American journal of physiology. Regulatory, integrative and comparative physiology最新文献

Estradiol activates the G protein-coupled estrogen receptor 1 (GPER1), which promotes natriuresis in female rats. Extracellular adenosine triphosphate (ATP) released via connexin 30 (Cx30) hemichannels activates purinergic P2Y₂ receptor, promoting Na⁺ excretion via inhibiting epithelial Na⁺ channel (ENaC) activity. Interestingly, ovariectomy downregulates renal P2Y₂ receptor expression in Sprague Dawley (SD) rats. We hypothesized that GPER1 activation regulates renal Cx30/ATP/P2Y₂/ENaC signaling pathway in females. To test our hypothesis, female SD rats were implanted with telemetry transmitters and then ovariectomized (OVX) and simultaneously implanted with osmotic minipumps to deliver either the selective GPER1 agonist G1 or vehicle for 3 wk. Rats were fed a normal-salt (0.4% NaCl) diet from the start of the experimental protocol until day 14 after ovariectomy. Afterward, rats were shifted to a high-salt diet (4% NaCl) for 7 days. Ovariectomy increased blood pressure during normal salt intake. High salt intake elicited further increases in mean arterial pressure. These increases in blood pressure were prevented by G1. Cx30 and P2Y₂ receptor mRNA expressions were higher in the cortex of OVX SD rats with G1 treatment plus high salt intake. Genetic deletion of GPER1 in mice reduced the renal expression of Cx30 and P2Y₂ receptor. Importantly, renal medullary infusion of G1 in ovary-intact female rats increased urinary ATP and Na⁺ excretion. Furthermore, P2 receptor blockade by suramin blocked GPER1-evoked natriuresis. These findings indicate that GPER1 upregulates the natriuretic Cx30/ATP/P2Y₂ receptor signaling pathway in the kidney, which may contribute to the blood pressure-lowering response to GPER1 activation.NEW & NOTEWORTHY Systemic GPER1 activation upregulated renal Cx30 and P2Y₂ receptor mRNA expression in ovariectomized rats, whereas genetic deletion of GPER1 downregulated renal Cx30 and P2Y₂ receptor mRNA expression in ovary-intact female mice. Acute renal medullary GPER1 activation enhances natriuresis and urinary ATP excretion in ovary-intact female rats. These findings indicate that GPER1 regulates the natriuretic Cx30/ATP/P2Y₂ receptor signaling pathway in the kidney, which may contribute to the blood pressure-lowering response to GPER1 activation.

Early-life infections have enduring effects on the immune and endocrine systems. Glucocorticoids (GCs) are produced by the adrenal glands and also produced by lymphoid organs (immunosteroids). We investigated the impacts of early-life lipopolysaccharide (LPS) challenge on GC and mineralocorticoid regulation in blood and lymphoid organs. We administered saline vehicle (nVEH) or LPS (50 µg/kg body wt, ip) (nLPS) to neonatal mice on postnatal day (PND) 4 and 6 ("first hit"). We then administered saline vehicle (aVEH) or LPS (50 µg/kg body wt, ip) (aLPS) to adults on PND90 ("second hit"), in a 2 × 2 design. We collected whole blood, bone marrow, thymus, and spleen 4 h after treatment at PND90. We measured nine steroids via liquid chromatography-tandem mass spectrometry and measured transcripts of steroidogenic enzymes (Cyp11b1, Cyp11b2, Hsd11b1, and Hsd11b2), GC receptor, mineralocorticoid receptor, and hypothalamic-pituitary-adrenal axis components (Crh, Crhr1, Pomc, and Mc2r) via RT-qPCR. The nLPS treatment did not have significant effects on blood GC levels in adulthood. Nonetheless, nLPS treatment increased corticosterone and 11-dehydrocorticosterone levels in lymphoid organs of aLPS subjects. The nLPS treatment increased aldosterone levels in blood and bone marrow of aVEH females but decreased aldosterone levels in bone marrow and thymus of aVEH males. The nLPS treatment also increased transcripts for steroidogenic enzymes, especially the aldosterone-synthetic enzyme Cyp11b2, and modulated transcripts for steroid receptors, especially mineralocorticoid receptors, in lymphoid organs of aVEH and aLPS subjects. These findings suggest that elevated local GC and aldosterone production in lymphoid organs is a mechanism for the enduring effects of early-life infections on immune function.NEW & NOTEWORTHY Using a "two-hit" model in mice, we examined the effects of early-life lipopolysaccharide (LPS) administration on steroid regulation in blood and lymphoid organs. Mice received saline or LPS as neonates, and then saline or LPS as adults. Neonatal LPS heightened local glucocorticoid and systemic aldosterone responses to adult LPS treatment in bone marrow, thymus, and spleen. These data highlight the potential role of immunosteroids in developmental programming of immune function and health.

