0013-7227/78/1026-1662$02.00/0 Endocrinology Copyright © 1978 by The Endocrine Society
Vol. 102, No. 6 Printed in U.S.A.
Studies on the Mechanism of Goitrogenic Action of Diphenylthiohydantoin TOMOMICHI TSUKUI, TORU AIZAWA, TAKASHI YAM AD A,* AND TETSUYA KAWABE Department of Medicine, Institute of Adaptation Medicine, School of Medicine, Shinshu University, Matsumoto, Japan ABSTRACT. Diphenylthiohydantoin (DPTH) is a potent goitrogenic compound and produces goiters in rats. Like methimazole, DPTH depresses plasma T.< and T.i concentrations and elevates plasma TSH concentration. Unlike methimazole, however, DPTH does not suppress thyroidal radioiodine uptake and thyroid hormone synthesis, although the monoiodotyrosine to diiodotyrosine ratio is elevated by DPTH. DPTH does not inhibit thyroidal radioiodine release or augment the degrada-
A
STWOOD et al. (1) first showed that 5,5L diphenylthiohydantoin (DPTH), the sulfur analog of dilantin, produced goiter without markedly depressing thyroidal iodine concentration. In contrast to this effect of DPTH, thiouracil produced goiter with a very low iodine concentration (2). No further attempts have been made to clarify possible differences in the mode of action of these two goitrogens. Ruegamer et al. (3, 4). have shown that an increase of a-glycerophosphate dehydrogenase activity was a useful measurement for assessing the action of thyroid hormones. They reported that DPTH inhibited the T4induced increase of a-glycerophosphate dehydrogenase activity in the liver, kidney, and heart (5, 6), but that methimazole failed to do so (7). As diphenyl-2,4-dithiohydantoin, an analog of DPTH, has been claimed to inhibit deiodination of T4 (8) and as monodeiodination of T4 is physiologically important in the production of T 3 (9-11), it is possible that DPTH augments TSH secretion by inhibiting the conversion of T4 to T3 in peripheral tissues. It is also possible that DPTH, like propylthiouracil (12), augments TSH secretion by blocking thyroid hormone synthesis. To investigate Received October 14, 1976. * To whom requests for reprints should be addressed.
tion of thyroid hormone. DPTH depresses an increase of plasma T4 and T.-j in thyroidectomized rats maintained on T4 or T3 by augmenting fecal excretion of hormones. In addition, DPTH decreases conversion of T4 to T;) in vitro. It is suggested that DPTH is a unique goitrogen which acts at two different extrathyroidal sites, viz. fecal loss of thyroid hormone and conversion of T^ to T.i. (Endocrinology 102: 1662, 1978)
these possibilities, the present experiments were performed. Materials and Methods Male Wistar rats (n = 279), weighing approximately 150 g, were used in the experiments. In Exp 1, 66 animals were fed a moderately low iodine diet (MLID)1 containing graded doses of DPTH (0.001-0.05%) or methimazole (0.01-0.05%) for 14 days. The amount of food consumption was measured and pair-fed daily among the groups in this and following experiments. Thus, no difference in weight gain was found among the groups. All of the animals were healthy. Four hours after an injection of 20 juCi I3II, the animals were killed and their thyroids were removed. After measurement of thyroidal radioiodine uptake, the thyroids were homogenized and hydrolyzed. The hydrolysates were analyzed by paper chromatography in a butanolethanol-ammonia system, as reported previously (13). In Exp 2, thyroidal radioiodine release was measured, as reported previously (14). Thirty-two animals were fed a MLID for 10 days before the experiment. Beginning 24 h after an I3II (20 /xCi) injection, counts over the thyroid region were made four times daily with an externally placed scintillation counter using light ether anesthesia. Each count was expressed as a percentage of the initial 1
Composition of this low iodine diet was previously reported {Endocrinology 79: 138, 1966).
1662 The Endocrine Society. Downloaded from press.endocrine.org by [${individualUser.displayName}] on 14 November 2015. at 04:01 For personal use only. No other uses without permission. . All rights reserved.
