Role of nitric oxide in ovarian follicular development and egg production in Japanese quail (Coturnix coturnix japonica)

Role of nitric oxide (NO) in regulating the reproductive functions at hypothalamo-hypophysealovarian axis in Japanese quail was studied. In first experiment, metabolites of NO, i.e. nitrite and nitrate (NO2 and NO3) were estimated together in hypothalamus, serum and ovarian follicles of good and poor layers. In the second experiment, different NO modulators such as l-arginine (l-Arg), sodium nitroprusside (SNP) and NG-nitro-l-arginine methyl ester, HCl (l-NAME) were administered to the birds. In the first experiment, significantly higher (P < 0.01) NO2 and NO3 levels in serum, hypothalamus and largest (F1) ovarian follicles were observed in good layers as compared to poor layers. Higher (P < 0.05) NO2 and NO3 concentration was observed in F1 follicles than smaller follicles (F2) only in good layers. The NO2 and NO3 concentration was significantly reduced (P < 0.05) in post ovulatory follicles (POFs) in comparison to F1 and F2 follicles. In the second experiment, the serum NO2 and NO3 concentrations were higher (P < 0.05) in the SNP, lower (P < 0.05) in the l-NAME group and unchanged in the l-Arg treated group in comparison to control group. Compared to control, l-Arg and SNP increased (P < 0.05) the hypothalamic NO2 and NO3 concentration where as l-NAME reduced (P < 0.05) these levels. The NO2 and NO3 concentration was increased (P < 0.05) as the follicle size increased and it was significantly reduced (P < 0.05) in POFs. The higher (P < 0.05) follicular NO2 and NO3 concentration was observed in l-Arg group in comparison to control group. Egg production was also found to be higher (P < 0.05) in l-Arg group whereas it was not different (P > 0.05) in SNP and l-NAME treated groups. The yolk weight and yolk to albumin ratio was reduced (P < 0.05) in l-NAME group in comparison to control group. It may be concluded from the present study that NO plays a key role in regulating follicular development, ovulatory mechanisms and egg production in Japanese quail.