Does Perinatal Intermittent Hypoxia Affect Cerebrovascular Network Development?

Chronic constant hypoxia (CCH), such as in pulmonary diseases or high altitude, and chronic intermittent hypoxia (CIH), such as in sleep apnea, can lead to major changes in the heart. Molecular mechanisms underlying these cardiac alterations are not well understood. We hypothesized that changes in gene expression could help to delineate such mechanisms. The current study used a neonatal mouse model in CCH or CIH combined with cDNA microarrays to determine changes in gene expression in the CCH or CIH mouse heart. Both CCH and CIH induced substantial alterations in gene expression. In addition, a robust right ventricular hypertrophy and cardiac enlargement was found in CCH- but not in CIH-treated mouse heart. On one hand, upregulation in RNA and protein levels of eukaryotic translation initiation factor-2alpha and -4E (eIF-2alpha and eIF-4E) was found in CCH, whereas eIF-4E was downregulated in 1- and 2-wk CIH, suggesting that eIF-4E is likely to play an important role in the cardiac hypertrophy observed in CCH-treated mice. On the other hand, the specific downregulation of heart development-related genes (e.g., notch gene homolog-1, MAD homolog-4) and the upregulation of proteolysis genes (e.g., calpain-5) in the CIH heart can explain the lack of hypertrophy in CIH. Interestingly, apoptosis was enhanced in CCH but not CIH, and this was correlated with an upregulation of proapoptotic genes and downregulation of anti-apoptotic genes in CCH. In summary, our results indicate that 1) the pattern of gene response to CCH is different from that of CIH in mouse heart, and 2) the identified expression differences in certain gene groups are helpful in dissecting mechanisms responsible for phenotypes observed.

To investigate the mechanism of liver injury in rats exposed to chronic intermittent hypoxia (CIH) and to investigate the effect of tempol (4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl or 4-hydroxy-TEMPO). A CIH animal model of rats was established to mimic the intermittent hypoxia/re-oxygenation (IH/ROX) of obstructive sleep apnea syndrome in humans. Thirty-two healthy male Wistar rats were randomly assigned to 4 groups: conventional intermittent hypoxia group (CIH group), intermittent hypoxia Tempol treatment group (CIH + T group), intermittent hypoxia normal saline matched group (CIH + NS group), and normoxic control group (NC group), with 8 rats in each group. The frequency of every CIH group was 30 times/h, and the minimum oxygen concentration was 5%. After the experiment, sections of liver were stained with hematoxylin-eosin (HE) and the levels of nuclear factor-kappaB (NF-κB), glutathione peroxidase (GSH-PX) and malondialdehyde (MDA) in rat liver homogenate were measured. Liver histology revealed that the CIH group and the CIH + NS group showed hepatocellular swelling with rarefaction of the cytoplasm, hyperchromatosis and hepatocellular membrane disruption, but the liver histology of the CIH + T group and the NC group was normal. Compared with the NC group, the levels of NF-κB and MDA in the CIH group [(12.4 ± 2.0) ng/g, (101 ± 22) µmol/g] and the CIH + NS group [(12.2 ± 1.9) ng/g, (99 ± 18)µmol/g] were increased (all P < 0.05), but the activities of GSH-PX [(88 ± 17) U/mg, (90 ± 15) U/mg] were decreased (all P < 0.05). Compared with the CIH + NS group and the CIH group, the activity of GSH-PX in the CIH + T group [(181 ± 29) U/mg] was increased (P < 0.05), but the levels of NF-κB [(7.8 ± 1.3) ng/g] and MDA [(59 ± 10) µmol/g] were decreased (all P < 0.05). The levels of GSH-PX and MDA in the CIH + T group were not significantly different compared to the NC group (P were 0.242, 0.177 respectively), but the level of NF-κB in the CIH + T group was higher than that in the NC group (P < 0.05). The levels of NF-κB, GSH-PX, and MDA in the CIH + NS group were not significantly different as compared to those in the CIH group (all P > 0.05). The level of NF-κB was correlated negatively with GSH-PX, but positively with MDA (r = -0.754, 0.689, respectively, all P < 0.01) CIH could cause rat liver injury through oxidative stress and activating the proinflammatory transcription factors of NF-κB. Tempol could prevent CIH-induced liver injury through scavenging ROS by its anti-oxidative effect.

