IN-VITRO AND IN-VIVO THERMAL-ACTIVATION OF STEROID-RECEPTOR COMPLEXESFROM RATS AND GROUND-SQUIRRELS (SPERMOPHILUS-CITELLUS)

Using H-3-labelled triamcinolone acetonide ((3)HTA, synthetic steroid hormone), it was shown that the in vitro time course kinetics of therm al activation of (3)HTA-receptor complexes exhibited the same temperat ure dependence in liver cytosols prepared from hibernating ground squi rrels (Spermophilus citellus) as in cytosols from the rat, When (3)HTA was injected in vivo to animals hibernating with a body temperature o f 3 degrees C, the activation and nuclear uptake of the in vivo formed steroid-receptor complexes proceeded at a slow rate, comparable to th e one predicted by in vitro studies, In the hibernator, the results ar e not indicative of adaptive modifications at the level of thermal act ivation, but prove that steroid action does proceed at a temperature i ncompatible with hypothermic survival in the nonhibernator.