bluuebunny/crossref_metadata_2025 huggingface dataset:
ARMAX‐based Method Extends Knowledge of the Baroreflex
Authors: Lund Morten Toft , Salomonsson Max , Jonassen Thomas EN , von Holstein‐Rathlou Niels‐Henrik
Published: November 2023

Introduction

The arterial baroreceptor‐heart rate reflex (baroreflex) is a key mechanism in regulating the cardiovascular system, and alterations in baroreceptor function are seen in many disease states, including heart failure, obesity and hypertension. Recent studies have identified impairment of the baroreflex early in the clinical course of hypertension. We propose a new and simple method for analyzing these alterations in baroreceptor function. The method is validated to describe dynamic relationships in causal systems with feedback, and in addition to the traditional estimate of baroreflex sensitivity (BRS) it adds information on two new valuable components of the reflex. Firstly, the average time for the baroreflex to reach its maximal effect on heart rate (HR) following a change in blood pressure (BP), and secondly, the average maximal change in HR produced by the baroreflex. This study aims to validate the method against a traditional method of estimating BRS in both healthy animals and in a verified model of diet‐induced obesity and hypertension.

Methods

48‐hour data series of continuous BP and HR recordings were collected with telemetry and used for analysis. 16‐weeks‐old SD rats on standard chow (n=11) served as healthy controls, while a similar group of rats on a high‐fat, high‐fructose (HFHC) diet from 4 weeks of age (n=6) constituted the obese hypertension model. An Autoregressive–moving‐average model with exogenous inputs (ARMAX)‐based algorithm was applied to the data series and compared with the α‐coefficient.

Results

The ARMAX‐based method matched the traditional method, and interestingly when comparing the obese hypertension group with controls (body weight 531±27 vs. 458±19 g, p<0.05; mean arterial pressure 119±3 vs. 102±1 mmHg, p<0.05) the same degree of attenuation in BRS of ~50 % could be observed in the obese hypertensive group compared with controls with both methods (ARMAX: −0.08±0.01 vs. −0.15±0.01 Δbpm/heartbeat, p<0.05; α‐coefficient: 0.51±0.07 vs. 0.89±0.07 ms/mmHg, p<0.05). The ARMAX‐based method additionally demonstrated the maximal change in HR following a BP change to be reduced by ~50 % in the obese hypertensive group compared with controls (1.3±0.2 vs. −2.6±0.2 Δbpm, p<0.05), while the time until the maximal change in HR was reached was similar between groups.

Conclusion

The ARMAX‐based method confirms traditional methods and presents an unbiased method of characterizing HR changes in response to changes in BP. The method further contributes to our understanding of the reflex by providing information on time to maximal change in HR as well as the degree of maximal change in HR. The presented algorithm can potentially be applied to other species including humans.

Support or Funding Information

Pregraduate Research Scholarship from The Danish Council for Independent Research, Grant from Fru Ruth König Petersens Foundation, Helge Peetz and Verner Peetz and Hustrus Scholarship.
The Comparison of Multiple Chemosensitivity Tests in Healthy Adults
Authors: Collins Sophie É. , Fuhr Desi P. , Michaelchuk Wade W. , Byers Bradley W. , Stickland Michael K.
Published: November 2023

Chemoreceptor activity and sensitivity have been shown to be elevated in clinical conditions such as heart failure, hypertension and chronic obstructive pulmonary disease, with heightened chemosensitivity being predictive of mortality in heart failure. Various protocols have been used in these studies to evaluate chemosensitivity, and the purpose of our project was to examine the relationship between three of these chemoreceptor tests: 1) the transient hypoxic ventilatory drive test, 2) the single‐breath (SB) CO2 test, 3) the CO2 rebreathe test. It was hypothesized that the transient hypoxia test and the SB CO2 test would be correlated as both likely stimulate the carotid chemoreceptors and that they would be unrelated to the rebreathe test, as this test likely stimulates the central chemoreceptors. Ten healthy individuals (5 males, 5 females, mean age 27±10 yrs) were recruited. The SB CO2 test and the CO2 rebreathe test were performed first, with the order randomized within subjects. For the SB CO2 test, subjects were given a single breath of 13% CO2, 10 times at 2 min intervals. The hypercapnic ventilatory response was calculated by plotting the change in ventilation relative to the change in PETCO2 during the 20s following the SB of CO2. For the CO2 rebreathe protocol, subjects rebreathed 50% O2, 7% CO2 and 43% N2 from a 5L Douglas bag until PETCO2 reached 55mmHg, or until subjects requested termination of the test. The ventilatory response to the CO2 rebreathe was calculated by plotting the change in ventilation relative to the change in PETCO2. The transient hypoxia trial was conducted, where subjects were given 2–8 breaths of pure N2. The number of breaths was randomized and repeated 10–14 times. The slope of the regression line between the change in ventilation and the change in SpO2 represented the hypoxic ventilatory response. The average hypoxic ventilatory response was 0.56±0.09 L/min/% SpO2. The mean SB CO2 response was 0.37±0.07 L/min/mmHg and the mean rebreathe response was 1.81±0.94 L/min/mmHg. There was no significant correlation between the transient hypoxia test and SB CO2 test (r = 0.13, p = 0.72), no significant correlation between the SB CO2 test and the CO2 rebreathe test (r = 0.09, p = 0.81), and no significant correlation between the CO2 rebreathe test and the transient hypoxia test (r = 0.07, p = 0.85). Our results suggest that the transient hypoxic ventilatory drive test, the single‐breath CO2 test, and the CO2 rebreathe test are unrelated to each other in healthy humans. Our results support earlier suggestions that these tests may evaluate independent components of chemosensitivity.
Sleep Apnea Worsens Muscle Vasoconstriction During Central and Peripheral Chemoreceptors Stimulation in Patients with Systolic Heart Failure
Authors: Lobo Denise M L , Trevizan Patricia F , Toschi‐Dias Edgar , Oliveira Patricia A , Piveta Rafael B , Mady Charles , Bocchi Edimar A , Almeida Dirceu R , Lorenzi‐Filho Geraldo , Middlekauff Holly R , Negrão Carlos E
Published: November 2023

