A case of the syndrome of inappropriate secretion of TSH.

A girl aged 4 years with goiter and accelerated physical and skeletal growth was found to be hyperthyroid on the basis of elevated serum thyroid hormone level, nevertheless both the basal TSH and TSH responsiveness to TRH were maintained within the normal range. Serum TSH was suppressed by exogenous T3 and dexamethasone administration, but not significantly changed after propylthiouracil (PTU) treatment. The diurnal rhythmicity of anterior pituitary hormones was preserved with the high nocturnal peak of TSH and prolactin. Clinically, neither thyrotoxic signs nor evidences of pituitary tumor were observed. Her accelerated growth and elevated thyroid hormone level appeared to be induced by inappropriate secretion of TSH. In view of the literature, this is the first case of the syndrome of inappropriate secretion of TSH excluding the neoplastic origin in Japan.     

Effect of long-term injection of high doses of potassium iodide on iodine metabolism in rat thyroid gland

Concentration of thyroid hormones in the serum of the rats after 14-day injections of potassium iodide (1, 3, 10, 100, and 500 physiological daily doses) did not differ from the control values. Excessive administration of potassium iodide increased the total iodide content in the rat thyroid tissue by 60–121% (35–108% and 94–128% for the protein-bound and free iodide, respectively), indicating the activation of the uptake and organification of iodide. The long-term injection of both low and high doses of potassium iodide increased the activity of catalase by 8–18% and SOD by 33–50% and enhanced the level of toxic LPO products reacting with thiobarbituric acid by 15–38%. It is suggested that reactive oxygen species and the excessive iodination of proteins (particularly thyroglobulin) induced by the long-term administration of high doses of potassium iodide can play an important role in the development of thyroid dysfunctions and autoimmune diseases.     

Modulation of rat liver mitochondrial antioxidant defence system by thyroid hormone

In the present study the effect of thyroid hormone (T(3)) on oxidative stress parameters of mitochondria of rat liver is reported. Hypothyroidism is induced in male adult rats by giving 0.05% propylthiouracil (PTU) in drinking water for 30 days and in order to know the effect of thyroid hormone, PTU-treated rats were injected with 20 microg T(3)/100 g body weight/day for 3 days. The results of the present study indicate that administration of T(3) to hypothyroid (PTU-treated) rats resulted in significant augmentation of oxidative stress parameters such as thiobarbituric acid reactive substances and protein carbonyl content of mitochondria in comparison to its control and euthyroid rats. The hydrogen peroxide content of the mitochondria of liver increased in hypothyroid rats and was brought to a normal level by T(3) treatment. Induction of hypothyroidism by PTU treatment to rats also resulted in the augmentation of total and CN-sensitive superoxide dismutase (SOD) activities of the mitochondria, which was reduced when hypothyroid rats were challenged with T(3). Although CN-resistant SOD activity of the mitochondria remained unaltered in response to hypothyroidism induced by PTU treatment, its activity decreased when hypothyroid rats were injected with T(3). The catalase activity of the mitochondria decreased significantly by PTU treatment and was restored to normal when PTU-treated rats were given T(3). Total, Se-independent and Se-dependent glutathione peroxidase activities of the mitochondria were increased following PTU treatment and reduced when T(3) was administered to PTU-treated rats. The reduced and oxidised glutathione contents of the mitochondria of liver increased significantly in hypothyroid rats and their level was restored to normal when hypothyroid rats were injected with T(3). The results of the present study suggest that the mitochondrial antioxidant defence system is considerably influenced by the thyroid states of the body.     

Hypothyroidism in the fetal and neonatal rat does not impair the insulin secretory response to glucose

Fetal and neonatal hypothyroidism was induced by treating pregnant rats with propylthiouracil (PTU) in the drinking water from day 12 of gestation to day 7 postnatally. The serum levels of thyroxine and triiodothyronine were lowered in both mother and offspring and the neonates showed a 20% reduction in weight gain. An i.p. glucose tolerance test on the 7-day old neonates revealed no major disturbances in glucose tolerance or insulin response. The data suggest that thyroid hormones are not essential for the neonatal development of the B-cell secretory response to glucose.     

