Ⅰ.NF-κB Activation in PVN Contributes to Neurohumoral Excitation in HF Ⅱ.Sympathetic Effects on Islet, Heart and Kidney in NIDDM Rats
The morbility and mortality of heart failure(HF) are still very high despite recent advance treatment of this syndrome.Coronary artery ischemia is the primiary cause leading to HF. Neurohumoral excitation(NHE) is a cardinal manifestation of the HF syndrome,closely correlated with disease severity and adverse prognosis.Sympathoexcitation is considered a trigger point that promotes the excessive release of neurohormones in HF,where plasma norepinephrine(NE),angiotensinⅡ(ANGⅡ),aldosterone,endothelin-1,etc.were found to be correlated with severity of HF.Small dose ofβ1 blocker decreased mortality of HF in many clinical trials.Recent studies from Kang et al.found in rats with ischemia-induced HF,activity of the renin-angiotensin system(RAS) is upregulated,and PIC and reactive oxygen species (ROS) are increased in the hypothalamic paraventricular nucleus(PVN).These excess RAS,PIC and ROS in the PVN contribute to the augmented sympathetic drive in animals with HF.But the origin of these humoral factors in central nervous system is still poorly understood.With the development of cell biology,nuclear transcription factors kappa B(NF-κB) is considered as a major nuclear factor regulating inflammatory reaction and injury stress.Precursors for NF-κB are present in the cytoplasm,maintained there by the inhibitor protein IκB.Appropriate intracellular signals induce phosphorylation of IκB by an IκB kinase(IKK)-containing signalsome,dissociation of the inhibitory protein,and its consequent degradation. Phosphorylated IKKβ(p-IKKβ) is one marker of activated NF-κB.When NF-κB translocates to the nucleus,it will initiate gene transcription of a number of inflammatory mediators.In this study,we determined whether NF-κB in the PVN contribute to the NHE in HF and facilitate the effects ofRAS,PIC and ROS in the PVN.Firstly,we investigated whether NF-κB in the PVN contribute to the NHE in HF.Adult male Sprague-Dawley rats weighing 250～275 g were implanted with intracerebroventricular(ICV) cannulae.After 2 days recovery,all rats were subjected to coronary artery ligation to induce myocardial ischemia,or sham surgery without ligating the vessel(SHAM).Subsequently, animals were ICV treated with SN50(2μg/hr),which inhibits nuclear translocation of NF-κB,or vehicle(VEH,0.25μl/hr) for 4 weeks.Results:HF rats had a decreased±dp/dt_(max),a significant increase in left ventricular end diastolic pressure(LVEDP),the expression of Fra-LI(markers of activated neurons),NF-κBp50 and phosphorylated IKKβ(p-IKKβ) in the PVN,and plasma norepinephrine(NE) and angiotensinⅡ(ANGⅡ) levels when compared with SHAM rats.In contrast,ICV SN50 attenuated Fra-LI,NF-κBp50 and p-IKKβin the PVN compared with VEH-treated HF rats,and ameliorated cardiac function by reducing LVEDP and elevating±dp/dt_(max).Treatment with SN50 also reduced plasma levels of NE,ANGⅡ,and decreased RVW/BW and lung/BW.These findings indicate that activated NF-κB in the PVN contribute to the development of HF by inducing the peripheral NHE.Then the effects of NF-κB in the PVN on RAS,PIC and ROS were seperately investigated. Adult male Sprague-Dawley rats were implanted with intracerebroventricular(ICV) cannulae and subjected to coronary artery ligation,or sham surgery(SHAM).Subsequently,1) some animals were ICV treated with the angiotensin type 1 receptor(AT1-R) antagonist losartan(LOS, 20μg/hr),or SN50(2μg/hr),or vehicle(VEH) for 4 weeks.HF induced a significant increase in the expression of angiotensin converting enzyme(ACE),p-IKKβand NF-κB