physiology; Placenta - physiology; Pregnancy; Pregnancy, Animal - physiology; Pregnancy. Parturition. Lactation; Progesterone - pharmacology; Sheep - physiology; Testosterone - metabolism; Vertebrates: reproduction; Fetal membrane; Pregnancy; Ovary; Vertebrata; Mammalia; Placenta; Female genital system; Corpus luteum; Development; Sheep; Artiodactyla; Ovarian follicle; Ungulata
• ISSN: 1470-1626; 0022-4251; 1741-7899
• DOI: 10.1530/jrf.0.1200151

Ovarian follicular growth and maturation and its control throughout pregnancy have not been described fully in sheep. Experiment
1 characterized the size and maturation (steroid production in vitro and aromatase activity) of ovarian follicles obtained
at days 20, 50, 80 and 110 of pregnancy compared with those obtained at day 12 of the oestrous cycle. There was no difference
in the number of small follicles (< 3 mm in diameter) between cyclic and pregnant ewes, regardless of the stage of pregnancy.
There was a marked reduction (P < 0.01) in the number of medium follicles (3-5 mm) starting at day 80 of pregnancy. Large
follicles (> 5 mm) were not detected at day 110 of pregnancy. In vitro testosterone output by follicles was constant throughout
pregnancy. Oestradiol output remained steady until day 80, but decreased markedly at day 110 of pregnancy. This decrease was
associated with a reduction in aromatase activity in follicles obtained at this stage. Experiment 2 examined the effect of
administration of high concentrations of progesterone between day 100 and day 120 after mating on resumption of follicular
growth in ewes that underwent Caesarean section at day 99 of pregnancy. In ewes that underwent Caesarean section, progesterone
supplementation was successful in mimicking the profile found in pregnant ewes, but did not prevent re-initiation of follicular
growth, as demonstrated by the presence of large follicles (> 5 mm) at day 120 after mating. Experiment 3 examined the effects
of PGF(2alpha)-induced regression of the corpus luteum of day 100 of pregnancy on resumption of follicular growth. High concentrations
of PGF(2alpha) (0.28 mg kg(-1) body weight) administrated at day 100 of pregnancy were required to initiate regression of
the corpus luteum. At day 120 after mating, the mean (+/- SEM) diameter of the largest follicle in PGF(2alpha)-treated ewes
(3.40 +/- 0.47 mm) was significantly greater (P < 0.05) than that in control pregnant ewes (2.52 +/- 0.34 mm). Experiment
4 examined the effect of removal of the fetus and of the corpus luteum at day 100 of pregnancy on resumption of ovulation.
Removal of the corpus luteum by PGF(2alpha) treatment at the time of removal of the fetus resulted in earlier occurrence of
short luteal phases (27.8 versus 40.6 days, PGF(2alpha)-treated versus non-treated) but did not alter the timing of the first
normal luteal phases (41 days). In conclusion, the results from these experiments indicate that placental compounds play a
major role in inhibiting follicular growth and maturation during late pregnancy in sheep.