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Propylthiouracil disposition in older hypothyroid patients.

The pharmacokinetic disposition of propylthiouracil (PTU) after a single oral dose was studied in 6 severely hypothyroid patients. Severity of disease, as indicated by thyroid-stimulating hormone concentration, was inversely related to plasma clearance of PTU. There were trends to increased apparent volume of distribution and plasma half-life for PTU as a function of age. The large apparent volume of distribution for PTU in these patients compared to euthyroid and hyperthyroid subjects, after a single drug dose, suggests that hypothyroidism as well as chronic drug ingestion must be considered as possible factors mediating this change.

Aged↗

Ultrastructure of fetal pars-tuberalis-specific secretory cells under the influence of propylthiouracil and thyroxine.

The rat pituitary pars tuberalis (pt) is a functional and morphological unique component of the adenohypophysis. It mainly consists of specific secretory cells whose morphological and functional characterization is far from being complete. In this study the ultrastructure of fetal secretory pt cells developing under hypo- and hyperthyroid conditions was examined. Besides controls, young mature pregnant Wistar rats were treated with propylthiouracil (PTU) or thyroxine (T4). Areas of pt cells and of their nuclei were measured. Different cell organelles per cell were counted, and area densities of these organelles were determined. While the number of dictyosomes per cell area did not change, the area densities of long ribbons increased significantly in the experimental groups. Lysosomes and secretory granules, however, were found to be significantly diminished in pt cells of T4- and PTU-treated animals. The latter finding corresponds to earlier investigations when changes of the thyroid-stimulating-hormone-like immunoreactivity of fetal pt-specific cells were observed under the same experimental conditions. Results indicate that fetal pt-specific cells respond to changes of thyroid status in a manner different from pars distalis thyrotrophs. An interaction of pt-specific cells in thyroid regulation mechanisms is assumed.

Animals↗

Pharmacokinetics of propylthiouracil in children and adolescents with Graves' disease in the hyperthyroid and euthyroid states.

The pharmacokinetics of propylthiouracil (PTU) was studied in 7 patients having Graves' disease when they were hyperthyroid and then again when they were euthyroid. Two additional euthyroid patients were also studied. The t1/2, Ke, Ka, apparent Vd, AUC and clearance were calculated. Serum T3 and T4 were also measured. PTU had an immediate effect in reducing T3 levels. Although there were intraindividual variations, the mean PTU elimination half-time did not change from the hyperthyroid state (1.47 h) to the euthyroid state (1.53 h). The mean Ka when hyperthyroid (2.12 h-1) was significantly increased (p less than 0.005) compared to when euthyroid (1.00 h-1). The calculated kinetic information indicates that the disposition of PTU in children is similar to that reported in adults.

Adolescent↗

Protective effect of propylthiouracil independent of its hypothyroid effect on atherogenesis in cholesterol-fed rabbits: PTEN induction and inhibition of vascular smooth muscle cell proliferation and migration.

BACKGROUND: Propylthiouracil (PTU) is used to treat hyperthyroid patients by its hypothyroid effect. PTU also is found to have potent antioxidant and immunosuppressive effects. These findings suggest that PTU may play a role in the prevention of atherosclerosis. METHODS AND RESULTS: This study evaluates the effect of PTU on atherosclerotic change in rabbits fed a high-cholesterol diet. The pronounced atherosclerotic lesions in the aortas of rabbits fed a 2% cholesterol diet for 12 weeks were significantly attenuated by the concurrent addition of 0.1% PTU to the drinking water. However, exogenous supplementation of thyroid hormone in hypothyroid PTU-treated rabbits did not abrogate the protective effect of PTU on atherogenesis. Immunohistochemical analysis showed that PTU administration apparently reduced the intimal smooth muscle cell/macrophage ratio in the atherosclerotic plaques of rabbits fed a 2% cholesterol diet. In vitro, the addition of PTU to the medium of cultured rat vascular smooth muscle cells led to a dose-dependent inhibition of cell proliferation and migration. Furthermore, this study confirmed that PTU dose-dependently increased expression of PTEN, a tumor suppressor gene known to be involved in the coordinate inhibition of VSMC proliferation and migration. CONCLUSIONS: This study demonstrated that PTU inhibited the development of atherosclerosis through a thyroid-independent mechanism that may be explained, at least in part, by the ability of PTU to inhibit vascular smooth muscle cell proliferation and migration. Furthermore, PTEN induction, via disruption of the phosphatidylinsitol 3-kinase-mediated pathway, plays a crucial role in mediating the inhibitory action on vascular smooth muscle cell proliferation and migration.

