T3 Rats Research Articles

Chlorogenic Acid Protects Cell Death in the Cerebellum through Anti-Apoptotic Protein Bcl2 in Transient Global Ischemia Cases

Background: Cerebellum is one of the vital components of the brain that will be affected by ischemia-reperfusion (IR) injury. IR injury will increase free radicals, which in turn can trigger apoptosis and cell death. Therefore, this study was conducted to examine the effect of chlorogenic acid administration on apoptosis and the number of cells in the cerebellum of rats with global ischemic transients.Materials and methods: Wistar rats were divided into five groups: sham-operated (C1), IR (C2), IR + 15 mg/kgBW chlorogenic acid (T1), IR + 30 mg/kgBW chlorogenic acid (T2), and IR + 60 mg/kgBW chlorogenic acid (T3). C2, T1, T2, and T3 groups received bilateral common carotid occlusion (BCCO) surgery to induce IR injury. Thirty minutes after BCCO surgery, T1, T2, and T3 rats were administered chlorogenic acid in various doses intraperitoneally. RNA extraction and real-time polymerase chain reaction (PCR) measurements were then performed on NeuN, Bcl2, Bax, caspase 3, as well as on GAPDH as housekeeping genes.Results: There were significant differences in NeuN expressions between groups, with the highest expression shown in C1 followed by T3. Bcl2 expressions were also significantly different between groups, and rats in C1 and T3 showed to be significantly higher compared to C2, while T1 was significantly lower than C1. However, Bax and caspase 3 expressions showed no significant differences.Conclusion: Chlorogenic acid in 60 mg/kgBW dose increases NeuN expression and Bcl2 mRNA expression after transient global ischemia. These increases might correlate with the heightened level of protection against apoptosis in the cerebellum, hence showing its potential in protecting neuron cells.Keywords: transient global ischemia, chlorogenic acid, cerebellum, apoptosis

Effect of Bee Bread on Corticosterone Level in Rat Dams Exposed to Gestational Heat Stress.

Environmental temperature rises are powerful stimuli that can alter both the sympathetic nervous system and the hypothalamic-pituitary-adrenocortical axis (HPA). Heat stress has been shown to harm pregnancy outcomes such as causing spontaneous abortion, low birth weight, growth retardation and stillbirth. Supplementation of bee bread in pregnant rats under heat stress exposure has been shown to improve the pregnancy outcomes. However, whether supplementation of bee bread during heat stress exposure may also reduce the level of the stress hormone, corticosterone has yet been reported. Therefore, this study aims to determine the effect of bee bread on corticosterone level, progesterone level, oestradiol level and zonation of the adrenal cortex of pregnant rats under heat stress exposure. Pregnant rats were randomly categorised into four groups (n = 6): Control (C: standard feeding), Treatment 1 (T1: 0.5 g bee bread/kg body weight/day), Treatment 2 (T2: standard feeding with heat exposure), and Treatment 3 (T3: 0.5 g bee bread/kg body weight/day with heat exposure). Bee bread (0.5 g/kg body weight/day) was force-fed to pregnant rats through oral gavage beginning on day 0 of pregnancy and continuing until delivery. Heat stress was generated experimentally by putting both T2 and T3 rats in an egg incubator for 45 min daily at a temperature of 43°C till delivery. On a postnatal Day 21, dams were euthanised to assess serum corticosterone, progesterone, oestradiol levels and adrenal gland histology. Rats in the T2 group had a significantly (P < 0.05) increase in the zona fasciculata thickness (94.95 ± 1.55 μm) and higher corticosterone levels (49.57 ± 1.57 ng/mL) compared with control. However, supplementation of bee bread during heat stress was able to show an improvement in adrenal zona fasciculata thickness by decreasing to 79.89 ± 3.08 μm and corticosterone level reduced to 35.31 ± 1.73 ng/mL significantly (P < 0.05). Therefore, these findings may imply that bee bread is effective as a neutralizer in lowering the production of stress hormone.

α-Tocopherol restores semen quality in rats exposed to 2,3,7,8-tetrachlorodibenzo-p-dioxin.

