| Hypertension is one of the most common types of cardiovascular disease,in which primary hypertension accounts for at least 95% of the incidence of hypertension.Recently it has been gradually concerned about the sleep apnea syndrome and metabolic syndrome patients,which have a considerable proportion of varying degrees of hypertension.Severe hypertension is often associated with stroke,renal failure,heart failure and other complications,which exacerbating the morbidity and mortality,and seriously affecting people's health and quality of life.The etiology of hypertension has not yet been completely understood.Genetic,environmental and behavioral factors are closely related to high blood pressure,for example obesity,insulin resistance,high salt intake and stress.Epidemiological data show that hypertension is highly prevalent in China,so revealing the pathogenesis of the disease and performing early clinical intervention is of great importance.The sympathetic nervous system plays a key role in acute regulation of arterial blood pressure.However,its long-term regulation of arterial blood pressure is still controversial.Overactivation of sympathetic nervous system is closely linked to several chronic diseases,such as cardiovascular and cerebrovascular diseases,metabolic disorders(type 2 diabetes)and sleep disorders(sleep apnea).The essential hypertension is often accompanied by sympathetic overactivation,and the sympathetic activity increases with the development of hypertension.Sympathetic overactivation causes high blood pressure through the following avenues: increasing peripheral vascular resistance and cardiac output,activating the renin-angiotensin-aldosterone system,insulin resistance,and inducing central and peripheral inflammatory responses.Many factors affect the tension of the sympathetic nerves,such as hormones in the circulation,plasma osmolality,Na+ levels in blood,and afferent information about cardiopulmonary activity.In recent years,the changes in arterial oxygen partial pressure(PaO2)and carbon dioxide partial pressure(PaCO2)have been found to excite the sympathetic nerve activity in addition to activating chemoreceptors,and have become a hot topic in this field.Respiratory-sympathetic coupling is a homeostatic mechanism that optimizes the ventilation-blood flow ratio via anatomical and functional coupling of the respiratory and sympathetic nervous systems.According to neuroanatomy,the basic control center of the respiratory and circulatory system is mainly located in the brainstem,and there are complex synaptic connections between neural networks.Some nuclei(such as the nucleus of the solitary tract)regulate both breathing and blood pressure,so neural circuits involved in regulation of circulation and respiration systems may be shared partially towards a steady state mechanism.Functionally,respiratory movement produces fluctuations of heart rate(e.g.respiratory sinus arrhythmia)and arterial blood pressure(e.g.Traube-Hering wave)via regulating the balance between sympathetic and parasympathetic outflows.Thus,central control of respiratory and cardiovascular systems works together to maintain homeostasis.Respiratory-sympathetic coupling is modulated by changes in blood gas,such as hypoxia or hypercapnia.When hypoxia or hypercapnia occurs,it stimulates the chemoreceptors and produces chemoreflex,on the other hand the central nervous system excites the sympathetic center and then triggers the cardiovascular reflex.Abnormal changes in respiratory-sympathetic coupling are associated with many diseases,such as premature infants with apnea,infant sudden death syndrome,obstructive sleep apnea,familial autonomic dysfunction,Rett syndrome and hypertension.As a research hotspot,whether amplified respiratory-sympathetic coupling is an important pathogenesis of hypertension remains unresolved.Part one: Effects of acute hypoxia on cardiopulmonary activity inspontaneously hypertensive rats.Objective: To observe the effect of acute hypoxia on cardiopulmonary activity in conscious spontaneously hypertensive rats.Methods: Juvenile(5 weeks old)and adult(12-15 weeks old)male spontaneously hypertensive(SH)rats and age-and gender-matched normotensive Wistar-Kyoto(WKY)rats were enrolled in the experiment.The respiratory function,arterial blood pressure and heart rate(HR)in conscious animals during acute hypoxia(10% O2,5min)were recorded simultaneously by whole body plethysmography(WBP)and radio telemetry system.Blood pressure and HR,and phrenic nerve discharge(PND)were recorded in anesthetized animals.The respiratory and cardiovascular activity during acute hypoxic exposure was assessed in carotid body denervation(CBD)and carotid body innervated(CBI)rats.Oxygen saturation and oxygen partial pressure of arterial blood were measured respectively in SH and WKY rats during normoxia and acute hypoxia.The expression of hypoxia inducible factor 2?