Hypothyroidism enhances carbachol-induced hypothermia in the rat.

We studied cholinergic regulation of body temperature in hypothyroid rats. Thyroidectomy caused a progressive decrease in core temperature. Intraventricular injection of carbachol in a dose of 10 nmol did not change core temperature of the normal rat, whereas the same dose of carbachol significantly decreased the temperature of thyroidectomized rats. One hundred nmol carbachol decreased to a greater extent core temperature of the thyroidectomized rats than that of normal rats. Intraventricular injection of atropine significantly increased core temperature of thyroidectomized rats. The present data indicate that brain cholinergic mechanisms participate in controlling temperature in the hypothyroid status and thyroid hormones play a significant role in the brain cholinergic regulation of body temperature.