Pinealectomy alters adipose tissue adaptability to fasting in rats

A surgical modification in the technique of rat pinealectomy

BACKGROUND

Several experimental intents require pineal gland removal. The main challenge of the pinealectomy surgical procedure is the hemorrhage due to the transverse sinus torn. The study aimed to modify the rat pinealectomy surgical procedure to reduce the risk of bleeding and the mortality rate.

METHODS

Adult male rats experienced pinealectomy surgery. A mini-drill was used to remove a small skull area in the junction of the lambda and sagittal sutures. The pineal gland was removed using a curved-head hook. Animals experienced intensive post-surgical care. Locomotion, cerebellar motor function, working memory, and anxiety were evaluated 2 weeks after pinealectomy by the open field, rotarod, Y maze, and the elevated plus maze, respectively.

RESULTS

Surgical modification reduced the bleeding risk and animal mortality rate. No significant alteration was found in locomotion and working memory. However, the pinealectomy was anxiogenic and decreased entry to the open arm. The cerebellar motor performance did not change in the rotarod test. Hematoxylin-Eosin staining of removed tissue confirmed the histology of the pineal gland.

CONCLUSION

Advantages of this technique were removing a small skull area, modifying the hook insertion point to prevent damaging the brain veins, reducing the bleeding risk and the mortality rate. Surgery modification was associated with a decreased final number of animals used. Regardless of the melatonin shortage, pinealectomy affects different organs, which should be considered in the research study design.

Weighted single-step GWAS for body mass index and scans for recent signatures of selection in Yorkshire pigs

Controlling extra fat deposition is economically favorable in modern swine industry. Understanding the genetic architecture of fat deposition traits such as body mass index (BMI) can help in improving genomic selection for such traits. We utilized a weighted single-step genome-wide association study (WssGWAS) to detect genetic regions and candidate genes associated with BMI in a Yorkshire pig population. Three extended haplotype homozygosity (EHH)-related statistics were also incorporated within a de-correlated composite of multiple signals (DCMS) framework to detect recent selection signatures signals. Overall, the full pedigree consisted of 7,016 pigs, of which 5,561 had BMI records and 598 pigs were genotyped with an 80 K single nucleotide polymorphism (SNP) array. Results showed that the most significant windows (top 15) explained 9.35% of BMI genetic variance. Several genes were detected in regions previously associated with pig fat deposition traits and treated as potential candidate genes for BMI in Yorkshire pigs: FTMT, SRFBP1, KHDRBS3, FOXG1, SOD3, LRRC32, TSKU, ACER3, B3GNT6, CCDC201, ADCY1, RAMP3, TBRG4, CCM2. Signature of selection analysis revealed multiple candidate genes previously associated with various economic traits. However, BMI genetic variance explained by regions under selection pressure was minimal (1.31%). In conclusion, candidate genes associated with Yorkshire pigs’ BMI trait were identified using WssGWAS. Gene enrichment analysis indicated that the identified candidate genes were enriched in the insulin secretion pathway. We anticipate that these results further advance our understanding of the genetic architecture of BMI in Yorkshire pigs and provide information for genomic selection for fat deposition in this breed.

Agomelatine reduces circulating triacylglycerides and hepatic steatosis in fructose-treated rats

Agomelatine (AGO) is an antidepressant drug with agonistic activity at melatonin receptor 1 (MT1) and MT2 and with neutral antagonistic activity at serotonin receptor 5-HT2_C. Although experimental studies show that melatonin reduces hypertriglyceridemia and hepatic steatosis induced by excessive fructose intake, no studies have tested if AGO exerts similar actions. To address this issue we have treated male Wistar rats with fructose (15% in the drinking water) and/or AGO (40 mg/kg/day) for two weeks. AGO reduced body weight gain, feeding efficiency and hepatic lipid levels without affecting caloric intake in fructose-treated rats. AGO has also decreased very low-density lipoprotein (VLDL) production and circulating TAG levels after an oral load with olive oil. Accordingly, treatment with AGO reduced the hepatic expression of fatty acid synthase (Fasn), a limiting step for hepatic de novo lipogenesis (DNLG). The expression of apolipoprotein B (Apob) and microsomal triglyceride transfer protein (Mttp) in the ileum, two crucial proteins for intestinal lipoprotein production, were also downregulated by treatment with AGO. Altogether, the present data show that AGO mimics the metabolic benefits of melatonin when used in fructose-treated rats. This study also suggests that it is relevant to evaluate the potential of AGO to treat metabolic disorders in future clinical trials.

The effects of melatonin daily supplementation to aged rats on the ability to withstand cold, thermoregulation and body weight

AIMS

Investigate the role of melatonin on the regulation of body temperature in aged animals that have impaired melatonin production.

MATERIAL AND METHODS

Aged Male Wistar rats were randomly assigned to the following groups: 1) control (vehicle added to the water bottles during the dark phase) and 2) melatonin-treated (10 mg/kg melatonin added to the water bottles during the dark phase). Before and after 16 weeks of vehicle or melatonin treatment, control group and melatonin-treated animals were acutely exposed to 18 °C for 2 h for an acute cold challenge and thermal images were obtained using an infrared camera. After 16 weeks, animals were euthanized and brown and beige adipocytes were collected for analysis of genes involved in the thermogenesis process by real-time PCR, and the uncoupling protein expression was evaluated by immunoblotting. Browning intensity of beige adipocytes were quantified by staining with hematoxylin-eosin.

