Stimulation by Thyrotropin In Vitro of Uridine Incorporation Into the RNA of Thyroid Slices

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Abstract
Experimental conditions for the study of RNA synthesis in sheep and dog thyroid slices in vitro have been investigated. Best results were obtained with slices prepared at 20°C, preincubated for two hours and incubated in Parker 199 medium with 3H-uridine as precursor. Uridine metabolism in such preparations was characterized by the slow labelling of the uracil pool, a relatively slow labelling of the free pyrimidine nucleotide pool and by a fast equilibration of the free ribonucleotide pool with rapidly turning over RNA. TSH 200 mU/ml enhanced in parallel the incorporation of 3H-uridine in the various subcellular fractions of sheep thyroid slices. In dog thyroid slices this effect was irregular. The stimulation of 3H-uridine incorporation into RNA was related to an increased labelling of the pyrimidine nucleotide RNA precursors pools. No effect of TSH on RNA synthesis itself could be demonstrated under such conditions. The role of the action of TSH on free ribonucleotide metabolism is unknown. No effect of TSH on the pattern of RNA synthesis in sheep thyroid slices was demonstrated. 1 Work realized under Contract of the Ministère de la Politique Scientifique within the framework of the Association Euratom - University of Brussels - University of Pisa and thanks to grant 1011 of the Fonds de la Recherche Scientifique Médicale.

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