Requirement for, and patterns of, pyruvate and glutamine metabolism in the domestic dog oocyte in vitro

Supplementation of energy substrates to culture medium is essential for resumption and completion of meiosis in vitro for many mammalian species. Objectives were to study the dog oocyte, specifically the influences of pyruvate and glutamine on maturation and the utilization of these two substrates at various developmental stages and incubation times. Ovarian oocytes (n=681) were obtained from spayed bitches and cultured for 48 hr in TCM 199 medium containing various concentrations of pyruvate (0-2.5 mM) and glutamine (0-4 mM) before being assessed for nuclear status. For analyzing metabolic activity, 259 dog oocytes were cultured for 0, 12, 24, 36, or 48 hr, assessed for pyruvate and glutamine metabolism using the hanging drop method and then evaluated for nuclear status. Neither pyruvate nor glutamine had influence (P > 0.05) on oocyte maturation in vitro (IVM). However, both culture interval and meiotic status influenced pyruvate uptake (P < 0.05). Specifically, pyruvate uptake declined as the oocyte progressed from the germinal vesicle (GV) to metaphase II (MII) stage. Glutamine oxidation decreased as culture duration progressed (P < 0.05). In summary, pyruvate or glutamine is not required to promote successful IVM of dog oocytes. But, both substrates are being metabolized, and in patterns different to the domestic cat, another carnivore species. Pyruvate played an important role earlier in the maturational process, and less glutamine was oxidized as the oocyte neared nuclear maturation. These variations emphasize the importance of defining species specificities in carnivores before expecting consistently successful IVM/IVF.