Background and Aim:2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is a persistent organic pollutant toxic to the human reproductive system. This study aimed to evaluate the effect of α-Tocopherol administration on the male fertility parameters of a rat model exposed to TCDD.Materials and Methods:Fifty healthy 12-week-old male rats were randomly divided into five groups. Rats in the control group were given corn oil twice daily in 4 h intervals. In the treatment groups, all rats were given TCDD at a dose of 700 ng/kg of body weight (BW)/day for 45 days. Four hours after receiving the TCDD, T0 rats were given corn oil, and T1, T2, and T3 rats were given α-Tocopherol at doses of 77, 140, and 259 mg/kg BW/day, respectively, for 45 days. On day 46, experimental animals were sacrificed to collect blood and testicular samples.Results:TCDD exposure decreased superoxide dismutase activity, plasma membrane integrity, Leydig cell count, sperm cell count, sperm viability and motility, and increased malondialdehyde levels, serum testosterone levels, and sperm morphological abnormalities. The administration of α-Tocopherol mitigated the effects of TCDD exposure, and the 140 and 259 mg/kg BW/day treatments returned those male fertility parameters to normal levels.Conclusion:The administration of 140 mg/kg BW/day α-Tocopherol restored male semen quality in rats exposed to TCDD. We found dynamics serum testosterone levels in rats exposed to TCDD that need to be further studied.

Spirulina ameliorates arsenic induced reproductive toxicity in male rats.

Spirulina (Spirulina platensis), has numerous health benefits including antioxidant, immunomodulatory, and anti-inflammatory activities, works against heavy metal toxicity, and is often used as a food supplement in human, animals, birds and fishes. This study aimed to evaluate the protective ability of the dietary spirulina against the toxic effects of inorganic arsenic (iAs) on male reproductive parameters in rats. Seventy-two mature Long-Evans male rats, dividing into six groups (T0, T1, T2, T3, T4 and T5) (12 rats/group) were included in this study. The T3, T4 and T5 group rats were treated with three consecutive doses (1.0 g, 1.5 g and 2.0 g/kg feed) of spirulina in feed along with 3.0 mg NaAsO2/kg body weight (BW) in drinking water (DW) daily for 90 days. Each rat of group T1 received NaAsO2 (3.0 mg/kg BW) in DW, and those of T2 group were fed with spirulina (2.0 g/kg feed) daily for 90 days. The rats of group T0 served as the control with normal feed and water. Total arsenic (tAs) contents, reproductive parameters (testicular weight, sperm motility and morphology), and histological changes in the testicles were evaluated in these rats. Arsenic dosing significantly (p=0.003, Kruskal-Wallis test) increased the tAs contents in the testicles, decreased testes weight, sperm morphology and motility compared to the controls. The effect of arsenic dosing was also evidenced by the histological changes like decreased germinal layers in the seminiferous tubules of the treated rats. Moreover, dietary spirulina (2.0 g/kg feed) supplementation significantly (p=0.011, Kruskal-Wallis test) lowered tAs contents in testicles and increases testes weights, sperm motility and morphology. Therefore, spirulina can be used as an effective dietary supplement to ameliorate the adverse effects of arsenic induced reproductive toxicities. However, further study is required to elucidate the underlying molecular mechanisms of reduction of arsenic induced reproductive toxicity by spirulina.

Influence of Fat Burners and Functional Foods on Lipid Profile of Obese Rats

This study was designed to identify the effects of certain fat burners and functional foods on lipid profiles including total cholesterol (TC), triglycerides (TG), low-density lipoproteins (LDL-C), and antioxidants such as glutathione peroxidase (GPx) and malondialdehyde (MDA) in adult male Sprague–Dawley rats. The rats were separated into seven groups, each group containing six rats. Both the (T1) negative and (T2) positive control groups and the five other groups were fed with a high-calorie diet to achieve obesity. After the end of the feeding period, over 56 days the rats were treated with Orlistat 0.3mg/g (T3), C4 RIPPED 1.2 mg/g (T4), Garcinia Herb 0.5 mg/g (T5), Ispaghula Herb 0.02g/g (T6), and Functional Yoghurt 1ml (T7). The results showed significantly increased (p≤0.05) cholesterol in the serum of T2 rats compared with T1 rats. Transactions with T3, T4, T5, T6, and T7 rats led to a significant decrease in TC. There was a significant increase in TG and LDL-C in T2 rats compared with T1 rats; a significant decrease occurred in the serum of the animals treated in groups T3, T4, T5, T6, T7 and T7. Rats in groups T3, T5, T6, and T7 showed increased GPx and decreased MDA compared with T1 and T4.