To study the effects of chronic intermittent hypoxia (CIH) on learning and memory ability in Sprague–Dawley rats, we established a rat model of CIH. A total of 24 male Sprague–Dawley rats were included and were assigned to three experimental groups (n = 8/group): the unhandled control (UC) group (normal feeding for 4 weeks), the CIH group (CIH for 4 weeks), and the removal of hypoxia (RH) group (normal feeding for 4 weeks after CIH for 4 weeks). All the results were analyzed using one-way ANOVA and comparison between groups was performed using S–N–K method. Performance on the Morris water maze test (a learning and memory test) was significantly worse for CIH rats than for UC rats and RH rats (P < 0.05), but was significantly better for RH rats than for UC rats (P < 0.05). Synaptophysin expression in the CA3 region of the hippocampus was reduced in the CIH group and the RH group compared with the UC group (P < 0.05), but was significantly greater in the RH group than in the CIH group (P < 0.05). Synaptophysin is a calcium-binding protein located in the membranes of presynaptic vesicles. Changes of synaptophysin expression may indirectly reflect the structural changes in the hippocampal CA3 region. In rats, CIH can cause declines in learning ability and memory and reduce the expression of synaptophysin in the CA3 region of the hippocampus; these effects could be partially rescued by the removal of hypoxic factors. The observed decline in learning and memory ability in rats may relate to a decrease in synapse quantity and structural changes in the CA3 region of the hippocampus.

Lessons from chronic intermittent and sustained hypoxia at high altitudes.

What is the central question of this study? What are the effects of hypoxic preconditioning upon the cardiovascular and respiratory responses to subsequent episodes of chronic intermittent hypoxia? What is the main finding and its importance? The cardiovascular and respiratory responses to a chronic intermittent hypoxia protocol were not altered by previous exposure to intermittent or sustained hypoxia. These findings show that preconditioning to hypoxia produced neither facilitation nor protection from the cardiovascular and respiratory dysfunctions in response to subsequent episodes of chronic intermittent hypoxia in juvenile rats. Rats exposed to chronic intermittent hypoxia (CIH) develop hypertension, which is associated with changes in the coupling of sympathetic and respiratory activities. In this study, we hypothesized that previous preconditioning to intermittent or sustained hypoxia would affect cardiovascular and respiratory changes produced by subsequent protocols of CIH. To test this hypothesis, male Wistar rats were preconditioned to either 10 days of CIH or 24 h of sustained hypoxia (SH). After the initial exposure to hypoxia, rats were maintained in normoxic conditions for 15 days before a new protocol of CIH during 10 days. Cardiovascular and respiratory variables obtained from groups of preconditioned rats were compared with a group of rats exposed to CIH for the first time and also to a group of rats maintained in normoxic conditions throughout the period of time of the respective preconditioning protocol. The data show that CIH produced a similar increase in arterial pressure and heart rate in both CIH and SH preconditioning protocols. Respiratory parameters during basal conditions were also not affected by preconditioning to either CIH or SH. We conclude that previous exposure to CIH or SH preconditioning does not facilitate or prevent the cardiovascular changes produced by CIH.