In many species, the reproductive behavior of females is more sensitive than that of males to energetic challenges, but the physical location of this sex difference is not completely understood. Progress has been facilitated by using Drosophila melanogaster, a genetically tractable species in which reproductive success is closely linked to energetics, and in which only females significantly decrease copulation rate after 48 h of food deprivation (FD). To examine the locus of the sex difference, we masculinized cells of either the nervous system (NS) or the fat body, an analog of the mammalian liver, using transcription inhibition of the sex determination cofactor, transformer-2 (tra2). In genetic (XX) females with a masculinized NS, courtship behavior was masculinized so that they showed robust courtship toward other females, and yet, the response to FD was not masculinized (FD XX females with a masculinized NS and FD female controls both courted and copulated significantly less than their fed counterparts). Thus, a masculinized NS circuit that engages male-typical courtship behavior toward other females is not sufficient to create the male-typical low sensitivity to food deprivation. By contrast, in genetic XX females with a masculinized fat body, the reproductive response to FD was masculinized, perhaps increasing peripheral fuel availability to the brain. These results are consistent with the existence of an evolutionarily conserved mechanism whereby sex determining genes either masculinize or feminize the peripheral organs, such as the fat body, so that males and females use a different reproductive strategy in habitats where food availability fluctuates.NEW & NOTEWORTHY In Drosophila melanogaster, food-deprived (FD) females show significantly greater decreases in copulation rate and increases in time spent with food compared with males. Genetic XX females with a masculinized fat body, but not genetic females with a masculinized nervous system (NS), showed a masculinized response to FD, consistent with the idea that sex differences in the female reproductive response to FD lie primarily in the periphery and not the NS.

Exercise-induced fatigue is regulated by central nervous system (CNS)-derived factors, including neurotransmitters and metabolic signals; however, the underlying mechanisms remain incompletely understood. This study aimed to test whether lactate activates Gi-protein coupled receptor 81 (GPR81) in the motor cortex to inhibit protein kinase A (PKA) phosphorylation, thereby contributing to central fatigue during exercise. Using a murine weight-loaded swimming model, we found that PKA phosphorylation in the motor cortex increased significantly after 15 min of swimming, but decreased markedly after swimming to exhaustion. Notably, inhibition of PKA phosphorylation by local administration of H-89 in the motor cortex shortened the swimming time of mice (H-89: 20 ± 5 min vs. saline 38 ± 6 min, P < 0.05). In addition, we found that activation of the lactate receptor GPR81 by local administration of 3-chloro-5-hydroxybenzoic acid (CHBA) or l-lactate attenuated exercise-induced upregulation of PKA phosphorylation. Conversely, genetic ablation of GPR81 (GPR81^-/-) mitigated the inhibitory effect of lactate on PKA phosphorylation, resulting in a 33% increase in swimming endurance. Despite comparable peripheral fatigue markers (blood lactate, skeletal muscle glycogen, and gastrocnemius p-AMPK/AMPK ratio) after 30 min of swimming, GPR81^-/- mice exhibited elevated motor cortical glutamate/GABA ratios, indicating preserved neuronal excitability. Therefore, our study reveals a vital role of the lactate-GPR81 signaling axis in the motor cortex during exercise and provides a potential target for alleviating exercise-induced central fatigue.NEW & NOTEWORTHY Exercise-induced fatigue is regulated by factors derived from the central nervous system (CNS), including neurotransmitters and metabolic signals. However, the underlying mechanisms remain largely obscure. Here, we demonstrate that lactate activates GPR81 in the motor cortex to inhibit PKA phosphorylation, thereby contributing to central fatigue during exercise. These findings reveal a vital role of lactate-GPR81-PKA axis in the motor cortex during exercise and provide a potential target for alleviating exercise-induced central fatigue.

