Investigation of seasonality of human spontaneous physical activity and energy expenditure in respiratory chamber in Phoenix, Arizona

OBJECTIVE

The existence of seasonal changes in energy metabolism is uncertain. We investigated the relationship between the seasons and spontaneous physical activity (SPA), energy expenditure (EE), and other components measured in a respiratory chamber.

METHODS

Between 1985-2005, 671 healthy adults (aged 28.8 ± 7.1 years; 403 men) in Phoenix, Arizona had a 24-hour stay in the respiratory chamber equipped with radar sensors; SPA (expressed as a percentage over the time interval), the energy cost of SPA, EE, and respiratory exchange ratio (RER) were measured.

RESULTS

In models adjusted for known covariates, SPA (%) was lower during summer (7.2 ± 2.9, p = 0.0002), spring (7.5 ± 2.9, p = 0.025), and fall (7.6 ± 3, p = 0.038) compared to winter (8.3 ± 3.5, reference). Conversely, energy cost of SPA (kcal/h/%) was higher during summer (2.18 ± 0.83, p = 0.0008), spring (2.186 ± 0.83, p = 0.017), and fall (2.146 ± 0.75, p = 0.038) compared to winter (2.006 ± 0.76). Protein (292 ± 117 kcal/day, β = -21.2, p = 0.08) oxidation rates was lower in the summer compared to winter. Carbohydrate and lipid oxidation rates (kcal/day) did not differ across seasons. RER and 24-h EE did not differ by season.

CONCLUSION

SPA, representing fidgeting-like behavior in the chamber, demonstrated a winter peak and summer nadir in humans living in a desert climate. These findings indicate that the physiological propensity for movement may be affected by seasonal factors.

CLINICAL TRIAL REGISTRATION

ClinicalTrials.gov identifiers: NCT00340132, NCT00342732.

Hypothalamic orexinergic neuron changes during the hibernation of the Syrian hamster

Hibernation in small mammals is a highly regulated process with periods of torpor involving drops in body temperature and metabolic rate, as well as a general decrease in neural activity, all of which proceed alongside complex brain adaptive changes that appear to protect the brain from extreme hypoxia and low temperatures. All these changes are rapidly reversed, with no apparent brain damage occurring, during the short periods of arousal, interspersed during torpor—characterized by transitory and partial rewarming and activity, including sleep activation, and feeding in some species. The orexins are neuropeptides synthesized in hypothalamic neurons that project to multiple brain regions and are known to participate in the regulation of a variety of processes including feeding behavior, the sleep-wake cycle, and autonomic functions such as brown adipose tissue thermogenesis. Using multiple immunohistochemical techniques and quantitative analysis, we have characterized the orexinergic system in the brain of the Syrian hamster—a facultative hibernator. Our results revealed that orexinergic neurons in this species consisted of a neuronal population restricted to the lateral hypothalamic area, whereas orexinergic fibers distribute throughout the rostrocaudal extent of the brain, particularly innervating catecholaminergic and serotonergic neuronal populations. We characterized the changes of orexinergic cells in the different phases of hibernation based on the intensity of immunostaining for the neuronal activity marker C-Fos and orexin A (OXA). During torpor, we found an increase in C-Fos immunostaining intensity in orexinergic neurons, accompanied by a decrease in OXA immunostaining. These changes were accompanied by a volume reduction and a fragmentation of the Golgi apparatus (GA) as well as a decrease in the colocalization of OXA and the GA marker GM-130. Importantly, during arousal, C-Fos and OXA expression in orexinergic neurons was highest and the structural appearance and the volume of the GA along with the colocalization of OXA/GM-130 reverted to euthermic levels. We discuss the involvement of orexinergic cells in the regulation of mammalian hibernation and, in particular, the possibility that the high activation of orexinergic cells during the arousal stage guides the rewarming as well as the feeding and sleep behaviors characteristic of this phase.

Effects of Leptin, Growth Hormone and Photoperiod on Pituitary SOCS-3 Expression in Sheep

Simple Summary

Maintaining energy homeostasis requires numerous processes and interactions between many systems. This study investigated the relationships between leptin, growth hormone (GH), and factors involved in cell signaling, such as suppressors of cytokine signaling-3 (SOCS-3). Exogenous or endogenous factors affecting these relationships may have different origins, and their interactions are determined in this study. The finding that the length of day significantly influenced the concentrations of growth hormone as well as pituitary leptin- and GH-dependent SOCS-3 expressions suggests that photoperiod plays an important role in regulating the physiological processes underlying adaptive phenomena in response to changing seasons in sheep, which facilitates energy homeostasis despite changing external and internal conditions.