Animals↗

Reduction in extrathyroidal triiodothyronine production by propylthiouracil in man.

To determine if propylthiouracil (PTU) inhibited extrathyroidal thyroxine (T4) to triiodothyronine (T3) conversion in man, PTU was administered to T4-treated hypothyroid patients and serial measurements of T4, T3, and thyrotropin (TSH) carried out. All patients had proven thyroidal hypothyroidism and had been receiving 0.1 or 0.2 mg T4 daily for at least 2 mo before study. Hormone measurements were made for 5 consecutive days before and daily during a 7-day treatment period with PTU, 1,000 mg/day. In eight patients receiving 0.1 mg T4 daily, administration of PTU resulted in a prompt fall in mean serum T3 concentrations from 78 plus or minus 6 ng/100 ml (SEM) to 61 plus or minus 3 ng/100 ml after 1 day. The mean serum T3 concentrations ranged from 55 to 60 ng/100 ml during the remainder of the PTU treatment period (P less than 0.01). The mean control serum TSH concentration was 29.6 muU/ml and it increased to a peak of 40 muU/ml on the 5th and 6th days. In five patients receiving 0.2 mg T4 daily, the mean control serum T3 concentration was 84 plus or minus 7 NG/100ML. It fell to 70 plus or minus 5 ng/100 ml after 1 day and 63 plus or minus 7 ng/100 ml after 2 days of PTU administration and thereafter ranged from 6) to 69 ng/100 ml (P LESS THAN 0.01). Serum TSH concentrations did not increase. No changes in serum T4 concentrations were found in either group. In five patients who received 100 mg methimazole (MMI) daily for 7 days there were no changes in serum T4, T3, or TSH concentrations. These results indicate that PTU, but not MMI, produces a prompt and sustained, albeit modest, reduction in serum T3 concentrations in patients whose sole or major source of T3 is ingested T4. These findings most likely result from inhibition of extrathyroidal formation of T3 from T4.

Administration, Oral↗

Propylthiouracil blocks extrathyroidal conversion of thyroxine to triiodothyronine and augments thyrotropin secretion in man.

Propylthiouracil (PTU) inhibits peripheral deiodination of thyroxine (T4) and triiodothyronine (T3) and decreases the metabolic effectiveness of T4 in animals. To assess the effect of PTU on extrathyroidal conversion of T4 to T3 in man, 15 studies were performed in athyreotic patients treated with 100 or 200 mug of L-T4 daily for 1 mo before the addition of PTU, 250 mg every 6 h for 8 days. serum T3, T4, and thyrotropin (TSH) were measured daily by radioimmunoassay; serum TSH response to 500-mug thyrotropin-releasing hormone (TRH) was measured before and on the last day of giving PTU. On the 100-mug LT4 dose, serum T3 fell from 120 plus or minus 5 (SE) to 83 plus or minus 6 ng/dl (P less than 0.005) with return to 113 plus or minus 5 ng/dl after stopping PTU; serum T4 (4.5 plus or minus 0.3 mug/dl) did not change. Similar results were seen in patients taking 200 mug of L-T4 daily. On the 100-mug dose of L-T4 the fall in T3 was accompanied by a reciprocal rise in serum TSH to 195 plus or minus 33% of initial concentration (P less than 0.01) with return to 104 plus or minus 8% after PTU. The serum TSH response to TRH (DELTAMUU/ml over base line) was greater during PTU therapy than during the control period. On 100-mug L-T4 DELTA TSH rose from 64 plus or minus 19 to 101 plus or minus 23 muU/ml (P less than 0.005). Expressed as percent of base-line TSH concentration, TSH rose from 140 plus or minus 52 to 280 plus or minus 44% (control vs. PTU) at 15 min, 265 plus or minus 72 to 367 plus or minus 63% at 30 min, 223 plus or minus 54 to 313 plus or minus 54% at 45 min, 187 plus or minus 45 to 287 plus or minus 51% at 60 min, and 145 plus or minus 22 to 210 plus or minus 28% at 120 min after TRH. The data suggest that PTU blocks extrathyroidal conversion of T4 to T3, thus increasing pituitary TSH secretion and augmenting the TSH response to TRH.