Modification of cardiac thyroid hormone deiodinases expression in an ischemia/reperfusion rat model after T3 infusion.

The deiodinases regulate the activation and inactivation of Thyroid hormones (TH), in both physiological and pathological conditions. The three deiodinases, DIO1, DIO2 and DIO3, have different catalytic role and cellular and tissue distribution. Aim of this study is to evaluate a rat model of regional ischemia/reperfusion (I/R), the modification of cardiac main function after the administration of 6µg/kg/day of triiodothyronine (T3), and the associated to DIO1, DIO2 and DIO3 gene expression. We also aim to study DIO1 and DIO2 protein levels in different left ventricular regions after an ischemic event. Four groups of rats were studied: sham-operated, sham-operated + T3, I/R rats and I/R rats + T3. DIO1, DIO2 and DIO3 expression were evaluated in I/R region (AAR: area-at-risk) and in a more distant region from ischemic wound (RZ: remote zone). In I/R group, circulating free-T3 (FT3) levels were significantly decreased with respect to basal values, whereas in I/R + T3 rats, FT3 levels were comparable to basal values. In AAR of I/R + T3 rats, DIO1 and DIO2 gene expression significantly increased with respect to sham. In RZ, DIO1 and DIO3 gene expression was significantly lower in sham and I/R rats when compared to I/R + T3. In sham + T3 group, DIO1 and DIO2 gene expression was not detectable, whereas DIO3 was significantly higher than in the other three groups. The present study gives interesting new insights on DIO1, DIO2 and DIO3 in the ischemic heart and their role in relation to T3-mediated amelioration of cardiac function and structure.

Improved Functional Recovery in Rat Spinal Cord Injury Induced by a Drug Combination Administered with an Implantable Polymeric Delivery System.

Spinal cord injury (SCI) is an incurable condition, in which a cascade of cellular and molecular events triggered by inflammation and excitotoxicity impairs endogenous regeneration, namely remyelination and axonal outgrowth. We designed a treatment solution based on an implantable biomaterial (electrospun poly (l-lactic acid) [PLLA]) loaded with ibuprofen and triiodothyronine (T3) to counteract inflammation, thus improving endogenous regeneration. In vivo efficacy was tested by implanting the drug-loaded PLLA in the rat model of T8 contusion SCI. We observed the expected recovery of locomotion beginning on day 7. In PLLA-implanted rats (i.e., controls), the recovery stabilized at 21 days post-lesion (DPL), after which no further improvement was observed. On the contrary, in PLLA + ibuprofen (Ibu) + T3 (PLLA-Ibu-T3) rats a further recovery and a significant treatment effect were observed, also confirmed by the gait analysis on 49 DPL. Glutamate release at 24 h and 8 DPL was reduced in PLLA-Ibu-T3- compared to PLLA-implanted rats, such as the estimated lesion volume at 60 DPL. The myelin- and 200-neurofilament-positive area fraction was higher in PLLA-Ibu-T3-implanted rats, where the percentage of astrocytes was significantly reduced. The implant of a PLLA electrospun scaffold loaded with Ibu and T3 significantly improves the endogenous regeneration, leading to an improvement of functional locomotion outcome in the SCI.

Early and Short-term Triiodothyronine Supplementation Prevents Adverse Postischemic Cardiac Remodeling: Role of Transforming Growth Factor-β1 and Antifibrotic miRNA Signaling.

