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Horm Metab Res 1989; 21(2): 69-72
DOI: 10.1055/s-2007-1009153
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© Georg Thieme Verlag, Stuttgart · New York

A Study of Hepatic Metabolism of Thyroxine in BB/W Rats Treated with L-Thyroxine

K. Banovac, M. Zakarija, A. Rabinovitch
  • Department of Medicine, University of Miami School of Medicine, Miami, Florida, U.S.A.
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Publication History

1988

1988

Publication Date:
14 March 2008 (online)

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Summary

The effect of thyroxine (T4) on T4 conversion to triiodothyronine (T3) and reverse T3 (rT3) was studied in BB/W rats. A colony of 38 BB/W rats was obtained and half were treated with thyroxine (T4), 1 mg per liter of drinking water. At 106 days of age the following groups were identified: nondiabetic, no T4 treatment, 8 rats; nondiabetic, T4 treated, 8 rats; diabetic, no T4 treatment, 10 rats; diabetic, T4 treated, 7 rats. All animals with diabetes were treated with insulin. T4 conversion to T3 and rT3 was assessed in liver homogenates in 0.1 M Tris-HCl buffer, pH 7.4, with or without 5 mM dithiothreitol (DDT).

Serum T4 and rT3 were significantly elevated in both T4-treated groups (P < 0.001), while serum T3 was not affected in either. Basal T4 deiodination to T3 by the liver homogenate did not change on treatment with T4; the addition of DTT increased T3 production in the homogenate from T4 treated nondiabetic animals (P < 0.05). In both nondiabetic and insulin-treated diabetic rats there was no effect of T4 on the rate of rT3 production. Since, in the rat, 30-40% of circulating T3 is a direct contribution of thyroid gland secretion, and that would be absent in our T4-suppressed animals, the normal serum T3 may reflect increased absolute peripheral T3 production from the greater concentration of circulating T4.

Key-Words

Deiodination - Thyroxine - Liver - BB/W Rats - T4 Treatment

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