DPTH AND GOITER thyroid uptake on semilog paper. After a straight line of more than five individual points had been obtained, the half-life of thyroidal radioactivity was calculated from the line to express thyroidal radioiodine release. Thyroidal radioiodine release was measured for the first 56 h without administration of any test materials. After determination of the control value of thyroidal radioiodine release, the animals were divided into three groups (control, DPTH, and methimazole). Control animals received a saline injection (1 ml) sc daily for the next 2 days, while the other animals received a similar volume of saline containing DPTH (6 mg) or methimazole (5 mg) sc on the same schedule. In Exp 3,136 animals were divided into 22 groups and were fed an MLID with or without methimazole (0.05%), DPTH (0.05%), or both for 14 days. In addition, 1 ml saline or a similar volume of T4 (1-2 /xg) or T 3 (0.3-0.6 ^g) solution was injected sc daily for 14 days. Twenty-four hours after the last injection of T4 or T3, thyroids and blood were removed for further analysis. Plasma T4 and T3 were measured by RIA methods (15, 16). Rat TSH was measured by homologous RIA, using materials (NIAMDD rat TSH and its antibody) prepared by Dr. Albert F. Parlow and supplied by the Rat Pituitary Hormone Distribution Program of the NIH. The minimal detectable dose of TSH was 3.4 /iU/ml. When multiple determinations were made for one plasma, the difference was less than 1%. When the determination was made for one plasma at different occasions, the difference was less than 5%. In Exp 4, beginning 10 days after surgical thyroidectomy, 29 animals were fed a MLID with or without DPTH (0.05%) for 3 or 7 days, respectively, and injected with 1 ml T4 solution (2 /xg T4 with 0.5 /xCi [13II]T4) or 1 ml T 3 solution (0.6 /ug T 3 with 0.5 /iCi [I31I]T3)2 once daily ip for 7 or 3 days. The stock solutions of T4 and T 3 were kept refrigerated. Feces were collected daily, and 0.2 ml blood was obtained by cardiac puncture 24 h after the second, fourth, fifth, or seventh injection of T4 or 24 h after the third injection of T3. Fecal radioactivity was expressed as the percentage of the radioactivity of 1 ml stock T4 and T 3 solutions, and plasma T4 or T 3 concentration was calculated from the specific activity of the stock solution, as previously reported (17). In Exp 5,12 pieces of diaphragm weighing 50 mg were obtained from four animals. The muscle was then incubated in test tubes containing 0.2 ml dilute
1663
plasma (1:15), 0.2 ml radiolabeled T4 (3 x 10~8 M) and 0.2 ml test materials [DPTH, 0.03 mg/ml; butyl-3,5-diiodo-4-hydroxybenzoate (BHDB), 0.03 mg/ml] for 1 h. The muscle uptake of labeled T4 was calculated as reported previously (18). After addition of DPTH (0.03 mg/ml) or BHDB (0.3 mg/ml) to undiluted plasma, dialyzable fractions of T4 and T 3 were measured, according to the method of Sterling and Brenner (19), using [12r'I]T4 and [13II]T3. In Exp 6, 17 pieces of 100 mg diaphragm were obtained from 12 normal animals. The muscle was suspended in 1 ml Krebs-Ringer phosphate buffer (pH 7.4) containing radiolabeled T4 (final concentration, 2 X 10"7 M) and DPTH, and was incubated for 1 h. For comparison, boiled muscle (boiled for 30 min) was also incubated in the same medium for a similar period. At the end of incubation, 0.2 ml plasma was added to stop further deiodination of radiolabeled T4. The tissues were then homogenized with the medium, aliquots of the homogenates were applied to filter strips, and ascending chromatography was carried out in a butanolethanol-ammonia system. As previously reported (20), I31I content of the origin, iodide, and T4 was expressed as the percentage of the total 13II found on each strip. In Exp 7, rat liver homogenate was made according to the method reported by Visser et al. (21). T4 solution (1 jug) was incubated for 60 min at 37 C in the presence of test materials (liver homogenate, DPTH, and propylthiouracil). After incubation, T 3 concentration in the incubation medium was determined, according to the method reported by Visser et al. (21). Statistical analysis of the significance of difference between groups was done by means of Student's t test. A P value of less than 0.05 was considered statistically significant.