(HIF2?)in CBs of adult SH and WKY rats was revealed by Western blot.Results:1 There was no significant difference in tidal volume(TV),respiratory frequency(RF)and minute ventilation(MV)between junior SH and WKY rats under normoxia.The adult SH rat had a significant increase in tidal volume(P<0.01)and a decreasing trend in respiratory frequency than that in WKY rats,while there was no significant difference in minute ventilation.Indicating that there was no difference in respiratory parameters between adolescent SH and WKY rats,and adult SH rats showed a deep and slow breathing pattern in resting state.2 Acute hypoxia stimulation showed increased tidal volume,respiratory frequency,and minute ventilation in adolescent rats,but there was no significant difference between the SH and WKY groups.When exposed to acute hypoxia stimulation,the tidal volume and the minute ventilation were higher in adult SH rats than that in WKY rats(P<0.01),but no difference was found in the respiratory frequency between the two groups.No difference was found in MV in CSD SH and WKY rats during hypoxia.The results suggest that adult SH rats have increased hypoxic ventilatory response,which may be related with CB.3 Acute hypoxia resulted in a significant reduction in arterial blood pressure in adult SH and WKY rats,and there was no significant difference between them.The heart rate increased after acute hypoxia stimulation,and the increasement was higher in SH than that in WKY rats(P<0.05).The results showed that hypoxia activated CB induced cardiac sympathetic efferent activity was significantly enhanced in SH rats.4 Under anesthesia,the frequency of PND in CSI rats was increased after acute hypoxia,and SH was more obvious than WKY rats(P<0.01),while the frequency of PND was not changed in CSD animals in the hypoxia.Indicating that acute hypoxia leads to an increasement in the frequency of PND in SH rats is associated with carotid body.And the hypoxia sensitivity of carotid artery in SH rats was increased.5 Acute hypoxia significantly reduced arterial blood pressure in all four groups,and there was no difference in the amplitude in CSI rats.While the blood pressure decreased more in SH-CSD rats than that in WKY-CSD rats(P<0.05).Acute hypoxia resulted in a decrease in heart rate in WKY-CSI rats,and an increase in SH-CSI rats(P<0.01).CSD group had lower heart rate after acute hypoxia exposure,and SH rats decreased more than WKY rats(P<0.05).The results suggest that hypoxia-activated CB and induced sympathetic efferent activity is significantly enhanced in SH rats.6 The results of blood gas analysis showed that there was no significant difference in arterial oxygen pressure and oxygen saturation between SH and WKY rats under normoxia.After acute hypoxia,the oxygen partial pressure and oxygen saturation significantly decreased than those under the normoxic state,and there was no significant difference between the two groups.There was no significant difference in arterial blood p H between rats in normoxia.The pH values were increased in SH and WKY rats in CSI group after acute hypoxia(P<0.05),while the rats in the CBD group did not change.7 The results of Western blot showed that HIF2? protein in carotid body of adult SH rats was significantly lower than that in WKY rats.Summary: Acute hypoxia activates CB in the SH rats to induce enhanced HVR and sympathetic efferent activity,this may be due to the increased sensitivity of CB to oxygen in SH rats.Whether the low expression of HIF2? in carotid body of SH rats is related to the increase of oxygen sensitivity of CB remains to prove.Part two: The amplified respiratory-sympathetic couplingcontributes to the development of hypertension.Objective: To explore whether the respiratory-sympathetic coupling was amplified in SH rats.Methods: Junior(5 weeks old)and adult(12-15 weeks old)spontaneously hypertensive(SH)rats and age mathed normotensive Wistar-Kyoto(WKY)rats were enrolled in the experiment.The hypercapnic ventilation response(HCVR),arterial blood pressure and heart rate(HR)were measured using WBP in combination with radio telemetry system during exposure to hypercapnia.Animals were anesthetized,tracheal intubation and ventilator ventilator-assisted ventilation.The CO2 analyzer was used to measure the End-expiratory CO2 concentration(ETCO2)of