Depression, Chemical↗

Accumulation of plasma triiodothyronine sulfate in rats treated with propylthiouracil.

Triiodothyronine sulfate (T3S) is rapidly deiodinated by the propylthiouracil (PTU)-sensitive type I deiodinase. Here we examined the effects of PTU on plasma T3S levels in rats after intravenous administration of radiolabeled T3 or T3S. Sephadex LH-20 chromatography and high-performance liquid chromatography were used to quantify conjugated and nonconjugated iodothyronines, and iodide was measured as the TCA-soluble radioactivity. In control rats, radioiodide was the main metabolite of both T3 and T3S. Plasma T3S was cleared more rapidly than plasma T3 despite increased binding to plasma proteins. PTU reduced plasma iodide levels by 66 and 78% after T3 and T3S, respectively, and decreased plasma clearance of T3S by 81%. However, PTU had no effect on plasma T3 clearance but increased plasma T3S from injected T3 4.2 times. Biliary excretion of injected T3S was less than 20% in normal rats, in contrast to 70% within 4 h in PTU-treated rats. In conclusion, T3S is an important intermediate in the in vivo metabolism of T3 in rats and accumulates in plasma if type I deiodination is inhibited.

Animals↗

Alterations in 3,3'5'-triiodothyronine metabolism in response to propylthiouracil, dexamethasone, and thyroxine administration in man.

To elucidate the mechanisms involved in altering serum 3,3',5'-triiodothyronine (rT3) levels with absolute or relative low 3,5,3'-triiodothyronine (T3) states in man, agents capable of lowering circulating T3 levels were sequentially administered to six euthyroid subjects. These agents included propylthiouracil (PTU) (300 mg/6 h X 5 d), dexamethasone (DEX) (2 mg/6 h X 5 d), and thyroxine (T4) (3.0 mg load and 0.3 mg/d X 5 d). [125I] rT3 clearance rates and rT3 production rates were then determined. Increased serum rT3 levels and rT3/T4 values occurred with both PTU and DEX as compared with control, while T4 increased serum rT3 but did so without changing rT3/T4 values. The rT3 clearance rate was significantly decreased by PTU without altering production rate, while DEX increased the rT3 production rate without altering the rT3 clearance rate. T4 administration did not change rT3 clearance but proportionately increased rT3 production. These responses indicate that circulating rT3 predominantly originates from a non-PTU inhibitable deiodinase enzyme system located in extrahepatic tissues. This enzyme system appears to have a high capacity and low affinity for T4 and can be stimulated by DEX administration.

Adult↗

Propylthiouracil hepatotoxicity. A review and case presentation.

Propylthiouracil (PTU) is widely used to treat patients with hyperthyroidism. In rare cases, this drug has been found to have severe toxic effects on the liver. The case of a 14-year-old girl treated with PTU for hyperthyroidism who developed jaundice, severe hepatocellular dysfunction, and hepatomegaly is reported. Her condition gradually deteriorated, and she developed paranoid ideation, profound lethargy, and peripheral edema. After three weeks of prednisone therapy, clinical and laboratory signs of improvement were observed. This patient was one of only five pediatric cases among the 16 reported cases of PTU liver toxicity reported to date. Her history and the fatal outcome in some reported cases demonstrate the high degree of sensitivity required to recognize this potential complication in patients treated with PTU, particularly since its immediate discontinuance and steroid-therapy intervention may lead to recovery.

Adolescent↗

Hepatitis associated with propylthiouracil treatment.

A 12-year-old girl with hyperthyroidism who had started treatment with propylthiouracil (PTU) 100 mg tid developed hepatitis. The drug was stopped, and the clinical and laboratory findings of hepatitis disappeared within a week. She was not receiving other drugs that could cause hepatic damage, and investigations for various viral agents were negative. This is the ninth report of PTU-induced hepatitis. The clinical picture is similar to that of viral hepatitis. Recovery usually occurs after withdrawal of the drug, but there have been two fatal cases of PTU-induced hepatitis.