KEY FINDINGS

Chronic melatonin supplementation induced a minor increase in body mass and increased the animal's thermogenic potential in the cold acute challenge. Brown and beige adipocytes acted in a coordinated and complementary way to ensure adequate heat production.

SIGNIFICANCE

Melatonin plays an important role in the thermoregulatory mechanisms, ensuring greater capacity to withstand cold and, also, participating in the regulation of energy balance.

Effects of Melatonin on Lipid Metabolism and Circulating Irisin in Sprague-Dawley Rats with Diet-Induced Obesity

Melatonin, a pivotal photoperiodic signal transducer, may work as a brown-fat inducer that regulates energy balance. Our study aimed to investigate the effects of melatonin treatment on the body fat accumulation, lipid profiles, and circulating irisin of rats with high-fat diet-induced obesity (DIO). Methods: 30 male Sprague-Dawley rats were divided into five groups and treated for 8 weeks: vehicle control (VC), positive control (PC), MEL10 (10 mg melatonin/kg body weight (BW)), MEL20 (20 mg/kg BW), and MEL50 (50 mg/kg BW). The vehicle control group was fed a control diet, and the other groups were fed a high-fat and high-calorie diet for 8 weeks to induce obesity before the melatonin treatment began. Melatonin reduced weight gain without affecting the food intake, reduced the serum total cholesterol level, enhanced the fecal cholesterol excretion, and increased the circulating irisin level. Melatonin downregulated the fibronectin type III domain containing 5 (FNDC5) and lipoprotein lipase (LPL) mRNA expressions of inguinal white adipose tissue (iWAT) and induced the browning of iWAT in both the MEL10 and MEL20 groups. Conclusion: Chronic continuous melatonin administration in drinking water reduced weight gain and the serum total cholesterol levels. Additionally, it enhanced the circulating irisin, which promoted brite/beige adipocyte recruitment together with cholesterol excretion and contributed to an anti-obesity effect.

Physiological mechanisms underlying children's circannual growth patterns and their contributions to the obesity epidemic in elementary school age children

Several studies since the 1990s have demonstrated that children increase their body mass index at a faster rate during summer months compared with the school year, leading some to conclude that the out-of-school summer environment is responsible. Other studies, however, have suggested that seasonality may play a role in children's height and weight changes across the year. This article reviews evidence for seasonal differences in the rate of children's height and weight gain and proposes potential physiological mechanisms that may explain these seasonal variations.

Abnormal Hippocampal Melatoninergic System: A Potential Link between Absence Epilepsy and Depression-Like Behavior in WAG/Rij Rats?

Absence epilepsy and depression are comorbid disorders, but the molecular link between the two disorders is unknown. Here, we examined the role of the melatoninergic system in the pathophysiology of spike and wave discharges (SWDs) and depression-like behaviour in the Wistar Albino Glaxo from Rijswijk (WAG/Rij) rat model of absence epilepsy. In WAG/Rij rats, SWD incidence was higher during the dark period of the light-dark cycle, in agreement with previous findings. However, neither pinealectomy nor melatonin administration had any effect on SWD incidence, suggesting that the melatoninergic system was not involved in the pathophysiology of absence-like seizures. Endogenous melatonin levels were lower in the hippocampus of WAG/Rij rats as compared to non-epileptic control rats, and this was associated with higher levels of melatonin receptors in the hippocampus, but not in the thalamus. In line with the reduced melatonin levels, cell density was lower in the hippocampus of WAG/Rij rats and was further reduced by pinealectomy. As expected, WAG/Rij rats showed an increased depression-like behaviour in the sucrose preference and forced swim tests, as compared to non-epileptic controls. Pinealectomy abolished the difference between the two strains of rats by enhancing depression-like behaviour in non-epileptic controls. Melatonin replacement displayed a significant antidepressant-like effect in both WAG/Rij and control rats. These findings suggest that a defect of hippocampal melatoninergic system may be one of the mechanisms underlying the depression-like phenotype in WAG/Rij rats and that activation of melatonin receptors might represent a valuable strategy in the treatment of depression associated with absence epilepsy.

Leptin, neuropeptide Y (NPY), melatonin and zinc levels in experimental hypothyroidism and hyperthyroidism: relation with melatonin and the pineal gland

Background Melatonin, an important neurohormone released from the pineal gland, is generally accepted to exercise an inhibitor effect on the thyroid gland. Zinc mediates the effects of many hormones and is found in the structure of numerous hormone receptors. Aim The present study aims to examine the effect of melatonin supplementation and pinealectomy on leptin, neuropeptide Y (NPY), melatonin and zinc levels in rats with hypothyroidism and hyperthyroidism. Methods This study was performed on the 70 male rats. Experimental animals in the study were grouped as follows: control (C); hypothyroidism (PTU); hypothyroidism + melatonin (PTU + M); hypothyroidism + pinealectomy (PTU + Pnx); hyperthyroidism (H); hyperthyroidism + melatonin (H + M) and hyperthyroidism + pinealectomy (H + Pnx). Blood samples collected at the end of 4-week procedures were analyzed to determine melatonin, leptin, NPY and zinc levels. Results It was found that thyroid parameters thyroid stimulating hormone (TSH), free triiodthyronine (FT3), free thyroxine (FT4), total T3 (TT3) and total T4 (TT4) decreased in hypothyroidism groups and increased in the groups with hyperthyroidism. The changes in these hormones remained unaffected by melatonin supplementation and pinealectomy. Melatonin levels rose in hyperthyroidism and fell in hypothyroidism. Leptin and NPY levels increased in both hypothyroidism and hyperthyroidism. Zinc levels, on the other hand, decreased in hypothyroidism and pinealectomy, but increased in hyperthyroidism. Conclusion The results of the study demonstrate that hypothyroidism and hyperthyroidism affect leptin, NPY, melatonin and zinc values in different ways in rats. However, melatonin supplementation and pinealectomy do not have any significant influence on the changes occurring in leptin, NPY and zinc levels in thyroid dysfunction.

