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Significance of thyroid mast cells in thyroid hormone secretion.

The significance of thyroid mast cells in thyroid hormone secretion was investigated in 131I-injected, thyroxine-blocked rats and mice, by a combination of histochemical, light microscopical and bio-assay procedures. In the rat thyroid, numerous 5-hydroxytryptamine-(S-HT) and histamine-containing mast cells were present. A single injection of compound 48/ 80 released S-HT, histamine and metachromatic material from the mast cells. This was accompanied by a formation of intracellular colloid droplets and an increase in the blood 131I levels. In the mouse, virtually no mast cells were found in the thyroid, and treatment with 48/80 did not induce any colloid droplet formation or blood 131I increase. In both species, 5-HT evoked a blood 131I increase, whereas histamine yielded no such response. In rats, in which mast cells had been depleted by multiple, gradually increasing doses of 48/80, the blood 131I response to TSH was smaller than in intact controls, whereas similar pretreatment of mice did not affect th...