Acidic fibroblast growth factor modulates gene expression in the rat thyroid in vivo.

We have recently demonstrated that the iv administration of acidic fibroblast growth factor (a-FGF) to rats for 6 days results in a marked increase in thyroid weight with colloid accumulation and flat, quiescent follicular cells. Whereas a-FGF administration consistently increases thyroid weight, there are only minor alterations in serum TSH and thyroid hormones, and no change in intrathyroidal metabolism of 125I metabolism. In the present work, we studied the effects of 1 or 6 daily injections of a-FGF (60 micrograms/kg BW) or vehicle on the mRNA levels for histone, c-fos, actin, type I 5' deiodinase (5'D-I), thyroid peroxidase, and thyroglobulin and cathepsin D in the thyroid, liver and bone. Rats were sacrificed 0.5, 2, 4, 8 and 24 h after the 1st or the 6th a-FGF injection and thyroid, liver, and calvarium were removed. The relative amounts of mRNAs were determined by slot blot analysis. There was a 43% increase in thyroid weight in rats treated with a-FGF for 6 days compared to vehicle-treated rats. We observed an increase in c-fos mRNA content in the thyroid gland 0.5 to 4 h after 1 or 6 injections of a-FGF. In contrast, treatment with a-FGF for 1 or 6 days did not affect histone mRNA content, a marker of proliferative activity or actin mRNA levels. Treatment with a-FGF caused a marked decrease in thyroid 5' D-I mRNA content in the thyroid. The decrease was present 2 h after the first injection and reached a nadir 8 h later.(ABSTRACT TRUNCATED AT 250 WORDS)     

Therapeutic Potential of Date Palm Pollen for Testicular Dysfunction Induced by Thyroid Disorders in Male Rats

Hyper- or hypothyroidism can impair testicular function leading to infertility. The present study was designed to examine the protective effect of date palm pollen (DPP) extract on thyroid disorder-induced testicular dysfunction. Rats were divided into six groups. Group I was normal control. Group II received oral DPP extract (150 mg kg^-1), group III (hyperthyroid group) received intraperitoneal injection of L-thyroxine (L-T4, 300μg kg^-1; i.p.), group IV received L-T4 plus DPP extract, group V (hypothyroid group) received propylthiouracil (PTU, 10 mg kg^-1; i.p.) and group VI received PTU plus DPP extract. All treatments were given every day for 56 days. L-T4 or PTU lowered genital sex organs weight, sperm count and motility, serum levels of luteinizing hormone (LH), follicle stimulating hormone (FSH) and testosterone (T), testicular function markers and activities of testicular 3β-hydroxysteroid dehydrogenase (3β-HSD) and 17β-hydroxysteroid dehydrogenase (17β-HSD). Moreover, L-T4 or PTU increased estradiol (E2) serum level, testicular oxidative stress, DNA damage and apoptotic markers. Morphometric and histopathologic studies backed these observations. Treatment with DPP extract prevented LT4- or PTU induced changes. In addition, supplementation of DPP extract to normal rats augmented sperm count and motility, serum levels of LH, T and E2 paralleled with increased activities of 3β-HSD and 17β-HSD as well as testicular antioxidant status. These results provide evidence that DPP extract may have potential protective effects on testicular dysfunction induced by altered thyroid hormones.     

