Original Paper Neuroendocrinology 1992;56:453-458
CONICET, Centro de Medicina Nuclear, Hospital de Clínicas, Universidad de Buenos Aires, Argentina
Diphenylhydantoin Stimulates the Intrapituitary Conversion of Thyroxine to Triiodothyronine in the Rat
Key Words
Abstract
Thyroxine Diphenylhydantoin Pituitary 5'-Deiodinase
Treatment of normal rats with diphenylhydantoin (DPH) decreases serum thyroxine (Tj) and triiodothyronine (T3) levels without the anticipated rise in serum thyrotropin (TSH). The present work has studied the intrapituitary con version of T4 to T? in male Wistar rats, 200-250 g body weight (BW), treated with DPH 5 m g /100 g BW/day for 8 days. A tracer dose of 3',5'-[l25I]T4 (150 pCi) was injected intravenously, and 2 h later hypophyses were removed and homogenized individually at 4 °C in ice-cold PBS buffer (pH 7.4). T4 and T3 were extracted in 400 ul n-butanol:2 N HCI (9:1) and chromatographed in tertiary amyl alcohol:hexane: 1 N ammonia (5:1:6). In 11 untreated control rats, [125I]T3 generated from [l25I]T4 deiodination was 35 ± 6% and intact [ i25I]T4 was 49 ± 9% of total chromatographic radioactivity. In 11 DPHtreated rats [l25I]T3 increased (p < 0.001) and [1251]T4 decreased (p < 0.02). The DPH effect was blocked in rats treated for 2 days with iopanoic acid 10 m g /100 g BW, though blocking was not seen in rats treated with half the dose of iopanoic acid. In normal rats receiving supplemental doses ofT) (2 u g / 100 g BW/day for 8 days), DPH similarly increased pituitary 5'-deiodination. Ad ministration of propylthiouracil (PTU) to Tj-supplemented rats had no effect on pituitary 5'-deiodination of T4, whereas the addition of DPH to PTU treat ment increased [l25I]T3 production (p < 0.01). Serum T» (p < 0.001) and T3 (p < 0.01) were decreased after DPH therapy, while serum and pituitary TSH were not altered. The DPH-stimulated deiodination of T4 to Ts may contribute to depress the feedback response of the pituitary gland to low serum thyroid hormone levels.
The binding of diphenylhydantoin (DPH) to thyroid hormone-binding globulin (TBG) has long been known to alter the serum levels and the peripheral metabolism of thyroxine (T4) and triiodothyronine (TO in man [1-7]. It was nevertheless thought that the DPH effect on thyroidal economy was more extensive than that derived solely
Received: May 3,1991 Accepted after revision : January 31, 1992
from its binding to TBG [4], Consistent with this conclu sion were the findings that while serum T», free T» and T3 concentrations after DPH treatment were consistently low, the appropriate rise in serum thyrotropin (TSH) had failed to occur, and the TSH response to TSH-releasing hormone (TRH) was normal in man and the rat [8, 9],
Angel A. Zaninovich CONICET, Centro de Medicina Nuclear Hospital de Clínicas Universidad de Buenos Aires Buenos Aires (Argentina)
© 1992 S. Kargcr AG. Bascl 0028-3835/92/0564-0453 S 2.75/0
Downloaded by: King's College London 137.73.144.138 - 1/17/2019 2:27:52 AM
Laura F. Cageao Jorge A. Ceppi Rubén J. Boado Angel A. Zaninovich
Groups
[,25 I]T4
[,25I]T?
T3 pg/gland1
Untreated (11) DPH (11) Significance IA 10 mg2 (8) IA + DPH (8) IA 5 mg2 (8) IA + DPH Significance
6.9 5.5 p < 10.4 10.2 8.2 7.2 p
CONICET, Centro de Medicina Nuclear, Hospital de Clínicas, Universidad de Buenos Aires, Argentina
Diphenylhydantoin Stimulates the Intrapituitary Conversion of Thyroxine to Triiodothyronine in the Rat
Key Words
Abstract
Thyroxine Diphenylhydantoin Pituitary 5'-Deiodinase
Treatment of normal rats with diphenylhydantoin (DPH) decreases serum thyroxine (Tj) and triiodothyronine (T3) levels without the anticipated rise in serum thyrotropin (TSH). The present work has studied the intrapituitary con version of T4 to T? in male Wistar rats, 200-250 g body weight (BW), treated with DPH 5 m g /100 g BW/day for 8 days. A tracer dose of 3',5'-[l25I]T4 (150 pCi) was injected intravenously, and 2 h later hypophyses were removed and homogenized individually at 4 °C in ice-cold PBS buffer (pH 7.4). T4 and T3 were extracted in 400 ul n-butanol:2 N HCI (9:1) and chromatographed in tertiary amyl alcohol:hexane: 1 N ammonia (5:1:6). In 11 untreated control rats, [125I]T3 generated from [l25I]T4 deiodination was 35 ± 6% and intact [ i25I]T4 was 49 ± 9% of total chromatographic radioactivity. In 11 DPHtreated rats [l25I]T3 increased (p < 0.001) and [1251]T4 decreased (p < 0.02). The DPH effect was blocked in rats treated for 2 days with iopanoic acid 10 m g /100 g BW, though blocking was not seen in rats treated with half the dose of iopanoic acid. In normal rats receiving supplemental doses ofT) (2 u g / 100 g BW/day for 8 days), DPH similarly increased pituitary 5'-deiodination. Ad ministration of propylthiouracil (PTU) to Tj-supplemented rats had no effect on pituitary 5'-deiodination of T4, whereas the addition of DPH to PTU treat ment increased [l25I]T3 production (p < 0.01). Serum T» (p < 0.001) and T3 (p < 0.01) were decreased after DPH therapy, while serum and pituitary TSH were not altered. The DPH-stimulated deiodination of T4 to Ts may contribute to depress the feedback response of the pituitary gland to low serum thyroid hormone levels.
The binding of diphenylhydantoin (DPH) to thyroid hormone-binding globulin (TBG) has long been known to alter the serum levels and the peripheral metabolism of thyroxine (T4) and triiodothyronine (TO in man [1-7]. It was nevertheless thought that the DPH effect on thyroidal economy was more extensive than that derived solely
Received: May 3,1991 Accepted after revision : January 31, 1992
from its binding to TBG [4], Consistent with this conclu sion were the findings that while serum T», free T» and T3 concentrations after DPH treatment were consistently low, the appropriate rise in serum thyrotropin (TSH) had failed to occur, and the TSH response to TSH-releasing hormone (TRH) was normal in man and the rat [8, 9],
Angel A. Zaninovich CONICET, Centro de Medicina Nuclear Hospital de Clínicas Universidad de Buenos Aires Buenos Aires (Argentina)
© 1992 S. Kargcr AG. Bascl 0028-3835/92/0564-0453 S 2.75/0
Downloaded by: King's College London 137.73.144.138 - 1/17/2019 2:27:52 AM
Laura F. Cageao Jorge A. Ceppi Rubén J. Boado Angel A. Zaninovich
Groups
[,25 I]T4
[,25I]T?
T3 pg/gland1
Untreated (11) DPH (11) Significance IA 10 mg2 (8) IA + DPH (8) IA 5 mg2 (8) IA + DPH Significance
6.9 5.5 p < 10.4 10.2 8.2 7.2 p
