US EPA

The effects of gestation day (GD) 10 heat exposure in the rat were studied to determine the temperature-response relationship for the induction of skeletal and other defects. onscious pregnant rats were exposed to various temperatures in a warm air chamber. hose animals whose core body temperature was raised to 41-41.90C had over 90% malformed pups and a 25% reduction in the percent of live pups per litter. nimals whose temperature was raised to 39.2-40.90C had a low incidence of pups with similar types of malformations. he primary types of malformations were of the axial skeleton, consisting of fusions and other abnormalities of the ribs and vertebral elements, and a decrease in the total number of ribs and centra. he acute maternal effects of these temperature increases were signs of heat exhaustion during and 1-2 hr after exposure, but there were no permanent changes in weight gain or other signs. hen temperatures were raised to > 42 degrees Centigrade, all maternal animals died. n a second study, pregnant rats were anesthetized to determine the effect of reducing maternal stress and were exposed to heat as in Experiment 1. Those animals whose core body temperature was raised to 42-42.5 degrees C for 5 min had pups with similar responses to those in Experiment 1 at 41-41.9 degrees C, although the reduction in litter size was not as great. nimals whose temperature was raised to 41 degrees C had a much lower incidence of pups with similar defects, and animals whose temperature was raised to 430C did not survive. keletal defects in Experiment 2 showed rib and vertebral malformations that appear to be related to the stage of somite development at the time of exposure.

Kimmel, C., J. Cuff, G. Kimmel, D. Heredia, N. Tudor, P. Silverman, AND J. Chen. SKELETAL DEVELOPMENT FOLLOWING HEAT EXPOSURE IN THE RAT. U.S. Environmental Protection Agency, Washington, D.C., EPA/600/J-93/185 (NTIS PB93194520).

Teratology 47:229-242, 1993