We tested the hypothesis that muscle vasoconstriction in response to hypercapnia and hypoxia would be more pronounced in patients with chronic heart failure (CHF) and sleep apnea than patients with CHF alone. Ninety consecutive CHF patients, Functional Class II‐III NYHA, LVEF≤40% were selected to the study. Forty‐two patients who fulfilled all the inclusion criteria were enrolled in the study: No Sleep Disordered Breathing (NoSDB, n=13, 47±3y), Obstructive Sleep Apnea (OSA, n=22, 57±1y) and Central Sleep Apnea (CSA, n=07, 53±3y). Sleep apnea was characterized by apnea‐hypopnea index≥15 events/hour (polysomnography). Central (7%CO2 and 93%O2) and peripheral (10%O2 and 90%N2, with CO2 titrated) chemoreceptors were stimulated for 3 min. Muscle sympathetic nervous activity (MSNA) was evaluated by microneurography technique, forearm (FBF) and calf (CBF) blood flow by venous occlusion plethysmography, and blood pressure by beat‐to‐beat noninvasive technique. Baseline MSNA, FBF, forearm vascular conductance (FVC), CBF, and calf vascular conductance (CVC) were similar among groups. FBF (hypercapnia: P=0.001; and hypoxia: P=<0.001) and CBF (hypercapnia: P=<0.001; and hypoxia: P=0.002) responses were significantly lower in OSA and CSA groups compared to NoSDB group. FVC (hypercapnia: P=0.001; and hypoxia: P=<0.001) and CVC (hypercapnia: P=<0.001; and hypoxia: P=0.001) responses were also significantly lower in OSA and CSA groups compared to NoSDB group. MSNA responses were not different in all groups studied (hypercapnia: P=0.12; and hypoxia: P=0.17). Patients with CHF and obstructive or central sleep apnea have more severe muscle vasoconstriction during hypercapnia and hypoxia than patients with CHF alone. The similarities in MSNA suggest that these responses are associated with endothelial dysfunction.

Support or Funding Information

CNPq #140265/2013‐9 and FAPESP #2010/50048‐1
High Salt Challenge Augments Expression of Proinflammatory Cytokines and Contributes to Elevated Neuronal Activity in the Hypothalamic Paraventricular Nucleus
Authors: Zhu Fengli , Larson Robert A , Shi Peng , Li Ningjun , Chen Qinghui , Shan Zhiying
Published: November 2023

Previous studies have demonstrated that brain proinflammatory cytokines (PIC) play an important role in neurogenic hypertension. However, little is known about the role of brain inflammation in salt sensitive hypertension (SSHTN). In this study, we tested the hypothesis that the PIC expression is increased in the hypothalamic paraventricular nucleus (PVN) and contributes to increased neuronal activity in SSHTN. To test this hypothesis, 8‐week‐old Dahl salt sensitive (DS) rats were divided into two groups (n=3~ 5/group) and fed with either a high salt (HS, 4% NaCI) or normal salt (NS, 0.4% NaCl) diet. Four weeks following diet treatment, rats were euthanized, the PVN was punched out, and real time PCR were performed to assay genes of interest. HS treatment resulted in respective 8 fold, 4 fold, and 7 fold increases in TNFα, IL1β and IL6 mRNA levels in the PVN. In addition, Fra1, a chronic neuronal activation marker, was also increased by 4 fold. Additionally, in order to examine the action of acute hypertonic NaCI on the expression of PIC and neuronal activation marker, adult male SD rats were divided into two groups (n=3~4 per group) and received intracerbroventricular infusion of either hypertonic (2M, 2μl), or isotonic (0.15 M, 2μl) NaCI under anesthetized condition. Three hours following the infusion, rats were euthanized and PVN mRNA levels of PIC and Fra1 assayed. Results indicate that hypertonic saline infusion induced significant increases in mRNA levels of PIC including TNFα (6‐fold), IL1β (13‐fold) and IL6 (21‐fold), as well as neuronal activation marker Fra1 (8‐fold). Finally, we tested whether or not the increase in PIC expression occurred in neurons. Incubation of hypertonic saline (10 mM NaCI plus full medium) for 3 hours resulted in a 12‐fold increase in IL6 and 2.8 fold increase in Fra1 mRNA levels in neuronal cultures from the hypothalamus containing the PVN of neonatal SD rats. These observations suggest that HS intake induced inflammation in the PVN may contribute to increased sympathetic nerve activity and therefore to SSHTN development

Support or Funding Information

Funding support: AHA 11SDG7420029, Zhiying Shan; R15‐HL122952, Qinghui Chen
Central Anti‐inflammatory and Neuronal Effects of Butyrate in Wistar Kyoto and Spontaneously Hypertensive Rats
Authors: Yang Tao , Rodriguez Vermali , Colon‐Perez Luis , Redler Ty , Febo Marcelo , Sumners Colin , Zubcevic Jasenka
Published: November 2023

Introduction

Emerging evidence demonstrates a significant link between gut dysbiosis and hypertension (HTN). Recently, we observed a reduction in the butyrate‐producing bacteria in the gut of spontaneously hypertensive rats (SHR) compared to Wistar Kyoto (WKY) control, suggesting reduced butyrate availability in HTN. Butyrate, one of the major fermented end‐products of gut microbiota, reportedly produces beneficial effects in multiple dysbiosis‐related diseases, partly through its role in the regulation of inflammatory responses. Considering the established link between neuroinflammation and HTN, we hypothesized that some of the beneficial effects of butyrate may be via a central regulatory mechanism.