Results Exp 1: Effects of graded doses of DPTH and methimazole on thyroid weight, thyroidal radioiodine uptake, and thyroid hormone synthesis
Thyroid weight and thyroidal radioiodine uptake increased significantly at 0.03 and 0.05% levels of DPTH (Table 1, upper section). Diiodotyrosine (kTyr) decreased progressively with increasing doses of DPTH, but 2 ['"I]T4 and ['"IJTj were obtained from Abbott Lab- monoiodotyrosine (ITyr) increased progresoratories. SA: [I3II]T4) 45 mCi/mg, [I31I]T.,, 40 mCi/mg. sively. There was slightly more T4 in the
The Endocrine Society. Downloaded from press.endocrine.org by [${individualUser.displayName}] on 14 November 2015. at 04:01 For personal use only. No other uses without permission. . All rights reserved.
1664
TSUKUI ET AL.
Kndo Vol 102
1978 No 6
TABLE 1. Effect of graded doses of DPTH (D) and methimazole (M) on thyroid activity % Total thyroidal radioactivity after hydrolysis
Thyroidal
Thyroid wt (mg)
I'Hf
Control D (0.001%) D (0.005%) D (0.01%) D (0.03%) D (0.05%)
9.1 ± 1.1" 7.8 ± 0.5 7.8 ± 0.3 9.0 ± 0.3 14.3 ± 1.3" 22.2 ± 1.9"
Control D (0.05%) M (0.01%) M (0.03%) M (0.05%)
7.8 ± 0.9 19.0 ± 2.6' 17.9 ± 0.9' 18.8 ± 1.2' 19.4 ± 1.2*'
Group
«*.„!,—
1 uptake
T,
T..
11 yr:la l yr
14.4 ± 2.1 10.9 ± 0.7 9.6 ± 0.5 16.0 ± 1.1 31.0 ± 3.2' 41.0 ± 4.0"
Origin 9.0 ± 0.7 9.6 ± 0.6 9.6 ± 0.5 7.5 ± 0.2 8.1 ± 0.3 8.4 ± 0.3
I,Tyr 50.5 ± 1.1 43.6 ± 0.4* 35.3 ± 1.0" 31.7 ± 0.9' 26.9 ± 0.7'' 23.9 ± 0.3"
ITyr 26.8 ± 1.8 29.1 ± 1.3 33.9 ± 0.7* 38.7 ± 0.9" 43.4 ± 1.3'' 47.9 ± 0.8"
Iodide 3.8 ± 0.4 4.9 ± 0.2'' 5.6 ± 0.7* 5.3 ± 0.3'' 5.8 ± 0.4" 6.7 ± 0.3"
8.7 ± 1.0 11.1 ±0.6 11.8 ±0.6 12.7 ± 0.7* 10.2 ± 1.0 7.3 ± 0.4
1.2 ± 0.3 2.0 ± 0.4 3.7 ± 0.4'' 4.3 ± 0.6'' 5.8 ± 0.4" 6.0 ± 0.5"
0.53 0.68 0.96 1.22 1.61 2.00
21.4 ±9.1 49.6 ± 3.0'' 20.8 ± 4.2 13.5 ± 2.71' 6.4 ± 0.5
4.2 ± 1.1 5.0 ± 0.1 3.2 ± 0.3 2.0 ± 0.1 0.6 ± 0.2
45.4 ± 1.1 22.6 ± 0.7'' 29.0 ± 3.8' 13.5 ± 3.0'' 2.2 ± 0.9"
31.2 ±0.6 54.3 ± 1.8'' 49.3 ± 3.2'' 52.1 ± 2.5'' 30.9 ± 4.1
7.5 ± 0.1 4.9 ± 0.4" 13.4 ± 2.6'' 30.8 ± 5.5" 65.0 ±5.1"
9.9 ± 1.9 7.3 ± 0.8 3.1 ±0.7" 0.6 ± 0.2'' 0.3 ± 0.2"
2.0 ± 0.4 5.9 ± 1.0* 2.0 ± 0.3 1.0 ± 0.2' 0.4 ± 0.11'
0.69 2.40 1.70 3.85 4.05
(%>
Four hours after '"I (20 /tCi) injection, the thyroids were removed and hydrolyzed for 6 h with Pronase. D (0.001%), The animals were fed a MLID with DPTH (0.001%) for 2 weeks; M (0.01%), The animals were fed a MLID with methimazole (0.01%) for 2 weeks. " Mean ± SK, n = six animals per group. * P < 0.05 (significantly different from the controls). " P < 0.01 (significantly different from the controls). '' P < 0.005 (significantly different from the controls). " P < 0.001 (significantly different from the controls).