Abstract

This study examined how leptin affects growth hormone (GH) release and investigated the effects of leptin, GH, and day length on the suppressor of cytokine signaling-3 (SOCS-3) mRNA levels in the adenohypophyses of sheep. The study consisted of two experiments. The first experiment was conducted during long (LD) and short (SD) days. Within-season and replicate sheep were centrally infused with Ringer-Locke buffer or leptin three times at 60-min intervals at the beginning of experiments. The second experiment involved adenohypophyses collected from sheep that were euthanized in May or November. Pituitary explants were treated with medium alone (Control) or medium with leptin or GH at different concentrations and incubated for various times. The results of the first experiment indicated GH concentrations were seasonally dependent and that leptin had no effect on GH secretion. The results of the second experiment indicated a stronger influence of leptin on the expression of SOCS-3 during the SD season than the LD season. During SDs, significant effects of both GH doses on SOCS-3 expression were observed. These results indicate a strong association between leptin, GH, and SOCS-3, which may explain the disruption of SOCS-3 leptin and GH signaling and the dominant effect of photoperiod on the above relationships.

Roles of leptin and resistin in metabolism, reproduction, and leptin resistance

Increased adipose mass can cause insulin resistance and type 2 diabetes mellitus. This phenomenon is related to adipocyte-secreted signaling molecules that affect glucose balance, such as fatty acids, adiponectin, leptin, interleukin-6, tumor necrosis factor-α, and resistin. Among these hormones, leptin and resistin play important roles in regulating weight and glucose metabolism. Leptin and resistin work in both similar and opposite ways, and they interact with each other. Circulating concentrations of leptin and resistin are elevated in models of obesity and rodents fed a high-fat diet. In addition, leptin and resistin are similarly regulated by nutritional status: they are reduced by fasting and increased by feeding. This effect is mediated partially through insulin receptors and glucose transporters. Our latest data provided the first indication that in sheep, intravenous infusion of resistin increases the mean circulating concentrations of leptin and decreases luteinizing hormone in a dose-dependent manner during both the long-day (LD) and short-day seasons. Furthermore, exogenous resistin increased suppressor of cytokine signaling (SOCS)-3 mRNA expression only during the LD season, when the leptin resistance/insensitivity phenomenon was observed in the arcuate nucleus, preoptic area, and anterior pituitary. We concluded that one factor contributing to central leptin resistance is autosuppression, via which leptin and resistin stimulate the expression of SOCS-3, which inhibits leptin signaling. The increased expression of SOCS-3 in response to leptin and resistin may be a pivotal cause of leptin resistance/insensitivity, a pathological situation in obese individuals and a physiological occurrence in sheep during the LD season.

The Impact of Photoperiod on the Leptin Sensitivity and Course of Inflammation in the Anterior Pituitary

Leptin has a modulatory impact on the course of inflammation, affecting the expression of proinflammatory cytokines and their receptors. Pathophysiological leptin resistance identified in humans occurs typically in sheep during the long-day photoperiod. This study aimed to determine the effect of the photoperiod with relation to the leptin-modulating action on the expression of the proinflammatory cytokines and their receptors in the anterior pituitary under physiological or acute inflammation. Two in vivo experiments were conducted on 24 blackface sheep per experiment in different photoperiods. The real-time PCR analysis for the expression of the genes IL1B, IL1R1, IL1R2, IL6, IL6R, IL6ST, TNF, TNFR1, and TNFR2 was performed. Expression of all examined genes, except IL1β and IL1R2, was higher during short days. The leptin injection increased the expression of all examined genes during short days. In short days the synergistic effect of lipopolysaccharide and leptin increased the expression of IL1B, IL1R1, IL1R2, IL6, TNF, and TNFR2, and decreased expression of IL6ST. This mechanism was inhibited during long days for the expression of IL1R1, IL6, IL6ST, and TNFR1. The obtained results suggest the occurrence of leptin resistance during long days and suggest that leptin modulates the course of inflammation in a photoperiod-dependent manner in the anterior pituitary.