Methods

In situ rat preparation was used to test the effects of systemic butyrate application (500mg/kg in sterile saline) in juvenile SHR and control rats (4 weeks old). WKY and SHR primary astrocytes from two days old pups were cultured in DMEM, supplemented with 10% FBS and 1% pen/strep, for 14 days, prior to treatment with 1mM butyrate for 4 hours. Cells were collected for real time PCR analysis. Total RNA was isolated from the PVN region of 8 WKY and 8 SHR rats (12–14 weeks old) for real time PCR analysis of inflammatory factors. For functional magnetic resonance imaging (fMRI), adult WKY and SHR rats were briefly anaesthetized with 4% Isoflurane, and kept at 1.0%–1.5% during imaging. ICV catheters were implanted in all rats using the established Paxinos‐Watson coordinates. Images were collected prior to and immediately after a single butyrate injection (100 ng in aCSF), on an actively shielded 470MHz (4.7T‐Tesla) Magnex Scientific MR scanner controlled by Agilent Technologies VnmrJ 3.1 console software.

Results

Systemic application of 500 mg/kg butyrate produced an immediate reduction in BP in normotensive controls (Δ=18±1 mmHg). This effect of butyrate on BP was modestly but significantly lower in the juvenile SHR (Δ=12±1 mmHg, P<0.05, n=3 per group). Real time PCR revealed a ~56% reduction in expression of the butyrate‐sensing olfactory receptor (Olfr) 59 in the hypothalamus of SHR compared with WKY. In line with this, fMRI demonstrated reduced brainstem neuronal activation (by~40%) in the SHR compared to the WKY following a single ICV injection of butyrate (n=3 per group). In addition, butyrate treatment significantly lowered expression levels of Ccl2 (by 33 %, P value= 0.0082) and Tlr4 (by 48 %, P value =0.01) in the primary astrocyte culture from the SHR.

Conclusion

Butyrate reduced inflammatory mediators in the SHR astrocytes in vitro, and produced lower effects on the neural activation and BP in the SHR, possibly due to decreased expression of Olfr59. Therefore, effects of butyrate may also be mediated via a central regulatory mechanism.

Support or Funding Information

AHA 14SDG18300010;UF College of Veterinary Medicine
RENAL FUNCTION IN NORMOTENSIVE SHEEP IN THE FIRST FOURTEEN WEEKS AFTER CATHETER‐BASED RENAL DENERVATION
Authors: Booth Lindsea C , McArdle Zoe , Yao Song T , Malone Sally , Lankadeva Yugeesh , Kosaka Junko , Schlaich Markus , May Clive N
Published: November 2023

Background

Catheter‐based renal denervation (RDN) has emerged as a novel treatment for resistant hypertension by targeting the afferent sensory and efferent sympathetic renal nerves to reduce blood pressure. Recent evidence suggests that there is partial functional and anatomical reinnervation at 5 months after catheter‐based RDN and complete reinnervation after 11 months. The function of the reinnervated renal nerves has not been investigated in conscious animals.

Aim

To examine the effects of reinnervation of the renal nerves on renal function 1, 8 and 14 weeks after renal denervation using the Symplicity Flex catheter.

Methods

Normotensive merino ewes underwent a battery of physiological challenges, including salt load, salt depletion, periods of mild hypertension and mild hypotension, during which changes in renal blood flow, heart rate, mean arterial pressure and neurohormonal markers were measured. Ewes then underwent either sham or bilateral RDN using the Symplicity Flex catheter. Physiological challenges were repeated at 1, 8 and 14 weeks’ post‐RDN or sham denervation. Renal sympathetic nerve activity was recorded 8 and 14 weeks after sham or bilateral RDN.

Results

One week after RDN, cumulative sodium excretion was lower compared with pre‐RDN levels in response to 0.1 mM saline/kg/min i.v. for 100 min (935±49 mmol and 619±52 mmol, respectively). Eight weeks after RDN the cumulative sodium excretion was lower in the RDN group compared to pre‐RDN (58±10 mmol and 31 ± 3 mmol, respectively) at the end of a 135 mM i.v. saline load at 0.09 mL/kg/min for 4 hours. There were no changes with sham denervation. In addition, we made the first recordings in conscious animals of renal sympathetic nerve activity after bilateral catheter‐based RDN.

Conclusions

The preliminary data from the present study suggest that there are significant changes in renal function after catheter‐based RDN.
Macrophage‐Dependent Impairment of α2 Autoreceptor Inhibition of Ca2+ Currents in Sympathetic Neurons Contributes to Hypertension in DOCA‐Salt Rats
Authors: Mui Ryan , Fernandes Roxanne , Galligan James
Published: November 2023

Norepinephrine (NE) release from perivascular sympathetic nerves is regulated by prejunctional alpha‐2 autoreceptors (α2AR), which inhibit nerve terminal N‐type Ca2+ channels. We showed previously that macrophage infiltration and superoxide production in mesenteric arteries (MA) impairs α2AR‐mediated inhibition of NE release. We tested the hypothesis that macrophages disrupt α2AR coupling to N‐type Ca2+ channels in sympathetic neurons.

Methods

The DOCA‐salt rat model of hypertension was used for this study. Immunohistochemistry was used to localize macrophages in MA. Ca2+ current inhibition was evaluated using whole‐cell patch clamp on cultured sympathetic neurons of the celiac ganglion. Liposome‐encapsulated clodronate (LEC) was used to deplete macrophages.

