Thyroid hormones and lipolysis in physically trained rats

Role of aerobic exercise in ameliorating NASH: Insights into the hepatic thyroid hormone signaling and circulating thyroid hormones

AIM

Triiodothyronine (T3) administration significantly eliminates hepatic steatosis and also has a therapeutic effect on non-alcoholic steatohepatitis (NASH). However, the potential mechanism by which T3-mediated exercise improves NASH is unknow. This study aimed to explore the effect of aerobic exercise on liver injury in NASH.

METHODS

Aerobic exercise was conducted to explore the effects of exercise on liver injury in NASH model induced by Atherosclerotic (Ath) diet. Biochemical evaluations, histological staining and real-time PCR were first applied to confirm the amelioration effects of exercise on NASH. RNA-sequencing (RNA-seq) analysis for livers of each group were further used to identify the underlying mechanisms of aerobic exercise. Bioinformatics methods were used to explore the key functional pathways involved in the improvement of liver tissue in NASH mice by aerobic exercise.

RESULTS

Aerobic exercise improved hepatic steatosis, lobular inflammation and fibrosis in NASH mice. multiple inflammation-related pathways were significantly enriched in the liver of NASH group and improved by aerobic exercise. The results of gene set variation analysis (GSVA) showed a higher enrichment score of T3 response signature in NASH mice with exercise. Increased Dio1 expression in the liver of NASH with exercise mice and increased circulating FT3 and FT4 levels upon aerobic exercise were confirmed.

CONCLUSIONS

We found that aerobic exercise could significantly reduce hepatic lipid accumulation, inflammatory infiltration and fibrosis progression in the liver of NASH mice. Hepatic thyroid hormone signaling activation and circulating thyroid hormones is potentially involved in the amelioration effect of aerobatic exercise on NASH progression.

The change in thyroid hormone signaling by altered training intensity in male rat skeletal muscle

Aerobic (sub lactate threshold; sub-LT) exercise training facilitates oxidative phosphorylation and glycolysis of skeletal muscle. Thyroid hormone (TH) also facilitates such metabolic events. Thus, we studied whether TH signaling pathway is activated by treadmill training. Male adult rats received 30 min/day treadmill training with different exercise intensity for 12 days. Then plasma lactate and thyrotropin (TSH) levels were measured. By lactate levels, rats were divided into stationary control (SC, 0 m/min), sub-LT (15 m/min) and supra lactate threshold (supra-LT; 25 m/min) training groups. Immediately after the last training, the soleus muscles were dissected out to measure TH receptor (TR) mRNA and protein expressions. Other rats received intraperitoneal injection of T3, 24 h after the last training and sacrificed 6 h after the injection to measure TH target gene expression. TSH level was suppressed in both sub-LT and supra-LT groups during the exercise. TRβ1 mRNA and protein levels were increased in sub-LT group. Sensitivity to T3 was altered in several TH-target genes by training. Particularly, induction of Na(+)/K(+)-ATPase β1 expression by T3 was significantly augmented in sub-LT group. These results indicate that sub-LT training alters TH signaling at least in part by increasing TRβ1 expression. Such TH signaling alteration may contribute metabolic adaptation in skeletal muscle during physical training.

Voluntary exercise adapts the hypothalamus-pituitary-thyroid axis in male rats

The hypothalamic-pituitary thyroid (HPT) axis modulates energy homeostasis. Its activity decreases in conditions of negative energy balance but the effects of chronic exercise on the axis are controversial and unknown at hypothalamic level. Wistar male rats were exposed for up to 14 days to voluntary wheel running (WR), or pair-feeding (PF; 18% food restriction), or to repeated restraint (RR), a mild stressor. WR and RR diminished food intake; body weight gain decreased in the 3 experimental groups, but WAT mass and serum leptin more intensely in the WR group. WR, but not RR, produced a delayed inhibition of central markers of HPT axis activity. At day 14, in WR rats paraventricular nucleus-pro-TRH mRNA and serum TSH levels decreased, anterior pituitary TRH-receptor 1 mRNA levels increased, but serum thyroid hormone levels were unaltered, which is consistent with decreased secretion of TRH and clearance of thyroid hormones. A similar pattern was observed if WR animals were euthanized during their activity phase. In contrast, in PF animals the profound drop of HPT axis activity included decreased serum T3 levels and hepatic deiodinase 1 activity; these changes were correlated with an intense increase in serum corticosterone levels. WR effects on HPT axis were not associated with changes in the activity of the hypothalamic-pituitary adrenal axis, but correlated positively with serum leptin levels. These data demonstrate that voluntary WR adapts the status of the HPT axis, through pathways that are distinct from those observed during food restriction or repeated stress.

