Uridine Incorporation and Pyruvate Metabolism in Rabbit Eggs Cultured in Vitro at Normal and Elevated Temperatures

Summary. Effects of elevated maternal body temperature upon incorporation of an RNA precursor by rabbit eggs were evaluated by culture in vitro at 39·0 or 40·3°C. temperatures comparable to rectal temperatures of rabbits in normal and elevated ambient temperatures. One-cell fertilized eggs incorporated significantly less [3H]uridine during culture at the higher temperature, indicating a depression of RNA synthesis. Uridine incorporation was not significantly decreased when two-cell ova were incubated with [3H]uridine after completion of the first cleavage, but was decreased in two-cell ova that had been subjected to the higher temperature only while in the one-cell stage of development. The observed reductions in uridine incorporation at the higher temperature were not accompanied by a decrease in energy production as determined by CO2 production from [14C]pyruvic acid. These results suggest that such alterations of regulatory function are associated with the sensitivity of the early zygote to thermal stress and is a mechanism by which elevated maternal body temperatures adversely influence subsequent embryonic development.