Circadian and Metabolic Effects of Light: Implications in Weight Homeostasis and Health

Daily interactions between the hypothalamic circadian clock at the suprachiasmatic nucleus (SCN) and peripheral circadian oscillators regulate physiology and metabolism to set temporal variations in homeostatic regulation. Phase coherence of these circadian oscillators is achieved by the entrainment of the SCN to the environmental 24-h light:dark (LD) cycle, coupled through downstream neural, neuroendocrine, and autonomic outputs. The SCN coordinate activity and feeding rhythms, thus setting the timing of food intake, energy expenditure, thermogenesis, and active and basal metabolism. In this work, we will discuss evidences exploring the impact of different photic entrainment conditions on energy metabolism. The steady-state interaction between the LD cycle and the SCN is essential for health and wellbeing, as its chronic misalignment disrupts the circadian organization at different levels. For instance, in nocturnal rodents, non-24 h protocols (i.e., LD cycles of different durations, or chronic jet-lag simulations) might generate forced desynchronization of oscillators from the behavioral to the metabolic level. Even seemingly subtle photic manipulations, as the exposure to a “dim light” scotophase, might lead to similar alterations. The daily amount of light integrated by the clock (i.e., the photophase duration) strongly regulates energy metabolism in photoperiodic species. Removing LD cycles under either constant light or darkness, which are routine protocols in chronobiology, can also affect metabolism, and the same happens with disrupted LD cycles (like shiftwork of jetlag) and artificial light at night in humans. A profound knowledge of the photic and metabolic inputs to the clock, as well as its endocrine and autonomic outputs to peripheral oscillators driving energy metabolism, will help us to understand and alleviate circadian health alterations including cardiometabolic diseases, diabetes, and obesity.

Role of melatonin in glucose uptake by cardiomyocytes from insulin-resistant Wistar rats

Aim

Melatonin supplementation reduces insulin resistance and protects the heart in obese rats. However, its role in myocardial glucose uptake remains unknown. This study investigated the effect of short-term melatonin treatment on glucose uptake by cardiomyocytes isolated from obese and insulin-resistant rats.

Methods

Cardiomyocytes were isolated from obese rats fed a high-calorie diet for 16 to 23 weeks, their age-matched controls, as well as young control rats aged four to eight weeks. After incubation with melatonin with or without insulin, glucose uptake was initiated by the addition of 2-deoxy-D-[3H] glucose and measured after 30 minutes. Additional control and obese rats received melatonin in the drinking water (4 mg/kg/day) for the last six weeks of feeding (20 weeks) and glucose uptake was determined in isolated cardiomyocytes after incubation with insulin. Intraperitoneal glucose tolerance and biometric parameters were also measured.

Results

Obese rats (fed for more than 20 weeks) developed glucose intolerance. Cardiomyocytes isolated from these obese rats had a reduced response to insulin-stimulated glucose uptake (ISGU) (p < 0.05). Melatonin administration in vitro had no effect on glucose uptake per se. However, it increased ISGU by cardiomyocytes from the young rats (p < 0.05), while having no effect on ISGU by cardiomyocytes from the older control and obese groups. Melatonin in vivo had no significant effect on glucose tolerance, but it increased basal (p < 0.05) and ISGU by cardiomyocytes from the obese rats (50.1 ± 1.7 vs 32.1 ± 5.1 pmol/mg protein/30 min, p < 0.01).

Conclusion

These data suggest that short-term melatonin treatment in vivo but not in vitro improved glucose uptake and insulin responsiveness of cardiomyocytes in obesity and insulin-resistance states.

Inter-relationships of the chronobiotic, melatonin, with leptin and adiponectin: implications for obesity

Obesity and its medical complications represent a significant problem throughout the world. In recent decades, mechanisms underlying the progression of obesity have been intensively examined. The involvement of both the behavioral aspects, such as calorie-rich diet, low physical activity and sleep deprivation, and the intrinsic factors, including adipose tissue deregulation, chronic inflammation, oxidative stress, and chronodisruption, has been identified. The circadian disturbances of the adipose tissue endocrine function have been correlated with obesity. Leptin and adiponectin are adipokines strongly associated with glucose and lipid metabolism and with energy balance. Their synthesis and secretion display circadian rhythms that are disturbed in the obese state. Hyperleptinemia resulting in leptin resistance, and hypo-adiponectinemia have been linked to the pathophysiology of the obesity-related disorders. A deficiency of melatonin, one of the consequences of sleep deprivation, has also been demonstrated to correlate with obesity. Melatonin is a pineal secretory product involved in numerous actions, such as regulation of internal biological clocks and energy metabolism, and it functions as an antioxidant and as an anti-inflammatory agent. There exists a substantial amount of evidence supporting the beneficial effects of melatonin supplementation on obesity and its complications. In the current review, the results of studies related to the interactions between melatonin, and both leptin and adiponectin are discussed. Despite the existence of some inconsistencies, melatonin has been found to normalize the expression and secretion patterns of both adipokines. These results support the concept of melatonin as a potential therapeutic agent for obesity and related disorders.

