Cold Acclimation and Adrenal Cortical Activity as Measured by Eosinophil Levels

Abstract

Absolute eosinophil counts and change in eosinophil level 4 hrs. after injection of ACTH (Thorn index) were used as indices of adrenal cortical activity during development of cold acclimation in male white rats. ACTH, injected at intervals during acclimation to 6[degree]C, produced an increasing fall in eosipophils up to the 20th day, followed by a gradually decreasing response up to the 53rd day. The observed trend in eosinophil response to ACTH indicates that higher adrenal activity, known to occur during the first few days of exposure to cold, gradually reaches a maximum in about 20 days and then returns to its preacclimation level. The Thorn index provides further evidence that the adrenals of fully acclimated rats, although hypertrophied, are not hyperactive. The variations in adrenal activity measured by the Thorn index were not reflected in changes in absolute eosinophil levels, measured in rats acclimated for 2 months at 10[degree] and 6[degree]C. Absolute eosinophil counts are not believed to be reliable indices of adrenal activity during cold acclimation.