the animals.Blood pressure,heart rate phrenic nerve diacharge(PND)and renal sympathetic nerve activity(RSNA)were recorded in rats subjected to sectioning vagus nerves and carotid sinus nerves.The hypercapnia was achieved by inhalation of different concentrations of CO2.And hypocapnia was induced by hyperventilation in rats.The blood pressure,heart rate,PND and RSNA were observed in rats exposed to hypercapnia and hypocapnia respectively.Arterial blood samples were taken to analyze the difference in arterial blood pH and PaCO2 between SH and WKY rats at different ETCO2 levels.Results:1 There was no significant difference in tide volume(TV),respiratory frequency(RF)and minute ventilation(MV)between adolescent SH and WKY rats under pure oxygen(0% CO2).With the increase of CO2 concentration in the inhaled air,the TV,RF and MV increased gradually in adolescent rats.And MV in adolescent SH rats was significantly higher than that in WKY rats when exposed to 5% and 8% CO2(P<0.05).2 There was no significant difference in MV between adult SH and WKY rats under pure oxygen(0% CO2),but SH rats had higher TV than adult WKY rats(P<0.05),indicating that the respiratory pattern of adult SH rats changed.With the increasing of CO2 concentration in the inhaled gas,TV and RF increased gradually in the two groups of adlut rats,and MV in SH rats was significantly higher than that of WKY rats(P<0.01 at 5-8% CO2).And surgical resection of the carotid sinus nerve had no significant effect on the above results,demonstrating that peripheral chemoreceptors are not involved in the respiratory enhancement indused by CO2 stimulation in SH rats.3 The mean arterial pressure(MAP)and heart rate(HR)of the two groups increased with the CO2 concentration increased in the inhaled gas.The amplitude of HR increasement in SH rats was larger than that in WKY rats(P<0.01 at 5-8% CO2),and the TH wave of SH rats was higher than that in WKY rats(P<0.05 at 8% CO2).The effect of CO2 on cardiovascular activity still significantly higher in SH rats than that in WKY rats after resection of the carotid sinus nerve,demonstrating that peripheral chemoreceptors are not involved in the cardiovascular enhancement indused by CO2 stimulation in SH rats.4 In the anesthesia state,under hypercapnia(ETCO2=6% and 8%),the amplitude of PND gradually increased with the increase of ETCO2,and the amplitude of SH rats phrenic nerve was significantly higher than that of WKY rats(P<0.05).As ETCO2 increased the arterial blood pressure of rats increased gradually,and the MAP of SH rats increased more than WKY rats(P<0.05 at 6%,P<0.01 at 8%).The TH wave in SH rats was larger than that in WKY rats under hypercapnia(P<0.01).As ETCO2 increased rat renal sympathetic nerve discharge gradually increased(P<0.01),SH rats RSNA integral increased more than the WKY rats(P<0.01 at 8%).5 When expoded to hypocapnia,with the decreasement of ETCO2,the amplitude and frequency of phrenic nerve discharges decreased gradually,and there was no significant difference between SH and WKY rats at ETCO2=1%.Under hypocapnia,the blood pressure of rats decreased gradually,and SH rats decreased more obviously than that of WKY rats when ETCO2=1%(P<0.05).In ETCO2=1%,no difference was found between SH and WKY rats in blood pressure,TH wave or RSNA.6 The ETCO2 with PaCO2 and blood pH were linearly correlated.And there was no significant difference in blood PaCO2 and pH between SH and WKY rats when at the same ETCO2 level.Summary: The sensitivity of the central respiratory chemoreceptors in SH rats was raised,which contributes to enhanced HCVR and sympathetic nervous system over-activation,and promote the occurrence of hypertension.Part three: Mechanisms of increased sensitivity of respiratory centralchemosensors in spontaneously hypertensive rats.Objective: To investigate whether the CO2 sensitivity of the retrotrapezoid nucleus(RTN)and the nucleus of the solitary tract(NTS)in SH rats was elevated and to explore the possible mechanism.Methods: Male adult(12-15 weeks old)spontaneously hypertensive(SH)rats and age matched normotensive Wistar-Kyoto(WKY)rats were used in the experiment.To assess whether the sensitivity to CO2 of RTN and NTS neurons was elevated,c-fos was used to label CO2-sensitive neurons.And the number of c-fos immunoreactive(c-fos+)neurons between SH and WKY rats were counted.More over,Western blot was used to analysis the pH-sensitive channels and signal molecules related in respiratory regulation protein expression in RTN and NTS between SH and WKY rats.Results:1 The expression of c-fos was significantly increased in RTN