Melatonin promotes adipogenesis and mitochondrial biogenesis in 3T3-L1 preadipocytes

Melatonin is synthesized in the pineal gland, but elicits a wide range of physiological responses in peripheral target tissues. Recent advances suggest that melatonin controls adiposity, resulting in changes in body weight. The aim of this study was to investigate the effect of melatonin on adipogenesis and mitochondrial biogenesis in 3T3-L1 mouse embryo fibroblasts. Melatonin significantly increased the expression of peroxisome proliferator-activated receptor-γ (PPAR-γ), a master regulator of adipogenesis, and promoted differentiation into adipocytes. Melatonin-treated cells also formed smaller lipid droplets and abundantly expressed several molecules associated with lipolysis, including adipose triglyceride lipase, perilipin, and comparative gene identification-58. Moreover, the hormone promoted biogenesis of mitochondria, as indicated by fluorescent staining, elevated the citrate synthase activity, and upregulated the expression of PPAR-γ coactivator 1 α, nuclear respiratory factor-1, and transcription factor A. The expression of uncoupling protein 1 was also observable both at mRNA and at protein level in melatonin-treated cells. Finally, adiponectin secretion and the expression of adiponectin receptors were enhanced. These results suggest that melatonin promotes adipogenesis, lipolysis, mitochondrial biogenesis, and adiponectin secretion. Thus, melatonin has potential as an anti-obesity agent that may reverse obesity-related disorders.

Pinealectomy interferes with the circadian clock genes expression in white adipose tissue

Melatonin, the main hormone produced by the pineal gland, is secreted in a circadian manner (24-hr period), and its oscillation influences several circadian biological rhythms, such as the regulation of clock genes expression (chronobiotic effect) and the modulation of several endocrine functions in peripheral tissues. Assuming that the circadian synchronization of clock genes can play a role in the regulation of energy metabolism and it is influenced by melatonin, our study was designed to assess possible alterations as a consequence of melatonin absence on the circadian expression of clock genes in the epididymal adipose tissue of male Wistar rats and the possible metabolic repercussions to this tissue. Our data show that pinealectomy indeed has impacts on molecular events: it abolishes the daily pattern of the expression of Clock, Per2, and Cry1 clock genes and Pparγ expression, significantly increases the amplitude of daily expression of Rev-erbα, and affects the pattern of and impairs adipokine production, leading to a decrease in leptin levels. However, regarding some metabolic aspects of adipocyte functions, such as its ability to synthesize triacylglycerols from glucose along 24 hr, was not compromised by pinealectomy, although the daily profile of the lipogenic enzymes expression (ATP-citrate lyase, malic enzyme, fatty acid synthase, and glucose-6-phosphate dehydrogenase) was abolished in pinealectomized animals.

Streptozotocin-induced diabetes disrupts the body temperature daily rhythm in rats

BACKGROUND

In mammals, the temperature rhythm is regulated by the circadian pacemaker located in the suprachiasmatic nuclei, and is considered a "marker rhythm". Melatonin, the pineal gland hormone, is a major regulator of the endogenous rhythms including body temperature. Its production is influenced by many factors, such as type 1 diabetes mellitus. In rats, diabetes leads to hypothermia and reduced melatonin synthesis; insulin treatment reestablishes both.

AIM

To study the body temperature daily rhythm of diabetic animals and the effects of insulin and/or melatonin treatment on its structure.

METHODS

We studied the effects of streptozotocin-induced diabetes (60 mg/kg) on the body temperature rhythm of Wistar rats and the possible modifications resulting from early and late treatments with insulin (6U/day) and/or melatonin (daily 0.5 mg/kg). We monitored the daily body temperature rhythm, its rhythmic parameters (MESOR, amplitude and acrophase), glycemia and body weight for 55 days. Data were classified by groups and expressed as mean ± SEM. One-way ANOVA analysis was performed followed by Bonferroni posttest. Statistical significance was set at p < 0.05.

RESULTS

Diabetes led to complete disruption of the temperature rhythm and hypothermia, which were accentuated over time. All early treatments (insulin or/and melatonin) prevented the temperature rhythm disruption and hypothermia. Insulin plus melatonin restored the body temperature rhythm whereas insulin alone resulted less efficient; melatonin alone did not restore any of the parameters studied; however, when supplemented close to diabetes onset, it maintained the temperature rhythmicity. All these corrective effects of the early treatments were dependent on the continuous maintenance of the treatment.

CONCLUSIONS

Taken together, our findings show the disruption of the body temperature daily rhythm, a new consequence of insulin-dependent diabetes, as well as the beneficial effect of the complementary action of melatonin and insulin restoring the normal rhythmicity.