DPTH groups than in the controls, but the difference was statistically significant only with the dose of 0.01% DPTH. T3 increased progressively with increasing doses of DPTH; significant increases were observed with doses of 0.005-0.05% DPTH, although artificial production of T 3 from T4 during processing can not completely be ruled out. Iodide increased slightly but significantly with increasing concentration of DPTH. In the second part of this experiment, the goitrogenic actions of DPTH and methimazole were compared. As shown in the lower panel of Table 1, DPTH again produced goiter with a high radioiodine uptake and did not inhibit the synthesis of T4 and T3. Iodide was significantly less in this experiment, however. In contrast, methimazole produced goiter with a low thyroidal radioiodine uptake. Furthermore, intrathyroidal T4 and T3 were depressed progressively with increasing doses of methimazole. Iodide increased progressively with increasing doses of methimazole. Exp 2: Effect of DPTH and methimazole on thyroidal radioiodine release Because DPTH produced goiter without depressing thyroid hormone synthesis, the possible role of DPTH on thyroidal radioiodine release was studied. In the control group, thyroidal radioiodine release was exponential for the first 56 h and the release rate was not
altered by saline administration. In the DPTH group, the secretion rate during the control period was the same as that found in the control animals (Table 2), but it increased significantly 24 h after DPTH administration as evidenced by a shortening of the half-life of thyroidal radioactivity. Thyroidal radioiodine release also increased significantly after the administration of methimazole. The increase appeared as early as 1 h after the administration of methimazole. This increase of thyroidal radioiodine release was significantly greater in the methimazole group than in the DPTH group (P < 0.005). Exp 3: Effect of T4 and T3 on plasma thyroid hormone concentrations, thyroid weight, and plasma TSH in rats treated with methimazole, DPTH, or both Methimazole depressed plasma T 3 and T4 concentrations, but the decrease of T4 was greater than that of T 3 (Table 3, upper panel). As a result of decreased T 3 and T4 concentrations, plasma TSH concentration increased markedly and goiter developed. Plasma T.i and T4 concentrations increased progressively with increasing doses of T4. In addition, administration of 2 fig T4 restored the plasma T3:T4 ratio to normal. Associated with the increase of plasma thyroid hormones, plasma TSH concentrations and thyroid weights decreased markedly. Administration of DPTH
The Endocrine Society. Downloaded from press.endocrine.org by [${individualUser.displayName}] on 14 November 2015. at 04:01 For personal use only. No other uses without permission. . All rights reserved.
DPTH AND GOITER TABLE 2. Effect of DPTH and methimazole on thyroidal radioiodine release
Group
Control
DpTH«,
Methimazole''
No. of animals
P value Half-life of thyroidal radioactivity compared before and Before During during drug drug drug 124.4 ± 9.6" 136.6 ± 14.0 104.5 ± 10.2
124.4 ± 0.6 80.7 ± 6.1 31.3 ± 3.7
Vol. 102, No. 6 Printed in U.S.A.