Chemical and Drug Induced Liver Injury↗

Propylthiouracil-induced hepatic failure and encephalopathy in a child.

Propylthiouracil (PTU) is the most common antithyroid medication utilized in children for the treatment of hyperthyroidism. An adverse effect of PTU reported infrequently is hepatic injury. The child described here is the fifth reported case of severe hepatic injury in the pediatric age group and documents that clinical or biochemical evidence of hepatic injury requires immediate discontinuation of PTU.

Chemical and Drug Induced Liver Injury↗

Effects of thyroidectomy, propylthiouracil, and thyroxine on pituitary content and immunocytochemical staining of thyrotropin (TSH) and thyrotropin releasing hormone (TRH).

Previous studies have demonstrated immunocytochemical staining for beta chains of thyroid stimulating hormone (TSH-beta) in rough endoplasmic reticulum of pituitary cells hypertrophied after thyroidectomy ("thyroidectomy cells") (Moriarty CG(1976): J Histochem Cytochem (24:846; Moriarty GC, Tobin RB (1976): J Histochem Cytochem 24:1140). Here we report the localization of thyrotropin releasing hormone (TRH) in serial sections of the same pituitaries to determine if it could be found at similar sites. No staining for TRH was found in hypertrophied TSH cells formed 42 days after the surgery, or after 14, 34, and 70 days of propylthiouracil (PTU) treatment. The loss in immunostaining in the PTU-treated rats was correlated with radioimmunoassay (RIA) measurements that showed a 65% reduction in anterior pituitary TRH content after 34, 70, and 98 days of PTU treatment (from 22.9--7.8 pg/mg wet wt) and a 50% reduction in TSH content after 34 days of treatment. When thyroxine was administered to hypothyroid rats for 3 days before death, our previous studies had demonstrated intense staining for TSH in granules inside the rough endoplasmic reticulum. In this study, the radioimmunoassay showed that TSH content rose dramatically in the hypothyroid animals treated with PTU for 77 days and thyroxine for 2 days before death (from 8.5--64.1 mU/mg wet wt); however, the rise in TRH content was minimal (5.8--9.8 pg/mg wet wt). The immunocytochemical stain for TRH correlated well with the RIA showing a weak reaction mainly on small granules in the cytoplasm. No reaction for TRH was found in rough endoplasmic reticulum. These results suggest that TRH and TSH storage sites are dissimilar in the hypothyroid rat. The presence of stain for TRH in granules in the cytoplasm suggests that it might play a role in the storage or packaging of TSH. Its absence in profiles of rough endoplasmic reticulum staining intensely for TSH suggests that it is not synthesized at this site. No definite conclusions about its origin can be drawn at this time.

Animals↗

Influence of thyroxine and n-propylthiouracil on nephro-toxicity of inorganic arsenic in rat.

The effect of hyper or hypoactive thyroid on the renal toxicity of arsenic trioxide has been studied in rats. It was observed that pre-treatment of rats with thyroxine stimulates arsenic excretion in urine. The anti-thyroid drug n-propylthiouracil (PTU), inhibits the accumulation of arsenic in renal tissue. Both treatments affect the renal pathology. Histopathological lesions are less severe in PTU and arsenic-treated rats in comparison to thyroxine and arsenic-treated rats. Ultrastructural studies support light microscopical observations. An adaptive response was noticed against arsenic in PTU pre-treated rats. We attribute this response to decreased glutathione-S-transferase (GSH) activity and increased GSH synthesis in the kidney. A relationship between thyroidal activity and arsenic toxicity is suggested by present observations.

Animals↗

Premature rats treated with propylthiouracil show enhanced pulmonary antioxidant enzyme gene expression and improved survival during prolonged exposure to hyperoxia.