Melatonin, energy metabolism, and obesity: a review

Melatonin is an old and ubiquitous molecule in nature showing multiple mechanisms of action and functions in practically every living organism. In mammals, pineal melatonin functions as a hormone and a chronobiotic, playing a major role in the regulation of the circadian temporal internal order. The anti-obesogen and the weight-reducing effects of melatonin depend on several mechanisms and actions. Experimental evidence demonstrates that melatonin is necessary for the proper synthesis, secretion, and action of insulin. Melatonin acts by regulating GLUT4 expression and/or triggering, via its G-protein-coupled membrane receptors, the phosphorylation of the insulin receptor and its intracellular substrates mobilizing the insulin-signaling pathway. Melatonin is a powerful chronobiotic being responsible, in part, by the daily distribution of metabolic processes so that the activity/feeding phase of the day is associated with high insulin sensitivity, and the rest/fasting is synchronized to the insulin-resistant metabolic phase of the day. Furthermore, melatonin is responsible for the establishment of an adequate energy balance mainly by regulating energy flow to and from the stores and directly regulating the energy expenditure through the activation of brown adipose tissue and participating in the browning process of white adipose tissue. The reduction in melatonin production, as during aging, shift-work or illuminated environments during the night, induces insulin resistance, glucose intolerance, sleep disturbance, and metabolic circadian disorganization characterizing a state of chronodisruption leading to obesity. The available evidence supports the suggestion that melatonin replacement therapy might contribute to restore a more healthy state of the organism.

Influence of melatonin receptor signalling on parameters involved in blood glucose regulation

The pineal hormone melatonin is known to influence insulin secretion via the G-protein-coupled receptor isoforms MT1 and MT2. The present study was aimed to further elucide the impact of melatonin on blood glucose regulation. To this end, mouse lines were used, in which one of the two or both melatonin receptors were deleted. In comparison with wild-type mice of the same age (8-12 months old), increased plasma insulin and melatonin levels and decreased blood glucose levels and body weights were detected in the MT1- and double-knockout lines. The elimination of melatonin receptor signalling also altered blood glucose concentrations, body weight and melatonin and insulin levels when comparing wild-type and receptor knockout mice of different ages (6 wk and 8-12 months old); such changes, however, were dependent on the type of receptor deleted. Furthermore, reverse transcription polymerase chain reaction results provided evidence that melatonin receptor deficiency has an impact on transcript levels of pancreatic islet hormones as well as on pancreatic and hepatic glucose transporters (Glut1 and 2). Under stimulated insulin secretion in the presence of melatonin in the rat insulinoma β-cells INS-1, the Glut1 transcript level was decreased. In conclusion, the present findings demonstrate that melatonin receptor knockout types affect blood glucose levels, body weight, plasma levels of melatonin and insulin, as well as pancreatic hormone and Glut1 expression in significantly different manners.

Adaptations of the aging animal to exercise: role of daily supplementation with melatonin

The pineal gland, through melatonin, seems to be of fundamental importance in determining the metabolic adaptations of adipose and muscle tissues to physical training. Evidence shows that pinealectomized animals fail to develop adaptive metabolic changes in response to aerobic exercise and therefore do not exhibit the same performance as control-trained animals. The known prominent reduction in melatonin synthesis in aging animals led us to investigate the metabolic adaptations to physical training in aged animals with and without daily melatonin replacement. Male Wistar rats were assigned to four groups: sedentary control (SC), trained control (TC), sedentary treated with melatonin (SM), and trained treated with melatonin (TM). Melatonin supplementation lasted 16 wk, and the animals were subjected to exercise during the last 8 wk of the experiment. After euthanasia, samples of liver, muscle, and adipose tissues were collected for analysis. Trained animals treated with melatonin presented better results in the following parameters: glucose tolerance, physical capacity, citrate synthase activity, hepatic and muscular glycogen content, body weight, protein expression of phosphatidylinositol 3-kinase (PI3K), mitogen-activated protein kinase (MAPK), and protein kinase activated by adenosine monophosphate (AMPK) in the liver, as well as the protein expression of the glucose transporter type 4 (GLUT4) and AMPK in the muscle. In conclusion, these results demonstrate that melatonin supplementation in aging animals is of great importance for the required metabolic adaptations induced by aerobic exercise. Adequate levels of circulating melatonin are, therefore, necessary to improve energetic metabolism efficiency, reducing body weight and increasing insulin sensitivity.

The Angiotensin-melatonin axis

Accumulating evidence indicates that various biological and neuroendocrine circadian rhythms may be disrupted in cardiovascular and metabolic disorders. These circadian alterations may contribute to the progression of disease. Our studies direct to an important role of angiotensin II and melatonin in the modulation of circadian rhythms. The brain renin-angiotensin system (RAS) may modulate melatonin synthesis, a hormone with well-established roles in regulating circadian rhythms. Angiotensin production in the central nervous system may not only influence hypertension but also appears to affect the circadian rhythm of blood pressure. Drugs acting on RAS have been proven effective in the treatment of cardiovascular and metabolic disorders including hypertension and diabetes mellitus (DM). On the other hand, since melatonin is capable of ameliorating metabolic abnormalities in DM and insulin resistance, the beneficial effects of RAS blockade could be improved through combined RAS blocker and melatonin therapy. Contemporary research is evidencing the existence of specific clock genes forming central and peripheral clocks governing circadian rhythms. Further research on the interaction between these two neurohormones and the clock genes governing circadian clocks may progress our understanding on the pathophysiology of disease with possible impact on chronotherapeutic strategies.