Grazing behaviour, physical activity and metabolic profile of two Holstein strains in an organic grazing system

The challenge for sustainable organic dairy farming is identification of cows that are well adapted to forage-based production systems. Therefore, the aim of this study was to compare the grazing behaviour, physical activity and metabolic profile of two different Holstein strains kept in an organic grazing system without concentrate supplementation. Twelve Swiss (HCH ; 566 kg body weight (BW) and 12 New Zealand Holstein-Friesian (HNZ ; 530 kg BW) cows in mid-lactation were kept in a rotational grazing system. After an adaptation period, the milk yield, nutrient intake, physical activity and grazing behaviour were recorded for each cow for 7 days. On three consecutive days, blood was sampled at 07:00, 12:00 and 17:00 h from each cow by jugular vein puncture. Data were analysed using linear mixed models. No differences were found in milk yield, but milk fat (3.69 vs. 4.05%, P = 0.05) and milk protein percentage (2.92 vs. 3.20%, P < 0.01) were lower in HCH than in HNZ cows. Herbage intake did not differ between strains, but organic matter digestibility was greater (P = 0.01) in HCH compared to HNZ cows. The HCH cows spent less (P = 0.04) time ruminating (439 vs. 469 min/day) and had a lower (P = 0.02) number of ruminating boli when compared to the HNZ cows. The time spent eating and physical activity did not differ between strains. Concentrations of IGF-1 and T3 were lower (P ≤ 0.05) in HCH than HNZ cows. In conclusion, HCH cows were not able to increase dry matter intake in order to express their full genetic potential for milk production when kept in an organic grazing system without concentrate supplementation. On the other hand, HNZ cows seem to compensate for the reduced nutrient availability better than HCH cows but could not use that advantage for increased production efficiency.

Metabolism of grazed vs. zero-grazed dairy cows throughout the vegetation period: hepatic and blood plasma parameters

Grass may have a differential impact on the metabolism of the dairy cow, depending on the grazing system applied. In this study, the hypothesis was tested that metabolism of grazed vs. zero-grazed dairy cows is differently regulated throughout the vegetation period. The study included three experimental periods (p1, p2 and p3) of 14 days each, and two treatments [grazing from pasture, PASTURE, n = 9; or zero-grazing in a free-stall barn (BARN, n = 9)]. Blood and liver samples were collected at the end of each period when the cows were on average 64, 120 and 197 DIM. Concentrations of metabolites and hormones, and activities of various enzymes were determined in plasma. Liver samples were measured for mRNA abundance of genes encoding enzymes and nuclear receptors involved in metabolic pathways. PASTURE cows had higher plasma concentrations of T(3), BHB, and total protein than BARN cows across periods (p < 0.05). BARN cows had higher concentrations of NEFA (in p1) and urea (in p1 and p2) in relation PASTURE cows (p < 0.05), and had higher mRNA abundance of liver-X-receptor-α and glycerol-3-phosphate-acyltransferase across periods (p < 0.05). The results confirm the hypothesis that metabolism is different between BARN and PASTURE cows throughout the vegetation period, and show that the observed differences are mainly reflected in parameters of lipid metabolism.

