Rat Model Of Intermittent Hypoxia Research Articles

Contrast Enhanced Ultrasonography of Kidney in Chronic Intermittent Hypoxia Rat Model.

The objective of our study was to assess the ability of contrast-enhanced ultrasound (CEUS) in evaluating renal microperfusion in an animal model. Twenty Sprague-Dawley rats were subdivided into two groups: the normal and chronic intermittent hypoxia (CIH) groups. In the CIH model, 10 Sprague-Dawley rats were exposed to CIH for 8 weeks to mimic obstructive sleep apnea (OSA). The CEUS parameters of the renal cortex and medulla were obtained and compared between groups. The pathological changes of the kidney tissues were examined by histological staining such as hematoxylin and eosin (H&E) and Masson's trichrome. CIH caused morphological damage to kidneys. In the cortex, the peak intensity (PI) (P=.009) was significantly lower and time to peak (Ttop) (P=.019) was significantly prolonged in the CIH group compared with the controls. The area under ascending curve (WiAUC) in the medulla and cortex were both significantly lower in the CIH group than those in the control group (P both <.05). CEUS parameters (including PI and WiAUC of the cortex and WiAUC of the medulla) were negatively correlated with serum creatinine (P all <.05). In the medulla, the area under descending curve (WoAUC) was positively correlated with serum creatinine (P=.027), PI was negatively correlated with uric acid (P=.034). CEUS parameters (including Ttop, PI, WoAUC, and WiAUC) reflect renal microvascular changes in CIH. CEUS could be a safe and accurate imaging method to assess renal microvascular damage in CIH rats.

Analysis of miRNA expression profile in lung tissues of an intermittent hypoxia rat model

We screened key miRNAs in an intermittent hypoxia rat model and explored the biological roles of downstream target genes and related regulatory pathways. We analyzed the expression profile of miRNAs in the lung tissues of rats in the 5 % (IH1), 7.5 % (IH2), 10 % (IH3), 12.5 % (IH4) oxygen concentration and negative control (NC) groups and identified common miRNAs. Multiple differentially expressed miRNAs were detected, and intersection of their expression profiles yielded 10 common miRNAs with 929 target genes mainly distributed in the nucleus. Molecular functions pertained mainly to the activation of transcription factors, while biological processes focused on cell interaction and signal transduction. Among signaling pathways, the top 5 included the LKB1 signaling, nectin adhesion, and S1P pathways. 8 of 10 common miRNAs had excellent diagnostic value for detecting intermittent hypoxia. The miRNAs binds to the target gene might play a key role in the pathophysiological process of OSA through the LKB1/AMPK and S1P/Akt/eNOS signaling pathways.

Tribbles Homolog 3-Mediated Vascular Insulin Resistance Contributes to Hypoxic Pulmonary Hypertension in Intermittent Hypoxia Rat Model.

This study aimed to investigate the role of vascular insulin resistance (VIR) and Tribbles homolog 3 (TRIB3) in the pathogenesis of hypoxia-induced pulmonary hypertension (HPH). Rats were subjected to low air pressure and low oxygen intermittently for 4 weeks to induce HPH. The mean right ventricular pressure (mRVP), mean pulmonary arterial pressure (mPAP), and right ventricular index (RVI) were significantly increased in HPH rats. Pulmonary arteries from HPH rats showed VIR with reduced vasodilating effect of insulin. The protein levels of peroxisome proliferator-activated receptor gamma (PPARγ), phosphoinositide 3-kinase (PI3K), phosphorylations of Akt, and endothelial nitric oxide (NO) synthase (eNOS) were decreased, and TRIB3 and phosphorylated extracellular signal-regulated protein kinases (ERK1/2) were increased in pulmonary arteries of HPH rats. Early treatment of pioglitazone (PIO) partially reversed the development of HPH, improved insulin-induced vasodilation, and alleviated the imbalance of the insulin signaling. The overexpression of TRIB3 in rat pulmonary arterial endothelial cells (PAECs) reduced the levels of PPARγ, PI3K, phosphorylated Akt (p-Akt), and phosphorylated eNOS (p-eNOS) and increased p-ERK1/2 and the synthesis of endothelin-1 (ET-1), which were further intensified under hypoxic conditions. Moreover, TRIB3 knockdown caused significant improvement in Akt and eNOS phosphorylations and, otherwise, a reduction of ERK1/2 activation in PAECs after hypoxia. In conclusion, impaired insulin-induced pulmonary vasodilation and the imbalance of insulin-induced signaling mediated by TRIB3 upregulation in the endothelium contribute to the development of HPH. Early PIO treatment improves vascular insulin sensitivity that may help to limit the progression of hypoxic pulmonary hypertension.

