COMPARISON BETWEEN SEASONAL AND THERMAL ACCLIMATION IN WHITE RATS: III. STUDIES OF THE ADRENAL CORTEX
The rate of production of corticosteroids in vitro as well as the histological picture of the adrenal glands was studied in white rats exposed to cold for 3 months, either indoors at 6 °C in individual cages or outdoors during the winter in groups of 10.Under the indoor cold conditions, the adrenals hypertrophied within 1 week and their weight then remained constant for the following 11 weeks. The hypertrophy was due to an increase in the number of cells in the zona fasciculata. Relative to adrenal weight, the production of corticosteroids in vitro was less in the 6 °C rats than in the 30 °C controls. Under the outdoor cold conditions, the adrenal weight as well as the number of fasciculata cells remained normal, but the steroid production "in vitro" was greater than in the "summer controls". Since both "indoor" and "outdoor" cold-exposed rats have been shown previously to develop a similar degree of cold resistance as well as a similar capacity for elevating their metabolism through a non-shivering heat production mechanism, it appears that similar degrees of adaptation to cold can exist with different requirements of adrenocortical hormones.