Nitric oxide impacts bovine sperm capacitation in a cGMP-dependent and cGMP-independent manner

We aimed to elucidate whether NO acts in in vitro sperm capacitation in bovine via cGMP/PKG1 pathway. For this, cryopreserved bovine sperm were capacitated in vitro with 20 µg/ml heparin (Control) plus treatments: 1 mM L-arginine (L-arg, NO precursor), 50 µM Rp-8-Bromo-β-phenyl-1,N² -ethenoguanosine-3',5'-cyclic monophosphorothioate (Rp-8-Br-cGMPS, selective inhibitor of the binding site for cGMP in PKG1), 1 mM 2-Phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl 3-oxide (PTIO, NO scavenger), and the combinations of L-arg + RP-8-Br-cGMPS and L-arg + PTIO. Sperm motility and vigour were determined by phase-contrast microscopy, capacitation status by chlortetracycline staining, and the intracellular concentration of cGMP was measured by ELISA. Data were subjected to analysis of variance and means compared with SNK test at 5% probability. Motility and vigour were lower in sperm treated with PTIO when compared to Control and other treatments (p < .05). The L-arg treatment showed the highest percentage of capacitated sperm when compared to the Control and other treatments (Rp-8-Br-cGMPS, L-arg + Rp-8-Br-cGMPS and PTIO) (69.8 ± 3.4%, 51.2 ± 3.0, 51.1 ± 2.1, 51.2 ± 3.0 and 45.5 ± 2.7, respectively) (p < .05). The capacitation ratio (%) was lower in treatments with Rp-8-Br-cGMPS, L-arg + Rp-8-Br-cGMPS and PTIO, respectively (p < .05). Lastly, cGMP concentration (pmol/ml) was lower in PTIO and L-arg + PTIO (1.3 ± 0.3 and 1.6 ± 0.4) and was higher in Rp-8-Br-cGMPS and L-arg + Rp-8-Br-cGMPS (3.7 ± 0.4 and 4.0 ± 0.5) treatments. We showed that during in vitro capacitation of cattle: (a) NO influences sperm motility and vigour; (b) NO is associated with cGMP synthesis through two independent pathways and (c) the cGMP/PKG1 pathway has a partial role in sperm capacitation and does not involve the L-arg/NO.