Involvement of orexin A in nocturnal melatonin secretion into the cerebrospinal fluid and the blood plasma in seasonal sheep

In sheep, differences in orexin A (OXA) gene expression and activity are related to changes in energy demand and seasonal reproduction. However, the mechanism by which and the key place where the OXA signal is integrated with photoperiod, whose main biochemical expression is melatonin (MEL), remain unknown. We examined the effects of cisterna magna injections of OXA (0.3 μg/kg body weight) on nocturnal cerebrospinal fluid (CSF) and plasma MEL concentrations; mRNA and protein expression of two rate-limiting enzymes for MEL biosynthesis, tryptophan 5-hydroxylase-1 (TPH1) and arylalkylamine-N-acetyltransferase (AA-NAT); and OXA receptor (OX1R, OX2R) expression in the pineal gland (PG) obtained from twenty ewes during the short-day (SD) and long-day (LD) seasons. OXA increased (P < 0.001) CSF and plasma MEL concentrations regardless of the season. Plasma MEL was positively correlated (P < 0.001) with CSF MEL in the OXA-treated sheep in both seasons. OXA had no effect (P > 0.05) on TPH1 transcript or protein level but upregulated (P < 0.05) AA-NAT mRNA and protein expression in both seasons. OXA enhanced (P < 0.05) OX1R mRNA level only during the LD season. Our results show that the endocrine activity of the ovine PG is regulated by day length and non-photic signals via hypothalamic OXA. These results are important for understanding the work of the biological clock and recognizing mechanisms responsible for the adaptation of seasonal animals to the changing external environment conditions. OXA and MEL are both involved in the regulation of the sleep-wakefulness system, therefore our results can be used in the study on the circadian rhythm disorders in humans (e.g. jet lag, insomnia, seasonal depression).

Annual rhythms of milk and milk fat and protein production in dairy cattle in the United States

An annual pattern of milk composition has been well recognized in dairy cattle, with the highest milk fat and protein concentration observed during the winter and lowest occurring in the summer; however, rhythms of milk yield and composition have not been well quantified. Cosinor rhythmometry is commonly used to model repeating daily and annual rhythms and allows determination of the amplitude (peak to mean), acrophase (time at peak), and period (time between peaks) of the rhythm. The objective of this study was to use cosinor rhythmometry to characterize the annual rhythms of milk yield and milk fat and protein concentration and yield using both national milk market and cow-level data. First, 10 yr of monthly average milk butterfat and protein concentration for each Federal Milk Marketing Order were obtained from the US Department of Agriculture Agricultural Marketing Service database. Fat and protein concentration fit a cosine function with a 12-mo period in all milk markets. We noted an interaction between milk marketing order and milk fat and protein concentration. The acrophase (time at peak) of the fat concentration rhythm ranged from December 4 to January 19 in all regions, whereas the rhythm of protein concentration peaked between December 27 and January 6. The amplitude (peak to mean) of the annual rhythm ranged from 0.07 to 0.14 percentage points for milk fat and from 0.08 to 0.12 percentage points for milk protein. The amplitude of the milk fat rhythm generally was lower in southern markets and higher in northern markets. Second, the annual rhythm of milk yield and milk fat and protein yield and concentration were analyzed in monthly test day data from 1,684 cows from 11 tiestall herds in Pennsylvania. Fat and protein concentration fit an annual rhythm in all herds, whereas milk and milk fat and protein yield only fit rhythms in 8 of the 11 herds. On average, milk yield peaked in April, fat and protein yield peaked in February, fat concentration peaked in January, and protein concentration peaked in December. Amplitudes of milk, fat, and protein yield averaged 0.82 kg, 55.3 g, and 30.4 g, respectively. Milk fat and protein concentration had average amplitudes of 0.12 and 0.07, respectively, similar to the results of the milk market data. Generally, milk yield and milk components fit annual rhythm regardless of parity or diacylglycerol O-acyltransferase 1 (DGAT1) K232A polymorphism, with only cows of the low-frequency AA genotype (5.2% of total cows) failing to fit rhythm of milk yield. In conclusion, the yearly rhythms of milk yield and fat and protein concentration and yield consistently occur regardless of region, herd, parity, or DGAT1 genotype and supports generation by a conserved endogenous annual rhythm.