The effect of acute and chronic exercise on thyroid hormones in obesity

Thyroid hormones were measured before, during and after acute exercise (60 min) or physical training (3 months) in obese women. Thyroid stimulating hormone concentration increased during acute work and decreased immediately after. No changes were seen during the two following days. An increase was seen after ten days as well as after three months of physical training. Thyroxine concentrations showed no changes. 3,5,3'-Triiodothyronine decreased slightly immediately after acute exercise, and after three months of physical training, 3,3',5'-triiodothyronine (reverse triiodothyronine) increased slowly during and after acute exercise. A negative correlation was found between changes in fasting insulin and thyroxine and a positive correlation between changes in blood pressure and triiodothyronine after training. Lack of agreement in previous reports is probably due to methodological differences such as methods more or less susceptible to fatty acid interference, and thyroid hormones changing differently during acute work and before and after physical training. The duration of the study may also be of importance, even 3 months possibly being too short for attaining equilibrium in thyroid homeostasis.

Exercise and adrenaline increase PGC-1{alpha} mRNA expression in rat adipose tissue

The purpose of the present investigation was to explore the effects of exercise and adrenaline on the mRNA expression of PGC-1alpha, a master regulator of mitochondrial biogenesis, in rat abdominal adipose tissue. We hypothesized that (1) exercise training would increase PGC-1alpha mRNA expression in association with increases in mitochondrial marker enzymes, (2) adrenaline would increase PGC-1alpha mRNA expression and (3) the effect of exercise on PGC-1alpha mRNA expression in white adipose tissue would be attenuated by a beta-blocker. Two hours of daily swim training for 4 weeks led to increases in mitochondrial marker proteins and PGC-1alpha mRNA expression in epididymal and retroperitoneal fat depots. Additionally, a single 2 h bout of exercise led to increases in PGC-1alpha mRNA expression immediately following exercise cessation. Adrenaline treatment of adipose tissue organ cultures led to dose-dependent increases in PGC-1alpha mRNA expression. A supra-physiological concentration of adrenaline increased PGC-1alpha mRNA expression in epididymal but not retroperitoneal adipose tissue. beta-Blockade attenuated the effects of an acute bout of exercise on PGC-1alpha mRNA expression in epididymal but not retroperitoneal fat pads. In summary, this is the first investigation to demonstrate that exercise training, an acute bout of exercise and adrenaline all increase PGC-1alpha mRNA expression in rat white adipose tissue. Furthermore it would appear that increases in circulating catecholamine levels may be one potential mechanism mediating exercise induced increases in PGC-1alpha mRNA expression in rat abdominal adipose tissue.

Relation between plasma adenosine and serum TSH levels in women with hyperemesis gravidarum

INTRODUCTION

This study investigated the relation between adenosine and thyroid function associated with hyperemesis gravidarum.

METHODS

We examined 84 Japanese singleton pregnant women with an average age of 33.0+/-5.8 years at 9-12 weeks gestation being managed at our hospital. The patients were divided into three groups according to the severity of emesis: (1) those with hyperemesis gravidarum (nausea and vomiting with weight loss >5%, n=13), (2) those with emesis (nausea and vomiting with weight loss <5%, n=31), and (3) those with no symptoms as a control (n=40).

RESULTS

The average serum TSH levels in the emesis and hyperemesis groups were significantly higher than that in the control group (P<0.05). The average plasma adenosine level in the hyperemesis group was significantly higher than those in the control pregnant and emesis groups (P<0.05). There were no significant differences in plasma adenosine levels between the control pregnant and emesis groups. The serum TSH level showed significant correlations with weight loss (%) and plasma adenosine levels (P<0.05).

CONCLUSIONS

Our findings support the possible role of adenosine in counteracting the further progression of hyperemesis gravidarum associated with gestational thyrotoxicosis.

