The effects of selenium depletion and repletion on the metabolism of thyroid hormones in the rat

Rats were fed selenium-deficient (less than 0.005 mg selenium/kg) or selenium-supplemented diets (0.1 mg selenium/kg, as Na2SeO2) for up to five wks from weaning to assess the effects of developing selenium deficiency on the metabolism of thyroid hormones. Within two wks 3:5,3'-triiodothyronine (T3) production from thyroxine (T4) in liver homogenates from selenium-deficient rats was significantly lower compared with the activity in liver homogenates from selenium-supplemented rats. This decreased activity was probably responsible, in part, for the higher T4 and lower T3 concentrations in plasma from the selenium-deficient rats after 3, 4, and 5 weeks of experiment. Repletion of selenium-deficient rats with single intra-peritoneal injections of 200 micrograms selenium/kg body wt. (as Na2SeO3) 5 days before sampling reversed the effects of the deficiency on thyroid hormone metabolism and significantly increased liver and plasma glutathione peroxidase activities. However a dose of 10 micrograms selenium/kg body wt given to rats of similar low selenium status had no effect on thyroid hormone metabolism or glutathione peroxidase activity but did reverse the increase in hepatic glutathione S-transferase activity characteristic of severe selenium deficiency. Imbalances in thyroid hormone metabolism are an early consequence of selenium deficiency and are probably not related to changes in hepatic xenobiotic metabolizing enzymes associated with severe deficiency.     

Experimental acute poisoning in mice induced by emestrin,a new mycotoxin isolated from Emericella species

The effects of emestrin (EMS), a secondary metabolite of the Emericella species, on male ICR mice were examined. The intraperitoneal LD₅₀ values of EMS were 17.7 and 13.0 mg/kg at 24 and 48 hr, respectively. The target organs of EMS were the heart, liver and thymus. In doses over 30 mg/kg the experimental animals died from cardiac failure shortly after the injections. Several survivors that were given EMS in doses under 20 mg/kg showed severe centrilobular necrosis in the liver at 24 hr. Marked degeneration of mitochondria was seen in electron micrographs of both cardiac muscle cells and hepatocytes. In the degenerated hepatocytes, prominent proliferation of RER, membrane-limited inclusions containing both ribosome-like granules and RER, and fenestrated lamella-like structures were observed. Massive necrosis of lymphocytes was always observed in the cortical layer of the thymus of the survivors within 24 hr, while bilateral adrenalectomized mice showed no discernible pathomorphological changes in the lymphoid tissues. Pretreatment of mice with diethyl maleate increased the incidence and severity of hepatic necrosis, whereas that with either cysteine or CoCl₂ reduced the severity of centrilobular necrosis of the liver. Pretreatment with phenobarbital had no significant effect on EMS-induced hepatic lesions.     

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.     

Iodine Excess Induces Hepatic Steatosis Through Disturbance of Thyroid Hormone Metabolism Involving Oxidative Stress in BaLB/c Mice

Iodine excess is emerging as a new focus. A better understanding of its hazardous effects on the liver will be of great benefit to health. The aim of this study is to illustrate the effects of iodine excess on hepatic lipid homeostasis and explore its possible mechanisms. One hundred twenty BaLB/c mice were given iodine at different levels (0, 0.3, 0.6, 1.2, 2.4, and 4.8 mg I/L) in drinking water for 1 or 3 months. Lipid parameters and serum thyroid hormones were measured. Hepatic type 1 deiodinase activity and oxidative stress parameters were evaluated. The mRNA expression of sterol regulatory element-binding protein-1c (SREBP-1c) and fatty acid synthase (FAS) was detected by real-time polymerase chain reaction. Dose-dependent increase of hepatic triglyceride content was detected (r?=?0.680, P?<?0.01) in iodine-loaded groups. Evident hepatic steatosis was observed in 2.4 and 4.8 mg I/L iodine-loaded groups. The activities of antioxidant enzymes (glutathione peroxidase and superoxide dismutase) were decreased, and the malondialdehyde level was increased by excessive iodine in both serum and liver in a dose-dependent manner, accompanying the decrease of hepatic D1 activity. That resulted in the increase of serum total thyroxine and the decrease of serum total triiodothyronine in iodine-loaded groups. The mRNA expression of SREBP-1c and FAS was increased in iodine-loaded groups in response to the change of serum triiodothyronine. Present findings demonstrated that iodine excess could dose dependently induce hepatic steatosis. Furthermore, our data suggested that the disturbance of thyroid hormone metabolism involving oxidative stress may play a critical role in iodine excess-induced hepatic steatosis.     