Studies on the Mechanism of Goitrogenic Action of Diphenylthiohydantoin TOMOMICHI TSUKUI, TORU AIZAWA, TAKASHI YAM AD A,* AND TETSUYA KAWABE Department of Medicine, Institute of Adaptation Medicine, School of Medicine, Shinshu University, Matsumoto, Japan ABSTRACT. Diphenylthiohydantoin (DPTH) is a potent goitrogenic compound and produces goiters in rats. Like methimazole, DPTH depresses plasma T.< and T.i concentrations and elevates plasma TSH concentration. Unlike methimazole, however, DPTH does not suppress thyroidal radioiodine uptake and thyroid hormone synthesis, although the monoiodotyrosine to diiodotyrosine ratio is elevated by DPTH. DPTH does not inhibit thyroidal radioiodine release or augment the degrada-
A
STWOOD et al. (1) first showed that 5,5L diphenylthiohydantoin (DPTH), the sulfur analog of dilantin, produced goiter without markedly depressing thyroidal iodine concentration. In contrast to this effect of DPTH, thiouracil produced goiter with a very low iodine concentration (2). No further attempts have been made to clarify possible differences in the mode of action of these two goitrogens. Ruegamer et al. (3, 4). have shown that an increase of a-glycerophosphate dehydrogenase activity was a useful measurement for assessing the action of thyroid hormones. They reported that DPTH inhibited the T4induced increase of a-glycerophosphate dehydrogenase activity in the liver, kidney, and heart (5, 6), but that methimazole failed to do so (7). As diphenyl-2,4-dithiohydantoin, an analog of DPTH, has been claimed to inhibit deiodination of T4 (8) and as monodeiodination of T4 is physiologically important in the production of T 3 (9-11), it is possible that DPTH augments TSH secretion by inhibiting the conversion of T4 to T3 in peripheral tissues. It is also possible that DPTH, like propylthiouracil (12), augments TSH secretion by blocking thyroid hormone synthesis. To investigate Received October 14, 1976. * To whom requests for reprints should be addressed.
tion of thyroid hormone. DPTH depresses an increase of plasma T4 and T.-j in thyroidectomized rats maintained on T4 or T3 by augmenting fecal excretion of hormones. In addition, DPTH decreases conversion of T4 to T;) in vitro. It is suggested that DPTH is a unique goitrogen which acts at two different extrathyroidal sites, viz. fecal loss of thyroid hormone and conversion of T^ to T.i. (Endocrinology 102: 1662, 1978)
these possibilities, the present experiments were performed. Materials and Methods Male Wistar rats (n = 279), weighing approximately 150 g, were used in the experiments. In Exp 1, 66 animals were fed a moderately low iodine diet (MLID)1 containing graded doses of DPTH (0.001-0.05%) or methimazole (0.01-0.05%) for 14 days. The amount of food consumption was measured and pair-fed daily among the groups in this and following experiments. Thus, no difference in weight gain was found among the groups. All of the animals were healthy. Four hours after an injection of 20 juCi I3II, the animals were killed and their thyroids were removed. After measurement of thyroidal radioiodine uptake, the thyroids were homogenized and hydrolyzed. The hydrolysates were analyzed by paper chromatography in a butanolethanol-ammonia system, as reported previously (13). In Exp 2, thyroidal radioiodine release was measured, as reported previously (14). Thirty-two animals were fed a MLID for 10 days before the experiment. Beginning 24 h after an I3II (20 /xCi) injection, counts over the thyroid region were made four times daily with an externally placed scintillation counter using light ether anesthesia. Each count was expressed as a percentage of the initial 1
Composition of this low iodine diet was previously reported {Endocrinology 79: 138, 1966).
1662 The Endocrine Society. Downloaded from press.endocrine.org by [${individualUser.displayName}] on 14 November 2015. at 04:01 For personal use only. No other uses without permission. . All rights reserved.
