Relaxin-Induced Angiogenesis in Ovary Contributes to Follicle Development

: CD31‐positive blood vessels increased in human ovarian cortical tissues cultured with relaxin than in tissues cultured without relaxin. The number of vWF‐positive vessels counted in rat ovaries after relaxin injection (40.5 ± 4.3) significantly increased compared to that in saline‐injected rats (24.3 ± 3.0). The proportion of primordial follicles was significantly decreased, that of primary follicles was significantly increased at 16 h, and that of early antral follicles was significantly increased at 24 h in rats after relaxin injection. These results suggest that relaxin may contribute to follicle development through the mechanism of angiogenesis in the ovary.