Role of Glutathione and Hsp 70 in the Acquisition of Thermotolerance in Postimplantation Rat Embryos

Studies were initiated to determine the extent to which reduced glutathione (GSH) may be involved in the capacity of cultured rat embryos to develop heat-induced tolerance to the deleterious effects of exposure to high temperatures (heat shock). Investigations of the modulation of dysmorphogenic responses of embryos to heat shock (43 degrees C, 30 min) as well as to the expression of the hsp70 gene and subsequent formation of hsps indicated that the acquisition of thermotolerance by rat embryos could be significantly influenced by the inhibition of GSH synthesis. Treatment of conceptuses with L-buthionine-S,R-sulfoximine (BSO) reduced intracellular GSH concentrations and compromised the capacity of embryos to mount a thermotolerance response as assessed by alterations in indices of growth and development. Embryonic thermotolerance elicited by preexposure to 42 degrees C for 30 min was accompanied by increases in GSH to levels greater than those measured in control embryos at 37 degrees C just prior to the subsequent 43 degrees C heat exposure. Expression of hsp70 mRNA was detectable soon after elevation of the temperature to 42 degrees C and reached its highest level of accumulation 1.5 hr after the 43 degrees C heat shock. BSO treatment had little if any effect on hsp70 message levels or on the synthesis of hsp70. The fact that BSO-treatment attenuated the thermotolerance response but did not produce a decrease in hsp70 RNA or the synthesis of hsp70 suggests that hsp70 alone is not sufficient to confer thermotolerance upon cultured rat embryos.