DPTH AND GOITER thyroid uptake on semilog paper. After a straight line of more than five individual points had been obtained, the half-life of thyroidal radioactivity was calculated from the line to express thyroidal radioiodine release. Thyroidal radioiodine release was measured for the first 56 h without administration of any test materials. After determination of the control value of thyroidal radioiodine release, the animals were divided into three groups (control, DPTH, and methimazole). Control animals received a saline injection (1 ml) sc daily for the next 2 days, while the other animals received a similar volume of saline containing DPTH (6 mg) or methimazole (5 mg) sc on the same schedule. In Exp 3,136 animals were divided into 22 groups and were fed an MLID with or without methimazole (0.05%), DPTH (0.05%), or both for 14 days. In addition, 1 ml saline or a similar volume of T4 (1-2 /xg) or T 3 (0.3-0.6 ^g) solution was injected sc daily for 14 days. Twenty-four hours after the last injection of T4 or T3, thyroids and blood were removed for further analysis. Plasma T4 and T3 were measured by RIA methods (15, 16). Rat TSH was measured by homologous RIA, using materials (NIAMDD rat TSH and its antibody) prepared by Dr. Albert F. Parlow and supplied by the Rat Pituitary Hormone Distribution Program of the NIH. The minimal detectable dose of TSH was 3.4 /iU/ml. When multiple determinations were made for one plasma, the difference was less than 1%. When the determination was made for one plasma at different occasions, the difference was less than 5%. In Exp 4, beginning 10 days after surgical thyroidectomy, 29 animals were fed a MLID with or without DPTH (0.05%) for 3 or 7 days, respectively, and injected with 1 ml T4 solution (2 /xg T4 with 0.5 /xCi [13II]T4) or 1 ml T 3 solution (0.6 /ug T 3 with 0.5 /iCi [I31I]T3)2 once daily ip for 7 or 3 days. The stock solutions of T4 and T 3 were kept refrigerated. Feces were collected daily, and 0.2 ml blood was obtained by cardiac puncture 24 h after the second, fourth, fifth, or seventh injection of T4 or 24 h after the third injection of T3. Fecal radioactivity was expressed as the percentage of the radioactivity of 1 ml stock T4 and T 3 solutions, and plasma T4 or T 3 concentration was calculated from the specific activity of the stock solution, as previously reported (17). In Exp 5,12 pieces of diaphragm weighing 50 mg were obtained from four animals. The muscle was then incubated in test tubes containing 0.2 ml dilute
1663
plasma (1:15), 0.2 ml radiolabeled T4 (3 x 10~8 M) and 0.2 ml test materials [DPTH, 0.03 mg/ml; butyl-3,5-diiodo-4-hydroxybenzoate (BHDB), 0.03 mg/ml] for 1 h. The muscle uptake of labeled T4 was calculated as reported previously (18). After addition of DPTH (0.03 mg/ml) or BHDB (0.3 mg/ml) to undiluted plasma, dialyzable fractions of T4 and T 3 were measured, according to the method of Sterling and Brenner (19), using [12r'I]T4 and [13II]T3. In Exp 6, 17 pieces of 100 mg diaphragm were obtained from 12 normal animals. The muscle was suspended in 1 ml Krebs-Ringer phosphate buffer (pH 7.4) containing radiolabeled T4 (final concentration, 2 X 10"7 M) and DPTH, and was incubated for 1 h. For comparison, boiled muscle (boiled for 30 min) was also incubated in the same medium for a similar period. At the end of incubation, 0.2 ml plasma was added to stop further deiodination of radiolabeled T4. The tissues were then homogenized with the medium, aliquots of the homogenates were applied to filter strips, and ascending chromatography was carried out in a butanolethanol-ammonia system. As previously reported (20), I31I content of the origin, iodide, and T4 was expressed as the percentage of the total 13II found on each strip. In Exp 7, rat liver homogenate was made according to the method reported by Visser et al. (21). T4 solution (1 jug) was incubated for 60 min at 37 C in the presence of test materials (liver homogenate, DPTH, and propylthiouracil). After incubation, T 3 concentration in the incubation medium was determined, according to the method reported by Visser et al. (21). Statistical analysis of the significance of difference between groups was done by means of Student's t test. A P value of less than 0.05 was considered statistically significant.