Activation of transforming growth factor (TGF)-β1 signaling in the ischemia/reperfusion (I/R) injured myocardium leads to dysregulation of miR-29-30-133, favoring the profibrotic process that leads to adverse cardiac remodeling (CR). We have previously shown that timely correction of the postischemic low-T3 syndrome (Low-T3S) exerts antifibrotic effects, but the underlying molecular players are still unknown. Here we hypothesize that a prompt, short-term infusion of T3 in a rat model of post I/R Low-T3S could hamper the early activation of the TGFβ1-dependent profibrotic cascade to confer long-lasting cardioprotection against adverse CR. Twenty-four hours after I/R, rats that developed the Low-T3S were randomly assigned to receive a 48-h infusion of 6 μg/kg/d T3 (I/R-L+T3) or saline (I/R-L) and sacrificed at 3 or 14 d post-I/R. Three days post-I/R, Low-T3S correction favored functional cardiac recovery. This effect was paralleled by a drop in TGFβ1 and increased miR-133a, miR-30c and miR-29c in the infarcted myocardium. Consistently, connective transforming growth factor (CTGF) and matrix metalloproteinase-2(MMP-2), validated targets of the above miRNAs, were significantly reduced. Fourteen days post-I/R, the I/R-L+T3 rats presented a significant reduction of scar size with a better preservation of cardiac performance and LV chamber geometry. At this time, TGFβ1 and miR-29c levels were in the normal range in both groups, whereas miR-30c-133a, MMP-2 and CTGF remained significantly altered in the I/R group. In conclusion, the antifibrotic effect exerted by T3 in the early phase of postischemic wound healing triggers a persistent cardioprotective response that hampers the progression of heart dysfunction and adverse CR.

Increased Serca Pump Expression is Associated with Slow Termination of Calcium Sparks and Delayed Local Recovery in Vascular Smooth Muscle Cells of Hyperthyroid Rats

In vascular smooth muscle cells of cerebral arteries (VSMCs), spontaneous and repetitive local Ca2+ signals produced by the Ca2+ channel/Ryanodine Receptor (RyRs), known as Ca2+ sparks, are involved in the regulation of vascular myogenic tone. However, the molecular mechanisms behind the frequency and properties of Ca2+ sparks in VSMCs are still under study. Considering that in VSMCs, spontaneous Ca2+ sparks are generated at preferred subcellular locations, we have analyzed the spatio-temporal properties of repetitive same-location Ca2+ sparks, its time-dependent recovery (or restitution) and the regulation that luminal Ca2+ might exert in this phenomenon by using the experimental model of hyperthyroid rat (T3).Ca2+ sparks recorded in VSMCs from T3 rats showed similar frequency, amplitude, and Ca2+ flux compared with those recorded in control cells. However, Ca2+ spark properties such as duration, size, time-to-peak, and k decay were significantly increased in T3 cells; and as a consequence, spark-mediated Ca2+ leak was augmented by 3.3-fold. In both experimental groups, amplitude recovery of repetitive Ca2+ sparks was an all-or-none phenomenon and did not show any time-dependency. Histogram distribution of spark-to-spark delays from T3 cells showed a 4-fold reduction in shorter delays (0-200 ms), with the shortest spark-to-spark delay of 115.9 ms in T3 cells and of 67.2 ms in control cells. Although SERCA pump expression was increased in vascular tissue from T3 rats, both basal Ca2+ concentration and intracellular SR Ca2+ load, determined by caffeine, remained unchanged. Our data suggest that in VSMCs of T3 rats spontaneous Ca2+ sparks decrease SR Ca2+ content not only by increasing its frequency but also by delaying its termination to counteract SR Ca2+ overload resulting from the overexpression of SERCA pump.