Expression of MHC-beta and MCT1 in cardiac muscle after exercise training in myocardial-infarcted rats

To evaluate the hypothesis that increasing the potential for glycolytic metabolism would benefit the functioning of infarcted myocardium, we investigated whether mild exercise training would increase the activities of oxidative enzymes, expression of carbohydrate-related transport proteins (monocarboxylate transporter MCT1 and glucose transporter GLUT4), and myosin heavy chain (MHC) isoforms. Myocardial infarction (MI) was produced by occluding the proximal left coronary artery in rat hearts for 30 min. After the rats performed 6 wk of run training on a treadmill, the wall of the left ventricle was dissected and divided into the anterior wall (AW; infarcted region) and posterior wall (PW; noninfarcted region). MI impaired citrate synthase and 3-hydroxyacyl-CoA dehydrogenase activities in the AW (P < 0.01) but not in the noninfarcted PW. No differences in the expression of MCT1 were found in either tissues of AW and PW after MI, whereas exercise training significantly increased the MCT1 expression in all conditions, except AW in the MI rats. Exercise training resulted in an increased expression of GLUT4 protein in the AW in the sham rats and in the PW in the MI rats. The relative amount of MHC-beta was significantly increased in the AW and PW in MI rats compared with sham rats. However, exercise training resulted in a significant increase of MHC-alpha expression in both AW and PW in both sham and MI rats (P < 0.01). These findings suggest that mild exercise training enhanced the potential for glycolytic metabolism and ATPase activity of the myocardium, even in the MI rats, ensuring a beneficial role in the remodeling of the heart.

Exercise training improves cardiac function-related gene levels through thyroid hormone receptor signaling in aged rats

Exercise training improves the aging-induced downregulation of myosin heavy chain (MHC) and sarcoplasmic reticulum (SR) Ca(2+)-ATPase, which participate in the regulation of cardiac contraction and relaxation. Thyroid hormone receptor (TR), a transcriptional activator, affected the regulation of gene expression of MHC and SR Ca(2+)-ATPase. We hypothesized that myocardial TR signaling contributes to a molecular mechanism of exercise training-induced improvement of MHC and SR Ca(2+)-ATPase genes with cardiac function in old age. We investigated whether TR signaling and gene expression of MHC and SR Ca(2+)-ATPase in the aged heart are affected by exercise training, using the hearts of sedentary young rats (4 mo old), sedentary aged rats (23 mo old), and trained aged rats (23 mo old, swimming training for 8 wk). Trained aged rats showed improvement in cardiac function. Expression of TR-alpha1 and TR-beta1 proteins in the heart were significantly lower in sedentary aged rats than in sedentary young rats and were significantly higher in trained aged rats than in sedentary aged rats. The activity of TR DNA binding to the transcriptional regulatory region in the alpha-MHC and SR Ca(2+)-ATPase genes and the mRNA and protein expression of alpha-MHC and SR Ca(2+)-ATPase in the heart and plasma 3,3'-triiodothyronine and thyroxine levels were altered in association with changes in the myocardial TR protein levels. These findings suggest that exercise training improves the aging-induced downregulation of myocardial TR signaling-mediated transcription of MHC and SR Ca(2+)-ATPase genes, thereby contributing to the improvement of cardiac function in trained aged hearts.

Bioassayable growth hormone release in rats in response to a single bout of treadmill exercise

Plasma growth hormone (GH) measured by immunoassay [immunoassayable GH (IGH)] and by tibial bioassay [bioassayable GH (BGH)] increases in humans in response to exercise. In rats, however, IGH does not change in response to exercise. The objective of this study was to determine the BGH response to an acute exercise bout in rats. The rats ran on a treadmill at a rate of 27 m/min for 15 min, after which plasma and pituitary hormones, including IGH and BGH, and plasma metabolites were measured. Plasma and pituitary IGH were unchanged from control groups after the acute exercise bout, whereas plasma BGH was increased by 300% and pituitary BGH was decreased by 50%. Plasma thyroxine and corticosterone levels were significantly increased after a single exercise bout, but plasma testosterone, 3,5, 3'-triiodothyronine, glucose, lactate, and triglyceride concentrations were unchanged. Given previous results from in situ nerve stimulation studies (Gosselink KL, Grindeland RE, Roy RR, Zhong H, Bigbee AJ, Grossman EJ, and Edgerton VR. J Appl Physiol 84: 1425-1430, 1998), these in vivo results are consistent with the rapid BGH response during exercise being induced by the activation of muscle afferents.

