Melatonin potentially acts directly on swine ovary by modulating granulosa cell function and angiogenesis

Melatonin exerts well-known reproductive effects, mainly acting on hypothalamic gonadotrophin-releasing hormone release. More recent data suggest that melatonin acts directly at the ovarian level, even if, at present, these aspects have been only partly investigated. Swine follicular fluid contains melatonin and its concentration is significantly reduced during follicular growth. Therefore, the present study was undertaken to examine the effects of melatonin, used at physiological concentrations, on cultured swine granulosa cells collected from small (<3mm) and large (>5mm) follicles on the main parameters of granulosa cell function such as proliferation and steroidogenesis, namely oestradiol 17β and progesterone (P4) production. Moreover, the effects of melatonin on superoxide anion and nitric oxide (NO) generation by swine granulosa cells were also investigated. Finally, since angiogenesis is crucial for follicle growth, the effects of melatonin on new vessel growth were studied. Collected data indicate that melatonin interferes with cultured granulosa cell proliferation and steroidogenesis, specifically in terms of P4 production and NO output. In addition, the events of physiological follicular angiogenesis were stimulated by melatonin as evidenced by angiogenesis bioassay. Therefore, we suggest that physiological melatonin concentrations could potentially be involved in local modulation of swine ovarian follicle function.