and NTS neurons after CO2 stimulation,and the number of c-fos+ RTN and NTS neurons in SH rats was significantly higher than that in WKY rats(P<0.05).Suggesting that more CO2-sensitive neurons in SH rats provide excitatory drive for the respiratory rhythm center.2 TASK-1,TASK-2,ASIC3,Kv12.1 and Orexin receptor 2 protein up-regulated in SH rats RTN region(P<0.05),while TASK-3 down-regulated(P<0.05).And no difference was found in ASIC1,ASIC2,Kv12.2,Kv7.2,Kv7.3,Kv7.5,Kir2.3 and Orexin receptor 1 expression between the two strains(P>0.05).3 ASIC1,ASIC2 and Kv12.1 protein expression up-regulated in NTS region in SH rats(P<0.05),while TASK-2,ASIC3,Kv12.2 and Orexin receptor 1 protein expressions were significantly decreased(P<0.05).And no difference was found in TASK-1,TASK-3,Kv7.2,Kv7.3,Kv7.5,Kir2.3 and orexin receptor 2 protein expression between the two strains(P>0.05).Summary: The chemosensitivity of RTN and NTS neurons in SH rats was increased,and the mechanism may be related to the abnormal expression of CO2/H+ sensitive channels and orexin receptors.Part four: Protective effect of chronic hypoxia adaptation on kidneyin diabetes with hypertension rats.Objective: The aim of present study was to explore the renal protective effect of chronic hypoxia adaptation in diabetes with hypertension rats.Methods: Sprague–Dawley rats were randomly divided into three groups: diabetes mellitus group(DM,induced by high-fat diet combined with low-dose streptozotocin),diabetes plus CIHH treatment group(DM+CIHH,simulated 5000-m altitude,6 h per day for 28 days,after diabetes model confirmed)and control group(CON).Food intake,water intake,urine volume,body weight and systolic arterial blood pressure were tested weekly.Blood biochemicals,urinary albumin,and histopathology of kidney were determined.The superoxide dismutase(SOD)activity,malondialdehyde(MDA)level,protein levels of hypoxia induced factors(HIFs)and transforming growth factor b1(TGF-?1)in kidney were assayed.Results:1.The fasting blood glucose were increased in DM and DM+CIHH rats compared to that in CON rats(P<0.01),while no difference was found between DM and DM+CIHH rats(P>0.05).The serum triglycerides and cholesterol were both increased in DM and DM+CIHH rats compared with CON rats(P<0.01),and were decreased in DM+CIHH rats compared with DM rats(P<0.01).Compared with CON rats,DM and DM+CIHH rats displayed increased energy and water intake,increased urine output,and decreased body weight(P<0.05),while no difference was found between DM and DM+CIHH rats(P>0.05).2.Artery blood pressure increased in DM and DM+CIHH rats compared with CON rats(P<0.01),and the high artery blood pressure was decreased significantly in DM+CIHH rats compared with DM rats(P<0.01).3.The 24 h urinary albumin were significantly increased in DM and DM + CIHH rats compared to CON rats(P<0.05),and the urinary albumin in DM + CIHH rats were much lower than that in DM rats(P<0.01).4.The glomerular area,mesangial area and relative mesangial area in DM rats were significantly increased compared to CON rats(P<0.05),and were obviously ameliorated by CIHH treatment(P<0.05).Glomerular and renal interstitial fibrosis were apparent in DM rats compared to CON rats,and were significantly ameliorated in DM+CIHH rats(P<0.05).5.The activity of SOD was significantly decreased in DM rats compared to CON rats(P<0.01),and was significantly increased in DM+CIHH rats compared to DM rats(P<0.05).In addition,the levels of MDA were significantly increased in DM rats compared to CON rats(P<0.01),and decreased prominently in DM+CIHH rats compared to DM rats(P<0.05).6.TGF-?1 protein expression was significantly increased in DM rats compared to CON rats(P<0.05),and was reduced in DM+CIHH rats compared to DM rats(P<0.05).HIF1 a and HIF2 a were both down-regulated in DM rats compared to CON rats(P<0.05),HIF1? was increased(P<0.05),while HIF2? was unchanged(P<0.05)in DM+CIHH rats compared to DM rats.Summary: Chronic hypoxia adaptation has renal protection on high-fat diet combined with low-dose streptozotocin induced type 2 diabetes with hypertension rats model with,this may be related to activation of HIF1?,improve oxidative stress,decrease TGF-?1 expression and blood pressure.Conclusion: Increased chemosensitivity of peripheral and central respiratory chemoreceptors enhances respiratory chemoreceptor reflex,and the sympathetic nervous system,which promote the occurrence of high blood pressure in SH rats.The mechanism may be related to abnormal expression of pH-sensitive channels in CB,RTN and NTS neurons. |
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