p50 in the PVN, and in plasma levels of norepinephrine(NE) and angiotensinⅡ(ANGⅡ) when compared with SHAM rats.In contrast,ICV LOS attenuated NF-κB p50,ACE and p-IKKβin the PVN,and ICVSN50 also decreased ACE in this region compared with VEH-treated HF rats.Treatment with LOS or SN50 also reduced plasma levels of norepinephrine,angiotensinⅡ,and decreased LVEDP and increased±dp/dt_(max2) some animals were ICV treated with cytokine synthesis inhibitor pentoxifylline(PTX,10μg/hr),or SN50(2μg/hr),or vehicle(VEH) for 4 weeks.HF induced a significant increase in the expression of TNF-α,IL-1β,p-IKKβand NF-κB p50 in the PVN,and in plasma levels of NE and ANGⅡwhen compared with SHAM rats.In contrast,ICV PTX attenuated NF-κB p50,TNF-α,IL-1βand p-IKKβin the PVN,and ICVSN50 also decreased TNF-αand IL-1βin this region compared with VEH-treated HF rats.Treatment with PTX or SN50 also reduced plasma levels of NE,ANGⅡ,and decreased LVEDP and increased±dp/dt_(max3) some animals were ICV treated with superoxide dismutase mimetic tempol(TEMP, 80μg/hr),or SN50(2μg/hr),or vehicle(VEH) for 4 weeks.HF induced a significant increase in the expression of DHE,gp91~(phox),p-IKKβand NF-κB p50 in the PVN,and in plasma levels of NE and ANGⅡwhen compared with SHAM rats.In contrast,ICV TEMP attenuated NF-κB p50, DHE,gp91~(phox) and p-IKKβin the PVN,and ICVSN50 also decreased DHE and gp91~(phox) in this region compared with VEH-treated HF rats.Treatment with TEMP or SN50 also reduced plasma levels of NE,ANGⅡ,and decreased LVEDP and increased±dp/dt_(max).These results suggest that NF-κB in the PVN in HF is activated by increased RAS,PIC and ROS,and NF-κB is further to improve the NHE mechanism of RAS,PIC and ROS in the PVN.NF-κB in the PVN is the important factor promoting the development of HE Treatment with NF-κB blockers will be a potential way to delay the process of HE The abnormality of autonomic nervous system has been suggested to be involved in the development of diabetes,which includes the activation of sympathetic nerves.Accordingly, 6-hydroxydopamine(6-OHDA;100 mg/kg) was used to commit chemical sympathectomy to determine whether sympathetic hyperactivity participate the diabetes and its\' complication mechanism.Feeding of high fat diets for six weeks produces hyperinsulinaemia and insulin resistance followed by treatment with streptozocin(STZ,35mg/kg,i.p.),which causes the beta cell damage and frank hyperglycaemia with almost normal insulin circulating concentrations in 80～100g male Sprague-Dawley rats.Diabetic rats or normal control rats were given an intraperitoneal injection of 6-OHDA in PBS containing 0.1%ascorbic acid or ascorbic acid alone. Four weeks later,it was found that dopamine beta hydroxylase(DBH,markers of sympathetic nerves) immunoreactive nerve fibers innervating islets,heart and kidney in 6-OHDA-treated rats disappeared.Plasma glucose and insulin in diabetic rats were not affected by 6-OHDA,but the area percent of beta cells in islet was elevated by 6-OHDA.6-OHDA reversed heart function (LVEDP and±dp/dt_(max)) and renal function(BUN and Cr) in NIDDM rats. Immunohistochemistry and western blot revealed the expression of PKC-βⅡin the heart and TGF-βin the kidney increased in diabetic rats,which is the markers of exacerbated pathology in heart and kidney,and 6-OHDA evidently reversed the development of this process.We concluded that sympathectomy can,at least partly,initiate the increase of beta cells in diabetic islet,and the activation of sympathetic nerves may contribute to the diabetic cardiopathy by promoting the production of PKC-βⅡand diabetic nephropathy by inducing the expression of TGF-β.