Results

Macrophage infiltration is increased in MA of DOCA‐salt hypertensive rats. The α2AR agonists NE and UK14304 inhibit Ca2+ currents in neurons from normotensive but not hypertensive rats. In all neurons, yohimbine (α2AR antagonist) attenuates the effects of NE and dialysis of GppNHp (non‐hydrolyzable GTP analog) inhibits Ca2+ current equally. In DOCA‐salt rats, LEC treatment prevents macrophage infiltration in MA, reduces blood pressure elevation, and preserves α2AR‐mediated inhibition of Ca2+ current in sympathetic neurons.

Conclusions

In DOCA‐salt hypertensive rats, α2AR dysfunction leads to impaired modulation of Ca2+ current that is independent of factors downstream of receptor activation. Macrophage depletion preserves α2AR function and protects against blood pressure elevation.

Support or Funding Information

P01 HL070687
EETs oppositely regulate pulmonary and systemic pressure in hypoxia
Authors: Kandhi Sharath , Qin Jun , Froogh Ghezal , Alruwaili Norah , Wolin Michael S. , Huang An , Sun Dong
Published: November 2023

Aim

To study the effects of epoxyeicosatrienoic acids (EETs) on the pulmonary and systemic circulations in response to hypoxia.

Methods

Male wild type (WT) and soluble epoxide hydrolase knockout (sEH‐KO) mice, and WT mice fed with a sEH inhibitor (t‐TUCB; 1mg/kg/day) via oral gavage for 4 weeks, were used. Right ventricular systolic pressure (RVSP) and systemic arterial pressures (MABP) were recorded via catheterizations, in response to breathing 100% and 10% oxygen (hypoxia).

Results

Baseline of RVSP was comparable among the three groups of mice, whereas, MABP was significantly lower in sEH‐KO and TUCB‐treated groups compared to WT mice. Exposure of mice to hypoxia elicited significant increases in RVSP with more predominant increases in TUCB‐treated and sEH‐KO than WT mice. 14,15‐EEZE that had no effects on responses of WT mice, prevented hypoxia‐induced elevation of RVSP in other two groups. Hypoxia decreased MABP, which was reversed by EEZE in sEH‐KO and TUCB‐treated mice.

Conclusions

Hypoxia elicited the elevation of RVSP but reduction of MABP, responses that were potentiated, as a function of the deletion of sEH gene and inhibition of sEH activity.

Support or Funding Information

(This work was supported by NIH HL070653 and HL115124)
Stellate and Pyramidal Neurons in Goldfish Telencephalon Respond Differently to Anoxia and GABA Receptor Inhibition
Authors: Hossein‐Javaheri Nariman
Published: November 2023

During anoxia the mammalian brain undergoes hyper‐excitability and cell death while the common goldfish (Carassius auratus) is anoxia tolerant and by suppressing electrical activity of the brain, prevents excitotoxic cell death. This mechanism in goldfish is not fully understood however they may rely on neurotransmitters and neuromodulators to suppress energy consumption during anoxia. In our experiment we investigated the possible roles of γ‐amino butyric acid (GABA), the major inhibitory neurotransmitter, in goldfish telencephalon neurons during anoxia. Utilizing whole‐cell and perforated patch clamp recording techniques, we found that with anoxia, membrane potential in inhibitory stellate neurons and excitatory pyramidal neurons increased; however, stellate cells became more depolarized and generated action potentials while the pyramidal neurons showed suppressed electrical activity. To further investigate the importance of GABA in anoxic survival, we blocked the GABAA receptors during anoxia using an antagonist (gabazine, 25μM). Gabazine significantly suppresses neuronal activity in stellate neurons and increased action potential firing in the pyramidal cells, suppressing the anoxic response in these neurons. Since membrane potential depolarized with anoxia, we applied GABA (5mM) to both cell types during normoxia and measured changes in membrane potential. We calculated the GABA reversal potential (EGABA) and observed that with anoxia, membrane potential shifts towards a depolarizing EGABA. We were able to conclude that GABA release during anoxia significantly suppresses neuronal activity and increases anoxic survival. This is an example of natural adaptive mechanism in goldfish which could also be investigated in mammalian brain as a protective mechanism against anoxic injuries.

Support or Funding Information

discovery accelerator supplement grant
Amino Acids as Fates of Anoxia‐Induced Lactate Loads in the Painted Turtle
Authors: Hill Craig A. , Yarasheski Kevin E. , Warren Daniel E.
Published: November 2023

The painted turtle is the most anoxia tolerant tetrapod known. During its over‐winter hibernation which often occurs in anoxic ponds, it is capable of accumulating lactate to greater than 200mM in the plasma alone. We sought to determine whether or not amino acid synthesis serves as a metabolic fate of the lactate carbon accumulated during anoxia and recovery following anoxia at 10°C and 20°C. We hypothesized that most amino acid synthesis would occur during the recovery following anoxia. To investigate this, a bolus of [U‐13C]‐lactate tracer was delivered via an arterial catheter during the anoxia and allowed to equilibrate prior to recovery. Plasma was sampled throughout the dive and subsequent recovery, and liver, pectoralis, and ventricle were sampled at the end of anoxia and at the end of recovery. The enrichments of alanine, glycine, valine, methionine, aspartate, and glutamate in plasma samples and tissue extracts were measured using gas chromatography and mass spectrometry. Results show a clear difference between the end of anoxia versus the end of recovery following anoxia in both the plasma and in the cytosolic free amino acids. Furthermore, enrichment was significantly different in the liver versus pectoralis and ventricle. Direct enrichment of alanine as M+3 alanine from pyruvate was observed, but the remaining amino acids were primarily enriched as M+2, with less M+3 and M+4, showing that the lactate carbon persists for at least one turn of the citric acid cycle (CAC). The anaplerotic amino acids, glutamate and aspartate, were also highly enriched, indicating elevated pyruvate carboxylase activity and potentially representing an auxiliary pool for rapid replenishment of CAC intermediates when needed. Future studies include amino acid tracer experiments to investigate the specific utilization of amino acids during anoxia and particularly during recovery, as well as further investigation of the amphibolic metabolism inherent to the citric acid cycle. This work is the first of its kind, and makes a significant contribution towards the development of the turtle model for metabolic studies.

