TSH-Induced Mobilization of Serotonin from Perivascular Mast Cells in the Rat Thyroid

Acute injection of TSH produced within 5 min a mobilization of serotonin from storage sites in the rat thyroid. Fluorescence microscopy combined with conventional histochemical procedures established that discharge of the vasoactive amine was initiated in perivascular mast cells. Within 15 min, the hormone-induced depletion was propagated throughout the gland, while the serotonin in mast cells of ventral abdominal skin was not detectably affected by TSH. With account taken of the rapid hyperemic response of the thyroid to its trophic hormone, the postulated mediation of TSH influence on its target organ through discharge of intrinsic serotonin is discussed. (Endocrinology 83: 263, 1968)