Transient receptor potential canonical 5 channel is involved in the cardiac damage related to obstructive sleep apnea-hypopnea syndrome in rats.

Obstructive sleep apnea-hypopnea syndrome (OSAHS) is recognized as an independent risk factor of cardiovascular disease. The release of Ca2+ mediated by transient receptor potential canonical (TRPC) channels participates in the hypoxia-induced pathophysiological changes in the cardiovascular systems in case of OSAHS. This study aimed to investigate which subtypes of TRPCs were involved in OSAHS in a rat model of intermittent hypoxia. OSAHS was induced by exposure of rats to intermittent hypoxia. The expression of TRPCrelated genes and proteins in the cardiomyocytes by qRT-PCR and Western Blotting, respectively. The mRNA expression of TRPC3/TRPC4/TRPC5 increased significantly in OSAHS group compared with the control group (P<0.05). The TRPC5 protein expression was significantly higher in the OSAHS control than the control group (P<0.05). The TRPC5 channel is likely to be involved in the OSAHS induced pathophysiological changes in the myocardium and may become a target to prevent OSAHS related cardiac damage.

Cardiac Sympathetic Denervation Suppresses Atrial Fibrillation and Blood Pressure in a Chronic Intermittent Hypoxia Rat Model of Obstructive Sleep Apnea.

BackgroundChronic intermittent hypoxia (CIH) is a distinct pathological mechanism of obstructive sleep apnea (OSA), which is recognized as an independent risk factor for cardiovascular diseases. The aims of this study were to ascertain whether CIH induces atrial fibrillation (AF), to determine whether cardiac sympathetic denervation (CSD) can prevent it and suppress blood pressure, and to explore the potential molecular mechanisms involved.Methods and ResultsSixty Sprague‐Dawley male rats were randomly divided into 4 groups: sham, CSD, CIH, CIH+CSD. The rats were exposed either to CIH 8 hours daily or normoxia for 6 weeks. Cardiac pathology and structure were analyzed by hematoxylin and eosin staining and echocardiogram. ECG, blood pressure, body weight, and blood gas were recorded. Connexin 43 and tyrosine hydroxylase were detected by western blot, immunohistochemistry, and immunofluorescence. CIH induced atrial remodeling, and increased AF inducibility. CSD treatment reduced postapneic blood pressure rises and AF susceptibility, which could attenuate CIH‐associated structural atrial arrhythmogenic remodeling. In addition, CIH‐induced sympathetic nerve hyperinnervation and CSD treatment reduced sympathetic innervation, which may affect CIH‐induced AF‐associated sympathovagal imbalance. Connexin 43 was specifically downregulated in CIH, whereas CSD treatment increased its expression.ConclusionsThese results suggested CIH induces atrial remodeling, increases AF inducibility, results in sympathetic nerve hyperinnervation, and decreases connexin 43 expression, but CSD treatment reduces AF susceptibility, postapneic blood pressure increase, sympathetic innervation, and the alteration of Cx43, which may be a key point in the genesis of CIH‐induced AF.

Hepatic Cyp1a2 Expression Reduction during Inflammation Elicited in a Rat Model of Intermittent Hypoxia.

