Intracellular adenosine triphosphate and glutathione concentrations in oocytes from first estrous, multi-estrous, and testosterone-treated gilts

Cytoplasmic maturation refers to a variety of cellular changes that must occur in the oocyte in order to progress through subsequent fertilization and embryonic development. Intracellular concentrations of ATP (ATPi) or glutathione (GSHi), indicative of metabolic activity or the ability of the oocyte to form a male pronucleus and cope with cellular stress, respectively, have been used as markers of cytoplasmic maturation in vitro. In the current study, our objective was to determine if concentrations of ATPi and GSHi in oocytes recovered from three groups of gilts were associated with known differences in developmental competence within these populations. In vivo matured oocytes were surgically recovered 36-38 h after the onset of estrus from, first estrous gilts, multi-estrous gilts, and multi-estrous gilts receiving testosterone (1 mg/2 ml per day; day 13 to estrus, day 0 = day of estrus). Concentrations of ATPi and GSHi were determined using a bioluminescent somatic cell assay kit (luciferin-luciferase reaction) and the dithiobisnitrobenzoic acid (DTNB)-glutathione reductase recycling reaction, respectively. There were no differences (P > 0.05) between ATPi concentrations in oocytes from the three groups (1.52 ± 0.10, 1.51 ± 0.11, 1.56 ± 0.11 pmol per oocyte). In contrast, oocytes from multi-estrous gilts had higher (P < 0.05) concentrations of GSHi (31.53 ± 1.66 to 33.67 ± 2.30 pmol per oocyte) than oocytes from first estrous gilts (25.07 ± 0.82). Administration of testosterone did not affect (P > 0.05) GSHi concentrations in oocytes from multi-estrous gilts. Differences in developmental potential between the three groups of gilts were apparently not due to different concentrations of ATPi. However, GSHi concentrations were higher in oocytes from multi-estrous gilts, suggesting that reduced developmental potential of oocytes from first-estrus gilts may be related to insufficient amounts of GSHi. The beneficial effect of exogenous testosterone on the percentage of embryos surviving early gestation does not appear to be due to increased GSHi. Of the numerous potential markers of developmental potential, two were examined in the current study, and GSHi appeared to be useful for assessing porcine oocytes.