Methylthiouracil (M. T. U.) was administered to rats for a prolonged period, and hypothalamic neurosecretion (by CH-P method), PBI, 131I uptake and histological picture and paperchromatographic finding of the thyroid gland were investigated.
The remarkable goiter development, the productive change of the thyroid gland, decrease of the thyroid hormone both in the tissue and circulating blood on one side, and the increasing production of the neurosecretory material i a the cells and the increasing release of the material into the nerve fibers arising from the cells in the supraoptic and paraventricular nuclei on the other side, were apparently intiately related each other. In the histological observations, the secretory activity of the paraventricular nucleus was always accelerated than that of supraoptic nucleus.