Localization of nitric oxide-related substances in the quail ovary during folliculogenesis

In the present study, nitric oxide (NO)-related substances, namely NO synthase (NOS), L-citrulline, cGMP and nitrotyrosine, have been localized in the quail ovary, using NADPH-diaphorase staining and immunohistochemical methods. The results indicate the presence of the NOS isoforms, showing distinct cell-specific distribution patterns in the quail ovary. Inducible NOS is primarily present in leukocytes, endothelial NOS in granulosa cells, and neuronal NOS in nerve cells, oocytes, interstitial cells and granulosa cells of pre-hierarchal follicles and of the germinal disc region of pre-ovulatory follicles. NOS activity, indicated by the presence of L-citrulline, is observed in oocytes, nerve cells, interstitial cells and a few granulosa cells of pre-hierarchal follicles. Detection of accumulated cGMP indicates that granulosa cells of pre-hierarchal and of pre- and post-ovulatory follicles, the theca interna of pre-ovulatory follicles, and oocytes are main targets of NO. Nitrotyrosine, a marker of peroxynitrite activity, is mainly localized in atretic follicles and in post-ovulatory follicles. It is concluded that the quail ovary possesses a NO/NOS system, and that NO may be considered as a mediator involved in various ovarian processes, including atresia.