In full-term newborn rats, propylthiouracil (PTU) treatment has been previously shown to decrease susceptibility to O2-induced lung damage and improve survival during hyperoxic exposure. However, no differences were found in lung antioxidant enzyme (AOE) activity responses to hyperoxia compared with O2-exposed untreated (control) term rats. To further explore possible pulmonary protective effects of PTU treatment in prematurely delivered animals, we administered PTU (0.015%) in drinking water to timed-pregnant rats for the final 10 d of gestation prior to delivery 1 d before term, and during lactation; control pregnant/nursing rats received untreated water. Both groups of 21-d premature rat pups were randomized to either > 95% O2 or room air exposure after birth for up to 14 d. The left lungs of 7-d exposure pups were used to quantitate the concentrations of AOE mRNA by solution hybridization; the right lungs of the same pups were assayed for AOE activities. PTU treatment resulted in survival rates of O2-exposed preterm rat pups that were consistently higher at all time periods in hyperoxia including 7 d [PTU, 67 of 82 (82%) versus control pups, 58 of 113 (51%); p < 0.001] and 14 d [PTU, 31 of 39 (79%) versus control, 15 of 66 (23%); p < 0.001]. Further evidence of increased tolerance to > 95% O2 in PTU pups included a significant decrease in the incidence of microscopic intraalveolar edema and a significant increase in lung tissue surfactant-related phospholipids compared with O2-exposed control pups.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

Pre- and postnatal propylthiouracil-induced hypothyroidism impairs synaptic transmission and plasticity in area CA1 of the neonatal rat hippocampus.

Thyroid hormones are essential for neonatal brain development. It is well established that insufficiency of thyroid hormone during critical periods of development can impair cognitive functions. The mechanisms that underlie learning deficits in hypothyroid animals, however, are not well understood. As impairments in synaptic function are likely to contribute to cognitive deficits, the current study tested whether thyroid hormone insufficiency during development would alter quantitative characteristics of synaptic function in the hippocampus. Developing rats were exposed in utero and postnatally to 0, 3, or 10 ppm propylthiouracil (PTU), a thyroid hormone synthesis inhibitor, administered in the drinking water of dams from gestation d 6 until postnatal day (PN) 30. Excitatory postsynaptic potentials and population spikes were recorded from the stratum radiatum and the pyramidal cell layer, respectively, in area CA1 of hippocampal slices from offspring between PN21 and PN30. Baseline synaptic transmission was evaluated by comparing input-output relationships between groups. Paired-pulse facilitation, paired-pulse depression, long-term potentiation, and long-term depression were recorded to examine short- and long-term synaptic plasticity. PTU reduced thyroid hormones, reduced body weight gain, and delayed eye-opening in a dose-dependent manner. Excitatory synaptic transmission was increased by developmental exposure to PTU. Thyroid hormone insufficiency was also dose-dependently associated with a reduction paired-pulse facilitation and long-term potentiation of the excitatory postsynaptic potential and elimination of paired-pulse depression of the population spike. The results indicate that thyroid hormone insufficiency compromises the functional integrity of synaptic communication in area CA1 of developing rat hippocampus and suggest that these changes may contribute to learning deficits associated with developmental hypothyroidism.

Action Potentials↗

The effect of basal hypothalamic isolation on pituitary-thyroid activity and the response to propylthiouracil.

Basal hypothalamic deafferentation extending from the posterior border of the optic chiasm to the mid-mammillary bodies resulted in depression of plasma TSH, thyroxine (T4), and triiodothyronine (T3) concentration to 50% of normal controls within 7 days. Administration of 0.15% propylthiouracil (PTU) in the diet form postoperative day 26 caused a pronounced drop in the plasma T3 level and a rise in plasma TSH level within two days in the control animals, but had little effect during this interval in the deafferented animals. After 12 days of PTU, plasma T3 and T4 concentrations had dropped to undetectable concentrations in the control animals but both were still detectable in the deafferented animals. After 25 days of PTU, plasms T4 and T3 levels were undetectable and plasma TSH levels were significantly elevated above normal in all animals. Thyroid hypertrophy at that time was as great in the deafferented as in the control rats, although plasma TSH concentration was 50% lower in the former. Administration of 0.1 mug/100 g BW TRH iv on postoperative day 37, when plasma T4 and T3 were undetectable in the controls but still present in the deafferented animals, produced an equally high concentration of plasma TSH in all animals. We interpret these data to support the concepts that: 1) a major source of neural drive of that TRH which stimulates the secretion of TSH by the adenohypophysis lies outside the medial basal hypothalamus, 2) a decrease in TRH reaching the adenohypophysis causes a lower setting of the "thyrostat" sensitive to the concentration of circulating thyroid hormone, and 3) increased TSH secretion and resultant goitrogenesis is delayed in animals with impaired TRH secretion because of the slower rate of secretion of thyroid hormone than in intact controls and the longer time thus required to markedly reduce the concentration of circulating thyroid hormone.

