Nitric oxide synthase expression and nitric oxide/cyclic GMP pathway in swine granulosa cells

The present investigation was undertaken to verify if the two nitric oxide synthase isoforms, eNOS and iNOS, are present in swine granulosa cells and whether the enzyme soluble guanylate cyclase is functionally active in the same cells and can account for NO effects. Using western blotting, the presence of endothelial NO synthase was demonstrated in freshly collected cells; on the contrary, iNOS expression was not observed in the same cells either before or after culture with the inflammatory cytokine hTNF-alpha. The treatment with a strong NO donor (S-Nitroso-L-acetyl penicillamine, SNAP) determined an increase of cGMP levels in culture media, which was attenuated by the combined treatment with an inhibitor of NO-sensitive soluble guanylate cyclase, 1H-[1,2,3]oxadiaziolo [4,3a]quinoxaline -1-one (ODQ). The cGMP analog, 8 bromo-cGMP, mimicked the strong inhibitory effect exerted by SNAP on estradiol 17 beta and progesterone production, while ODQ did not modify steroids concentrations in culture media. These observations demonstrate the presence of a follicular NO-generating system, which in swine granulosa cells seems to include only the endothelial NOS isoform. Furthermore, the nitric oxide/cyclic GMP system seems to be functionally active in these cells, since cGMP appears to mediate NO action, even if it cannot account completely for NO inhibitory effect on steroidogenesis.