Effect of thyroid hormones on histamine formation in the rat.

Treatment with thyroxine or liothyronine increased the urinary excretion of free histamine in male and female rats under the influence of aminoguanidine, a histaminase inhibitor. There was no evidence for an altered catabolism of histamine in rats treated with liothyronine, since the same percentage of subcutaneously injected [(14)C]-histamine appeared unchanged in the urine. After subcutaneous injection of [(14)C]-L-histidine, rats treated with liothyronine excreted more [(14)C]-histamine than control rats. An increased formation of [(14)C]-histamine from [(14)C]-histidine could also be demonstrated in vitro, in the glandular portion of the stomach, while no increase was found in the skin.