Nitrogen dioxide (NO₂) is an environmental air pollutant and a potent oxidant. Epidemiological studies have revealed a close association between chronic cough and long-term inhalation exposure to NO₂. ATP can be released from airway/lung epithelial cells upon inhalation exposure to oxidants, and convincing evidence established in recent clinical studies indicated that extracellular ATP in the respiratory tract plays an important role in the pathogenesis of refractory chronic cough. However, whether inhalation exposure to NO₂ elevates the ATP release in the lung is not yet known. Results of this study showed: 1) in awake rats, acute and chronic inhalation exposures to NO₂ (5-10 ppm) evoked an increase in the ATP release in the bronchoalveolar lavage fluid (BALF), reaching >225% of that in the control (room air) group. 2) The NO₂-induced increase in ATP release in the lung generated by chronic exposure was substantially greater than that by acute exposure to the same concentration of NO₂. 3) Chronic but not acute exposure to NO₂ induced a mild and transient airway inflammation. 4) The elevated ATP release in the lung returned to control within 1-2 days after the acute exposure to NO₂; in sharp contrast, the increase in ATP in BALF persisted for >11-15 days following the chronic exposure when the airway inflammation had already completely recovered. These results suggest that the sustained elevation of ATP release in the lung may act as a contributing factor to the pathogenesis of chronic cough associated with long-term inhalation exposure to NO₂ in humans.NEW & NOTEWORTHY This study demonstrates that chronic inhalation exposure to NO₂, an air pollutant, induced a long-sustaining elevation of the extracellular ATP (eATP) concentration in rat lungs. This finding suggests that the elevated eATP concentration in the lungs may be an important contributing factor to the close association between chronic cough and long-term inhalation of NO₂ observed in humans. Furthermore, it presents a promising experimental animal model for future studies of the pathogenic mechanisms of chronic cough.

Endothelial monocyte-activating polypeptide II (EMAP-II) is a pro-inflammatory cytokine that has been recently shown to be involved in the cellular heat stress response following prolonged work in the heat. However, its response during prolonged passive heat exposure, such as during extreme heat events, or how chronic disease and aging modify this response, is not well characterized. We assessed serum EMAP-II concentrations at baseline and at the end of 9 h of passive heat exposure (end-exposure) (40°C, 9% relative humidity) in 19 young adults (21-27 yr) and 37 older adults (68-73 yr), including subgroups with hypertension (HTN) and/or type 2 diabetes (T2D). EMAP-II concentrations were significantly higher at end-exposure in young adults compared with older adults without HTN or T2D [mean difference (95% confidence interval): 1.9 (0.8, 3.0) pg/mL; P < 0.014], with a greater relative increase from baseline (P = 0.017). EMAP-II concentrations were significantly elevated at baseline in older adults with HTN [4.7 (3.3, 6.1) pg/mL; P < 0.001] and T2D [5.6 (4.2, 7.0) pg/mL; P < 0.001] compared with older adults without HTN or T2D. These elevations persisted at end-exposure in both the older adults with HTN [5.6 (4.2, 7.0) pg/mL; P < 0.001] and/or T2D [5.4 (4.3, 6.4) pg/mL; P < 0.001]. Prolonged passive heat exposure elicited a significant EMAP-II response in young adults. In older adults without HTN or T2D, the response was attenuated, potentially reflecting age-related reductions in cellular stress signaling. In contrast, older adults with HTN and/or T2D showed significant responses, suggesting that chronic disease may heighten inflammatory responses to extreme heat. (ClinicalTrials.gov identifier: NCT04353076)NEW & NOTEWORTHY This study is the first to demonstrate that prolonged passive heat exposure (9 h at 40°C, 9% relative humidity) elicits differential EMAP-II cytokine responses across age and health status. Young adults exhibited significant increases in EMAP-II, whereas older adults without HTN or T2D showed a blunted response. In contrast, older adults with HTN and/or T2D displayed elevated baseline and postexposure EMAP-II, revealing disease-specific inflammatory responses linked to heat vulnerability.

Behavioral thermoregulation (e.g., cool-seeking) is thought to proceed autonomic heat-loss responses (e.g., sweating), due to energy-conservation requirements. However, the energy cost of cool-seeking behaviors in humans has been rarely quantified. Here, we present a novel approach to characterize the energy cost of a common human cool-seeking behavior (i.e., manual fanning) and its individual variability during heat stress. Ten healthy males (20 ± 1 yr) participated in two 60-min trials (CONTROL and FAN) consisting of resting exposure to 37(±0.4)°C and 44(±6)% relative humidity (RH). During FAN, participants freely used a hand-held fan instrumented with an accelerometer, to offset thermal discomfort. During CONTROL, no fan was provided. We measured energy expenditure (breath-by-breath gas analysis), core temperature (T_c), mean skin temperature ([Formula: see text]), forehead T_sk, microclimate (next-to-skin) relative humidity ([Formula: see text]), heart rate (HR), and thermal discomfort during both trials, and used FAN accelerometery data to characterize cool-seeking behavior's onset, duration, bout frequency, and work rate. Seven participants engaged with self-fanning, which varied individually in onset time [mean: 12:30 min:s (range: 00:49-30:19)], total duration [05:54 min:s (01:04-17:53)], and bouts [6 (1-17)], but not work rate (308 ± 51 strokes·min^-1). Energy expenditure did not differ between FAN vs. CONTROL in those who fanned (433 ± 28 vs. 447 ± 64 kJ; P = 0.993), nor time-dependent changes in T_c, [Formula: see text], [Formula: see text], and HR. Our results indicate that our novel approach, which combines accelerometery (to quantify movement patterns) and indirect calorimetry (to measure associated energy expenditure), is both feasible and effective in quantifying the energetic cost of voluntary, behaviorally mediated thermoregulatory actions and their individual variability during heat stress.NEW & NOTEWORTHY We present a novel approach to characterize the energy cost of a common human cool-seeking behavior (i.e., manual fanning) and its individual variability during heat stress. Results indicate that our novel approach, which combine accelerometery (movement patterns) and indirect calorimetry (energy expenditure), is feasible and effective. This approach could be applied to a variety of thermal behaviors, thereby broadening the methodological toolkit available to researchers to study the relationship between behavioral and autonomic human thermoregulation.