Lowering of T3 and rise in reverse T3 induced by hyperglucagonemia: altered thyroid hormone metabolism, not altered release of thyroid hormones

Recently we reported that hyperglucagonemia induced by glucagon infusion causes a decline in serum T3 and a rise in reverse T3 in euthyroid healthy volunteers. These changes in T3 and rT3 levels were attributed to altered T4 metabolism in peripheral tissues. However, the contribution of altered release of thyroid hormones by the thyroid gland could not be excluded. Since the release of thyroid hormones is inhibited in primary hypothyroidism and is almost totally suppressed following L-thyroxine replacement therapy, we studied thyroid hormone levels for up to 6 hours after intravenous administration of glucagon in subjects with primary hypothyroidism who were rendered euthyroid by appropriate L-thyroxine replacement therapy for several years. A control study was conducted using normal saline infusion. Plasma glucose rose promptly following glucagon administration demonstrating its physiologic effect. Serum T4, Free T4, and T3 resin uptake were not altered during both studies. Glucagon infusion induced a significant decline in serum T3 (P less than 0.05) and a marked rise in rT3 (P less than 0.05) whereas saline administration caused no alterations in T3 or rT3 levels. Thus the changes in T3 and rT3 were significantly different during glucagon study when compared to saline infusion. (P less than 0.01 for both comparisons). Since, the release of thyroid hormones is suppressed by exogenous LT4 administration in these subjects; we conclude that changes in serum T3 and rT3 observed following glucagon administration reflect altered thyroid hormone metabolism in peripheral tissues and not altered release by the thyroid gland.     

The possible role of L-carnitine on the skeletal muscle of ovariectomized rats

Low muscle strength is observed during the peri-and postmenopausal periods, when the secretion of ovarian hormones is drastically reduced. It is also a predictive of adverse health events as well as incident mobility limitation and disability. The objective of the present study is to study the biochemical and the histological changes in the skeletal muscle of premature menopause-induced rats and the possible protective role of L-carnitine. Ovariectomized (OVX) rats were gavaged with L-carnitine (100 mg/kg) daily for 60 days starting from the second post-operative day. Serum levels of estradiol and markers of skeletal muscle damage (creatine kinase and lactic dehydrogenase activities) were determined. Light and electron microscopic study of the quadriceps femoris muscle (QFM) specimens were done. OVX rats showed significant decrease in the serum estradiol level with significant increase the markers for skeletal muscle damage. Histopathological examination of the QFM showed degenerated myofibers, apoptotic changes and compensatory hypertrophy. Degenerated mitochondria, multiple lysosomes and lipid droplets among the damaged myofibrils were also noticed. L-carnitine administration to the OVX rats resulted in non-significant change in the serum estradiol level with significant attenuation of skeletal muscle damage either biochemically or histopathologically. In conclusion, L-carnitine administration recovered muscle degeneration after ovariectomy. This finding suggested that L-carnitine could be recommended in the management of post-menopausal myopathy.     

Therapeutic exploration of betulinic acid in chemically induced hypothyroidism

Hypothyroidism is a chronic condition characterized by abnormally low thyroid hormone production. The decreased serum level (>5.1 mIU/l) of thyroid-stimulating hormone (TSH) in blood indicates hypothyroidism. The study was an attempt to access the effect of betulinic acid on chemically induced hypothyroidism in female albino rats. Betulinic acid is a naturally occurring pentacyclic triterpenoid, which has antiretroviral, antimalarial, and anti-inflammatory properties, as well as anticancer potential, by inhibiting topoisomerase. Hypothyroidism was induced in female albino rats using propylthiouracil (PTU) at a dose of 60 μg/kg body weight orally for 1 month. Induction of hypothyroidism was confirmed by increased TSH level. At the end of second month, blood was collected, centrifuged and serum was analyzed for TSH, T3, and T4 level and protocol was terminated by killing of animals. The animals exposed to PTU were treated with pure standard drug thyroxine at a dose of 10 μg/kg of body weight by oral route and the test drug betulinic acid 20 mg/kg by oral route through force feeding in their respective groups. Treatment was carried out for a period of 2 months. Group with PTU-induced hypothyroidism showed an elevation in serum TSH and reduction level, which was restored by the betulinic acid in treated female albino rats. Betulinic acid also reduced the damage caused in the thyroid tissues by PTU, thus minimizing the symptoms of hypothyroidism. Histopathological examinations of the thyroid tissue showed changes in the thyrocytes of PTU-treated group while thyroxine group showed normal thyroid follicles cell architecture and the group treated with betulinic acid also showed marked improvement in the follicles integrity which shows that betulinic acid has some protective activity. This study shows that the betulinic acid has thyroid-enhancing potential by lowering down the TSH levels and reducing the damage caused in the thyroid tissues, thus minimizing the symptoms of hypothyroidism when used anaphylactically in rats.     

