In vitro matured (IVM) porcine oocytes utilize less endogenous lipid and have poorer developmental competence than those matured in vivo. Previous studies have indicated that oocyte developmental competence may be improved by supplementing IVM medium with L-carnitine, which stimulates lipid metabolism and has antioxidant properties. The objective of this study was to determine the effects of L-carnitine on porcine oocyte maturation and post-fertilization events.
Porcine Oocyte Medium was supplemented without (control) or with 12mM L-carnitine (LC) and/or 100 µM etomoxir (Etox), an inhibitor of lipid metabolism, during the final 22h of IVM. Treatment effects on cumulus-oocyte complexes (COCs) and denuded oocytes (DOs) were compared. The concentrations of ATP and glutathione (GSH) were measured at 22 and 44h of IVM in a cohort of oocytes. After IVF, presumptive zygotes were either stained to assess pronuclear (PN) formation, or cultured for 7d to assess embryo development.
The levels of both ATP and GSH in DOs were about 40% lower than those in COCs (P<0.05). In both COCs and DOs, exposure to LC did not alter the ATP levels compared with the untreated controls (P>0.05), whereas exposure to LC+Etox suppressed them (P<0.05). The concentration of GSH in LC-treated oocytes was greater than that of control oocytes (8.20 vs 7.19 pmol/oocyte; P<0.05), which in turn was greater than that of LC+Etox-treated oocytes (7.19 vs 5.44 pmol/oocyte; P<0.05). Also, the PN formation rate was significantly reduced in control DOs (30%), but not in LC-treated DOs (61%), compared with the control and LC-treated COCs (87 and 90%, respectively). Blastocyst formation rates of the Etox and LC+Etox groups were significantly lower than those of the control and LC groups.
The results show that the LC treatment improved the maturation of denuded oocytes through an antioxidant protective action, and not via an overall enhancement of ATP production.