Background and RationaleSleep apnea (SA) is associated with hypertension and chronic kidney disease. Dysregulation of blood pressure control and renal damage may occur because of the chronic intermittent hypoxia (CIH) that occurs during SA. Reductions in renal blood flow (RBF) during or after CIH may lead to renal injury by contributing to recurrent tissue hypoxia and alterations in shear‐stress (SS) related signaling. Krüppel‐like factor 2 (KLF2) is a SS‐sensitive transcription factor that controls expression of antioxidant and anti‐inflammatory gene programs.HypothesisWe hypothesized that CIH would result in baseline reductions in RBF and exacerbate subsequent reductions in RBF during hypoxia. Furthermore, renal KLF2 expression will be reduced along with attendant changes in its downstream targets.MethodsAdult male Sprague Dawley rats were exposed to 10 days CIH (60 sec. 10% O2, 120 sec. 21% O2) for 8h/d. Post‐CIH (or sham) RBF was measured using Transonic flow probes before, during, and after exposure to 10% O2. After euthanasia, renal cortical and medullary tissue was probed for expression of KLF2, interleukin 6 (IL‐6), superoxide dismutase (SOD1), neutrophil gelatinase‐associated lipocalin (NGAL) via western blot.ResultsBaseline weight‐corrected RBF was lower in CIH vs. sham (1.89±0.13 mL/min/g vs. 1.42±0.16 mL/min/g, p&lt;0.05), and the RBF response to 10% O2 was accentuated in CIH vs. sham (−45±14% CIH vs. −26±4% sham, p&lt;0.05). During recovery, RBF at 20 min post‐hypoxia remained below baseline values in both groups (93±3% of baseline sham vs. 85±4% of baseline CIH, P&gt;0.05). Ten consecutive episodes of 10% O2 elicited reductions in RBF that persisted after return to 21% oxygen and which were significantly reduced from baseline for the duration of the exposure period (p&lt;0.05). Cortical and medullary KLF2 expression were decreased by 40–50% in CIH relative to sham (1.00±0.21 sham cortex vs. 0.46±0.08 CIH cortex, and 1.00±0.24 sham medulla vs. 0.44±0.10 CIH medulla, p&lt;0.05 for both comparisons). Cortical SOD1 expression was reduced in CIH relative to sham (1.00±0.00 sham vs. 0.72±0.12 CIH, p&lt;0.05), whereas IL‐6 expression was increased (1.00±0.19 sham vs. 1.56±0.21 CIH cortex, p&lt;0.05). Medullary NGAL was increased in CIH vs. sham (p&lt;0.05).ConclusionPersistent reductions in RBF during and after apneic episodes (CIH) may contribute to renal inflammation, oxidative stress, and injury via downregulation of KLF2.Support or Funding InformationSupported by a grant from NHLBI (R15 HL138600‐01 to NJM)This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Obstructive sleep apnea (OSA) is associated with oxidative stress and myocardial dysfunction. We hypothesized that the chronic intermittent hypoxia (CIH) component of OSA is sufficient to lead to these adverse effects. Rats were exposed to CIH (nadir O2, 4-5%) for 8 hours/day, 5 days/week, for 5 weeks. Results were compared with similarly handled controls (HC). Outcomes included blood pressure (tail cuff plethysmograph), echocardiographic and invasive measures of left-ventricular (LV) function, and indices of oxidative stress that included levels of myocardial lipid peroxides and Cu/Zn superoxide dismutase. Blood pressure was greater in CIH (n=22) than in HC (n=22) after 2 weeks of exposure (136+/-12 vs. 128+/-8 mm Hg; p<0.05). However, the difference disappeared by 5 weeks (127+/-13 vs. 127+/-13 mm Hg). LV weight/heart weight was greater with CIH (CIH, 0.52+/-0.05; HC, 0.47+/-0.06; p<0.005). Echocardiograms revealed LV dilation, as well as decreased LV fractional shortening (CIH, 29.7+/-9.8%; HC, 37.4+/-7.1%; p<0.001). LV end-diastolic pressure was increased with CIH (CIH, 13.7+/-5.5; HC, 8.0+/-2.9 mm Hg; p<0.001), decreased LV dp/dtmax (CIH, 5072+/-2191; HC, 6596+/-720 mm Hg/second; p<0.039), and decreased cardiac output (CIH, 48.2+/-10.5; HC, 64.1+/-10.9 ml/minute; p<0.001). LV myocardial lipid peroxides were greater (CIH, 1,258+/-703; HC 715+/-240 microm/mg protein; p<0.05) and LV myocardial superoxide dismutase levels were lower (CIH, 10.3+/-4.9; HC, 18.6+/-8.2 U/mg protein; p<0.05) with CIH. CIH leads to oxidative stress and LV myocardial dysfunction.

