In vivo effect of thyrotropin on intracellular translocation of thyroid peroxidase in rat thyroid cells by an indirect immunofluorescence method.

The in vivo effect of thyrotropin (TSH) on the intracellular localization of thyroid peroxidase (TPO) in rat thyroid epithelial cells was examined by an indirect immunofluorescence method. The staining for TPO in the epithelial cells of normal rats appeared all over the cytoplasm, especially in the apical region. The injection of propylthiouracil for 3-10 days increased the staining in the apical region. The administration of L-thyroxine for 7-10 days to normal rats abolished the relatively high localization of TPO in the apical region, and resulted in TPO staining all over the cytoplasm. Six hours after TSH was injected into the thyroxine-treated rats, localization of TPO staining in the apical region was observed. These results suggest that TSH may play a role in the translocation of preexisting TPO to the apical region before TSH-induced biosynthesis becomes evident.