In Vivo Identification of Multiple Response Elements Mediating Thyroid Hormone Stimulation of Hepatic HMG‐CoA Reductase Transcription

Hepatic HMG‐CoA reductase (HMGR) is the enzyme that catalyzes the rate‐limiting step in cholesterol biosynthesis. Hypothyroidism is a known risk factor for cardiovascular disease. HMGR transcription is decreased in hypothyroid mammals. Treatment of hypothyroid (Hx) Sprague Dawley rats with triiodothyronine (T3) increased HMGR mRNA by approximately 2.7‐fold. We have utilized in vivo electroporation to introduce HMGR promoter‐luciferase constructs directly into the livers of Hx Sprague Dawley rats treated ±T3 in an effort to identify the regions of the HMGR promoter responsible for this T3‐mediated regulation. Electroporation of an HMGR promoter construct inclusive of the ‐325/+70 promoter region resulted in a 2.6‐fold induction of promoter activity in the T3‐treated animal. Mutations in the sterol response element (SRE), nuclear factor‐y site (NF‐Y), and the sequence AGGTCA at ‐316/‐321 identified the necessity of these elements for the T3 response. EMSAs with liver nuclear extracts from +T3 rats showed strong shifted bands with probes to each of these elements. Antibody supershift assays revealed that SREBP‐2 binds to the SRE, NF‐Y binds to the NF‐Y site, and USF‐2 binds to the AGGTCA element at ‐316/‐321. In vivo electroporation of siRNA to SREBP‐2 was shown to reduce HMGR mRNA in normal Sprague Dawley rats to an average of 60% of control. These data suggest that the SRE, NF‐Y site, ‐316/‐321 element and their corresponding binding proteins appear to mediate the T3 response. (This investigation was supported by NIH grant DK075414).

Thyroid hormone effect on activity levels and tissue mitochondrial biogenesis and function in young and old rats

Triiodothyronine (T3) has a major impact on the regulation of energetics and mitochondrial (mt) function. We determined whether chronic T3 administration alters the age‐related decline in mt function. Ten young (Y, 8 mo) and ten old (O, 27 mo) F344/BN rats were randomized to receive T3 (200 mg/d) or placebo for 14d via subcutaneous osmotic pump. Because OT3 rats decreased food consumption by 39%, we added ten pair fed rats (OPF). T3 treatment caused a significant weight loss (Y, −11.97%; O, −17.49%), while energy expenditure increased in both Y (50.86%) and O (54.40%), but decreased in PF (17.55%). Fat and muscle loss were similar in Y and O in response to T3 (fat, −52.53%(Y) vs −51.69% (O); muscle, −21.50% (Y) vs −21.03% (O) in soleus and −16.70% (Y) vs −17.35% (O) in plantaris), whereas these changes were minor with OPF (fat, −10.4%; soleus −1.69% ; plantaris 7.69%). While mt ATP production and citrate synthase activity in heart and soleus muscle were lower in O, these measures increased equally in Y and O in response to T3. In the soleus, mt DNA abundance increased in Y (54.39%) and O (23.36%) and UCP3 expression increased 10‐fold in both age groups. Gene transcripts levels of PGC1α, COX3&amp;4 and NADH4, UCP2&amp; 3 increased in soleus of T3 rats. In conclusion, T3 similarly increased energy expenditure, weight loss and mt biogenesis in both Y and O rats, despite differences in food intake.NIH grant PO1 AG09531 and Mayo Foundation

Derangement of Kupffer cell functioning and hepatotoxicity in hyperthyroid rats subjected to acute iron overload

Liver oxidative stress, Kupffer cell functioning, and cell injury were studied in control rats and in animals subjected to L-3,3′,5-tri-iodothyronine (T3) and/or acute iron overload. Thyroid calorigenesis with increased rates of hepatic O2 uptake was not altered by iron treatment, whereas iron enhanced serum and liver iron levels independently of T3. Liver thiobarbituric acid reactants formation increased by 5.8-, 5.7-, or 11.0-fold by T3, iron, or their combined treatment, respectively. Iron enhanced the content of protein carbonyls independently of T3 administration, whereas glutathione levels decreased in T3- and iron-treated rats (54%) and in T3Fe-treated animals (71%). Colloidal carbon infusion into perfused livers elicited a 109% and 68% increase in O2 uptake in T3 and iron-treated rats over controls. This parameter was decreased (78%) by the joint T3Fe administration and abolished by gadolinium chloride (GdCl3) pretreatment in all experimental groups. Hyperthyroidism and iron overload did not modify the sinusoidal efflux of lactate dehydrogenase, whereas T3Fe-treated rats exhibited a 35-fold increase over control values, with a 54% reduction by GdCl3 pretreatment. Histological studies showed a slight increase in the number or size of Kupffer cells in hyperthyroid rats or in iron overloaded animals, respectively. Kupffer cell hypertrophy and hyperplasia with presence of inflammatory cells and increased hepatic myeloperoxidase activity were found in T3Fe-treated rats. It is concluded that hyperthyroidism increases the susceptibility of the liver to the toxic effects of iron, which seems to be related to the development of a severe oxidative stress status in the tissue, thus contributing to the concomitant liver injury and impairment of Kupffer cell phagocytosis and particle-induced respiratory burst activity.