Melatonin affects steroidogenesis and delayed ovulation during winter in vespertilionid bat, Scotophilus heathi

The aim of this study was to evaluate the role of melatonin in ovarian activity of Scotophilus heathi particularly in reference to changes in steroidogenesis and steroid receptor expression during the anovulatory period of delayed ovulation. Female S. heathi showed an increased circulating melatonin level during the period of delayed ovulation in winter coinciding with the increased androstenedione (A(4)) levels, body fat and ovarian androgen receptor expression. The circulating melatonin level decreased to a low level after winter during the period of ovulation in March which also coincided with the decreased circulating A(4) levels and body fat. The circulating estrogen (E(2)) showed two peaks corresponding with the two waves of follicular development in November and February. Both the isoforms of progesterone receptor (PR), PR-A and PR-B, remained high throughout the follicular development, but expression of PR-A declined significantly during the ovulation. The treatment with melatonin, both in vitro and in vivo, significantly increased progesterone and A(4), but not the estradiol synthesis by the ovaries of S. heathi. The study further suggested that the increased androgens during winter may be primarily due to the stimulatory effect of melatonin on steroidogenic enzyme 3beta-hydroxysteroid dehydrogenase (3beta-HSD) activity. Therefore the increased circulating melatonin level in S. heathi during winter delay (inhibits) ovulation through increased androgen synthesis, but suppression of estradiol synthesis.

Effects of melatonin administration on plasma leptin concentration and adipose tissue leptin secretion in mice

Both melatonin and leptin show a circadian variation in circulating levels and participate in energy metabolism. An interrelationship between these two hormones has thus been proposed. In addition, melatonin has been shown to be capable of influencing circulating leptin concentration. However, whether melatonin will increase or decrease leptin production is still uncertain. This study was undertaken to examine the effect of melatonin on leptin production using male C57BL/6 adult mice treated with or without daily melatonin supplements (10 mug/mL) in drinking water for 1 month. In addition, in vitro experiments using adipose tissue fragments derived from epididymal fat pads of adult mice incubated with or without melatonin (1 nM) administration were also conducted. The results showed that melatonin-supplemented mice had significantly higher plasma leptin levels than control mice. However, melatonin incubation did not cause any marked changes in the amount of leptin secreted from adipose tissue fragments. Our findings from this study indicate that melatonin does not affect leptin secretion via mouse adipose tissue. Nevertheless, melatonin could still influence leptinemia indirectly via regulatory effects in intact animals.

Adipocyte differentiation is inhibited by melatonin through the regulation of C/EBPbeta transcriptional activity

Considering that melatonin has been implicated in body weight control, this work investigated whether this effect involves the regulation of adipogenesis. 3T3-L1 preadipocytes were induced to differentiate in the absence or presence of melatonin (10(-3) m). Swiss-3T3 cells ectopically and conditionally (Tet-off system) over-expressing the 34 kDa C/EBPbeta isoform (Swiss-LAP cells) were employed as a tool to assess the mechanisms of action at the molecular level. Protein markers of the adipogenic phenotype were analyzed by Western blot. At 36 hr of differentiation of 3T3-L1 preadipocytes, a reduction of PPARgamma expression was detected followed by a further reduction, at day 4, of perilipin, aP2 and adiponectin protein expression in melatonin-treated cells. Real-time PCR analysis also showed a decrease of PPARgamma (60%), C/EBPalpha (75%), adiponectin (30%) and aP2 (40%) mRNA expression. Finally, we transfected Swiss LAP cells with a C/EBPalpha gene promoter/reporter construct in which luciferase expression is enhanced in response to C/EBPbeta activity. Culture of such transfected cells in the absence of tetracycline led to a 2.5-fold activation of the C/EBPalpha promoter. However, when treated with melatonin, the level of C/EBPalpha promoter activation by C/EBPbeta was reduced by 50% (P = 0.05, n = 6). In addition, this inhibitory effect of melatonin was also reflected in the phenotype of the cells, since their capacity to accumulate lipids droplets was reduced as confirmed by the poor staining with Oil Red O. In conclusion, melatonin at a concentration of 10(-3 ) m works as a negative regulator of adipogenesis acting in part by inhibiting the activity of a critical adipogenic transcription factor, C/EBPbeta.

Modulation of bone morphogenetic protein-9 expression and processing by insulin, glucose, and glucocorticoids: possible candidate for hepatic insulin-sensitizing substance

Bone morphogenetic protein 9 (BMP-9), a member of the TGF-beta superfamily predominantly expressed in nonparenchymal liver cells, has been demonstrated to improve glucose homeostasis in diabetic mice. Along with this therapeutic effect, BMP-9 was proposed as a candidate for the hepatic insulin-sensitizing substance (HISS). Whether BMP-9 plays a physiological role in glucose homeostasis is still unknown. In the present study, we show that BMP-9 expression and processing is severely reduced in the liver of insulin-resistant rats. BMP-9 expression and processing was directly stimulated by in situ exposition of the liver to the combination of glucose and insulin and oral glucose in overnight fasted rats. Additionally, prolonged fasting (72 h) abrogated refeeding-induced BMP-9 expression and processing. Previous exposition to dexamethasone, a known inductor of insulin resistance, reduced BMP-9 processing stimulated by the combination of insulin and glucose. Finally, we show that neutralization of BMP-9 with an anti-BMP-9 antibody induces glucose intolerance and insulin resistance in 12-h fasted rats. Collectively, the present results demonstrate that BMP-9 plays an important role in the control of glucose homeostasis of the normal rat. Additionally, BMP-9 is expressed and processed in an HISS-like fashion, which is impaired in the presence of insulin resistance. BMP-9 regulation according to the feeding status and the presence of diabetogenic factors reinforces the hypothesis that BMP-9 might exert the role of HISS in glucose homeostasis physiology.

