Electron Microscopic Radioautography of125I-Triiodothyronine in Rat Posterior Pituitary and Median Eminence

Abstract
Labeled 125I-T3 in a dose range of 250–670 ng was injected into rats through an aortic cannula, the tip of which was located at the aortic arch, so that the T3 circulated only in the rostral half of the body. After 5–30 min, 18– 92 pg T3 were found in the posterior pituitary. The glands were also exposed in vitro to concentration of 125I_T3 ranging from 9–198 ng/ml and the uptake by the glarid was 61–390 pg/mg after 2 hr. Autoradiographic localization of the labeled hormone was carried out. In the posterior pituitary, the T3 was mostly concentrated in the cytoplasm of the pituicytes. Within the cytoplasm the hormone was associated with membranous elements, particularly those of mitochondria and the Golgi apparatus. After injection, 125I-T3 was also found to be concentrated in the median eminence. The hormone was localized to (a) the ependymal cells and their processes and (b) the axon terminals of the tuberohypophyseal tract. (Endocrinology93: 1410, 1973)

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