Localized skeletal muscle injury [e.g., volumetric muscle loss (VML)] can disrupt diurnal metabolic flexibility. However, it remains unclear how the evaluation of whole body metabolism and physical activity following a prandial stimuli may reveal differences in metabolic flexibility between injured and uninjured states. This study aimed to develop a novel tool to examine whole body metabolic impairments following VML injury, with consideration of lipid-related mechanisms. Adult C57BL/6J mice (n = 50; equal males and females) were randomized to a methodology development cohort to undergo VML injury, intramuscular glycerol injection, or remain as controls. The developed tool using an intraperitoneal glucose injection and indirect calorimetry was used to characterize the dynamic nature of whole body metabolism. Whole body metabolism, in vivo muscle function, and markers of lipid and glycemic regulation were evaluated 6 wk following injury. Females, regardless of injury, exhibited greater daily energy expenditure alongside increases in activity. Females exhibit lower whole body lipid oxidation during the inactive period, despite higher in active period, suggesting more coordinated substrate utilization. Biological sex differences in postprandial substrate utilization reveal that males fail to suppress whole body lipid oxidation, exhibiting marked impairments in postprandial metabolic flexibility. VML injury increases protein expression of perilipin 2 and SIRT1 in the muscle remaining, while inducing sex-specific changes, with adipose triglyceride lipase (ATGL) expression markedly increased and with perilipin 5 expression markedly reduced in females. The remaining muscle following VML accumulates neutral lipids and perilipin 1-positive adipocytes. This work highlights sex-specific mechanisms of metabolic disruption following traumatic skeletal muscle injuries, such as VML.NEW & NOTEWORTHY We developed a novel, freely ambulatory preclinical tool to assess dynamic postprandial metabolic flexibility. Using this tool, we identified sex differences in whole body energy expenditure and substrate utilization. The use of a single intramuscular glycerol injection model is not sufficient as a comparative model for evaluating chronic ectopic lipid accumulation and metabolic disruptions. In the context of volumetric muscle loss injury, disruptions in metabolic flexibility occur alongside alterations in lipid handling and ectopic lipid accumulation.

There is considerable heterogeneity in the thermal and cardiovascular responses to heat stress, even among older adults within a similar age range; hence, age alone may not predict heat-related risks. This variability may be in part explained by differences in cardiorespiratory fitness. We aimed to identify whether left ventricular end-diastolic volume (LVEDV), a characteristic of cardiorespiratory fitness, was associated with core temperatures and heart rate responses in older adults exposed to 3 h of very hot and dry heat stress. We hypothesized that individuals with smaller LVEDV would exhibit higher ending core temperature and heart rates following heat stress. Twenty-two older adults (73 ± 5 yr; 10 females) were exposed to 3 h of very hot and dry ambient heat stress (47°C, 15% relative humidity) with accompanying activities of daily living. We assessed thermal and cardiovascular responses at baseline and end-heating. End core temperature ranged from 37.4°C to 38.9°C, whereas end heart rate ranged from 53 to 113 beats/min. Baseline LVEDV was associated with end-heating core temperature (β = -0.018, SE = 0.004; P = 0.003) after controlling for body surface area and baseline core temperature. Likewise, LVEDV was associated with end-heating heart rate (β = -0.595, SE = 0.126; P < 0.001), after controlling for body surface area. However, LVEDV was not associated with whole body sweat rate (P = 0.100) or the change in forearm blood flow (P = 0.331) indexed to changes in core temperature. These findings suggest that individuals with small LVEDV may be susceptible to hyperthermia and tachycardia associated with environmental heat stress.NEW & NOTEWORTHY There is considerable heterogeneity in the thermal and cardiovascular responses to heat stress, even among older adults within a similar age range; hence, age alone may not predict heat-related risks. This variability may be in part explained by differences in physical fitness. Our findings show that individuals with low left ventricular end-diastolic volumes have greater core temperature and heart rate responses to environmental heat stress.