Results Exp 1: Effects of graded doses of DPTH and methimazole on thyroid weight, thyroidal radioiodine uptake, and thyroid hormone synthesis
Thyroid weight and thyroidal radioiodine uptake increased significantly at 0.03 and 0.05% levels of DPTH (Table 1, upper section). Diiodotyrosine (kTyr) decreased progressively with increasing doses of DPTH, but 2 ['"I]T4 and ['"IJTj were obtained from Abbott Lab- monoiodotyrosine (ITyr) increased progresoratories. SA: [I3II]T4) 45 mCi/mg, [I31I]T.,, 40 mCi/mg. sively. There was slightly more T4 in the
The Endocrine Society. Downloaded from press.endocrine.org by [${individualUser.displayName}] on 14 November 2015. at 04:01 For personal use only. No other uses without permission. . All rights reserved.
1664
TSUKUI ET AL.
Kndo Vol 102
1978 No 6
TABLE 1. Effect of graded doses of DPTH (D) and methimazole (M) on thyroid activity % Total thyroidal radioactivity after hydrolysis
Thyroidal
Thyroid wt (mg)
I'Hf
Control D (0.001%) D (0.005%) D (0.01%) D (0.03%) D (0.05%)
9.1 ± 1.1" 7.8 ± 0.5 7.8 ± 0.3 9.0 ± 0.3 14.3 ± 1.3" 22.2 ± 1.9"
Control D (0.05%) M (0.01%) M (0.03%) M (0.05%)
7.8 ± 0.9 19.0 ± 2.6' 17.9 ± 0.9' 18.8 ± 1.2' 19.4 ± 1.2*'
Group
«*.„!,—
1 uptake
T,
T..
11 yr:la l yr
14.4 ± 2.1 10.9 ± 0.7 9.6 ± 0.5 16.0 ± 1.1 31.0 ± 3.2' 41.0 ± 4.0"
Origin 9.0 ± 0.7 9.6 ± 0.6 9.6 ± 0.5 7.5 ± 0.2 8.1 ± 0.3 8.4 ± 0.3
I,Tyr 50.5 ± 1.1 43.6 ± 0.4* 35.3 ± 1.0" 31.7 ± 0.9' 26.9 ± 0.7'' 23.9 ± 0.3"
ITyr 26.8 ± 1.8 29.1 ± 1.3 33.9 ± 0.7* 38.7 ± 0.9" 43.4 ± 1.3'' 47.9 ± 0.8"
Iodide 3.8 ± 0.4 4.9 ± 0.2'' 5.6 ± 0.7* 5.3 ± 0.3'' 5.8 ± 0.4" 6.7 ± 0.3"
8.7 ± 1.0 11.1 ±0.6 11.8 ±0.6 12.7 ± 0.7* 10.2 ± 1.0 7.3 ± 0.4
1.2 ± 0.3 2.0 ± 0.4 3.7 ± 0.4'' 4.3 ± 0.6'' 5.8 ± 0.4" 6.0 ± 0.5"
0.53 0.68 0.96 1.22 1.61 2.00
21.4 ±9.1 49.6 ± 3.0'' 20.8 ± 4.2 13.5 ± 2.71' 6.4 ± 0.5
4.2 ± 1.1 5.0 ± 0.1 3.2 ± 0.3 2.0 ± 0.1 0.6 ± 0.2
45.4 ± 1.1 22.6 ± 0.7'' 29.0 ± 3.8' 13.5 ± 3.0'' 2.2 ± 0.9"
31.2 ±0.6 54.3 ± 1.8'' 49.3 ± 3.2'' 52.1 ± 2.5'' 30.9 ± 4.1
7.5 ± 0.1 4.9 ± 0.4" 13.4 ± 2.6'' 30.8 ± 5.5" 65.0 ±5.1"
9.9 ± 1.9 7.3 ± 0.8 3.1 ±0.7" 0.6 ± 0.2'' 0.3 ± 0.2"
2.0 ± 0.4 5.9 ± 1.0* 2.0 ± 0.3 1.0 ± 0.2' 0.4 ± 0.11'
0.69 2.40 1.70 3.85 4.05
(%>
Four hours after '"I (20 /tCi) injection, the thyroids were removed and hydrolyzed for 6 h with Pronase. D (0.001%), The animals were fed a MLID with DPTH (0.001%) for 2 weeks; M (0.01%), The animals were fed a MLID with methimazole (0.01%) for 2 weeks. " Mean ± SK, n = six animals per group. * P < 0.05 (significantly different from the controls). " P < 0.01 (significantly different from the controls). '' P < 0.005 (significantly different from the controls). " P < 0.001 (significantly different from the controls).
