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Regulation of thyroid hormone metabolism in rat liver fractions
Authors:Bernd Höffken  Reinhard Ködding  Alexander von zur Mühlen  Tainer Hehrmann  Rolf-Dieter Hesch
Institution:Medizinische Hochschule Hannover, Abteilung für Klinische Endokrinologie, Department Innere Medizin, D-3000, Hannover G.F.R.
Abstract:The nature of the conversion of thyroxine (T4) to triiodothyronine (T3) and reverse triiodothyronine (rT3) was investigated in rat liver homogenate and microsomes. A 6-fold rise of T3 and 2.5-fold rise of rT3 levels determined by specific radioimmunoassays was observed over 6 h after the addition of T4. An enzymic process is suggested that converts T4 to T3 and rT3. For T3 the optimal pH is 6 and for rT3, 9.5. The converting activity for both T3 and rT3 is temperature dependent and can be suppressed by heat, H2O2, merthiolate and by 5-propyl-2-thiouracil. rT3 and to a lesser degree iodide, were able to inhibit the production of T3 in a dose related fashion. Therefore the pH dependendy, rT3 and iodide may regulate the availability of T3 or rT3 depending on the metabolic requirements of thyroid hormones.
Keywords:PTU  5-propyl-2-thiouracil  TRH  thyrotropin releasing hormone
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