The objective of our research was to explore the effects of maternal and postpartum chronic intermittent hypoxia (CIH) exposure on atherosclerosis in adulthood offspring of rats, and the role of Caveolin-1 in the course. Sixteen rats were assigned to two groups (n = 8), maternal normoxia and CIH group. After delivery, two male pups per litter were selected and breastfed for 1month, which then randomly received postpartum normoxia or CIH. Thus, 4 groups were created as follows (n = 8): (1) maternal normoxia and postpartum normoxia group, (2) maternal CIH and postpartum normoxia group, (3) maternal CIH and postpartum CIH group, and (4) maternal normoxia and postpartum CIH group. The offspring were weighed at birth and weaning. After the duration of 12-week experiment, morphological changes, the expression of Caveolin-1 and NF-κB p65 in the aorta were detected. Maternal CIH resulted in significantly lower body weight and thicker intima (P < 0.001). CIH upregulated the expression of Caveolin-1 and NF-κB p65 significantly (P < 0.01). There was a synergistic effect of maternal and postpartum CIH on the thickening of intima (P < 0.05), also on the expression of Caveolin-1 and NF-κB p65 (P < 0.01). The results demonstrate that maternal CIH exposure causes a postpartum catch-up growth and early atherosclerotic changes followed by upregulating Caveolin-1 expression. Besides, maternal CIH enhances the atherosclerotic changes caused by postpartum CIH. Oxidative stress probably implicates in above effects.

Obstructive sleep apnea (OSA), a condition resulting in chronic intermittent hypoxia (CIH), is an independent risk factor for ischemic stroke, but the mechanisms of the effect are unknown. We hypothesized that CIH increases stroke risk by altering the regulation of cerebral blood flow (CBF) and increasing the brain’s susceptibility to ischemia. Male C57Bl/6 mice (n=5/group) were subjected to CIH (10% O 2 for 90 sec/room air for 90 sec; during sleep hours) for 14 or 35 days (d). Sham-treated mice received room air according to the same schedule. Somatosensory cortex CBF was assessed by laser-Doppler flowmetry in anesthetized mice equipped with a cranial window. CIH increased mean arterial pressure only at 35d (from 74±2 to 83±3 mmHg (p&lt;0.05). However, CIH attenuated the CBF increase produced by neocortical application of the endothelium-dependent vasodilator acetylcholine (sham: 22±1%; CIH:13±1%;p&lt;0.05) and by whisker stimulation (sham: 23±1%;CIH: 14±1%;p&lt;0.05) both at 14 and 35d. CIH did not alter the CBF increase evoked by adenosine (sham: 23±3%; CIH: 25±1%; p&gt;0.05), indicating that smooth muscle relaxation was not compromised. The effects of CIH were prevented by neocortical application of the endothelin (ET) type A (ET A ) receptor antagonist BQ123 (1µM;p&lt;0.05) and were associated with ET1 up-regulation in cerebral blood vessels (sham: 52±26;CIH: 5,486±2,466 pg/mg;p&lt;0.05;by ELISA). The angiotensin-II AT1 receptor inhibitor losartan (5µM) did not affect the dysfunction (p&gt;0.05). CIH increased reactive oxygen species (ROS) by 2.3±0.5 folds (p&lt;0.05), assessed by hydroethidine, an effect blocked by the ROS scavenger MnTBAP (100µM; p&lt;0.05) or by BQ123 (p&lt;0.05). Furthermore, the cerebrovascular dysfunction was absent in mice lacking the Nox2-/- subunit of the superoxide-producing enzyme NADPH oxidase and was reversed by neocortical application of a NADPH oxidase peptide inhibitor. The data show that CIH, induces profound alterations of key regulatory mechanisms of cerebral circulation through ET1 and Nox2-dependent ROS production, and raises the possibility that cerebrovascular dysfunction may underlie the increased stroke risk in patients with OSA.

A new therapy for sleep apnea?