Effect of acetaminophen on hepatic content and biliary efflux of glutathione disulfide in mice

The increased expiration of ethane and pentane by mice treated with hepatotoxic doses of acetaminophen suggests the possibility of oxidant mechanisms associated with the necrosis. However, studies in rats are not consistent with oxidant stress mechanisms causing the damage, because acetaminophen given to rats does not increase GSSG efflux, a sensitive index of intrahepatic oxidant stress. To compare the extent of oxidant stress generated by acetaminophen in mice versus rats, hepatic content and biliary efflux of GSSG and GSH in mice have been examined. Bile was collected from anesthetized male ICR mice before and after intraperitoneal administration of acetaminophen (325 mg/kg, 2.15 mmol/kg), t-butyl hydroperoxide (TBHP) (1.5 mmol/kg), diethyl maleate (400 mg/kg, 2.33 mmol/kg, in corn oil) or saline (control) and GSH and GSSG were measured by the enzymatic recycling method of Tietze. An increase in biliary GSSG efflux was produced by t-butyl hydroperoxide, but not by the other agents. Biliary GSH/GSSG ratios decreased in acetaminophen-treated animals, presumably reflecting the marked depletion of hepatic GSH, since a similar decrease was observed with non-hepatotoxic doses of diethyl maleate. The failure of acetaminophen to increase the hepatic content or biliary efflux of GSSG in ICR mice is not consistent with the view that oxidant stress mechanisms cause the damage, despite the increases in alkanes expired after acetaminophen administration in this specific animal model.     

Immunohistochemical demonstration of decreased L-pyruvate kinase in enzyme altered rat liver lesions produced by different carcinogens

Preneoplastic liver lesions were produced in female Wistar rats by application of 25 mg/kg N-nitrosomorpholine (NNM), 14 mg/kg diethylnitrosamine (DENA), 0.075 mg/kg aflatoxin B1 (AFB1) or 160 mg/kg safrole. These carcinogens were administered in two equal doses 12 and 24 h after partial hepatectomy. The animals then received sodium phenobarbital (0.1% in tap water) for up to 410 days. Numerous altered hepatic foci (AHF) and hyperplastic nodules (HN) were detected enzyme histochemically by their negative ATPase reaction after application of AFB1, DENA and NNM; some AHF and HN were also caused by the weak carcinogen safrole. Immunohistochemically these lesions were also L-pyruvate kinase (L-PK)-negative with a high coincidence with regard to their number and area. These results confirm the role of L-PK, an enzyme affecting the pentose phosphate pathway, as a negative marker of preneoplastic liver lesions.     

N-acetil-l-cysteine and 2-amino-2-thiiazoline N-acetyl-l-cysteinate as a possible cancer chemopreventive agents in murine models

The aim of this study was to investigate N-acetyl-cysteine (NAC) and its 2-amino-2-thiazoline salt (NACAT) as potential chemopreventive agents on experimentally induced lung tumours by urethane (U) in mice. Female BALB/c mice were used. U was given by intraperitoneal injections during 2 weeks (single dose - 10 mg/mouse, total - 50 mg/mouse). Mice were treated daily per os with NAC 1/10 LD50, NACAT 1/10 or 1/100 LD50 starting 2 weeks prior U administration, then during U treatment and thereafter for 2 months. The duration of experiment was 4 months. The results showed that NAC (1000 mg/kg) reduced the lung tumour incidence to 30% that of controls, P < or = 0.05. Most effective of NACAT was 100 mg/kg dose; it reduced an average of lung adenomas per mouse by 26%, P < or = 0.05, but lower dose (10 mg/kg) was less effective. In order to achieve similar chemopreventive effect (approximately 30%) on mice, it is necessary to use 0.38 mM/kg of NACAT or 6.13 mM/kg of NAC. It means that 16 times less of NACAT is required, if calculated by molar concentration. In general, NAC and NACAT have a moderate chemopreventive effect on lung tumorigenesis induced by urethane in mice.     