Support or Funding Information

This work was supported by the NIH; Dr. Daniel Warren (R15 DK097700), and the Washington University Biomedical Mass Spectrometry Research Facility (P41 GM103422, P30 DK020579, P30 DK056341).
Structure and Function of Dragonfly Looming‐Sensitive Neurons
Authors: Slugaski Cara
Published: November 2023

In this project, I aim to identify specific neurons in the dragonfly brain that respond selectively to looming stimuli. In the dragonfly nerve cord, there are large visual neurons, called Target Selective Descending Neurons (TSDNs). These neurons respond selectively to small moving stimuli, which mimic the movements of dragonfly prey. The response of these neurons is the steering movement of the dragonfly's wings, allowing them to predict the location of their prey for accurate interception. A subset of the TSDNs show large and precisely timed responses to the expanding image of an approaching object. I will be studying these “looming‐sensitive” neurons, researching what visual information they are sending to the flight system. This material will allow for the analysis of the anatomical structure in the dragonfly brain. The visual responses of these dragonflies suggests that the looming‐sensitive neurons are the specific TSDNs called MDT3 and DIT3, but in order to confirm this prediction, we must visualize the anatomy of the brain. With the use of a dye called Lucifer yellow, we can trace the response of the looming stimuli to a specific area of the brain. By injecting the dye with a recording microelectrode, we can positively identify these specific neurons.

Support or Funding Information

Union College Undergraduate Research Committee
Does pulse contour analysis provide a valid estimate of cardiac output during spaceflight?
Authors: Yee Nicholas J , Zuj Kathryn A , Greaves Danielle K , Hughson Richard L
Published: November 2023

Model flow is a pulse contour analysis method that provides non‐invasive ambulatory cardiac output, which can characterize potential degradation of cardiovascular function due to long‐duration spaceflight. However, the model flow algorithm has not been tested in altered gravitational environments. The purpose of this study was to use a standard rebreathing measure of cardiac output (COre) to validate the model flow cardiac output (COmf) and to detect potential changes in cardiovascular physiology during spaceflight using the stiffness index, model flow Aortic Age (AGEmf). Data were collected from nine male astronauts (45 ± 7 years old) who were aboard the International Space Station for 6 months. Testing occurred pre‐flight and inflight approximately 3 weeks before returning to Earth. Rebreathing cardiac output was collected using the Pulmonary Function System. The arterial pressure waveform was collected using finger photoplethysmography for the determination of COmf and AGEmf. Changes in COmf with spaceflight did not match changes in COre (p < 0.001). COre increased from pre‐flight to inflight (4.8 ± 0.7 L/min and 7.0 ± 1.4 L/min, respectively; p < 0.01) while COmf remained constant with spaceflight (pre‐flight: 6.2 ± 1.4 L/min and inflight: 5.8 ± 1.1 L/min, respectively; p > 0.05). The model flow algorithm assumes central arterial properties based on age but as changes in COmf were not similar to COre with spaceflight, this assumption appears to have been violated. As well, the stiffness index AGEmf decreased with spaceflight (pre‐flight: 68 ± 16 years old and inflight: 41 ± 9 years old; p < 0.01). These results suggest changes in cardiac function and in arterial properties that invalidate pulse contour analysis during spaceflight.

Support or Funding Information

The research was supported by the Canadian Space Agency, Natural Sciences and Engineering Research Council of Canada, and the American Physiological Society.
Endothelin‐1 Modulates Methacholine‐Induced Cutaneous Vasodilation but not Sweating in Young Human Skin
Authors: Halili Lyra , Singh Maya Sarah , Fujii Naoto , Alexander Lacy M. , Kenny Glen P.
Published: November 2023

The present study investigated the effect of endothelin‐1 (ET‐1) on cholinergic mechanisms of end‐organs (i.e. skin blood vessels and sweat glands) for heat dissipation. We evaluated the hypothesis that ET‐1 attenuates cholinergic cutaneous vasodilation and sweating through a nitric oxide synthase (NOS)‐dependent mechanism. Cutaneous vascular conductance (CVC) and sweat rate were assessed in three protocols. CVC was normalized to maximal CVC (%CVCmax). In Protocol 1 (n = 8), microdialysis forearm skin sites were perfused with lactated Ringer (Control), 40 pM, 4 nM or 400 nM ET‐1. In Protocol 2 (n = 11) sites were perfused with lactated Ringer (Control), 400 nM ET‐1, 10 mM L‐NNA (a NOS inhibitor) or a combination of 400 nM ET‐1 and 10 mM L‐NNA. In Protocol 3 (n = 8), only two sites (Control and 400 nM ET‐1) were utilized to assess the influence of ET‐1 on the dilation capacity of vascular smooth muscle cells using a dual administration of sodium nitroprusside (SNP). Methacholine (MCh) was co‐administered in a dose‐dependent manner (0.0125, 0.25, 5, 100, 2000 mM, each for 25 min) at all skin sites. 400 nM ET‐1 significantly attenuated increases in CVC compared to Control in response to 0.25 (40 ± 13 vs. 75 ± 10 %CVCmax) and 5 mM (55 ± 11 vs. 91 ± 11 %CVCmax) MCh (both P < 0.05). A high dose of ET‐1 (400 nM) co‐infused with L‐NNA further attenuated CVC relative to the ET‐1 site during 0.25 (23 ± 9 vs. 43 ± 14 %CVCmax), 5 (35 ± 10 vs. 61 ± 12 %CVCmax) and 100 mM (43 ± 12 vs. 70 ± 10 %CVCmax) MCh administration (all P < 0.05). Cutaneous vasodilation in response to SNP was significantly blunted (perfusion units mmHg−1: 1.66 ± 0.30 vs. 0.80 ± 0.17) after administration of 400 nM ET‐1 (P < 0.05). Therefore, we show that ET‐1 attenuates cutaneous vasodilation through a NOS‐independent, possibly through a vascular smooth muscle cell‐dependent mechanism, and that methacholine‐induced sweating is not modulated by ET‐1.

