Interaction of adrenals and thyroid in maintenance of body temperature of rats exposed to cold

¹ Department of Physiology, College of Medicine, University of Florida, Gainesville, Florida

The effects of cortisone acetate and thyroxine, administered separately or in combination, on colonic cooling rate (CCR) have been studied in restrained, adrenalectomized rats subjected to air at 5°C. Thyroxine alone at 5.0 µg/day reduced the rapid CCR of adrenalectomized rats but failed to return it to that of sham-operated rats. Cortisone acetate alone at 1.0 mg/day reduced CCR but also failed to restore it to normal. A higher dose (2.0 mg/day) was even less effective. Administration of 5.0 µg/day thyroxine simultaneously with 2.0–2.5 mg cortisone acetate returned CCR to that of sham-operated rats. Simultaneous administration of cortisone acetate with graded doses of thyroid stimulating hormone (TSH) to adrenalectomized rats resulted in greater reduction of CCR than with either treatment alone. Cortisone acetate did not appear to interfere either with tissue utilization of thyroxine or with thyroid gland response to TSH administration. The cooling test has also proved a useful tool for comparing potencies of a synthetic (dexamethasone) and a naturally occurring steroid (progesterone) with that of cortisone acetate. Dexamethasone is estimated to have a potency 700 times that of cortisone acetate, while progesterone is only one-third as potent.