Mutagenicity evaluation of HC Blue No. 1 and HC Blue No. 2, I. Effect on the induction of micronuclei in mouse bone marrow cells

Two hair-dye chemicals, HC Blue No. 1 and HC Blue No. 2, were assessed for the ability to produce chromosome breakage and/or spindle malformation in vivo by evaluating the capacity of these compounds to induce micronuclei in polychromatic erythrocytes of mouse bone marrow. Initial studies were conducted in ICR male and female mice given a single intraperitoneal dose of 1000, 500 or 250 mg/kg body weight and examined for micronucleus induction 24 or 48 h later. Activity was observed in female mice given 1000 mg/kg of HC Blue No. 1 at the 24-h harvest time. A questionable response was noted with HC Blue No. 2 in males at the 1000 mg/kg, 24-h time point. No activity was observed in either sex at the 48-h harvest time. In a second set of studies, mice from two strains, ICR and CD-1, were administered a single intraperitoneal dose of 1000 mg/kg of each chemical and the bone marrow was extracted 24 h later. In these experiments, HC Blue No. 1 again produced a statistically significant elevation of micronuclei in female ICR mice. No significant effect was observed in CD-1 mice of either sex. HC Blue No. 2 did not produce any significant elevation of micronuclei in either sex of ICR or CD-1 mice.     

Development and inducibility of the hepatic and renal hippurate-synthesizing system in sparse-fur (spf) mutant mice with ornithine transcarbamylase deficiency

The development of the hepatic and renal hippurate-synthesizing system, as represented by the overall reaction of the benzoyl CoA: glycine N-acyltransferase (EC 2.3.1.13) was studied in 0, 4, 8, 13, 17, 21-day and 8-week old sparse-fur (spf) mutant mice with X-linked ornithine transcarbamylase (OTC) deficiency. The enzyme system in mutant males (spf/Y) showed a retarded development in both liver and kidney cortex, which was statistically significant between 13 and 21 days of age, as compared to normal males (+/Y). Hippurate synthesis in preparations from adult (8-week old) spf/Y mice was not significantly different than the normal. Daily intraperitoneal injections of sodium benzoate in increasing concentrations (125-375 mg/kg), given between 17 and 21 days, did not cause any induction in spf/Y or +/Y mice. However, intraperitoneal sodium phenobarbital (80 mg/kg) increased the specific and total activities of the hepatic enzyme system in normal +/Y mice significantly. spf/Y tolerated a dose of 40 mg/kg only, which resulted in no significant increase of hepatic enzyme activity. The results indicate that barbiturates may induce the hippurate-synthesizing system, whereas benzoate treatment has no effect on changing its developmental profile.     

Thyroid hormone status of Atlantic croaker exposed to Aroclor 1254 and selected PCB congeners

Atlantic croaker (Micropogonias undulatus) were exposed to the polychlorinated biphenyl (PCB) mixture (Aroclor 1254) or one of three individual congeners (planar PCB 77 or ortho-substituted PCB 47 and PCB 153) in the diet for 30 days to investigate the effects of PCBs on circulating thyroid hormones, thyroxine (T4) and triiodothyronine (T3). Aroclor 1254 (0.2 and 1.0 mg/kg body mass/day) decreased plasma T3 levels consistently, but the effects on T4 levels were inconsistent from year to year. Exposure to PCB 153 (0.1 and 1.0 mg/kg body mass/day) significantly lowered both T4 and T3, while PCB 47 at the same doses had no effect on thyroid hormone levels. The lower doses of PCB 77 (0.004, 0.01 and 0.02 mg/kg body mass/day) had no effect on T4 or T3, whereas the highest dose (0.1 mg/kg body mass/day) increased T4 levels significantly. The results of the present study demonstrate that exposure to PCBs at environmentally realistic concentrations can have profound effects on the thyroid status of Atlantic croaker. The ortho-substituted PCB 153 appears to contribute at least partially to the deleterious effects of Aroclor 1254 on thyroid status, whereas the planar PCB 77 at concentrations present in the mixture is unlikely to alter thyroid hormone levels.     