Background:Intermittent hypoxia (IH) is a key element of obstructive sleep apnea (OSA) that can lead to disorders in the liver. In this study, IH was established in a rat model to examine its effects on the expression of hepatic cytochrome P450 (CYP) and CYP regulators, including nuclear receptors.Methods:Hematoxylin and eosin staining was conducted to analyze the general pathology of the liver of rats exposed to IH. The messenger RNA (mRNA) expression levels of inflammatory cytokines, CYPs, nuclear factor-κB (NF-κB), and nuclear factors in the liver were measured by quantitative reverse transcription polymerase chain reaction.Results:We found inflammatory infiltrates in the liver of rats exposed to IH. The mRNA expression level of interleukin-1beta was increased in the liver of the IH-exposed rats (0.005 ± 0.001 vs. 0.038 ± 0.008, P = 0.042), whereas the mRNA expression level of Cyp1a2 was downregulated (0.022 ± 0.002 vs. 0.0050 ± 0.0002, P = 0.029). The hepatic level of transcription factor NF-κB was also reduced in the IH group relative to that in the control group, but the difference was not statistically significant and was parallel to the expression of the pregnane X receptor and constitutive androstane receptor. However, the decreased expression of the glucocorticoid receptor upon IH treatment was statistically significant (0.056 ± 0.012 vs. 0.032 ± 0.005, P = 0.035).Conclusions:These results indicate a decrease in expression of hepatic CYPs and their regulator GR in rats exposed to IH. Therefore, this should be noted for patients on medication, especially those on drugs metabolized via the hepatic system, and close attention should be paid to the liver function of patients with OSA-associated IH.

Abstract P343: A Dual Endothelin A/B Receptor Blocker in a Rat Model of Sleep Apnea and Chronic Kidney Disease

Obstructive sleep apnea (OSA) is characterized by recurrent episodes of pharyngeal collapse during sleep resulting in intermittent hypoxia (IH) and sleep fragmentation. OSA affects 5% to 20% of the US population, is associated with high incidence of hypertension, and is a prognostic indicator of accelerated renal failure. More than 20 million people in the US have chronic kidney disease (CKD). In rodents, endothelin-1 (ET-1) contributes to IH-induced hypertension, and ET-1 levels inversely correlate with GFR in end-stage CKD patients. These findings provide the rationale to test the hypothesis that a dual ET receptor antagonist will attenuate the development of hypertension and renal dysfunction in a combined rat model of IH and CKD. Male Sprague Dawley rats received one of three diets: A) control, B) 0.2% adenine, C) 0.2% adenine + 30 mg/kg/day of macitentan (dual ET A /ET B receptor antagonist, Actelion Pharmaceuticals) for 2 weeks followed by 2 weeks of recovery (regular chow or chow+macitentan). Rats were then exposed to sham or IH (20 short exposures/hr to 5% O 2 and 5% CO 2 7 hr/day during sleep) for 4 weeks. Changes in mean arterial blood pressure (MAP) recorded by telemetry are in Figure 1A and estimated glomerular filtration rate in Figure 1B . In summary, macitentan prevents increases in blood pressure caused by CKD, IH and by the combination of CKD+IH. However, it does not improve kidney function. Our data suggest that macitentan could be an effective antihypertensive in CKD patients with irreversible kidney damage as a way to protect the heart, brain and eyes from elevated arterial pressure but it does not reverse toxin-induced tubule atrophy in our experimental conditions.

Altered gene expression of hepatic cytochrome P450 in a rat model of intermittent hypoxia with emphysema.

Patients with respiratory overlap syndrome (OS), defined as concomitant chronic obstructive pulmonary disease and obstructive sleep apnea syndrome, may exhibit an increased blood concentration of ingested drugs. This poor elimination of drugs is primarily attributed to downregulated gene expression of the drug‑metabolizing cytochrome P450 enzymes (CYPs) in the liver. However, the underlying mechanisms of the decreased expression of CYPs in OS are poorly understood. In order to address this, a rat model of intermittent hypoxia with emphysema was evaluated in the present study, by analyzing liver gene expression using the reverse transcription‑quantitative polymerase chain reaction. Intermittent hypoxia and cigarette smoke exposure caused upregulation of hepatic inflammatory cytokines, while CYPs were downregulated. This downregulation of CYPs was associated with an increase in nuclear factor (NF)‑κB expression and a decrease in the expression of nuclear receptors pregnane X receptor, constitutive androstane receptor and glucocorticoid receptor, which are the upstream regulatory molecules of CYPs. The results of the present study indicated that, during the development of OS, systematic inflammatory reactions may downregulate hepatic CYP gene expression via the NF‑κB signaling pathway.