Support or Funding Information

This study was supported by grants from the Natural Sciences and Engineering Research Council of Canada (Discover grant, RGPIN‐06313‐2014; Discovery Grants Program ‐ Accelerator Supplement, RGPAS‐462252‐2014; funds held by Dr. Glen P. Kenny).
Aging Slows Vasoconstriction Dynamics in Skeletal Muscle Resistance Vessels
Authors: Gittemeier Elizabeth Marie , Ericson Tyler J , Verma Rahul , Ghosh Payal , Garcia Emmanuel , Opoku‐Acheampong Alexander , Behnke Bradley Jon
Published: November 2023

With advancing age there is a reduced ability to tolerate orthostatic stress and perform exercise. An increase in peripheral vascular resistance (PVR) during both of these challenges, facilitated in part by sympathetically mediated vasoconstriction of resistance arteries, is requisite to maintain central venous return and arterial blood pressure. In aged subjects, the ability to rapidly enhance PVR during orthostatic challenges is diminished, which contributes to orthostatic intolerance in many aged individuals. The purpose of this preliminary investigation was to determine the rate of vasoconstriction to an alpha‐adrenergic agonist (i.e., sympathetic mimetic) in skeletal muscle arteries of young (6 mo old; n=4) and aged (24 mo old; n= 4) Fisher‐344 rats. Resistance arteries from the highly‐oxidative red portion of the gastrocnemius muscle were isolated and cannulated. Thereafter, the temporal characteristics of vasoconstriction [i.e., time‐delay (TD), rate of constriction, time to steady‐state (SS)] were quantified after exposure to 10−4M norepinephrine. With old age, the delay before the onset of constriction was ~ 5x longer than younger counterparts (young, 0.7 ± 0.1 vs. aged, 3.7 ± 0.4 s) and the time to SS was substantially prolonged with old age (young, 6.6 ± 0.4 vs. aged, 19.5 ± 1.2 s). Despite no difference in the overall magnitude of vasoconstriction between groups, the rate of vasoconstriction was blunted with old age (young, 35.9 ± 9.1 vs. aged, 14.1 ± 0.9 μm/s). With old age, there appears to be a severely diminished ability to rapidly vasoconstrict skeletal muscle resistance arteries. During orthostatic stresses, a reduced ability to vasoconstrict peripheral arteries would lead to blood pooling in the periphery and, subsequently, diminished venous return and an inability to maintain mean arterial pressure. The precise mechanisms responsible for the reduced rate of vasoconstriction (e.g., Ca2+ handling, altered vascular mechanical properties) are unknown and are currently being investigated. Whether the same deficits in vasoconstriction are present in arteries of other vascular beds (e.g., splanchnic region) remains to be determined.

Support or Funding Information

National Institutes of Health (AG25622), American Cancer Society (RSG‐14‐150‐01‐CCE)
Repeated moderate heat exposure improves limb endothelial function in humans
Authors: Cui Jian , Lott Mary , Blaha Cheryl , Sinoway Lawrence I.
Published: November 2023

Limited reports suggest that sauna baths or dry sauna may improve vascular function in patients with peripheral artery disease or heart failure. However, it is unclear if repeated moderate heat exposure (RMHE) with regular warm water baths can improve endothelial function in normal aged individuals. We assessed limb endothelial‐dependent function via measuring brachial flow‐mediated dilation (FMD) in 6 elder volunteers (5 M and 1 F, 59 ± 3 yrs, 177 ± 4 cm, 88 ± 10 kg) after 4 weeks (5 days/week) of warm baths (39–42 °C for 30 min). During each bath, subjects were in the recumbent position in the bathtub with water up to their mid chest, while their forearms were not kept in water. On the days of prior, 1 day post 4 weeks of RMHE and 1 week after end of RMHE, FMD was measured with Doppler ultrasound following 5 minutes of forearm ischemia in a laboratory at ~23 °C. Endothelium‐independent vasodilation was quantified by measuring the brachial artery dilator response to sublingual nitroglycerin (0.4 mg). RMHE led to significant increases in FMD (one‐way repeated measures ANOVA, P=0.019). Compared with prior RMHE (Δ4.98 ± 0.98% from prior ischemia baseline), the FMD increased in all subjects after 4 weeks of RMHE (Δ8.48 ± 1.33%, P=0.033), and returned to baseline diameters one week after completion of RMHE (Δ5.71 ± 0.68%, P=0.915). In contrast, RMHE did not induce significant changes in the dilator response to sublingual nitroglycerin (prior, post, post 1‐wk: Δ11.91 ± 0.70%, Δ11.84 ± 1.05%, Δ11.21 ± 0.33%, P=0.684). These data suggest that repeated moderate heat exposure improves limb endothelial‐dependent function, and does not alter endothelium‐independent vasodilation in normal aged individuals. We speculate the increased blood flow seen with heat exposure may increase vessel shear stress and eNOS activity, which may in turn contribute to the improved chronic endothelial function by the repeated heat exposures. The mechanism(s) should be examined in future studies.