Dose-dependant hypothyroidism in mice induced by commercial trimethoprim-sulfamethoxazole rodent feed

Trimethoprim-sulfamethoxazole (TMP-SMX) medication in the feed or water is commonly administered to immunocompro mised mice to prevent the occurrence of Pneumocystis murina (formerly P. carinii) pneumonia. Therapeutic doses of SMX can cause decreased total and free thyroxine (T4) levels in dogs and thyroid hypertrophy and hyperplasia in mice, rats, and dogs. Our primary objective was to determine whether SMX at doses present in commercially available rodent TMP-SMX feed would pro duce hypothyroidism in mice. Plasma T4 levels were determined prior to and after placement of Brand A TMP-SMX feed (daily SMX dose, 240 mg/kg), Brand B TMP-SMX feed (daily SMX dose, 2400 mg/kg), and their respective controls (doses calculated for a 25-g mouse according to vendor's information). T4 levels in the mice fed Brand B TMP-SMX feed were significantly decreased by 2 wk after feed placement. Levels of thyroid stimulating hormone in male and female mice given Brand B TMP-SMX feed were significantly elevated compared with those of control groups at 6 wk after feed placement, when only these mice showed evidence of thyroid hypertrophy and hyperplasia. No significant change in T4 levels occurred over the course of 11 wk in mice given the Brand A TMP-SMX chow or either control feed. In light of the significant clinical hypothyroidism that occurred in our mice while receiving Brand B TMP-SMX diet, we recommend SMX levels more similar to that of Brand A to avoid such unwanted effects which could confound research data.     

Effect of excitatory amino acids on serum TSH and thyroid hormone levels in freely moving rats

The actions of glutamate (L-Glu), and glutamate receptor agonists on serum thyroid hormones (T4 and T3) and TSH levels have been studied in conscious and freely moving adult male rats. The excitatory amino acids (EAA), L-Glu, N-methyl-D-aspartate (NMDA), kainic acid (KA) and domoic acid (Dom) were administered intraperitoneally. Blood samples were collected through a cannula implanted in the rats jugular 0--60 min after injection. Thyroid hormone concentrations were measured by enzyme immunoassay, and thyrotrophin (TSH) concentrations were determined by radioimmunoassay. The results showed that L-Glu (20 and 25 mg/kg) and NMDA (25 mg/kg) increased serum thyroxine (T4), triiodothyronine (T3) and TSH concentrations. Serum thyroid hormone levels increased 30 min after treatment, while serum TSH levels increased 5 min after i.p. administration, in both cases serum levels remained elevated during one hour. Injection of the non-NMDA glutamatergic agonists KA (30 mg/kg) and Dom (1 mg/kg) produced an increase in serum thyroid hormones and TSH levels. These results suggest the importance of EAAs in the regulation of hormone secretion from the pituitary-thyroid axis, as well as the importance of the NMDA and non-NMDA receptors in this stimulatory effect.     

Comparison of the incidence of 5-azacytidine-induced exencephaly between MT/HokIdr and Slc:ICR mice.

The incidence of 5-azacytidine-induced exencephaly was compared between MT/HokIdr strain (MT) and Slc:ICR strain (ICR) mice. MT mice have a genetic predisposition for exencephaly, but ICR mice do not. Pregnant mice were given 5-azacytidine (1 mg/kg to 100 micrograms/kg) injected intraperitoneally on Day 7.5 of gestation (vaginal plug day = Day 0.5), and fetuses were observed for external malformations on Day 18.5 of gestation. One hundred micrograms/kg 5-azacytidine induced exencephaly in MT mice but not in ICR mice, and 1 mg/kg 5-azacytidine resulted in resorptions in MT mice but caused exencephaly in ICR mice. These results indicated that MT mice had 10-fold more sensitivity to 5-azacytidine than ICR mice. It seems likely that less than effective doses of teratogens for animals without genetic predispositions are still effective in inducing malformations in animals with a genetic predisposition for malformations. When 4-somite-stage embryos of both MT and ICR mice were cultured in rat serum supplemented with 5-azacytidine, 0.02 micrograms/ml 5-azacytidine induced the failure of closure of cephalic neural tube in MT embryos but not in ICR embryos, and 0.2 micrograms/ml 5-azacytidine induced severe growth retardation in MT embryos but in ICR embryos it only induced embryos with smaller heads and fewer somites than in control. These results indicated that MT mouse embryos in culture also had a 10-fold-increased sensitivity to 5-azacytidine compared with ICR mouse embryos, suggesting maternal effects play no significant role in their increased sensitivity to 5-azacytidine.     

