Nitric oxide and meiotic competence of porcine oocytes

Abstract

Reproductive biotechnology such as in vitro fertilization, the creation of transgenic animals or cloning by nuclear transfer depends on the use of fully grown, meiotically competent oocytes capable of completing meiotic maturation by reaching the stage of metaphase II. However, there exists only a limited quantity of these oocytes in the ovaries of females. In view of their limited number, growing oocytes without meiotic competence represent a possible source. The mechanisms controlling the acquisition of meiotic competence, however, are still not completely clear. A gas with a short half-life, nitric oxide (NO), produced by NO-synthase (NOS) enzyme can fulfill a regulatory role in this period. The objective of this study was to ascertain the role of NO in the growth phase of pig oocytes and its influence on the acquisition of meiotic competence with the help of NOS inhibitors, NO donors and their combinations. We demonstrated that the selective competitive iNOS inhibitor aminoguanidine and also the non-selective NOS inhibitor L-NAME block meiotic maturation of oocytes with partial or even full meiotic competence at the very beginning. NOS inhibitors influence even competent oocytes in the first stage of meiotic metaphase. However, blockage is less effective than at the beginning of meiotic maturation. The number of parthenogenetically activated competent oocytes greatly increased in a pure medium after inhibitor reversion. A large quantity of NO externally added to the in vitro cultivation environment disrupts the viability of oocytes. The effectiveness of the inhibitor can be reversed in oocytes by an NO donor in a very low concentration. However, the donor is not capable of pushing the oocytes farther than beyond the first stage of meiotic metaphase. The experiments confirmed the connection of NO with the growth period and the acquisition of meiotic competence. However, it is evident from the experiments that NO is not the only stimulus controlling the growth period.

Nitric Oxide-Donor SNAP Induces Xenopus Eggs Activation

“…It has been previously reported differences in mammalian oocytes regarding sensitivity on nitric oxide during maturation. High concentration of NO donors supress nuclear maturation in bovine [65] and porcine oocyte [66]. However low doses of NO donor stimulate nuclear maturation in mouse [39] or cattle oocyte [65].…”

Nitric Oxide Synthase (NOS) Inhibition during Porcine In Vitro Maturation Modifies Oocyte Protein S-Nitrosylation and In Vitro Fertilization

“…A third isoform, inducible NOS (iNOS or NOS type II), which is calcium-independent, is expressed in response to inflammatory cytokines and lipopolysaccharide [15] . All three NOS isoforms have been identified in the ovary [16] and are involved in ovarian follicular development [17] , oocyte meiotic maturation [18] – [21] , oocyte activation, fertilization and embryo implantation in the uterus [8] , [11] .…”

Pyrethroids cypermethrin, deltamethrin and fenvalerate have different effects on in vitro maturation of pig oocytes at different stages of growth

“…Partial meiotic competence, when maturation is spontaneously blocked at the metaphase I stage, occurs when oocytes reach an internal diameter of about 110 mm. Porcine oocytes with an internal diameter smaller than 90 mm are meiotically incompetent and do not mature in vitro (Wassarman, 1988;Tichovská et al, 2011).…”