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T. L. CRIBLEZ and C. W. ALLISTON

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.

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C. W. ALLISTON, B. HOWARTH Jr. and L. C. ULBERG

Summary.

In-vitro culture of 1-cell fertilized rabbit ova for 6 hr at a temperature corresponding to elevated body temperature (40°C) resulted in increased post-implantation embryonic mortality following the transfer of such eggs to synchronous pseudopregnant females. This increased mortality was not observed when culture temperatures corresponded to normal body temperature (38° C) or in cultures that were begun after completion of the first cleavage.

It is concluded that the early rabbit embryo is directly affected by the increased maternal body temperature that accompanies thermal stress of the female. Such effects may not become apparent until the late stages of embryonic development.