Teratogenic effects of a single oral administration of methylmercuric chloride in mice.

The teratogenic effects of methylmercuric chloride (MMC) given orally as a single dose to pregnant ICR mice on day 10 of gestation were examined. The doses tested were 25, 20, 15 and 10 mg/kg. Controls received distilled water orally. Each group consisted of 20 females. Fetuses were taken on day 18 of gestation for teratological study. The number of resorbed or dead embryos was moderately increased in the 25 mg/kg group. Fetuses from dams given 25, 20 and 15 mg/kg MMC weighed significantly less than those in the control group. Many fetuses with malformations were observed in the treated groups; cleft palate occurred in 100, 58.6 and 28.0% of fetuses from dams given 25, 20 and 15 mg/kg MMC, respectively (statistically significant). Hydronephrosis appeared in 23.8 and 18.5% of fetuses from dams given 25 and 20 mg/kg MMC, respectively (statistically significant). Skeletal variations, incomplete ossification of sternebrae, for example, were also observed in the treated groups. These results indicate that MMC is teratogenic so far as cleft palate is concerned and embryotoxic in ICR mice.     

Effects of ovulen-50, diethylnitrosamine and phenobarbital on liver regeneration in female rats

Short term effects of ovulen-50, a combination type oral contraceptive agent and phenobarbital—an established hepatic tumour promoter, were examined in the livers of diethylnitrosamine-initiated and uninitiated female rats. Liver mitotic activity as judged by liver weight, [³H] thymidine incorporation into DNA and levels of DNA, RNA and protein were measured in non-regenerating and regenerating liver. Hepatic γ-glutamyl transpeptidase activity and hepatocyte agglutination with concanavalin A were examined in diethylnitrosamine- and/or phenobarbital-treated rats. The results indicate that diethylnitrosamine or ovulen-50 individually are mitoinhibitory in regenerating liver. Phenobarbital alone has a slight mitostimulatory effects in non-regenerating liver, but no effect on liver regeneration. Administration of ovulen-50 and phenobarbital to diethylnitrosamine initiated rats mitigated the mitoinhibition during regeneration. Contrary to the earlier observation with ovulen-50, neither phenobarbital nor diethylnitrosamine induced hepatocyte agglutination in the presence of concanavalin A. Like ovulen-50, diethylnitrosamine also increased the level of hepatic γ-glutamyl transpeptidase. Phenobarbital produced only insignificant rise and did not substantially exacerbate the effect diethylnitrosamine. The data show that though some of the effects of ovulen-50 resemble those of diethylnitrosamine or phenobarbital, the changes observed may not be related to the neoplastic phenomenon since they were not seen in an initiator-promoter combination regimen.     

Maotai Ameliorates Diethylnitrosamine-Initiated Hepatocellular Carcinoma Formation in Mice

