Metabolism of pyruvate by pre-elongation sheep embryos and effect of pyruvate and lactate concentrations during culture in vitro.

In the first of two experiments, utilization of [1-14C]pyruvate by 8-cell and blastocyst-stage embryos derived in vivo was examined during a 3-h incubation in HEPES-buffered synthetic oviduct fluid (SOF) medium in the presence or absence of other substrates. In the second, a factorial design examined the effect of pyruvate (0, 0.33, 1.0 and 3.3 mM) and lactate (3.3, 10 and 33 mM) on development of 1- and 2-cell sheep embryos cultured in vitro in a modified SOF medium (containing glucose, glutamine and modified Eagle's medium non-essential amino acids). Peak utilization of [1-14C]pyruvate was unaffected by the presence or absence of other energy substrates. In contrast, rate of utilization was affected by the addition of other energy substrates, with half maximal utilization occurring at either 0.4 +/- 0.2 mM or 1.2 +/- 0.2 mM for 8-cells and either 0.2 +/- 0.2 mM or 1.3 +/- 0.3 mM for blastocysts when incubated in the absence or presence of other energy substrates respectively. In the second experiment the proportion of embryos developing to blastocysts was inhibited by high lactate levels (P < 0.001), but was generally not affected by pyruvate concentration. However, there was a significant interaction (P < 0.001) between pyruvate and lactate when both were present in the medium. At 0.33 mM pyruvate, 3.3 mM lactate supported good development (83 +/- 8% blastocysts) whereas 10 mM lactate supported less development (50 +/- 11%). However, at the higher levels of pyruvate this effect was lost.(ABSTRACT TRUNCATED AT 250 WORDS)