Obstructive sleep apnoea syndrome (OSAS) is the most prevalent form of sleep disordered breathing (SDB) which affects 1 in 5 people worldwide. Chronic intermittent hypoxia (CIH) is a hallmark feature of SDB as a consequence of repetitive upper airway occlusions in patients during sleep. These recurring hypoxia‐reoxygenation cycles result in the overproduction of reactive oxygen species (ROS), ultimately yielding a state of oxidative stress. Excessive levels of ROS have been associated with aberrant plasticity at multiple levels of the respiratory system including impaired upper airway muscle function. However, there is a paucity of information regarding the molecular mechanisms underlying these effects. The NADPH oxidase (NOX) family of enzymes have been linked to a multitude of CIH induced morbidities in a range of organs and systems with NOX subunits also having been identified in skeletal muscle.A mouse model of CIH was generated by the cycling of gas from normoxia (21% O2) for 210 seconds to hypoxia (5% O2 at the nadir) for 90 seconds 8 hr/day for 2 weeks during light hours. 10–11 week old male mice (C57BL/6J) were randomly assigned to one of 3 groups: Normoxic controls (sham; n=24), CIH exposed (n=24), and CIH + Apocynin (2 mM; n=24) treated throughout the gas exposure. 10–11 week old NOX2 null (B6.129S‐Cybbtm1Din/J) male mice were also assigned to a sham (n=12) or CIH (n=12) group. Following this, sternohyoid muscle contractile function was examined ex vivo. Gene expression of the entire family of NOX enzymes was examined by RT‐PCR. Western blot was used to quantify NOX2 and NOX4 protein expression. NOX enzyme activity was determined using a NOX activity assay. Data were expressed as mean±SD and were statistically compared by unpaired Student t‐test or two‐way ANOVA with Bonferroni post‐hoc test.2 weeks of exposure to CIH resulted in a significant decrease of ~45% in the peak specific force (Fmax) of the sternohyoid muscle when compared to normoxic controls (sham). CIH resulted in no significant alteration to the gene expression of any members of the NOX family of enzymes when compared to sham controls. There was no significant difference in NOX2 or NOX4 protein expression between CIH and sham groups. However, CIH exposure resulted in a significant increase in sternohyoid NOX enzyme activity compared to shams. Treatment with Apocynin (2 mM) throughout the 2 week CIH exposure prevented sternohyoid muscle weakness, restoring force to levels equivalent to controls. Furthermore, NOX2 knockout prevented CIH induced sternohyoid muscle weakness.Adult male C57BL/6J mice show signs of profound sternohyoid muscle dysfunction following exposure to 2 weeks of CIH when compared with sham animals. This occurs without alteration to the gene or protein expression of various NOX subunits. Increased NOX activity suggests a CIH induced increase in NOX enzyme assembly rather than abundance. Administration of the putative NOX inhibitor, Apocynin, prevents sternohyoid muscle weakness. NOX2 knockout also entirely prevents sternohyoid muscle weakness confirming its specific role in CIH induced muscle dysfunction. The striking muscle phenotype in the C57 mouse and its prevention in the absence of NOX2 provides a novel and robust platform for the study of mechanisms of hypoxia‐related muscle dysfunction, which may have relevance to respiratory conditions characterised by CIH, such as sleep apnoea.Support or Funding InformationDepartment of Physiology, University College Cork, Cork, IrelandThis abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Chronic intermittent hypoxia (CIH), the main feature of obstructive sleep apnea, enhances carotid body (CB) chemosensory responses to hypoxia and produces autonomic dysfunction, cardiac arrhythmias, and hypertension. We tested whether autonomic alterations, arrhythmogenesis, and the progression of hypertension induced by CIH depend on the enhanced CB chemosensory drive, by ablation of the CB chemoreceptors. Male Sprague-Dawley rats were exposed to control (Sham) conditions for 7 days and then to CIH (5% O2, 12/h 8 h/d) for a total of 28 days. At 21 days of CIH exposure, rats underwent bilateral CB ablation and then exposed to CIH for 7 additional days. Arterial blood pressure and ventilatory chemoreflex response to hypoxia were measured in conscious rats. In addition, cardiac autonomic imbalance, cardiac baroreflex gain, and arrhythmia score were assessed during the length of the experiments. In separate experimental series, we measured extracellular matrix remodeling content in cardiac atrial tissue and systemic oxidative stress. CIH induced hypertension, enhanced ventilatory response to hypoxia, induced autonomic imbalance toward sympathetic preponderance, reduced baroreflex gain, and increased arrhythmias and atrial fibrosis. CB ablation normalized blood pressure, reduced ventilatory response to hypoxia, and restored cardiac autonomic and baroreflex function. In addition, CB ablation reduced the number of arrhythmias, but not extracellular matrix remodeling or systemic oxidative stress, suggesting that reductions in arrhythmia incidence during CIH were related to normalization of cardiac autonomic balance. Present results show that autonomic alterations induced by CIH are critically dependent on the CB and support a main role for the CB in the CIH-induced hypertension.

