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Induced Unidirectional Transport of Protein into the Thyroid Follicular Lumen
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1974
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Induced Unidirectional TransportCytoskeletonCellular PhysiologyEmbryologyReproductive EndocrinologyThyroid ProteinsSecretory GranulesThyroid PhysiologyAnimal PhysiologyBiochemistryCell TraffickingSuch VesiclesMembrane BiologyProtein TransportEndocrinologyCell BiologyApical RegionSignal TransductionNatural SciencesPhysiologyThyroid DiseaseThyroid DisordersIntracellular TraffickingCellular BiochemistryThyroid HormoneMedicine
In normal rats, the apical region of the thyroid follicle cells harbors a heterogeneous population of vesicular elements. Functionally, these are of at least two categories: endocytotic and exocy-totic. Elimination of TSH secretion, either by hypophysectomy or by suppression with daily doses (of L-thyroxine (T4), was followed by marked changes in the population of vesicles: the heterogeneity disappeared, and only one type of vesicles remained. These remaining vesicles had a diameter of 1,000–3,000 A and they were characterized by a very dense content and a bounding membrane of 60 A. During continuous suppression of TSH secretion, the number of such vesicles decreased, but at a slow rate and they were still present at the sixth day. In contrast, colloid droplets vanished within one day. In T4-suppressed animals, the rate of incorporation of leucine-l4C into thyroid proteins, including thyroglobulin, was slowly affected, being reduced by only 15% after 1 day and by 50% after 6 days. In contrast, plasma prot...