Extrathyroidal effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin on thyroid hormone turnover in male Sprague-Dawley rats.

Treatment of rats with different polyhalogenated aromatic hydrocarbons strongly decreases plasma T4, with little or no decrease in plasma T3. The extrathyroidal effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on thyroid hormone turnover were studied by i.p. administration of a single dose of 10 microg TCDD/kg BW or vehicle (corn oil) to euthyroid (Eu) rats, thyroidectomized (Tx) rats, and Tx rats infused with 1 microg T4 (Tx+T4) or 0.4 microg T3 (Tx+T3)/100 g BW x day by osmotic minipumps. Tx rats showed decreased plasma T4 and T3 and increased plasma TSH levels, decreased hepatic type I deiodinase (D1) and malic enzyme activities, and increased brain type II deiodinase (D2) activities. All parameters were largely restored to Eu levels in Tx+T4 rats and, except for plasma T4 and brain D2 activity, in Tx+T3 rats, validating the thyroid hormone-replaced Tx rats as models to study the peripheral effects of TCDD. Three days after TCDD administration, plasma T4 and free T4 levels were significantly reduced in Eu and Tx+T4 rats, and plasma T3 was significantly reduced in Tx+T3, but not in Eu or Tx+T4 rats. Plasma TSH was not affected by TCDD in any group. Hepatic T4 UDP-glucuronyltransferase (UGT) activity was induced approximately 5-fold by TCDD, whereas T3 UGT activity was only increased by about 20% (P = NS) in the different groups. TCDD produced an insignificant decrease in liver D1 activity in Tx rats and an insignificant increase in brain D2 activity in Tx rats and hormone-replaced Tx rats. Hepatic malic enzyme activity was significantly increased by TCDD in all groups, except Tx rats. These results strongly suggest that the thyroid hormone-decreasing effects of TCDD are predominantly extrathyroidal and mediated by the marked induction of hepatic T4 UGT activity.

Tissue-specific regulation of medium-chain acyl-CoA dehydrogenase gene by thyroid hormones in the developing rat

During development, gene expression of medium-chain acyl-CoA dehydrogenase (MCAD), a nuclear-encoded mitochondrial enzyme that catalyses the first step of medium-chain fatty acid beta-oxidation, is highly regulated in tissues in accordance with fatty acid utilization, but the factors involved in this regulation are largely unknown. To investigate a possible role of thyroid hormones, rat pups were made hypothyroid by the administration of propylthiouracyl to the mother from day 12 of gestation, and their kidneys, heart and liver were removed on postnatal day 16 to determine MCAD mRNA abundance, protein level and enzyme activity. Similar experiments were run in 3,3',5-tri-iodothyronine (T3)-replaced hypothyroid (1 microg of T3/100 g body weight from postnatal day 5 to 15) and euthyroid pups. Hypothyroidism led to an increase in MCAD mRNA abundance in kidney and a decrease in abundance in heart, but had no effect in liver. The protein levels and enzyme activity were lowered in hypothyroid heart and kidney, suggesting that hypothyroidism affects post-transcriptional steps of gene expression in the kidney. All the effects of hypothyroidism were completely reversed in both heart and kidney by T3 replacement. Injection of a single T3 dose into 16-day-old euthyroid rats also led to tissue-specific changes in mRNA abundance. Nuclear run-on assays performed from hypothyroid and hypothyroid plus T3 rats showed that T3 stimulates MCAD gene transcription in heart and represses it in the kidney. These results indicate that the postnatal rise in circulating T3 is essential to the developmental regulation of the MCAD gene in vivo.

