Role of nitric oxide in motility and fertilizing ability of sperm of Heteropneustes fossilis (Bloch.)

The presence of neuronal nitric oxide synthase (nNOS), inducible NOS (iNOS) and nitric oxide (NO) in the testis of seasonally breeding catfish has previously been demonstrated. The present study was aimed to investigate the presence of NO in fish gametes and its role in sperm physiology and strengthen the previous findings. NO, a biological signalling molecule is synthesized during the conversion of l-arginine to l-citrulline by nitric oxide synthases (NOS) in the presence of NADPH and oxygen. In the present study, a considerable amount of NO content was detected in the fresh sperm suspension of fish. A drastic reduction in NO content of the sperm suspension was observed after cryopreservation. Ovarian fluid collected from freshly stripped eggs also contained a substantial amount of NO. Further, effects of a NO donor, sodium nitroprusside (SNP), and NOS inhibitor, N-(G)-nitro-l-arginine-methyl ester (l-NAME) were evaluated on motility and fertilizing ability of fresh and cryopreserved sperm. The percentage of motile fresh sperm (66.2 ± 3.7%) was enhanced (P < 0.05) by SNP at the dose of 10−3 M, whereas the greater and lesser concentrations of SNP did not influence the percentage of motility as compared to the control. However, a significant reduction in the percentage of motile fresh sperm was observed at the tested doses of 10−3 M and 10−4 M of l-NAME. The maximum reduction (23.0 ± 3.4%) was evoked at the greatest concentration (10−3 M); while at the smallest dose of 10−5 M, reduction was insignificant. Ovarian fluid also enhanced sperm motility. Altogether, findings of the present study suggest that NO plays an important role in sperm performance of fish.