Melatonin and the circadian entrainment of metabolic and hormonal activities in primary isolated adipocytes

The aim of this work was to investigate the effect of the in vitro circadian-like exposure to melatonin [in the presence or absence of insulin (Ins)] on the metabolism and clock gene expression in adipocytes. To simulate the cyclic characteristics of the daily melatonin profile, isolated rat adipocytes were exposed in a circadian-like pattern to melatonin added to the incubating medium for 12 hr (mimicking the night), followed by an equal period without melatonin (mimicking the day) combined or not with Ins. This intermittent incubation was interrupted when four and a half 24-hr cycles were fulfilled. At the end, either during the induced night (melatonin present) or the induced day (melatonin absent), the rates of lipolysis and D-[U-(14)C]-glucose incorporation into lipids were estimated, in addition to the determination of lipogenic [glucose-6-phosphate dehydrogenase and fatty acid synthase (FAS)] and lipolytic (hormone sensitive lipase) enzymes and clock gene (Bmal-1b, Clock, Per-1 and Cry-1) mRNA expression. The leptin release was also measured. During the induced night, the following effects were observed: an increase in the mRNA expression of Clock, Per-1 and FAS; a rise in lipogenic response and leptin secretion; and a decrease in the lipolytic activity. The intermittent exposure of adipocytes to melatonin temporally and rhythmically synchronized their metabolic and hormonal function in a circadian fashion, mimicking what is observed in vivo in animals during the daily light-dark cycle. Therefore, this work helps to clarify the physiological relevance of the circadian pattern of melatonin secretion and its interactions with Ins, contributing to a better understanding of the adipocyte biology.

Pinealectomy and melatonin administration in rats: their effects on plasma leptin levels and relationship with zinc

The aim of this study was to examine effects of pinealectomy and melatonin administration plasma leptin levels and its relationship with zinc in rats. The study was conducted on 40 adult male Sprague-Dawley rats. They were divided into four groups each containing 10 animals. Group 1 served as control. Group 2 was pinealectomized group. Animals in Group 3 were pinealectomized and injected with melatonin (3 mg/kg/day, ip). Group 4 received melatonin alone (3 mg/kg/day, ip). At the end of the experiments, all animals were decapitated and trunk blood collected. Plasma leptin and zinc levels were determined by radioimmunoassay and Atomic Absorption Spectrophotometer methods, respectively. Although mean weights of the animals at the beginning were not significantly different among the groups, the mean weight of the pinealectomized group was found to be significantly lower than all other groups at the end of a six-month period (p < 0.01). Plasma leptin and zinc levels were the highest in melatonin-administered group (group 4; p < 0.01). The lowest plasma leptin and zinc levels were obtained in the pinealectomized group (group 2; p < 0.01). Changes in these two parameters were not statistically significant in groups 1 and 3. Our findings indicate that pinealectomy results in a decrease in leptin and zinc levels in rats, and that melatonin administration to pinealectomized rats prevents the decrease in the these parameters. In addition, long-term administration of melatonin to rats leads to an increase in both leptin and zinc concentrations.

Intermittent and rhythmic exposure to melatonin in primary cultured adipocytes enhances the insulin and dexamethasone effects on leptin expression

Considering the cyclic characteristic of production and secretion of pineal melatonin, it is reasonable to assume that this oscillation might be important in determining the variety of its circadian and seasonal effects. To simulate this physiological condition in vitro, isolated adipocytes were exposed to melatonin in a circadian-like pattern by adding the hormone to the incubating medium during 12 hr (mimicking the night), followed by an equal period without melatonin (mimicking the day). This intermittent procedure was interrupted when three cycles with melatonin were fulfilled (60-hr incubation). Here, we report the effects of melatonin (1 nM) added intermittently or continuously to the incubating medium alone or in combination with insulin (5 nM) and/or dexamethasone (7 nM) on leptin release and expression by rat adipocytes. After acute 12-hr incubation neither melatonin nor insulin alone affected leptin expression, but together they increased it by 105%. Dexamethasone increased leptin mRNA content and release (70%) but this effect was not enhanced by melatonin. Nevertheless, after 60 hr under intermittent melatonin, we observed a synergism between melatonin and dexamethasone. This interaction promoted an increment (75% compared with dexamethasone alone) in leptin release and expression. Our results suggest that circadian-like exposure to melatonin potentiates the dexamethasone action and is important to the effects promoted by insulin on leptin expression. Based on an in vitro approach, this work helps to clarify the physiological relevance and the repercussions of the in vivo circadian pattern of melatonin secretion.

