The combination of P4 and FSH promotes the formation of small antral follicles by up-regulating FSHR and CYP19A1 in Hu Sheep at the late luteal phase

Assisted reproductive technology is vital to improve the reproductive performance of ewe. The objective of this study is to evaluate the impact of progesterone (P₄) and follicle-stimulating hormone (FSH) on follicular development, reproductive hormone secretion, and the expression of associated reproductive genes in ovarian tissues of ewes. Seven-months-old Hu Sheep (n = 45) were randomly allocated into 9 groups. Estrous cycles of all ewes were synchronized using the P₄ + Prostaglandin F_2α (PGF_2α) + equine chorionic gonadotropin (eCG) induction protocol before the onset of the experiment. In this study, we used a 3 × 3 factorial design, where 3 periods of P₄ duration and 3 moments of FSH administration were evaluated. In the P₄ treatment, ewes received sponges (45 mg flugestone acetate) at the onset of the experiment for 5, 8, or 11 days (GP₄5, GP₄8, GP₄11), respectively. In the FSH treatment, ewes were injected with 100 IU FSH twice on days 4, 7, or 10 (GFSH4, GFSH7, FSH10), respectively. In the P₄ + FSH treatment (GFSH5 +P₄5, GFSH8 +P₄8, GFSH11 +P₄11), ewes received sponges and FSH injections for the same period. Our results indicated that the P₄+FSH treatment increased (P < 0.05) small and total follicle counts compared to P₄ or FSH alone. The mRNA expression of follicle-stimulating hormone receptor (FSHR, P < 0.05) and cytochrome P450 family 19 (CYP19A1, P < 0.05) were increased in the P₄ + FSH treatment at day 11 compared to days 5 and 8. Immunohistochemical results showed high immune activity for FSHR and CYP19A1 proteins in granulosa and theca cells of small antral follicles. In conclusion, P₄ + FSH treatment up-regulate the mRNA expression of FSHR and CYP19A1 at the late luteal phase, finally promoting the small antral follicles formation. Our results concerning the follicular development are promising.