Consumption of alcohol is closely related to liver disease, such as hepatic fibrosis or even hepatocellular carcinoma (HCC). However, epidemiological and experimental studies indicated that consumption of Maotai, one of the famous liquors in China, exhibits no significant correlation with hepatic fibrosis or cirrhosis as other beverage sources do. This study detected the relationship of Maotai consumption and HCC development in a diethylnitrosamine (DEN)-initiated HCC animal model. DEN was given to mice at a dose of 100 mg/kg, ip, and 50 mg/kg, ip in the following week. Mice were simultaneously given Maotai or an equal amount of ethanol (53%, 5 ml/kg/day, 5days/week for up to 35weeks). At 3-week and 35- week of the experiment, serum and livers were collected for biochemical and histopathological examination of liver injury and incidence of HCC. Real-time RT-PCR, immunohistochemistry and Western blotting were used to examine the expression of metallothionein-1/2 (MT-1/2), NF-E2-related factor 2 (Nrf2), glutamate-cysteine ligase catalytic subunit (GCLC) and modified subunit (GCLM). We identified tissue damage and dysfunction of liver in ethanol + DEN-treated mice, whereas the extent of injury was reduced in Maotai+ DEN –treated mice. Significant Glypican-3(GPC3) expression and precancerous injury or HCC were seen in approximately 50% of mice with ethanol+ DEN, but barely be seen in Maotai + DEN-treated mice. A higher expression of MT-1/2, Nrf2 and GCLC could be seen in Maotai + DEN-treated mice. Thus, Maotai liquor ameliorates the formation of DEN-induced HCC in mice, and the protection mechanism is possibly related with the activation of anti-oxidation factors, such as MTs, Nrf2 and GCLC.     

Effect of thiourea on intracranial bone tumour formation in AkR mice.

The effect of administration of thiourea (5 g/kg in diet) alone or simultaneously with thyroxine (1 mg/l in drinking water) on the frequency of hyperplastic benign osteoma of the skull was studied in AkR mice. Animals treated with both thiourea and thyroxine were in hyperthyroidism: the thyroxine dose received was higher that that required to prevent thiourea-induced thyroid gland hypertrophy. A significant increase of the intracranial bone tumour (IBT) frequency was observed both in mice treated with thiourea alone and those which received thiourea and thyroxine simultaneously. Increase of IBT frequency was not due to the antithyroid effect of thiourea but seems due to a direct toxic action of thiourea on the pituitary.     

The effects of diethylnitrosamine on ribonucleic acid and protein synthesis in the liver and lung of the Syrian golden hamster

1. Syrian golden hamsters were treated with a single subcutaneous dose of 200mg of diethylnitrosamine/kg. In the liver the treatment produced a significant and early inhibition of the incorporation of orotic acid into RNA and of leucine into protein. Diethylnitrosamine also lowered basal and 20-methylcholanthrene-stimulated activities of hepatic aryl hydrocarbon hydroxylase. 2. RNA synthesis, protein synthesis and aryl hydrocarbon hydroxylase activity were also evaluated in the lungs of the same animals. In this organ only protein synthesis was affected by diethylnitrosamine, but not RNA synthesis or aryl hydrocarbon hydroxylase activity. 3. The incorporation of thymidine into DNA was inhibited in both organs early after diethylnitrosamine treatment and increased 2–3 days later. 4. Although diethylnitrosamine, injected subcutaneously, accumulates in liver and lung in toxicologically active amounts, the acute biochemical responses of the two organs are not identical.     

Piperine lowers the serum concentrations of thyroid hormones, glucose and hepatic 5'D activity in adult male mice.

Piperine, the main alkaloid of Piper nigrum fruits, was evaluated for its thyroid hormone and glucose regulatory efficacy in adult male Swiss albino mice. Its daily oral administration (2.50 mg/kg) for 15 days lowered the serum levels of both the thyroid hormones, thyroxin (T (4)) and triiodothyronine (T (3)) as well as glucose concentrations with a concomitant decrease in hepatic 5'D enzyme and glucose-6-phospatase (G-6-Pase) activity. However, no significant alterations were observed in animals treated with 0.25 mg/kg of piperine in any of the activities studied except an inhibition in serum T (3) concentration. The decrease in T (4), T (3) concentrations and in G-6-Pase were comparable to that of a standard antithyroid drug, Proylthiouracil (PTU). The hepatic lipid-peroxidation (LPO) and the activity of endogenous antioxidants, superoxide dismutase (SOD), and catalase (CAT) were not significantly altered in either of the doses. It appears that the action of P. nigrum on thyroid functions is mediated through its active alkaloid, piperine. We also suggest that a higher dose of piperine may inhibit thyroid function and serum glucose concentration in euthyroid individuals.     

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.