Study on Endogenous Cannabinoid Receptors CB1 of Bone Metabolism in Chronic Intermittent Hypoxia Rat Model

Study on Endogenous Cannabinoid Receptors CB1 of Bone Metabolism in Chronic Intermittent Hypoxia Rat Model

Atrial Arrhythmia and Autonomics in an Intermittent Hypoxia Rat Model of Obstructive Sleep Apnea

IntroductionObstructive sleep apnea (OSA) is a risk factor for developing atrial fibrillation (AF), but the mechanisms underlying AF are unknown. OSA is characterized by airway obstruction and intermittent hypoxia (IH), which has been implicated in the induction of cardiovascular dysfunction. However, the role of IH in predisposing the atria to AF is not understood.HypothesisThis study tested the hypothesis that chronic repetitive IH enhances autonomic responses, and predisposes the atria to AF.Materials and MethodsAdult, male Sprague‐Dawley rats were exposed to normoxia or repeated cycles of 120 s 21% O2 alternated with 80 s 6.5–8% O2 for 8h/day for 7 days. Rats exposed to 7 days of IH or normoxia had in vivo intracardiac electrophysiology studies to evaluate electrophysiological characteristics and susceptibility to electrical inducibility of AF. Atrial effective refractory periods were determined using programmed electrical stimulation (PES) at two atrial locations. Susceptibility to electrically induced AF was determined using PES with 8 stimuli at basic drive cycle lengths of 150 or 100 ms followed by a sequentially premature single extrastimumus and burst pacing using up to 30, 1 sec burst at 50 Hz.ResultsRats following 7‐days of IH exposure were more susceptible to electrical induction of atrial arrhythmia than normoxic controls (50% vs 0%, respectively, P &lt; 0.05). This was accompanied by an increase in inducibility in the presence of carbachol which was blocked by atropine and darifenacin. The response to isoproterenol were enhanced in the normoxic but not in the IH rats, and the effects of propranolol were less pronounced in the IH rats.ConclusionsWe have demonstrated for the first time that repeated exposure to IH in rats produced enhanced sensitivity to atrial arrhythmias. These novel findings implicating IH as a critical promoter of AF in an OSA model. Accentuation with cholinergic agonists and blockade with nonspecific and M3 specific antagonists is consistent with sensitivity to parasympathetic activation which is known to predispose the atria to AF. The diminished response to sympathetic agents suggests a potential desensitization to adrenergic activation in the IH rats. These novel findings provide an indication of the importance of IH in OSA and susceptibility to atrial arrhythmia and potential for novel therapies in OSA.Support or Funding InformationSupported in part by the Heart and Stroke Foundation of Ontario

Study on Endogenous Cannabinoid Receptors CB1 of Brain Injury in Chronic Intermittent Hypoxia Rat Model

Study on Endogenous Cannabinoid Receptors CB1 of Brain Injury in Chronic Intermittent Hypoxia Rat Model

Disrupted intestinal structure in a rat model of intermittent hypoxia.

Obstructive sleep apnea (OSA) is a chronic condition characterized by chronic intermittent hypoxia (IH) and subsequent reoxygenation (ROX). The gastrointestinal system, which is particularly sensitive to tissue hypoxia and reduced perfusion, is likely to be affected by OSA. A rat model of IH was used to analyze oxidative stress-associated genes and tight junction proteins by reverse transcription‑quantitative polymerase chain reaction. Subsequently, altered morphology of the duodenal mucosa and elevated Chiu scores were observed in the IH‑exposed rats. In addition, IH exposure resulted in upregulation of the nicotinamide adenine dinucleotide phosphate(NADPH) oxidase subunits, NADPH oxidase2 and p22phox, in the small intestine, and upregulation of transcription factors, including hypoxia‑inducible factor-1, nuclear factor‑κB and activator protein-1. Furthermore, the mRNA expression levels of intestinal tight junction (TJ)-related proteins, claudin-1 and claudin-4, were decreased in the IH‑exposed group, as compared with in the control group. In conclusion, the present study demonstrated that OSA, which is characterized by IH and ROX, may lead to disruption of the duodenum. The mechanism underlying the effects of OSA on duodenal morphology may be associated with increased oxidative stress and activation of transcription factors, subsequently inducing intestinal TJ disruption and intestinal injury.

Vaspin as a Risk Factor of Insulin Resistance in Obstructive Sleep Apnea-Hypopnea Syndrome in an Animal Model.