Decline of T3 and elevation in reverse T3 induced by hyperglucagonemia: changes in thyroid hormone metabolism, not altered release of thyroid hormones

Recently we reported that hyperglucagonemia induced by glucagon infusion causes a decline in serum Triiodothyronine (T3) and a rise in reverse T3 (rT3) in euthyroid healthy volunteers. These changes in T3 and rT3 levels were attributed to altered T4 metabolism in peripheral tissues. However, the contribution of altered release of thyroid hormones by the thyroid gland could not be excluded. Since the release of thyroid hormones is suppressed by exogenous administration of L-thyroxine (L-T4) in appropriate dosage, we studied thyroid hormone levels for up to 6 hours after intravenous administration of glucagon in euthyroid healthy subjects after administration of L-T4 for 12 weeks. A control study was conducted using normal saline infusion. Plasma glucose rose promptly following glucagon administration demonstrating its physiologic effect. Serum T4, Free T4 and T3 resin uptake were not altered during both studies. Glucagon infusion induced a significant decline in serum T3 (P less than 0.01) and a marked rise in rT3 (P less than 0.01) whereas saline administration caused no alterations in T3 or rT3 levels. Thus the changes in T3 and rT3 were significantly different during glucagon study when compared to saline infusion. (P less than 0.01 for both comparisons). Therefore, this study demonstrates that changes in serum T3 and rT3 caused by hyperglucagonemia may be secondary to altered thyroid hormone metabolism in peripheral tissues and not due to altered release by the thyroid gland, since the release of thyroid hormones is suppressed by exogenous L-T4 administration.     

Comparison of potential protective effects of melatonin, indole-3-propionic acid, and propylthiouracil against lipid peroxidation caused by potassium bromate in the thyroid gland

Potassium bromate (KBrO3) is a prooxidant and carcinogen, inducing thyroid tumors. Melatonin and indole-3-propionic acid (IPA) are effective antioxidants. Some antioxidative effects of propylthiouracil (PTU)--a thyrostatic drug--have been found. The aim of the study was to compare protective effects of melatonin, IPA, and PTU against lipid peroxidation in the thyroids, collected from rats treated with KBrO3, and in homogenates of porcine thyroids, incubated in the presence of KBrO3. Wistar rats were administered KBrO3 (110 mg/kg b.w., i.p., on the 10th day of the experiment) and/or melatonin, or IPA (0.0645 mmol/kg b.w., i.p., twice daily, for 10 days), or PTU (0.025% solution in drinking water, for 10 days). Homogenates of porcine thyroids were incubated for 30 min in the presence of KBrO3 (5 mM) plus one of the antioxidants: melatonin (0.01, 0.1, 0.5, 1.0, 5.0, 7.5 mM), or IPA (0.01, 0.1, 0.5, 1.0, 5.0, 7.5, 10.0 mM), or PTU (0.01, 0.1, 0.5, 1.0, 5.0, 7.5, 10.0 mM). The level of lipid peroxidation products (MDA + 4-HDA) was measured spectrophotometrically in thyroid homogenates. In vivo pretreatment with either melatonin or with IPA or with PTU decreased lipid peroxidation caused by KBrO3--injections in rat thyroid gland. Under in vitro conditions, PTU (5.0, 7.5, and 10.0 mM), but neither melatonin nor IPA, reduced KBrO3-related lipid peroxidation in the homogenates of porcine thyroids. In conclusion, melatonin and IPA may be of great value as protective agents under conditions of exposure to KBrO3.     

Nonresponsiveness of the thyroid gland to goitrogen in the early neonatal period in the rat: light- and electron-microscopic observations.