The effects of aerobic and anaerobic exercise conditioning on resting metabolic rate and the thermic effect of a meal

This study examined resting metabolic rate (RMR) and thermic effect of a meal (TEM) among athletes who had participated in long-term anaerobic or aerobic exercise. Nine collegiate wrestlers were matched for age, weight, and fat-free weight with 9 collegiate swimmers. Preliminary testing included maximal oxygen consumption, maximal anaerobic capacity (MAnC) for both the arms and the legs, and percent body fat. On two separate occasions, RMR and TEM were measured using indirect calorimetry. VO2max was significantly higher in the swimmers while MAnC was significantly higher in the wrestlers for both the arms and the legs. RMR adjusted for fat-free weight was not significantly different between groups. The differences in total and percentage of TEM between the groups were not statistically significant, and there were no differences in baseline thyroid hormones. These data suggest that despite significant differences in VO2max and WAnT values following long-term aerobic and anaerobic exercise training, resting energy expenditure does not differ between these college athletes.

Exercise training and dietary carbohydrate: effects on selected hormones and the thermic effect of feeding

To determine relationships among dietary carbohydrate, aerobic exercise training, the thermic effect of food (TEF), and hormonal responses to feeding, 8 trained and 7 sedentary men consumed diets providing 15, 45, or 75% of energy as carbohydrate for 5 days. On Day 6, metabolic rate was measured before as well as 30, 60, 90, and 120 min after an 868-kcal liquid test breakfast. Blood was sampled hourly during Day 5 and during each metabolic rate measurement. The trained group had a larger TEF (40 +/- 2.4 vs. 31 +/- 3.0 kcal/2 hrs), greater insulin sensitivity, and greater plasma prolactin and cortisol levels. As carbohydrate in the treatment diet increased, carbohydrate utilization and thyroid stimulating hormone were higher and thyroxine was lower, but TEF was not significantly different. After the test meal, trained individuals had a higher TEF but the carbohydrate content of the treatment diet did not influence TEF.

Sex differences in lactate and glycerol levels during maximal aerobic and anaerobic running

Lactate, glycerol, adrenaline, and noradrenaline in venous blood following 400 m and 3000 m runs were measured in 6 untrained male students, 5 female handball players, 6 female sprinters and 6 female long-distance runners. Physical performance in the two events by the untrained males was the same as for the female handball players, but was less than that by the female sprinters and female long-distance runners. Peak blood lactate levels obtained after 400 m sprinting, and glycerol concentration following the 3000 m run were not significantly different between the untrained males and the female handball players. On the other hand, both peak blood lactate concentrations after 400 m sprinting for female sprinters and peak blood glycerol levels following a 3000 m run for female long-distance runners were significantly higher than those in the untrained male subjects. In both runs there was no significant difference in adrenaline and noradrenaline between the untrained male group and the female handball players. These results suggest that blood lactate in a 400 m run, and glycerol in a 3000 m run might be a reflection of physical performance level but not of sex difference.

Thyroid hormone action on intermediary metabolism. Part II: Lipid metabolism in hypo- and hyperthyroidism

Despite their enhanced endogenous de novo cholesterol synthesis, hyperthyroid patients exhibit decreased total and low-density lipoprotein (LDL) cholesterol levels in the serum because of a concomitant increase in LDL catabolism, cholesterol excretion by bile and a reduced enterohepatic bile acid circulation. Hypothyroidism exhibits a reduction (1) in the synthesis of cholesterol and (2) in LDL catabolism, whereas cholesterol reabsorption is unchanged or even enhanced. In addition, obese hypothyroid patients showed an increased cholesterol synthesis which is independent of thyroid hormones and which contributes to the observed LDL cholesterolaemia. Thyroid hormones per se have only a minor influence on plasma triglyceride (TG) levels, but they induce an acceleration of TG turnover and chylomicron clearance rate. In addition, the hepatic lipogenic capacity is increased in hyperthyroidism and reduced in hypothyroidism. However, hepatic total and very low-density lipoprotein (VLDL) triglyceride output is decreased by thyroid hormones due to a reduced re-esterification and a simultaneously increased oxidation of newly synthesized fatty acids. Hypothyroid livers, by contrast, reveal an increased VLDL secretion. Despite their reduced lipogenesis, obese hypothyroidism is often accompanied by a hypertriglyceridaemia type III. The simultaneous stimulation of the synthesis of fatty acids, which are still in part converted to TG, and the degradation of TG contributes to the enhanced thermogenesis in hyperthyroid patients. The concentration and turnover of free fatty acids (FFA) are increased in hyperthyroidism, resulting from a thyroid hormone-induced increase in: (1) lipolysis, explained by an increased adipose tissue sensitivity for lipolytic hormones; and (2) oxidation of fatty acids to CO2 as well as to ketone bodies (KB).(ABSTRACT TRUNCATED AT 250 WORDS)