Orexin A but not orexin B regulates lipid metabolism and leptin secretion in isolated porcine adipocytes

It is well known that orexins are involved in the metabolism and endocrine function of rodent adipocytes, but there are no data on other animal species, including pigs. Therefore, in this study, we tested the hypothesis that orexin A (OxA) and orexin B (OxB) modulate the metabolism and endocrine functions of isolated porcine adipocytes and adipose tissue explants. Moreover, we characterized the possible mechanism of OxA action in porcine adipocytes. According to the results, both orexin receptor 1 and orexin receptor 2 were expressed in the porcine adipose tissue. We found that OxA suppressed the release of glycerol from porcine adipocytes both in the absence (basal lipolysis; P < 0.05) and in the presence (stimulated lipolysis; P < 0.05) of isoproterenol. Orexin A increased basal and insulin-stimulated glucose uptake (P < 0.05), as well as it enhanced the rate of glucose incorporation into lipids with insulin (stimulated lipogenesis; P < 0.01) or without insulin (basal; P < 0.05). We have also shown that OxA stimulated the mRNA expression of glucose transporter 4 (P < 0.05) and its translocation into the plasma membrane (P < 0.01). Moreover, OxA upregulated the mRNA expression of leptin in isolated porcine adipocytes (P < 0.05) and increased the secretion of leptin (P < 0.05). We have also demonstrated one of the possible mechanisms of OxA action in adipocytes. In the presence of extracellular-signal-regulated kinase 1 and 2 (ERK1/2) inhibitor, the effect of OxA was not detectable in porcine adipocytes, which indicates that this peptide increased cell viability via ERK1/2 pathway (P < 0.05). However, OxB did not show any effect on the metabolism and endocrine functions of porcine adipocytes. In summary, we have shown for the first time that OxA has a significant impact on the intensity of lipolysis, glucose uptake, lipogenesis, as well as on the expression and secretion of leptin. Therefore, we conclude that OxA but not OxB regulates lipid metabolism in porcine adipose tissue and that this regulation is partly mediated via ERK1/2 pathway. The action of orexins should be further explored to better understand their role in the regulation of adiposity in pigs.

The Effects of Various Weather Conditions as a Potential Ischemic Stroke Trigger in Dogs

Stroke is the fifth leading cause of death in the United States, and is the leading cause of serious, long-term disability worldwide. There are at least 795,000 new or recurrent strokes each year, and approximately 85% of all stroke occurrences are ischemic. Unfortunately, companion animals are also at risk for ischemic stroke. Although the exact incidence of ischemic stroke in companion animals is unknown, some studies, and the veterinary information network (VIN), report that approximately 3% of neurological case referrals are due to a stroke. There is a long list of predisposing factors associated with the risk of ischemic stroke in both humans and canines; however, these factors do not explain why a stroke happens at a particular time on a particular day. Our understanding of these potential stroke “triggers” is limited, and the effect of transient environmental exposures may be one such “trigger”. The present study investigated the extent to which the natural occurrence of canine ischemic stroke was related to the weather conditions in the time-period immediately preceding the onset of stroke. The results of the present study demonstrated that the change in weather conditions could be a potential stroke trigger, with the strokes evaluated occurring after periods of rapid, large fluctuations in weather conditions. There are currently no epidemiological data on the seasonal variability of ischemic stroke in dogs, and determining whether canine stroke parallels human stroke would further validate the use of companion dogs as an appropriate naturally occurring model.

Orexin receptor expression in the hypothalamic-pituitary-adrenal and hypothalamic-pituitary-gonadal axes of free-living European beavers (Castor fiber L.) in different periods of the reproductive cycle

Orexins are hypothalamic neuropeptides acting via two G protein-coupled receptors in mammals: orexin receptor 1 (OX1R) and orexin receptor 2 (OX2R). In European beavers, which are seasonally breeding animals, the presence and functions of orexins and their receptors remain unknown. Our study aimed to determine the expression of OXR mRNAs and the localization of OXR proteins in hypothalamic-pituitary-adrenal/gonadal (HPA/HPG) axes in free-living beavers. The expression of OXR genes (OX1R, OX2R) and proteins was found in all analysed tissues during three periods of beavers' reproductive cycle (April, July, November). The expression of OXR mRNAs in the beaver HPA axis varied seasonally (P<0.05). The levels of OX1R mRNA also differed between the sexes (P<0.05). In the mediobasal hypothalamus, OX1R transcript content increased in pregnant females in April (P<0.05) and OX2R expression increased in males in July (P<0.05). In the pituitary and adrenals, OX1R mRNA levels were relatively constant in females and peaked in July in males (P<0.05), whereas the OX2R was most highly expressed in males in November and in females in April (P<0.05). In gonads, OX1R expression did not fluctuate between seasons or sexes, but transcript levels were elevated in the testes in November and in the ovaries in July (P<0.05). In turn, OX2R mRNA levels varied between the sexes (P<0.05) and were higher in females (July and November) than in males (P<0.05). The circannual variations in OXR mRNA levels in HPA and HPG axes suggest that the expression of these receptors is associated with sex-specific changes in beavers' reproductive activity and their environmental adaptations.