The thyroid response of fetal and neonatal rats to propylthiouracil (PTU) as a goitrogen was studied with observation of the thyroid glands by light and electron microscopy. On day 19 of gestation and on days 1, 3, 5 and 8 after birth, fetal and neonatal rats were given a subcutaneous injection of PTU and were autopsied 2 days later. PTU induced conspicuous goiters in fetal rats but did not in neonatal rats aged up to day 5 after birth. Beyond that age, PTU again induced goiters. Histologically, the follicular cell height in goitrous thyroid glands was significantly increased. Ultrastructurally, follicular cells in goitrous thyroid glands often had colloid droplets and lysosomes. It seems that nonresponsiveness of the thyroid glands in early neonatal rats to goitrogen is due to a temporary decline of the pituitary activity of thyrotropin secretion. About 5 days or more after birth, the pituitary-thyroid system begins to operate again in response to goitrogen.     

The effect of manganese supply on thyroid hormone metabolism in the offspring of manganese-depleted dams

The present study was performed to investigate the effect of manganese (Mn) supply on metabolism of thyroid hormones in the rat. A study with rats was carried out over two generations. Female rats were raised with a Mn-deficient diet (0.1 mg Mn/kg), and mated to produce a second generation. The male rats of the second generation were used as subjects for the investigation. They were divided into five groups and fed diets with Mn concentrations of 0.1, 0.5, 2.2, 10, and 46 mg/kg for 40 d. For assessment of thyroid hormone metabolism, concentrations of thyroid hormones in serum and activity of hepatic type I 5′ deiodinase (5′ D-I) were measured. Feeding diets with 0.1 mg Mn/kg impaired growth and food conversion, influenced parameters of thyroid hormone metabolism, and changed some clinical-chemical parameters, such as concentrations of total protein, albumin, calcium (Ca) and magnesium (Mg) as well as activity of alkaline phosphatase in serum. Regarding the thyroid hormone metabolism, rats fed the diet with a Mn level of 0.1 mg/kg had a higher 5′D-I activity in liver, and consequently a higher concentration of triiodothyronine in serum than the rats fed the other diets. In contrast, the concentrations of total and free thyroxine were not influenced by the Mn intake. Growth, clinical-chemical parameters, concentrations of thyroid hormones in serum, and activity of hepatic 5′ D-I were similar in the rats fed diets with Mn concentrations between 0.5 and 46 mg/kg. The present study shows that feeding a diet with a very low Mn concentration affects growth and thyroid hormone metabolism and that a dietary level of 0.5 mg Mn/kg is adequate for growth and thyroid hormone metabolism in the off-spring of Mn-depleted dams.     

Effects of thyroid state on AMP-activated protein kinase and acetyl-CoA carboxylase expression in muscle.

AMP-activated protein kinase (AMPK) consists of three subunits: alpha, beta, and gamma. Two isoforms exist for the alpha-subunit (alpha(1) and alpha(2)), two for the beta-subunit (beta(1) and beta(2)), and three for the gamma-subunit (gamma(1), gamma(2), and gamma(3)). Although the specific roles of the beta- and gamma-subunits are not well understood, the alpha-subunit isoforms contain the catalytic site and also the phosphorylation/activation site for the upstream kinase. This study was designed to determine the role of thyroid hormones in controlling expression levels of these AMPK subunits and of one downstream target, acetyl-CoA carboxylase (ACC), in muscle. AMPK subunit and ACC levels were determined by Western blots in control rats, in rats given 0.01% propylthiouracil (PTU) in drinking water for 3 wk, and in rats given 3 mg of thyroxine and 1 mg of triiodothyronine per kilogram chow for 1 or 3 wk. In gastrocnemius muscle, all isoforms of AMPK subunits were significantly increased in rats given thyroid hormones for 3 wk vs. those treated with PTU. Similar patterns were seen in individual muscle types. Expression of muscle ACC was also significantly increased in response to 3 wk of treatment with excess thyroid hormones. Muscle content of malonyl-CoA was elevated in PTU-treated rats and depressed in thyroid hormone-treated rats. These data provide evidence that skeletal muscle AMPK subunit and ACC expression is partially under the control of thyroid hormones.     