Introduction Type II cardiorenal syndrome (CRSII) is characterized by declining renal function in the face of chronic heart failure (CHF). Abnormal renal hemodynamics and neurohormonal activation are thought to play prominent roles in this process and are initiated in part via aberrant carotid body chemoreflex‐mediated (CBC) increases in sympathetic nerve activity. Sleep apnea (SA) is a common comorbidity in CHF patients and is independently associated with renal dysfunction. Chronic intermittent hypoxia (CIH) in SA may play a key role in driving development of CRSII as it adversely affects CBC function, autonomic control, renal hemodynamics, and renal oxygen flux. In this study, we sought to determine if CIH has additive effects in CHF that hasten the decline of renal function, and if this is mediated by the CBC. Hypothesis CIH will exacerbate reductions in renal blood flow (RBF), glomerular filtration rate (GFR), and renal tissue oxygenation (RPO2) in CHF, and carotid body denervation (CBD) will attenuate these changes. Methods Adult male SD rats (n=7‐10/group) were randomly assigned to sham, CHF, CHF‐CIH, and CHF‐CIH‐CBD groups. CHF was induced by ligation of the LAD coronary artery (CAL), and cardiac function was assessed in all groups via M‐mode echocardiography. CBD was performed 4 weeks post‐CAL, while RBF (Transonic), RPO2 (Oxford Optronix Oxylite), and GFR (Medibeacon) were measured at 8‐weeks post‐CAL. Results RBF was significantly decreased (p&lt;0.05) in CHF and CHF CIH groups relative to sham (0.024±0.002 ml/min/gBW sham vs. 0.013±0.001 ml/min/gBW CHF, and 0.012±0.002 ml/min/gBW CHF‐CIH). CBD significantly attenuated the reductions in RBF in the CHF CIH group(0.017±0.002 ml/min/gBW CHF CIH CBD, p&lt;0.05 vs. CHF CIH). Cortical RPO2 decreased in CHF relative to sham (39±3 mmHg sham vs. 28±2 mmHg CHF, p&lt;0.05), but was not significantly lower in CHF‐CIH (23.4±4.3). CBD attenuated decreases in cortical RPO2 in CHF‐CBD‐CIH (39±3 mmHg, p&lt;0.05 vs. CHF CIH). GFR was lower in CHF vs. sham (0.92±0.07 vs. 1.30±0.13, p&lt;0.05) but not significantly lower in CHF CIH vs. CHF (0.89±0.06 vs. 0.92±0.07) . GFR was lowest in CHF CIH CBD (0.76±0.05 ml/min/100g, p&lt;0.05 vs. CHF and CHF CIH). Conclusions CBD improved renal perfusion and PO2 in CHF animals exposed to CIH but failed to improve GFR. Additional hypoxic stress due to a blunted hypoxic ventilatory response during CIH may result in renal damage/nephron loss that counter‐balances any beneficial effect that CBD has on RBF in CHF. These results suggest a complex interplay between chemoreflex activity and renal hemodynamics in CHF and the diffuse effects of concomitant CIH.