Fatty acid synthesis in adipose tissues of physically trained rats in vivo

The effect of physical training on fatty acid synthesis in vivo was studied. After the rats had free access to a running wheel for 50 days, the rate of fatty acid synthesis estimated using 3H2O in adipose tissues of trained rats was about three times higher than that of sedentary rats in both the light and dark period. The rate of fatty acid synthesis in the liver but not in the brown adipose tissue was also slightly enhanced by physical training. The number of adipocytes was not affected, but the size of adipocytes was reduced by physical training. In trained rats, the rate of fatty acid synthesis in adipocytes whose diameter was similar to that of sedentary rats was about 10 times higher than that of sedentary rats. Within adipose tissue, the rate of fatty acid synthesis correlated positively to the diameter of adipocytes both in the sedentary and trained rats. These findings mean that the adaptive increase in fatty acid synthesis seen in adipocytes of trained rats is not secondary to the reduction in size of adipocytes.

Effect of prolonged exercise on serum lipids and lipoproteins

It has been shown that physical exercise lowers serum triglyceride levels and may increase high density lipoprotein-cholesterol levels. Understanding of the mechanisms responsible for these beneficial adaptations is still incomplete. Twenty-six men, who played soccer continuously for 64 hours to establish a world's record, were monitored for acute changes in lipid metabolism. Food intake was determined before and during the exercise period. Blood specimens were taken before and repeatedly during the match for the measurement of triglycerides (TG), total cholesterol (CH), glycerol, apolipoprotein A-I (apoA-I), and cholesterol in various lipoprotein fractions (quantitative lipoprotein electrophoresis). During exercise TG levels decreased from 116 +/- 26 to 66 +/- 13 mg/dL and CH from 180 +/- 22 to 135 +/- 25 mg/dL. Both TG and glycerol showed an initial increase followed by a continuous decrease. Alpha-CH increased by 19% whereas beta-CH and pre-beta-CH decreased markedly (39% and 78%, respectively). In contrast to alpha-CH, apo A-1 fell only slightly by 10%. These results indicate that the effect of chronic exercise on lipids and lipoproteins can be mimicked by acute prolonged exercise. Similar mechanisms may be involved in these adaptations. Moreover, the extreme length of physical exertion substantially lowered CH.

Thermic effects of food and exercise in lean and obese women

The thermogenic responses of ten lean and ten moderately obese women to food, exercise, and food plus exercise were measured using open circuit respirometry for five minutes every half hour for four hours under six conditions: during five minutes of bicycle exercise at a workload of 300 kpm/min with and without eating a 910 kcal mixed meal; cycling at a workload just below the anaerobic threshold with and without food; and at rest with and without food. Over the four-hour period, the thermic effect of food at rest was similar for the lean and obese groups: 50 kcal and 47 kcal, respectively. Eating before exercise increased the exercise metabolic rate by 11% for the lean women and by 4% for the obese women (P less than 0.005). Exercise potentiated the thermic effect of food for the lean women but nor for the obese women: the thermic effect of food was 2.54 times greater during exercise than at rest for the lean group, but only 1.01 times greater for the obese women (P less than 0.005). This reduced response to the combined stimulus of food plus exercise may constitute a subtle metabolic factor associated with obesity.