Afferent Pathways↗

Growth hormone, somatomedin and cartilage sulfation in failure of catch-up growth after propylthiouracil-induced hypothyroidism in the rat.

Male Long-Evans rats 36 to 39 days of age were fed a diet containing 0.1% propylthiouracil (PTU) for 17 to 20 days followed by the resumption of normal diet. Growth rates of body weight and tail length decreased during PTU treatment and increased during recovery; yet only slight catch-up (compensatory) growth occurred in either body weight or tail length. Although serum thyroxine and triiodothyronine concentrations (radioimmunoassay) decreased significantly during PTU treatment, they returned to normal by recovery day 14. Pituitary immunoassayable growth hormone (GH) content and concentration dropped during PTU-feeding. By recovery day 14 there was significant, but incomplete, repletion of the gland. Serum GH during ether anesthesia was increased significantly during PTU treatment; it remained elevated (NS) and showed greater variability during recovery than in controls. Bioassayable serum somatomedin (Sm) activity decreased during PTU treatment in one of two experiments but returned to a normal level by recovery day 7. The addition of PTU to normal rat serum in concentrations used during PTU treatment failed to alter Sm activity. The addition of L-triiodothyronine and/or L-thyroxine to hypothyroid serum also did not alter Sm activity. In vitro and in vivo cartilage sulfate incorporation decreased during PTU treatment but it rose to greater than control values during the recovery period. The difference in sulfate incorporation between treated and control rats was maintained throughout the observation periods. The results indicate that incomplete catch-up growth following transient hypothyroidism is the result of factors other than deficient GH or Sm production. The implications of the persistent changes in cartilage sulfate metabolism are not clear, but these findings during recovery suggest the possibility that a disturbance of intrinsic cartilage function is a limiting factor preventing full catch-up growth after PTU-induced hypothyroidism.

Animals↗

Selective inhibition of the secretion of triiodothyronines from the perfused canine thyroid by propylthiouracil.

In order to assess a possible influence on the relative proportions of T4, T3, and rT3 in thyroid effluent, the thyroid-blocking agents, propylthiouracil (PTU) and methylmercaptoimidazol (MMI), were administered to perfused canine thyroids. The dog has two distinct thyroid lobes which were both perfused independently, one acting as a control for the other. T4, T3, and rT3 in thyroid effluents and thyroid hydrolysates were measured radioimmunologically. During control perfusion the T4:T3 and T4:rT3 ratios in thyroid effluent were considerably lower than in thyroid hydrolysates [t4:t3 (wt/wt), 6.1 +/- 2.0 vs. 12.8 +/- 4.4; T4:rT3, 23.0 +/- 5.9 vs. 69.7 +/- 29.1; mean +/- SD; n = 8; P less than 0.001], i.e. T3 and rT3 were secreted preferentially to T4. Infusion of PTU (1 mmol/liter) induced a gradual increase in both the T4:T3 and T4:rT3 ratios in thyroid effluent. The variation in the T4:rT3 ratio appeared somewhat earlier than that in the T4:T3 ratio. Both ratios eventually approached the ratios in thyroid hydrolysates. The change in ratios was caused by a PTU-induced decrease in the release of T3 and rT3 while the release of T4 was practically unaffected. In contradistinction, infusion of MMI did not affect the T4:T3 or T4:rT3 ratios in thyroid effluent. As PTU but not MMI inhibits T4 deiodination in peripheral tissues, the results of the present study suggest that part of the T3 and rT3 secreted from the thyroid stems from T4 deiodinated during the secretion by a mechanism similar to the T4-deiodinating processes in peripheral tissues.

Animals↗