Nitric oxide (NO) stimulates steroidogenesis and folliculogenesis in fish.

The present study was undertaken to understand the physiological significance of the existence of nitric oxide synthase (NOS)/nitric oxide (NO) system in fish ovary. For this, two doses of NO donor, sodium nitroprusside (SNP, 25 µg and 50 µg) and NOS inhibitor, N-nitro-l-arginine methyl ester (l-NAME, 50 µg and 100 µg)/100 g body weight were administered during the two reproductive phases of reproductive cycle of the Clarias batrachus During the late-quiescence phase, high dose of l-NAME decreased the NO, testosterone, 17β-estradiol, vitellogenin contents in serum and ovary and activities of 5-ene-3β-hydroxysteroid dehydrogenases (3β-HSD) and 17β-hydroxysteroid dehydrogenases (17β-HSD) in ovary, whereas higher dose of SNP increased these parameters. l-NAME also reduced oocytes-I but increased perinucleolar oocytes in the ovary, whereas SNP treatment increased the number of advanced oocytes (oocytes-I and II) than the perinucleolar oocytes when compared with control ovary. During the mid-recrudescence phase, both doses of SNP increased NO, testosterone, 17β-estradiol and vitellogenin in serum and ovary; however, l-NAME treatment lowered their levels. The activities of ovarian 3β-HSD and 17β-HSD were also stimulated by SNP, but l-NAME suppressed their activities compared to the control. The SNP-treated ovaries were dominated by oocyte-II and III stages, whereas l-NAME-treated ovary revealed more perinucleolar oocytes and oocytes-I and practically no advanced oocytes. Expression of endothelial NOS (eNOS), inducible NOS (iNOS) and neuronal NOS (nNOS) was augmented by the SNP and declined by l-NAME treatments as compared to the control. This study, thus, provides distinct evidence of NO-stimulated steroidogenesis, vitellogenesis and folliculogenesis in fish.