Abstract:
Nitric oxide (NO, nitrogen monoxide), a short-lived, free radical carrying an unpaired electron, is one of the
smallest molecules synthesized in the biological system. In addition to its role in angiogenesis, neuronal function
and inflammatory response, NO has wide-spread significance in regulation of ovarian function in vertebrates.
Based on tissue-specific expression, three different nitric oxide synthase (NOS) isoforms, neuronal (nNOS) or
NOS1, inducible (iNOS) or NOS2 and endothelial (eNOS) or NOS3 have been identified. While expression of both
inducible (iNOS) and constitutive NOS (eNOS) isoforms varies considerably in the ovary at various stages of
follicular growth and development, selective binding of NO with proteins containing heme moieties have significant
influence on ovarian steroidogenesis. Besides, NO modulation of ovulatory response suggests physiological
significance of NO/NOS system in mammalian ovary. Compared to the duality of NO action on follicular
development, steroidogenesis and meiotic maturation in mammalian models, participation of NO/NOS system in
teleost ovary is less investigated. Genes encoding nos1 and nos2 have been identified in fish; however, presence
of nos3 is still ambiguous. Interestingly, two distinct nos2 genes, nos2a and nos2b in zebrafish, possibly arose
through whole genome duplication. Differential expression of major NOS isoforms in catfish ovary, NO inhibition
of meiosis resumption in Anabas testudineus follicle-enclosed oocytes and NO/sGC/cGMP modulation of
oocyte maturation in zebrafish are some of the recent advancements. The present overview is an update on the
advancements made and shortfalls still remaining in NO/NOS modulation of intercellular communication in
teleost vis-à-vis mammalian ovary.