Effects of thyroid hormones on the evolution of monoamine oxidase activity in the brain and heart of the developing rat

The evolution of monoamine oxidase (MAO) activity towards tryptamine has been studied from birth to 20 days post-natal in the brain and heart of male rats. Hyperthyroidism was induced by thyroxine injections and hypothyroidism by PTU administration. The results are expressed per unit of fresh weight and per unit of protein weight. Cardiac MAO is higher in the hyperthyroid animals than in controls as soon as 5 days following birth; the difference between the 2 groups increases until 20 days. The deficiency in thyroid hormones, on the other hand, was followed by a slight decrease in the cardiac enzyme, this decrease reflecting the general deficit in protein synthesis. Brain MAO is not affected by hyperthyroidism, but a clear deficit follows PTU administration. This deficit is significant beginning at 10 days and the difference between the 2 groups increases up to 20 days. The effects of PTU-induced hypothyroidism can be corrected by thyroxine injections. Except for the decrease in the level of cardiac enzyme in hypothyroid animals, all the effects on MAO activity are independent of the total protein content of both organs.     

Thyroid Hormone Influences Antioxidant Defense System in Adult Rat Brain

The objective of the current study was to find out whether thyroid hormone influences antioxidant defense parameters of rat brain. Several oxidative stress and antioxidant defense parameters of mitochondrial (MF) and post-mitochondrial (PMF) fractions of cerebral cortex (CC) of adult rats were compared among euthyroid (control), hypothyroid [6-n-propylthiouracil (PTU)-challenged], and hyperthyroid (T3-treatment to PTU-challenged rats) states. Oxidative stress parameters, such as thiobarbituric acid-reactive substances (TBA-RS) and protein carbonyl content (PC), in MF declined following PTU challenge in comparison to euthyroid rats. On the other hand, when PTU-challenged rats were treated with T3, a significant increase in the level of oxidative stress parameters in MF was recorded. Hydrogen peroxide content of MF as well as PMF of CC was elevated by PTU-challenge and brought to normal level by subsequent treatment of T3. Although mitochondrial glutathione (reduced or oxidized) status did not change following PTU challenge, a significant reduction in oxidized glutathione (GSSG) level was noticed in PMF following the treatment. T3 administration to PTU-challenged rats had no effect on mitochondrial glutathione status. Total and CN-resistant superoxide dismutase (SOD) activities in MF of CC augmented following PTU challenge. CN-resistant SOD activity did not change when PTU-challenged rats were treated with T3. Although CN-sensitive SOD activity of PMF remained unaltered in response to PTU challenge, its activity increased when PTU-challenged rats were treated with T3. Catalase activity in PMF of CC of PTU-challenged rats increased, whereas the activity was decreased when hypothyroid rats were treated with T3. Similarly, total and Se-dependent glutathione peroxidase (GPx) activities of MF increased following PTU challenge and reduced following administration of T3. Se-independent GPx activity of MF and PMF and glutathione reductase activity of PMF decreased following PTU challenge and did not change further when rats were treated with T3. On the other hand, glutathione S-transferase activity of MF and PMF of CC did not change following PTU challenge but decreased below detectable level following T3 treatment. Results of the current investigation suggest that antioxidant defense parameters of adult rat brain are considerably influenced by thyroid states of the body.     

Thyroid Hormones affect the Level and Activity of Nitric Oxide Synthase in Rat Cerebral Cortex during Postnatal Development

The effects of thyroid hormones (TH) on the enzyme level and activity of neuronal nitric oxide synthase (nNOS) were studied in the rat cerebral cortex during postnatal life. As revealed by arginine/citrulline conversion assay and Western blot analysis of the homogenate of the parietal cortex T4 significantly increased nNOS activity and nNOS protein level to 153 ± 25% and to 178 ± 20%, respectively. In contrast, 6-n-propyl-2-thyouracil (PTU) decreased nNOS activity and nNOS level to 45 ± 10% and to 19 ± 4%, respectively. The number of nNOS-immunoreactive neurons did not change after either T4 or PTU treatment, however, following T4 administration the percentage of intensively immunoreactive neurons increased to 85 ± 3% compared to control (65 ± 6%), whereas it decreased to 49 ± 2% after PTU treatment. Our findings indicate that abnormal TH levels differentially regulate the activity and the level of nNOS and suggest a cross-talk between the TH and NO signaling pathway in the developing cerebral cortex of rats.     

