Comparative expression of luteinizing hormone and follicle-stimulating hormone receptors in ovarian follicles from high and low prolific sheep breeds

Expression of gonadotropin receptors and granulosa cell sensitivity to gonadotropin hormones by small (1-3 mm) and large (3.5-7 mm) follicles were compared in Romanov (ROM, ovulation rate = 3) and Ile-de-France (IF, ovulation rate = 1) ewes in the early and late follicular phase. In healthy follicles, LB-l receptor levels in granulosa cells increased with increasing follicular size (p < 0.001) while FSH receptor levels decreased (p < 0.05). In granulosa cells of large follicles, LH receptor (LHR) mRNA levels were greater in the late than in the early follicular phase (p < 0.001, p <0.05, for ROM and IF, respectively). In the early follicular phase, LHR levels in granulosa (p < 0.001) and theca cells (p < 0.05) of small follicles were greater in ROM than in IF ewes. FSH receptor mRNA levels in granulosa cells of small and large ROM follicles were greater than in the corresponding IF follicles (p < 0.05). Finally, a greater responsiveness (increase in cAMP secretion) to both FSH and hCG was observed by granulosa cells collected during the early follicular phase from ROM vs. IF ewes. Data provide evidence that the greater ovulation rate in the ROM as compared to the IF breed is associated with a greater gonadotropin responsiveness during the early follicular phase.