DPTH groups than in the controls, but the difference was statistically significant only with the dose of 0.01% DPTH. T3 increased progressively with increasing doses of DPTH; significant increases were observed with doses of 0.005-0.05% DPTH, although artificial production of T 3 from T4 during processing can not completely be ruled out. Iodide increased slightly but significantly with increasing concentration of DPTH. In the second part of this experiment, the goitrogenic actions of DPTH and methimazole were compared. As shown in the lower panel of Table 1, DPTH again produced goiter with a high radioiodine uptake and did not inhibit the synthesis of T4 and T3. Iodide was significantly less in this experiment, however. In contrast, methimazole produced goiter with a low thyroidal radioiodine uptake. Furthermore, intrathyroidal T4 and T3 were depressed progressively with increasing doses of methimazole. Iodide increased progressively with increasing doses of methimazole. Exp 2: Effect of DPTH and methimazole on thyroidal radioiodine release Because DPTH produced goiter without depressing thyroid hormone synthesis, the possible role of DPTH on thyroidal radioiodine release was studied. In the control group, thyroidal radioiodine release was exponential for the first 56 h and the release rate was not
altered by saline administration. In the DPTH group, the secretion rate during the control period was the same as that found in the control animals (Table 2), but it increased significantly 24 h after DPTH administration as evidenced by a shortening of the half-life of thyroidal radioactivity. Thyroidal radioiodine release also increased significantly after the administration of methimazole. The increase appeared as early as 1 h after the administration of methimazole. This increase of thyroidal radioiodine release was significantly greater in the methimazole group than in the DPTH group (P < 0.005). Exp 3: Effect of T4 and T3 on plasma thyroid hormone concentrations, thyroid weight, and plasma TSH in rats treated with methimazole, DPTH, or both Methimazole depressed plasma T 3 and T4 concentrations, but the decrease of T4 was greater than that of T 3 (Table 3, upper panel). As a result of decreased T 3 and T4 concentrations, plasma TSH concentration increased markedly and goiter developed. Plasma T.i and T4 concentrations increased progressively with increasing doses of T4. In addition, administration of 2 fig T4 restored the plasma T3:T4 ratio to normal. Associated with the increase of plasma thyroid hormones, plasma TSH concentrations and thyroid weights decreased markedly. Administration of DPTH
The Endocrine Society. Downloaded from press.endocrine.org by [${individualUser.displayName}] on 14 November 2015. at 04:01 For personal use only. No other uses without permission. . All rights reserved.
DPTH AND GOITER TABLE 2. Effect of DPTH and methimazole on thyroidal radioiodine release
Group
Control
DpTH«,
Methimazole''
No. of animals
P value Half-life of thyroidal radioactivity compared before and Before During during drug drug drug 124.4 ± 9.6" 136.6 ± 14.0 104.5 ± 10.2
124.4 ± 0.6 80.7 ± 6.1 31.3 ± 3.7
![Studies on the mechanism of action of cyclosporin A [proceedings].](/assets/img/hold.png)
