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 gona dotropin hormones by small (1-3 mm) and large (3.5-7 mm) follicles were com pared in Romanov (ROM, ovulation rate = 3) and Ile-de-France (IF, ovulation rate = 1) ewes in the early and late follicular phase. In healthy follicle s, LB-l receptor levels in granulosa cells increased with increasing follic ular size (p < 0.001) while FSH receptor levels decreased (p < 0.05). In gr anulosa cells of large follicles, LH receptor (LHR) mRNA levels were greate r in the late than in the early follicular phase (p < 0.001, p <0.05, for R OM and IF, respectively). In the early follicular phase, LHR levels in gran ulosa (p < 0.001) and theca cells (p < 0.05) of small follicles were greate r in ROM than in IF ewes. FSH receptor mRNA levels in granulosa cells of sm all and large ROM follicles were greater than in the corresponding IF folli cles (p < 0.05). Finally, a greater responsiveness (increase in cAMP secret ion) to both FSH and hCG was observed by granulosa cells collected during t he 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 associ ated with a greater gonadotropin responsiveness during the early follicular phase.