[The adipose tissue as a regulatory center of the metabolism]

The recent progress in the research about the metabolic properties of the adipose tissue and the discovery of its ability to produce hormones that are very active in pathophysiologic as well as physiologic processes is rebuilding the concepts about its biology. Its involvement in conditions like obesity, type 2 diabetes mellitus, arterial hypertension, arteriosclerosis, dislipidemias and chronic and acute inflammatory processes indicate that the understanding of its functional capacities may contribute to improve the prognosis of those diseases whose prevalence increased in a preoccupying manner. Here we review some functional aspects of adipocytes, such as the metabolism, its influence on energy homeostasis, its endocrine ability and the adipogenesis, i.e., the potential of pre-adipocytes present in adipose tissue stroma to differentiate into new adipocytes and regenerate the tissue. In addition, we are including some studies on the relationship between the adipose tissue and the pineal gland, a new and poorly known, although, as will be seen, very promising aspect of adipocyte physiology together with its possible favorable repercussions to the therapy of the obesity related diseases.

Reduced lipolysis and increased lipogenesis in adipose tissue from pinealectomized rats adapted to training

The current study investigated the effects of chronic training and pinealectomy on the lipogenic and lipolytic activity of adipose tissue. Pinealectomized and sham-operated adult male Wistar rats were distributed in to four subgroups: pinealectomized untrained, pinealectomized trained, control untrained and control trained. At the end of the training period (8 wk) the rats were killed. Blood samples were collected for glucose, insulin and leptin determinations. Peri-epididymal adipocytes were isolated for measurement of in vitro rates of lipolysis and incorporation of substrates (D-[U-14C]-glucose, L-[U-14C]-lactate, [2-14C]-acetate and [1-14C]-palmitate) into lipids, and samples of epididymal adipose tissue were homogenized for evaluation of glucose-6-phosphate dehydrogenase maximal activity. Pinealectomy resulted in a significantly increased lipolytic capacity in response to isoproterenol and a decrease in circulating leptin levels without affecting the rates of incorporation of different substrates into lipids. However, only in the intact control group did training promote a higher basal and isoproterenol-stimulated lipolysis, increase the incorporation of palmitate (esterification), decrease the incorporation of acetate (lipogenesis) into lipids and diminish circulating leptin levels. These effects of exercise training were not seen in pinealectomized rats. However, pinealectomized trained animals showed a marked reduction in lipolysis and an increased rate of acetate incorporation. In conclusion, we demonstrated for the first time that the pineal gland plays an important role in the regulation of lipid metabolism in such a way that its absence caused a severe alteration in the balance between lipogenesis and lipolysis, which becomes evident with the adaptation to exercise training.

Pinealectomy impairs adipose tissue adaptability to exercise in rats

This study investigated the effects of pinealectomy and exercise training on rat adipose tissue metabolism. Pinealectomized (PINX) and sham-operated (CONTROL) adult male Wistar rats were subdivided into four subgroups, including PINX untrained, PINX trained, CONTROL untrained and CONTROL trained. At the end of the training period (8 wk), the rats were killed and peri-epididymal adipocytes were isolated for in vitro insulin-stimulated glucose uptake, conversion of D-[U-14C]-glucose, l-[U-14C]-lactate, [2-14C]-acetate and [1-14C]-palmitate into 14CO2, and insulin binding. Pinealectomy resulted in a significantly decreased insulin-stimulated glucose uptake in adipocytes without affecting insulin-binding capacity. However, in intact control animals only, training promoted a higher baseline glucose uptake in adipocytes. Training influenced the adipocyte ability to oxidize the different substrates: the rates of glucose and palmitate oxidation increased while the rates of lactate and acetate diminished. Nevertheless, these effects of exercise training were not seen in pinealectomized rats. Additionally, an increase in palmitate oxidation was observed in sedentary pinealectomized animals. In conclusion, these data show that the pineal gland alters the patterns of substrate utilization by the adipocyte, in such a way that its absence disrupts the ability to adapt to the metabolic demands evoked by exercise training in rats.

Melatonin enhances leptin expression by rat adipocytes in the presence of insulin

Leptin and melatonin play an important role in the regulation of body mass and energy balance. Both hormones show a circadian rhythm, with increasing values at night. In addition, melatonin receptors were recently described in adipocytes, where leptin is synthesized. Here, we investigated the influence of melatonin and its interaction with insulin and dexamethasone on leptin expression. Isolated rat adipocytes were incubated with melatonin (1 nM) alone or in combination with insulin (5 nM) and/or dexamethasone (7 nM) for 6 h. Melatonin or insulin alone did not affect leptin expression, but together they increased it by 120%. Dexamethasone increased leptin mRNA content (105%), and this effect was not enhanced by melatonin. Simultaneous treatment with the three hormones provoked a further increase in leptin release (250%) and leptin mRNA (100%). Melatonin prevented the forskolin-induced inhibition (95%) of leptin expression. In addition, melatonin's ability to stimulate leptin release (in the presence of insulin) was completely blocked by pertussis toxin and luzindole. To gain further insight into the molecular basis of melatonin and insulin synergism, the insulin-signaling pathway was investigated. Melatonin increased the insulin-induced insulin receptor-beta tyrosine phosphorylation, which led to an increased serine phosphorylation of the downstream convergent protein Akt. We concluded that melatonin interacts with insulin and upregulates insulin-stimulated leptin expression. These effects are caused by melatonin binding to the pertussis toxin-sensitive G(i) protein-coupled membrane receptor (MT1 subtype) and the cross talk with insulin, since insulin receptor and its convergent target Akt are coactivated by melatonin.