Support or Funding Information

AHA 15GRNT24480051 (JC) and P01 HL096570‐05 (LIS)
Anabolic Response to Exercise is Not Limited in Older Adults Despite Lower Mitochondrial Respiratory Capacity Compared To Young
Authors: Lanza Ian , Lalia Antigoni , Dasari Surendra , Robinson Matthew , Abid Hinnah , Morse Dawn , Klaus Katherine
Published: November 2023

There is evidence that the anabolic response to exercise is blunted in skeletal muscle in older adults. Older adults also exhibit reduced mitochondrial content and lower oxidative capacity. Since mitochondria provide chemical energy for muscle protein synthesis, it is possible that age‐related changes to mitochondrial physiology may contribute to anabolic resistance. We evaluated this possibility by measuring mitochondrial function and anabolic responses to exercise in 12 young (19–34 yrs) and 12 older (67–83 yrs) adults. Serial vastus lateralis biopsies were collected during an infusion of 13C6 phenylalanine to measure muscle protein synthesis at baseline and 16 hours after a single bout of unaccustomed resistance exercise (unilateral knee extension, 8 sets, 10 repetitions at 70% of 1‐repetition maximum). Real‐time PCR and RNA sequencing were used to evaluate the transcriptional response to acute exercise in muscle tissue. Respiratory capacity of isolated mitochondria was measured by high‐resolution respirometry. Mitochondrial respiratory capacity was significantly lower in older adults (4.67±0.47 pmol/s/ug) compared to young (6.60±0.70 pmol/s/ug, p=0.024). Postabsorptive protein synthesis rates were similar in young and old for mixed muscle (Y: 0.067±0.005 %/hr, O: 0.104±0.030 %/hr, p=0.13), mitochondrial (Y: 0.076±0.014 %/hr, O: 0.089±0.017 %/hr, p=0.58), and myofibrillar fractions (Y: 0.073±0.005 %/hr, O: 0.072±0.015 %/hr, p=0.94). Exercise increased protein synthesis similarly in young and old for mixed muscle (Fold changes Y: 1.45±0.16, O: 1.46±0.18, p=0.98), mitochondrial (Y: 0.90±0.28, O: 1.74±0.41, p=0.11), and myofibrillar (Y: 1.35±0.13, O: 1.37±0.18, p=0.93). These data demonstrate older adults have lower mitochondrial respiratory capacity yet exhibit similar anabolic responses to resistance exercise compared to young. Protein synthesis does not appear limited by the decreased mitochondrial capacity with age.
Nur77 Inhibits Isoproterenol‐Induced Cardiac Fibrosis through Upregulation of Relaxin‐3
Authors: Guo Zhi‐Fu , Zhang Guanxin , You Xiaohua , Yi Bing , Cheng Fang , Sun Jianxin
Published: November 2023

Objective

The orphan nuclear receptor Nur77 plays critical roles in cardiovascular diseases and its expression is markedly induced in the heart after excessive β‐adrenergic receptor (β‐AR) activation and ischemia/reperfusion injury. However, the functional significance of Nur77 in cardiac fibrosis remains unclear. The objective of this study is to determine whether Nur77 is involved in the development of cardiac fibrosis, and if so, to determine the molecular mechanism (s) involved.

Methods and Results

By using a mouse model of isoproterenol (ISO)‐induced cardiac fibrosis, we show that the ISO‐induced cardiac fibrosis was markedly exacerbated in Nur77 knockout mice, hence highlighting a critical importance of Nur77 in cardiac remodeling. To determine the molecular mechanism involved, we investigated whether Nur77 affects the cardiac expression of relaxin, which has been shown to be a key anti‐fibrotic molecule in the heart under various pathophysiological circumstances. By using qPCR, we found that both relaxin‐1 and relaxin‐3 mRNA are predominantly expressed in mouse cardiomyocytes, as compared with that in cardiac fibroblasts. Importantly, we demonstrate that overexpressing Nur77 robustly increases the expression of relaxin‐3, but not relaxin‐1 in cardiomyocytes, suggesting the specificity of Nur77 regulation on relaxin‐3 in the heart. Indeed, sequential analysis identified two NGFI‐B response elements (NBRE) (5′‐AAAGGTCA‐3′) in the promoter region of relaxin‐3. Site‐directed mutagenesis and promoter functional analysis suggest that these two NBRE motifs are mainly responsible for the Nur77‐induced relaxin‐3 expression in cardiomyocytes. Furthermore, we show that Nur77 specifically binds to the promoter region of relaxin‐3, as demonstrated by electrophoretic mobility shift assay (EMSA) and chromatin immunoprecipitation (ChIP) assays, under both basal and ISO‐stimulated conditions. Moreover, ISO stimulation markedly increases the expression of relaxin‐3 in wild‐type (WT) mice, but not in Nur77 knockout (KO) mice, further indicating the important role of Nur77 in regulating relaxin‐3 expression in the heart. Continuous infusion of relaxin‐3 through the mini‐osmotic pump implanted subcutaneously for 14 days significantly attenuated cardiac fibrosis of both WT and Nur77 KO mice, as determined by Masson's trichrome (MTC) staining and hydroxyproline assay. Furthermore, pharmacological activation of Nur77 by cytosporone B (CsnB) potently inhibited ISO‐induced cardiac fibrosis in wild‐type mice, but not in Nur77 KO mice.