Triiodothyronine (T3) modifies cholinergic-induced hypothermia and tremor in rats.

Hypothermia and tremor responses of oxotremorine and eserine were studied in rats after several T3 treatment regimens. The T3 antagonized oxotremorine-induced hypothermia and failed to antagonize eserine hypothermic effect, but potentiated oxotremorine- and eserine-induced tremors. Acetylcholinesterase activity was not altered in T3 rats. The hypothetical mechanisms to explain changes of central cholinergic responses caused by T3 are discussed.

Studies on the rapid stimulation of mitochondrial respiration by thyroid hormones.

Injection of L-3,5-diiodothyronine (T2) into rats made hypothyroid by 6-n-propyl-2-thiouracil (PTU) increased the respiration rates of subsequently isolated liver mitochondria; this stimulation of respiration by T2 occurred in the presence of cycloheximide and is therefore independent of protein synthesis on cytoplasmic ribosomes. Injection of T3 into PTU-treated rats had a lesser effect than T2 on the respiration rates of subsequently isolated mitochondria; as PTU is an inhibitor of 5'-iodothyronine deiodinases, which convert T3 into T2 in vivo, the rapid stimulation of mitochondrial respiration by T3, which has been shown in a range of systems, may not be due directly to T3 itself, but may be mediated by its deiodination product T2. Injection of T2, or T3, into hypothyroid or euthyroid rats had no effect on the percentage activity of mitochondrial pyruvate hydrogenase assayed 30 min later. The amount of active pyruvate dehydrogenase is regulated by changes in mitochondrial calcium concentration and matrix ATP/ADP ratio; therefore these parameters are not persistently affected by treatment with T3 or T2. In addition, the total amount of pyruvate dehydrogenase present was the same in euthyroid and hypothyroid rats, indicating that the expression of this enzyme is not stringently controlled by thyroid hormone status.

Food intake, body and heart composition, and heart rate in T3 plus atenolol-treated rats.

Thyroid hormones and beta-blockers both affect energy balance and the heart. The interaction of 3,5,3'-triiodothyronine (T3) and the beta-blocker atenolol on some cardiac and energy balance parameters was therefore investigated. Stock-fed male Wistar rats (approximately 400 g) received 5 micrograms (expt 1) or 1.5 micrograms (expt 2) T3.100 g body wt-1.day-1 for 3 wk, with or without atenolol. In expt 3, rats were overfed with a "cafeteria" diet before and during the experiment and otherwise treated as in experiment 2. Compared with stock-fed (expt 1 and 2) or overfed (expt 3) controls, T3 caused an increase in food intake in experiments 1 and 2 but not in experiment 3. There was a large loss of body fat in all experiments, disproportionately greater than the body weight loss. Protein loss was significant only in experiment 1 and negligible in cafeteria rats. Heart rate and weight were increased, although heart composition remained unchanged. Atenolol, in a dose that abolished T3-induced tachycardia, did not modify any of the other T3 effects investigated, including the hypertrophy of the heart. These results indicate that T3-induced tachycardia can be abolished by concomitant treatment with a beta-blocker without altering parameters connected with energy balance, whereas protein loss caused by T3 can be attenuated by lowering the dose of T3 used and can be further blunted by dietary manipulation (cafeteria overfeeding).

