Nitric Oxide: A Prime Signaling Molecule in Bovine Male Reproduction

Abstract

Nitric oxide (NO^·) is an important bioactive molecule with a short half-life. It is synthesized from the enzymatic conversion of L-Arg to L-citrulline in presence of nitric oxide synthases (NOS) and cofactors. The level of NO^· is very important as it shows beneficial effects at lower concentration whereas cytotoxic at higher concentration. It acts as protective agent and maintains post thaw motility and viability of spematozoa. NO^· plays critical importance in penile erection by relaxing the smooth muscle via inhibiting Rho A/ Rho-kinase pathway. It also participates in spermatogenesis, capacitation and acrosome reaction via cAMP/ cGMP pathways in mammals. Systemic inhibition of NOS caused impaired copulation, decreased erections and alteration in aggressive behaviour. Inhibition of cNOS significantly reduced the invitro fertilization, sperm-zona pellucida binding and proper embryonic development. Therefore, the cross talk and multiple systems induced by NO^· act parallelly, safeguard the timely function of the spermatozoa responsible for fertilization.