In this study, we aimed to establish a chronic intermittent hypoxia model in rats and explore the possible role of vaspin in insulin sensitivity. Healthy male Wistar rats were randomly divided into two groups: normal control group (NC) and chronic intermittent hypoxia group (CIH). The NC group was raised under physiological conditions and the CIH group was kept in the plexiglass chamber between 9 am and 5 pm undergoing intermittent hypoxic challenge for 8 hours/day for 8 weeks. Arterial blood pressure of rats (tail cannulation) was measured before and after the study. Fasting plasma glucose (FPG), total cholesterol (TC), triglycerides (TG), fasting insulin (FINS), vaspin, and leptin levels were measured. Vaspin mRNA expression in visceral adipose tissues was measured with Real Time-PCR. The protein levels of vaspin, Akt and phospho-Akt in visceral tissues were determined by Western-blot. At baseline, all the measurements in the CIH and NC groups were comparable. By the end of the experiment, the blood pressure of the CIH group was significantly higher than the NC group. The levels of FPG, FINS, TG, TC, leptin, and vaspin in the CIH group were significantly higher than in NC group. Plasma vaspin levels were correlated with FINS, HOMA-IR, and TG levels. Vaspin expression in both mRNA and protein levels in visceral adipose tissues of the CIH group were clearly higher than the NC group. Phospho-Akt protein level was decreased in visceral adipose tissues of the CIH group compared to the NC group. In the chronic intermittent hypoxia rat model, the expression of vaspin in visceral adipose tissues and plasma were increased, which were correlated with insulin resistance.

Carotid body function and ventilatory responses in intermittent hypoxia. evidence for anomalous brainstem integration of arterial chemoreceptor input

Obstructive sleep apnea is a frequent medical condition consisting in repetitive sleep-related episodes of upper airways obstruction and concurrent events of arterial blood hypoxia. There is a frequent association of cardiovascular diseases and other pathologies to this condition conforming the obstructive sleep apnea syndrome (OSAS). Laboratory models of OSAS consist in animals exposed to repetitive episodes of intermittent hypoxia (IH) which also develop cardiovascular pathologies, mostly hypertension. The overall OSAS pathophysiology appears to be linked to the repetitive hypoxia, which would cause a sensitization of carotid body (CB) chemoreflex and chemoreflex-driven hyperreactivity of the sympathetic nervous system. However, this proposal is uncertain because hyperventilation, reflecting the CB sensitization, and increased plasma CA levels, reflecting sympathetic hyperreactivity, are not constant findings in patients with OSAS and IH animals. Aiming to solve these uncertainties we have studied the entire CB chemoreflex arch in a rat model of IH, including activity of chemoreceptor cells and CB generated afferent activity to brainstem. The efferent activity was measured as ventilation in normoxia, hypoxia, and hypercapnia. Norepinephrine turnover in renal artery sympathetic endings was also assessed. Findings indicate a sensitization of the CB function to hypoxia evidenced by exaggerated chemoreceptor cell and CB afferent activity. Yet, IH rats exhibited marked hypoventilation in all studied conditions and increased turnover of norepinephrine in sympathetic endings. We conclude that IH produces a bias in the integration of the input arising from the CB with a diminished drive of ventilation and an exaggerated activation of brainstem sympathetic neurons.

Detection of Oxygen Sensing During Intermittent Hypoxia

Publisher Summary This chapter discusses the detection of oxygen sensing during intermittent hypoxia. Intermittent hypoxia is associated with a number of clinical conditions, including sleep apneas, apneas in premature infants, asthma, and pulmonary fibrosis. Epidemiologic and cross-sectional studies on recurrent apnea patients have identified a strong association between apneas and serious cardiovascular disturbances, including the development of hypertension. Peripheral chemoreceptors, especially carotid bodies, sense the changes in arterial oxygen. Carotid bodies are located at the bifurcation of the common carotid artery and receive sensory innervation from the carotid sinus nerve, a branch of the 12th cranial nerve. Hypoxemia augments the sensory discharge of the carotid bodies, which in turn stimulates breathing and increases sympathetic nerve activity as well as blood pressure via reflex mechanisms, involving the central nervous system (CNS).. In this study, the rat model of intermittent hypoxia is presented. Experimental methods for exposure of rats to chronic intermittent hypoxia, the recording of carotid body sensory activity in vivo , the carotid body slice preparation and recording of ionic currents from glomus cells are described. Concepts related to membrane current recordings from rat carotid body tissue slices and monitoring of transmitter changes in carotid bodies are discussed as well.