Temperature regulation and metabolism in rats exposed perinatally to dioxin: permanent change in regulated body temperature?

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) has been shown to lower thyroxine levels and cause hypothermia in the adult rat; however, there is little known regarding the perinatal effects of TCDD on metabolism and temperature regulation of the offspring. To address this issue, thermoregulatory responses were assessed in adult male rat offspring exposed perinatally to 1.0 micrograms TCDD/kg body wt by gavage on Gestational Day 15. Individual castrated offspring were placed in a gradient-layer calorimeter for 5 hr during their nocturnal period while ambient temperature (Ta) was maintained at 10, 16, 24, or 28 degrees C. Metabolic rate (M), as measured from the total heat loss in the calorimeter, was determined along with evaporative heat loss (EHL), dry thermal conductance, and body core temperature (Tc). Animals exposed to TCDD had a significantly lower body temperature at TaS of 10, 16, and 24 degrees C and a higher thermal conductance. M was unaffected by TCDD, indicating that TCDD did not impair the effector to regulate Tc during cold exposure. EHL was also unaffected by TCDD. Skin blood flow of the interscapular area was measured in anesthetized rats with laser Doppler velocimetry and found to be the same in control and TCDD groups. The reduction in body temperature over a wide range of TaS concomitant with normal thermoregulatory effector function suggests that perinatal exposure to TCDD results in a reduction in the regulated body temperature (i.e., decrease in set-point).