| Hypertension is a common disease, and its complications such as stroke, heart failureand other cardiovascular diseases are seriously affecting human health and development.Research on hypertension has been the key point in the cardiovascular field. Large numbersof studies have shown that the renin-angiotensin system （RAS）has a very closelyrelationship with the occurrence, development and prognosis of hypertension, and theintervention target on the RAS pathway is one of the main treatment strategies forhypertension. Cardiovascular dysfunction caused by hypertension is characterized by highlevel of blood pressure (BP) and sympathetic tone. In addition to the peripheral RAS, there isalso a set of RAS in the central nervous system independent of the peripheral RAS andparticipates in regulation of cardiovascular activity. AngiotensinII (AngII) is an importantbioactive peptide in RAS, playing an important role in maintaining water and electrolytebalance, and in regulating BP as well.The medulla is a center of cardiovascular regulation, and the rostral ventrolateralmedulla (RVLM) is the important region of controlling sympathetic outflow and BP. It is notonly able to receive the introduction of peripheral cardiovascular information but sends fibersto regulat peripheral sympathetic activity. Accordingly, RVLM plays a key role in themaintaince of sympathetic tone and BP. Some studies have suggested that there are varietiesof neurotransmitters and receptor systems in the RVLM to participate in the regulation ofcardiovascular activity. It has been documented that Ang II and its receptor abundantly existin this area. The effect induced by AngII in the RVLM (via acting AT1R) is an important mechanism for increased central sympathetic outflow in hypertension and other diseases. TheAT1R-mediated mechanism resposible for cardiovascular dysfunction in hypertensionremains unclear. Enhancement in excitatory amino acid synaptic transmission is one of theimportant mechanisms responsible for neuronal excitation in the central nervous system. Thefunctional states of the excitatory amino acid receptors affect the excitability of RVLMneurons directly, influencing the sympathetic nerve activity and BP. This study was designedto explore the mechanism and pathway by which central AngII impacts on excitatory aminoacid receptor function, and determine the invovlment of this relationship in mediatingsympathoexcitation in hypertension. We hope that the evidence from this work would providea new theoretical foundation for prevention and development of therapeutic strategies forsympathetic hyperactivity in hypertension.Results1. NMDA receptor phosphorylation is involved in central AngII-mediated sympathetichyperactivity1.11Effects of central acute injection of AngII on basic cardiovascular activity in WKY ratsUnilateral microinjection of AngII (2pmol/100nl) into the RVLM significantly enhanced thecardiovascular activity（MAP=12±2mmHg；HR=40±8bpm；RSNA=30±4%）. After3min,MAP reached the peak and remained at a high level for about10min，and then recoveredafter30min. There was significant difference in BRS compared with aCSF control group （p＜0.05)1.12Effects of glutamate receptor antagonist Kyn on central AngII-induced cardiovascularactivityThe effect of AngII in the RVLM was significantly reduced after treatment withglutamate receptor blocker Kyn. Compared with AngII+a CSF group, kyn significantly reduced the effect of AngII (2pmol) in the RVLM MAP (-28±2mmHg), HR (-25±4bpm)and RSNA（-50±2%）.(P<0.05)1.13Effects of AngII on glutamate receptorRVLM unilateral microinjection NMDA (20pmol) increased MAP (20±3mmHg),HR(25±6bpm) and RSNA（32±4%）significantly. Compared with aCSF+NMDA group,RVLM pretreatment of AngII enhanced the effect on NMDA, MAP (30±2mmHg), HR (54±6bpm) and RSNA（62±2%）(P<0.05). At the same time, RVLM pretreatment of losartanblocked the effcet of AngII on NMDA completely.1.14AMPA is a glutamate non-NMDA receptor agonist, and the cardiovascular effect isvery similar to NMDA in the RVLMRVLM microinjection AMPA(5pmol) significantly increased MAP (18±4mmHg), HR(30±5bpm) and RSNA（34±4%）(P<0.05), but there was no significant change afterpretreatment AngII in RVLM(p>0.05)1.15NMDA receptor antagonist DAP-5inhibitory effect of AngII in RVLMThere was no significant change in the cardiovascular effect after DAP-5microinjectionin RVLM. Compared with the control group aCSF+AngII, DAP-5inhibited AngII in theRVLM MAP（20±4vs15±6mmHg）, HR（48±7vs36±8bpm） and RSNA（70±4vs50±8%）(P<0.05)。1.2The Cardiovascular effect of kyn on wky after icv AngIIRVLM infusion of AngII(800pmol) for1h strengthened the cardiovascular activitygradually（MAP=20±4mmHg；HR=6±4bpm；RSNA=20±4%, and RVLM microinjectionkyn1h later inhibited the effect of AngII（14±4mmHg），（12±2bpm） and RSNA（18±4%）.1.21Effects of icv AngII on basal cardiovascular response and metabolism in WKYCompared with aCSF group,icv AngII significantly increased the basis of MAP（4±2vs40±2mmHg,n=6）, but no significant change was observed in HR（6±2vs8±4bpm,n=6） Compared with aCSF group and AngII+losartan group, the experimental group AngIIchanged the metabolism of WKY after icv, body weight (265±3vs246±2g）, water intake（26±3vs53±4ml）and urine（12±3vs21±6ml）（P<0.05）.1.22RVLM microinjection of Glu receptor blockers kyn in WKY after icv AngIIAcute microinjection of Glu receptor antagonist kyn produced a significant fall in [？]4±3vs-20±2mmHg）,HR(5±2vs-25±13bpm) and RSNA（2±2vs-18±1%）（P<0.05）aftericv AngII.1.3Effect of AngII on protein expression in the RVLMThe data from Western blot showed that microinjection AngII in RVLM upregulated theprotein expression of AT1, NMDA and p-NMDA, and at the same time losartan significantlyinhibited NMDA receptor phosphorylation.2.1Effects of kyn on SHR in the RVLMCompared with aCSF control group, the RVLM microinjection kyn significantlyinhibited the SHR cardiovascular activities MAP（2±2vs-30±2%）, HR（1±4vs-11±13%）and RSNA（-1.5±2vs-18±1%）.2.2Effects of icv losartan on basal cardiovascular response and metabolism in SHRCompared with aCSF group,icv losartan significantly reduced the basis of MAP（4±2vs40±2mmHg,n=6）and improved the BRS. Compared with aCSF group, losartan changed themetabolism of SHR, body weight （280±2vs258±2g）, water intake（50±2vs36±3ml）and urine（12±4vs15±2ml）（P<0.05）2.3Effects of AngII on protein expression in the RVLMThe data from Western blot showed that microinjection losartan in RVLM downregulatedthe expression of AT1, NMDA and p-NMDA protein, and at the same time, losartansignificantly inhibited NMDA receptor phosphorylation. ConclusionThe study has demonstrated that the central AngII-mediated NMDA receptorenhancement in the RVLM led to an increase in sympathetic outflow and BP. In addition, itwas confirmed that the enhancement in NMDA receptor function could be reduced byblockade of AT1R receptor in the RVLM as shown in our spontaneously hypertensive ratmodel, thus reducing BP and sympathetic outflow. The current results may be helpful toprovide a new theoretical basis for developing a therapeutic strategy for hypertension. |
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