Capillarity and oxygen diffusion distances of the soleus muscle of guinea pigs and rats. Effects of hyperthyroidism

1. 1. The relationship between capillarity and oxidative capacity in the soleus muscle of rats and guinea pigs injected with triiodothyronine (T3) or with saline for up to 4 weeks was studied. 2. 2. The rats' soleus weight and FCSA were not affected by T3, but the guinea pigs that received T3 had smaller muscle weight and FCSA than the controls. 3. 3. The activities of cytochrome c oxidase and citrate synthase were significantly (41 and 65%) higher in the T3 than in the control rats. T3 administration did not affect the activities of these enzymes in the soleus of the guinea pigs. 4. 4. Capillary density (CD) was higher in T3 rats (892 ± 80 vs 622 ± 54 caps/mm 2), and in T3 guinea pigs (1219 ± 95 vs 739 ± 142 caps/mm 2). The higher CD in T3 rats was due to growth of new microvessels, while in the T3 guinea pigs it was due to a reduction in FCSA. 5. 5. Mean and maximal diffusion distances evaluated by the closest individual method were reduced by 2.02 and 3.37 μm in rats, and by 3.73 and 6.16 μm in guinea pigs. The magnitude of the reduction in diffusion distances brought about by the increased capillary density was partially offset by a concomitant change in the capillary arrangement from an ordered (hexagonal), towards a random distribution. 6. 6. These results seem to indicate that skeletal muscle capillarity is not necessarily determined by the oxidative capacity of the fibers.

Regulation of volume reabsorption by thyroid hormones in the proximal tubule of rat: minor role of luminal sodium permeability.

In order to investigate whether changes in luminal membrane sodium permeability can explain the increase in isotonic fluid reabsorption (Jv) found in proximal tubules of thyroidectomized rats (TX) treated with tri-iodothyronine (T3), experiments were carried out on TX rats and TX rats treated for 3 days (TX + T3) with physiological doses (10 micrograms/kg body wt) of T3. Two sets of experiments were performed: 1) in vivo, using the micropuncture technique for the measurements of Jv; 2) in vitro, using isolated brush border membrane vesicles for the direct measurement of Na+ permeability. In micropuncture studies a 65% increase in Jv of TX rats was observed after treatment with T3. Luminal perfusion of proximal tubules of TX rats with Amphotericin B (10 micrograms/ml), to increase luminal sodium permeability, enhanced Jv only by 15%. Brush border membrane vesicles isolated from TX and TX + T3 rats showed the same sodium permeability in uptake or efflux experiments. These results were confirmed by the fact that sodium gradient dependent histidine transport into brush border membrane vesicles did not change after T3 treatment. Finally, measuring the amiloride sensitive sodium uptake, it was also found that Na+-H+ exchange was also only slightly affected by T3. These micropuncture and vesicle data indicate that the large effect of T3 on the trans-cellular sodium transport and volume reabsorption in the proximal tubule, cannot be explained by an action of T3 on the sodium entry step across the brush border membrane.

High efficiency of energy utilization in 'cafeteria'-and force-fed rats kept at 29 degrees.

Male, Sprague-Dawley (Charles-River) rats, of initial weight 272 g, were given a powdered stock diet (T1) ad lib., force-fed a synthetic diet (T2) or offered a range of palatable foods in conjunction with the powdered stock diet (T3) or a similar diet supplemented with certain minerals and vitamins (T4). Metabolizable energy (ME) intake (kJ/d) averaged 303, 453, 402 and 383 for T1, T2, T3 and T4 respectively and corresponding weight gains were 5.5, 6.9, 8.2 and 7.9 g/d and were significantly different (P less than 0.001). The intakes of T3 and T4 rats ranged from 10 to 60% above the mean value for T1. Crude protein (CP; nitrogen X 6.25) retentions were similar for T1, T3 and T4 rats and significantly lower (P less than 0.01) for T2 rats. Fat retentions were 1.1, 4.1, 2.9 and 2.4 g/d for T1 to T4 respectively (P less than 0.001). The energy contents of the gain (MJ/kg) were 12.7, 26.0, 16.7 and 14.9 for T1 to T4 respectively (P less than 0.001) and energy retentions (kJ/d) were 70, 179, 139 and 117 respectively (P less than 0.001). A linear regression of energy retention (ER) on ME yielded a slope of 0.78 and a mean energy requirement for zero balance of 510 kJ/kg body- weight0 .75. These results are in conflict with reports of 'diet-induced thermogenesis' in 'cafeteria'-fed rats.