Effects of thyroid deficiency on the vasopressin receptors in the kidney of developing and adult rats. A comparative study of hormonal binding and adenylate cyclase activation

The effects of propylthiouracil (PTU) treatment on renal vasopressin sensitive adenylate cyclase in young and adult rats were studied by measuring the binding of tritiated vasopressin and adenylate cyclase activation by vasopressin in kidney medulla plasma membranes. Thyroxine therapy completely corrected the effects of PTU treatment on the vasopressin-adenylate cyclase system. Thus, the abnormalities observed after a such treatment are directly related to thyroid deficiency and not to toxic effects of PTU. The inability of the kidney to normally concentrate urine in developing and adult animals with induced hypothyroidism was mainly related to the reduction of the number of binding sites without significant changes in the basal and guanylyl-imidodiphosphate (Gpp(NH)p)-stimulated adenylate cyclase activities, the apparent dissociation constant (Kbind) of labeled vasopressin from its specific receptor and the apparent activation constant (Kact) of vasopressin for adenylate cyclase. These results also show that thyroid deficiency has more effect on the ontogenesis of receptors than on their turnover, and demonstrate that a normal antidiuretic response occurs at very low receptor occupancy. Since, on the one hand, the hypothyroidism-induced abnormalities in renal medulla responsiveness to vasopressin were reversible and, on the other, only a permanent therapy consisting of two daily physiological doses of thyroxine from birth to the age of sacrifice fully restored them, the responsiveness of developing kidney to thyroid hormones appears to be fundamentally different from that of the CNS.     

有机磷阻燃剂TDCIPP对雌性大鼠甲状腺的潜在毒性作用

目的: 研究磷酸三(1, 3-二氯-2-丙基)酯(TDCIPP)对雌性大鼠甲状腺系统的潜在毒性作用及机制。方法: 将32只离乳3周的雌性SD大鼠随机分为对照组(玉米油灌胃)及TDCIPP低、中、高剂量组(50、100、250 mg/kg·d,溶于玉米油)(n=8),灌胃给药21 d,每天1次。于末次给药后处死动物,取血和甲状腺、肝脏,检测血清中促甲状腺激素(TSH)、三碘甲腺原氨酸(T3), 甲状腺素(T4)和游离甲状腺素(FT4)水平变化;组织切片(HE染色)用于检测甲状腺形态学病变;RT-PCR技术与Western blot技术检测与甲状腺功能相关的基因和蛋白表达的变化。结果: 与对照组比较,TDCIPP染毒后大鼠甲状腺出现滤泡排列不规则、胶质变少、滤泡增生、肥大等现象,TDCIPP低剂量组的血清TSH水平和高剂量组的T3水平均显著升高(P＜0.05),低剂量组促甲状腺激素受体(TSHR)mRNA表达和中、高剂量组甲状腺激素受体β(TRβ)蛋白表达均显著降低(P＜0.05,P＜0.01),中、高剂量组甲状腺过氧化物酶(TPO)mRNA表达显著增高(P＜0.05,P＜0.01),三个剂量组尿苷二磷酸葡萄糖醛酸转移酶(UGTs)、细胞色素氧化酶-3A1(CYP3A1)蛋白表达水平显著上调(P＜0.05)。结论: 大鼠暴露在50 mg/(kg·d)以上剂量的TDCIPP,即可以刺激甲状腺组织的增生,改变血清中甲状腺素的水平,干扰甲状腺的功能,表现出对甲状腺的毒性作用。