Effects of a nitric oxide donor and nitric oxide synthase inhibitors on luteinizing hormone-induced ovulation in the ex-vivo perfused rat ovary

The aim of this study was to investigate the role of nitric oxide (NO) in o vulation and ovarian steroidogenesis by the use of NO synthase (NOS) inhibi tors and an NO donor administrated to the luteinizing hormone (LH)-stimulat ed ex-vivo perfused pre-ovulatory rat ovary. The ovaries ere stimulated wit h LH (0.2 mu g/ml) alone or in combination with the phosphodiesterase inhib itor IBMX (200 mu mol/l), The presence of both endothelial NOS (eNOS) and i nducible NOS (iNOS) in the perfused rat ovary were detected by immunoblotti ng and a clear increase in amount of iNOS protein was seen after LH + IBMX stimulation. The addition of a non-selective NOS inhibitor, N-G-monomethyl- L-arginine (L-NMMA; 300 mu mol/l), to the perfusate significantly decreased ovulation numbers (median = 4.0, range = 1-14) as compared with LH + IBMX stimulated control (12.0, 6-17). In contrast, an inhibitor with relative se lectivity towards iNOS, aminoguanidine bicarbonate (AG, 300 mu mol/l and 1 mmol/l), did not change the ovulation rate (11.5, 6-18 and 11.0, 7-15 respe ctively). In perfusions with only LH, a lower ovulation rate was seen but w ith similar effects (0.0, 0-8 for L-NMMA; 7.5, 3-12 for control and 7.0, 1- 15 for AG 300 mu mol/l). The administration of an NO donor, spermine NONOat e, resulted in similar ovulation numbers as in LH-stimulated controls. The NO inhibitors did not affect steroid concentrations in the perfusion media, while 100 mu mol/l NONOate increased progesterone production.