P-649 Unconventional action of Luteinizing Hormone

Study question: Has Luteinizing Hormone (LH) a role in the activation/survival of follicles of the primary ovarian reserve? Summary answer: LH promotes survival and perhaps activation/growth of primordial and primary follicles, proliferation of granulosa cells of secondary follicles, reduces follicle atresia at later growing stages. What is known already: In the mammalian ovary, Primordial Follicles (PMFs) constitutes the primary ovarian reserve, which declines over time due to physiological events such as atresia, recruitment, and ovulation. While in the adult, the role of LH in steroidogenesis and ovulation is well established, recent work from our laboratory has shown that under chemotherapeutic treatments, LH supports PMFs survival in prepuberal mouse ovary. Study design, size, duration: LH effects on follicle dynamics and some activities of pre-granulosa cells were investigated in vitro and in vivo. In vitroexperiments were performed on PD4 GFP/Kit mice ovarian fragments and on PD8 CD1 mice ovarian somatic cells cultured up to six days in continuous presence of 0.2, 0.5, 1IU LH. In vivo experiments were performed on 9 PD4 and 8 PD28 CD1 mice receiving an intra-peritoneal injection for eight consecutive days of 1-5IU LH. Participants/materials, setting, methods: Number and diameters of the GFP stained oocyte were counted in the ovarian fragments. Kit-Ligand and LH-R mRNA expression levels were analyzed by qPCR in pre-granulosa cells. For in vivo experiments, ovarian volume was measured by Micro-Ct and follicle counts were performed on histological sections. Estrous cycle phases were monitored by vaginal smear during the 8 days of treatment. Statistics was performed using Student’s t-test.