Obstructive sleep apnea syndrome, which is a risk factor for resistant hypertension, is characterized by chronic intermittent hypoxia (CIH) and is associated with many cardiovascular diseases. CIH elicits systemic oxidative stress and sympathetic hyperactivity, which lead to hypertension. Rho kinases (ROCKs) are considered to be major effectors of the small GTPase RhoA and have been extensively studied in the cardiovascular field. Upregulation of the RhoA/ROCK signaling cascade is observed in various cardiovascular disorders, such as atherosclerosis, pulmonary hypertension, and stroke. However, the exact molecular function of RhoA/ROCK in CIH remains unclear and requires further study. This study aimed to investigate the role of the NADPH oxidase 4 (Nox4)-induced ROS/RhoA/ROCK pathway in CIH-induced hypertension in rats. Male Sprague-Dawley rats were exposed to CIH for 21days (intermittent hypoxia of 21% O2 for 60s and 5% O2 for 30s, cyclically repeated for 8h/day). We randomly assigned 56 male rats to groups of normoxia (RA) or vertically implemented CIH together with vehicle (CIH-V), GKT137831 (CIH-G), N-acetyl cysteine (NAC) (CIH-N), or Y27632 (CIH-Y). The rats in the RA group were continuously exposed to room air, whereas the rats in the other groups were exposed to CIH. Systolic blood pressure (BP) was monitored at the beginning of each week. After the experiment, renal sympathetic nerve activity (RSNA) was recorded, and serum and renal tissues were subjected to molecular biological and biochemical analyses. Compared with the BP of RA rats, the BP of CIH-V rats started to increase 2weeks after the beginning of the experiment, subsequently stabilizing at a high level at the end of the third week. CIH increased both RSNA and oxidative stress. This response was attenuated by treatment of the rats with GKT137831 or NAC. Inhibiting Nox4 activity or ROS production reduced RhoA/ROCK expression. Treatment with Y27632 reduced both BP and RSNA in rats exposed to CIH. Hypertension can be induced by CIH in SD rats. The CIH-induced elevation of BP is at least partially mediated via the Nox4-induced ROS/RhoA/ROCK pathway.

Studies have shown that the median preoptic nucleus (MnPO) contributes to hypertension associated with chronic intermittent hypoxia (CIH), a model of the hypoxemia associated with sleep apnea. Virally mediated lesions of MnPO neurons prevent the development of a sustained hypertension associated with CIH. To gain more insight into the properties of excitatory transmission to MnPO neurons develops in CIH, whole cell patch clamp recordings were from MnPO neurons brain slices from rats exposed to 7 days of CIH (6 minute cycles; 3 minutes of 21% oxygen room air pumped in, 90 seconds of nitrogen pumped in to lower the chamber O2 to 10% oxygen, and then 90 seconds of maintenance at 10% oxygen) for 8 h during the light phase or were normoxic controls. Slices were perfused with oxygenates artificial cerebrospinal fluid and the MnPO was visually identified. Miniature excitatory postsynaptic currents (mEPSCs) were recorded in the presences of 25 µm SR95531 (GABAA antagonist) and 1 µm TTX (block Na+ channel-mediated action potentials) using a conventional whole cell patch clamp configuration. The mEPSCs were collected over a 4 min period and amplitude and frequency were compared between cells obtained from slice prepared from normoxic control rats (NORM) or rats exposed to CIH. CIH was associated with a significant increase in mean amplitude (CIH 17.15 ± 0.65 pA, n=19 cells; NORM (15.6 ± 0.6 pA; n=18 cells, P <0.05). Similarly, mean frequency was significantly elevated after CIH (CIH 4.05 ± 0.5 Hz, n=19 vs NORM 2.56 ± 0.37 Hz, n=18; p<0.05) and associated with a significant leftward shift in the cumulative probability of inter event intervals. The results suggest that CIH simultaneously increases enhances spontaneous presynaptic neurotransmitter release while also increasing postsynaptic responsiveness in MnPO. These presynaptic and postsynaptic changes in MnPO that are associated with CIH may represent mechanism contributing to CIH hypertension.