Influence of season and nutritional status on the direct effects of leptin, orexin-A and ghrelin on luteinizing hormone and growth hormone secretion in the ovine pituitary explant model

The aim of this study was to examine whether leptin (anorexigenic peptide), orexin-A, and ghrelin (orexigenic peptides) could directly (ie, independently of hypothalamic influences) affect the secretion of luteinizing hormone (LH) and growth hormone (GH) by adenohypophyseal (AP) explants obtained from normally fed or fasted (48 h) ewes during the breeding and nonbreeding seasons. In addition, a specific ovine super leptin antagonist (SLAN-3) was used to assess the interactions between leptin and ghrelin and/or orexin-A. Pituitary glands from 16 ovariectomized Polish Longwool ewes that had received estradiol-releasing subcutaneous implants were collected in the breeding (November; n = 8) and nonbreeding (May; n = 8) seasons. The AP explants were incubated for 240 min in a gas-liquid interface and treated with leptin (50 ng/mL), ghrelin (100 ng/mL), orexin-A (100 ng/mL), and SLAN-3 (500 ng/mL) with orexin-A or ghrelin. Treatments with leptin and SLAN-3 + orexin-A increased (P < 0.05) LH concentrations in the cultures of AP explants from fasted animals in the breeding season. Orexin-A increased (P < 0.05) LH secretion by AP explants from both fasted and fed animals in the breeding season. Ghrelin stimulated (P < 0.05) GH secretion by AP explants collected from fasted animals in nonbreeding season and from normally fed ewes in both seasons. Leptin decreased (P < 0.05) GH secretion by AP explants collected from fasted ewes in both seasons and from nonfasted ewes in the breeding season. However, the treatment with SLAN-3 + ghrelin resulted in greater (P < 0.05) GH concentrations compared with leptin treatment of AP explants from fasted ewes in the breeding season and from normally fed ewes in nonbreeding season. In summary, leptin, orexin-A, and ghrelin exerted direct effects on AP secretory function in an ex situ model and both the reproductive season and nutritional status of the animals impinged on the direct effects of the peptides on LH and GH release. Specifically, orexin-A was more potent than leptin in directly stimulating LH secretion in cycling ewes, whereas ghrelin and leptin generally had opposing effects on the secretory function of somatotrophs in sheep.

Food for thought: understanding the multifaceted nature of orexins

Orexins are a pair of hypothalamic neuropeptides that were discovered in the late 1990s and named initially for their ability to promote feeding. Subsequent studies have revealed the importance of orexins to a variety of physiological functions, including brown fat thermogenesis, sleep/wake cycles, physical activity, and cognition. We aim to elucidate the various roles of orexins and discuss how these multiple functions are interlinked. We explain that although the unique dual roles of orexins in increasing feeding while concomitantly elevating energy expenditure appear counterproductive, they are necessary for physiological scenarios during which simultaneous stimulation of energy expenditure and feeding occur, namely diet-induced thermogenesis and arousal from hibernation. The position of orexins at the interface between sleep/wake cycles, energy homeostasis, and environmental factors has important implications in the treatment of obesity.

A review on the effect of the photoperiod and melatonin on interactions between ghrelin and serotonin

Ghrelin and serotonin, which exhibit rhythmic secretion profiles under feeding/fasting conditions, are sensitive to increases and decreases in the day length and form a close web of interrelationships in the regulation of energy homeostasis. Ghrelin and serotonin are biochemically and functionally linked to the suprachiasmatic nucleus, which is a circadian pacemaker, and melatonin, which is an internal transducer of photic environmental changes. Ghrelin and serotonin might be candidates for integrating photic and nonphotic signals, such as light and food availability in the central nervous system. The mechanisms that convert a light signal into a variety of physiological and behavioral rhythms remain unknown. However, we know that the conversion of light signals is necessary to maximize an animal's chances of survival and reproduction.