Conclusion

Together, these results demonstrate for the first time that Nur77 is a novel regulator for cardiac fibrosis through upregulating of relaxin‐3, and that targeted activation of Nur77 in the heart may represent a potentially novel therapeutic strategy for preventing cardiac fibrosis.

Support or Funding Information

This research was supported by the US National Institutes of Health (HL103869)
Nutritional Status Affects Expression of Insulin Receptor mRNA in a Tissue Specific Manner in Channel Catfish
Authors: Leiker Alexyss , Evans Paige , Watkins Brianna , Kobayashi Yass
Published: November 2023

The objective of this study focused on the influence of nutritional status on the expression of two insulin receptor mRNA (IRa and IRb) in juvenile channel catfish. Obesity is a prevalent problem, affecting over 36% of the American population. Channel catfish could serve as an alternative model organism for the investigation of human metabolic disorders such as obesity due to its widely known genome and genetically increased growth leads to an obese‐like phenotype. However, the role of insulin and its receptor(s) on the development of obese‐like phenotypes in channel catfish is unclear. Juvenile channel catfish were randomly assigned to three treatments (n=4 tanks per treatment, 8 fish per tank). Fish assigned to the control group received food daily for 28 days, whereas fish assigned to the fasted group were fasted for 28 days. Fish assigned to the fasted‐fed group were fasted for 14 days and fed for the remaining 14 days. Brain, liver, and muscle tissues were collected from the fish on day 28 and expression of IRa and IRb mRNA were quantified using real‐time PCR. Expression of both IR mRNA in muscle and brain was similar among all treatments. In contrast, expression of both IRa and IRb was higher (p<0.01) in the liver in the fasted fish compared to the other two treatment fish. The results of this study showed that expression of IR mRNA is influenced by the nutritional status in a tissue‐specific manner regardless of the transcripts. Given the importance of insulin on nutrient metabolism, results of this study could provide insights to the mechanism(s) associated with the development of the obese‐like phenotype in channel catfish.

Support or Funding Information

This study is supported by the Kansas IDeA Network of Biomedical Research Excellence (Grant Number: 20GM103418).
Diabetes Mellitus Influences the Pattern of Distribution of Irisin in Pancreatic Islet Cells
Authors: Adeghate Ernest , D'Souza Crystal , Al Harthi Ahmed Mukhtar
Published: November 2023

Irisin is a newly discovered myokine, which enhances the turnover of white adipose cells into brown fat cells. Irisin is derived from FNDC5, a membrane‐bound protein. Moreover, irisin has been shown to play an important role in energy regulation especially in muscle cells. Although, irisin has been detected in many organs including the exocrine pancreas, liver, testes and sebaceous gland, a precise localization of this polypeptide in pancreatic islet cells has not been undertaken. Immunohistochemistry was used to determine the pattern of distribution of irisin in streptozotocin‐induced (60 mg/Kg body weight) diabetes in rats. Image J® software was used to quantify the number of irisin‐immunoreactive cells in diabetic and non‐diabetic rat pancreas. Our study shows that irisin is present in a large number of pancreatic beta cells where it co‐localizes with insulin. In contrast, irisin does not co‐localize with glucagon in normal rat pancreas. However, this pattern of distribution changes after the onset of diabetes mellitus (DM). DM is characterized by increased number of glucagon immunopositive cells. The newly formed glucagon‐positive cells now contain irisin as well. The reason why irisin co‐localizes with glucagon in diabetic rat pancreas and not in non‐diabetic rats is unclear. It is possible that in diabetic rats, insulin, the natural inhibitor of glucagon has been removed paving way for glucagon expression in pancreatic beta cells devoid of insulin. The presence of irisin in insulin secreting beta cells suggests that the beneficial effect of irisin on glucose metabolism could indeed be via the endocrine pancreas.

Support or Funding Information

United Arab Emirates University
Heat Shock Factor Activation in Skeletal Muscle Following Lengthening Contractions
Authors: Pollock‐Tahiri Evan , Locke Marius
Published: November 2023

Heat shock proteins (HSPs) are integral for the maintenance of proteostasis and allowing cells to cope with episodes of stress. HSPs are regulated by transcription factors known as heat shock transcription factors (HSFs). Given that when skeletal muscles are subjected to lengthening contractions (LCs) both muscle damage and HSPs are increased, it was of interest to investigate the mechanism of the LC‐induced increase in HSPs and assess the role of HSFs in this process. Thus, the purpose of this study was to determine if HSF activation (HSF trimerization and DNA binding) is elevated in rat skeletal muscle following exposure to 60 LCs. To do this, male sprague‐dawley rats were anaesthetized and one tibialis anterior (TA) muscle was subjected to 60 LCs (3 sets of 20 LCs with 5 minutes rest between sets) and removed at 0, 1, 3, or 24 hours after LCs, while the non‐stimulated contralateral TA served as a control. Hsp72 and Hsp25 content, HSF activation, muscle damage, and muscle glycogen content were assessed at various time points. Following 60 LCs, electrophoretic shift assay showed a transient increase in HSF activation (0–3 hours) that was followed by a significant (p<0.001) increase in Hsp72 (3.4±0.21 fold) and Hsp25 (3.2±1.2 fold) content 24 hours later as assessed by western blotting. Histological assessment of the TA muscle revealed evidence of muscle damage (measured as necrotic fibers and inflammatory infiltrates) and glycogen depletion. Taken together, the results suggest LCs induce structural and metabolic stress that results in muscle damage, increased HSF activation and the accumulation of Hsp72 and Hsp25.

Support or Funding Information

No external funding