A study of hepatic metabolism of thyroxine in BB/W rats treated with L-thyroxine.
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 less than 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 less than 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.
Banovac
K
K
Department of Medicine, University of Miami School of Medicine, Florida.
Zakarija
M
M
Rabinovitch
A
A
D000818:Animals; D003921:Diabetes Mellitus, Experimental / Q000378:metabolism; D004229:Dithiothreitol / Q000494:pharmacology; D005260:Female; D008099:Liver / Q000187:drug effects / Q000378:metabolism*; D008297:Male; D009929:Organ Size / Q000187:drug effects; D051381:Rats; D011919:Rats, Inbred Strains; D013237:Stereoisomerism; D013438:Sulfhydryl Compounds / Q000378:metabolism; D013974:Thyroxine / Q000097:blood / Q000378:metabolism* / Q000494:pharmacology; D014284:Triiodothyronine / Q000378:metabolism
D013438:Sulfhydryl Compounds; D014284:Triiodothyronine; D013974:Thyroxine; D004229:Dithiothreitol