Sensitivity of the hyperthyroid and hypothyroid mouse to histamine and 5-hydroxytryptamine.

Injections of thyroxine sodium increased the sensitivity of mice to histamine, the maximal effect occurring after 6 days. The sensitivity to 5-hydroxytryptamine was increased to a lesser extent. Hydrocortisone antagonized this effect of thyroxine, whereas anti-thyroid drugs alone decreased the sensitivity to histamine. Treatment with thyroxine also raised the metabolic rate, the peak again being reached after 6 days. As treatment was continued beyond 6 days, the adrenal gland enlarged and its secretion probably accounted for the decline in the histamine sensitivity.