| Part1Apelin-13 in paraventricular nucleus contributes to hypertension via sympathetic activation and vasopressin release in spontaneously hypertensive rats BackgroundSympathetic nervous system overactivity plays an important role in the pathogensesis of the hypertension. The paraventricular nuleus (PVN) in the hypothalamus is responsible for regulation of the sympathetic nervous system and referred to as a sympathetic nervous center. It is known that the parvocellular part of the PVN projects to autonomic nuclei in the brain stem and spinal cord and is responsible for the sympathetic activation and the magnocellular part of the PVN projects to the neurohypophysis and is involved in the AVP production. The PVN plays important roles in the sympathetic activation and hypertension in spontaneously hypertensive rats (SHR), renovascular hypertensive rats, and obesity hypertensive rats. Apelin is the specific endogenous ligand of orphan G protein-coupled receptor APJ. Diverse active apelin peptides exist under the form of 13,17 or 36 amino acids. Apelin-13 has the highest activity of the three, followed by apelin-17 then apelin-36. It is revealed apelin and APJ to be expressed in the brain and periphery. Apelin and APJ in the periphery are involved in the cardiovascular activity, fluid homeostasis, food intake, cell proliferation and angiogenesis. However, it is unknown whether apelin in the PVN regulates blood pressure and renal sympathetic nerve activity (RSNA) in normal rats and hypertensive rats. This study was designed to investigate the change of expression of apelin and APJ in the PVN in SHR and to determine whether apelin-13 in the PVN contributes to sympathetic activation, arginine vasopressin (AVP) release and hypertensionObjective1. To investigate apelin-13 and APJ levels in the PVN in SHR.2. To determine the effect of apelin-13 on blood pressure in the PVN in SHR.3. To determine whether apelin-13 in the PVN contributes to hypertension via arginine vasopressin (AVP) release and sympathetic activation in SHR.4. To determine the effect of infusion of apelin-13 into the PVN on MAP, RSNA and plasma NE and AVP levels in normotensive rats.MethodsExperiments were carried out in 13-week-old male WKY rats and SHR purchased from Vital River Laboratory Animal Technology Co. Ltd (Beijing, China). The rats were housed on a 12-hour light/dark cycle in a temperature-controlled room with standard chow and tap water ad libitum. Systolic blood pressure (SBP) of tail artery was measured in a conscious state with a non-invasive computerized tail-cuff system. Acute experiments were carried out under anesthesia. The coordinates for PVN were determined in a stereotaxie instrument according to the Paxinos and Watson rat atlas. Drugs are bilaterally microinjected into PVN or chronic unilateral PVN infusion with Alzet micro-osmotic pump. RSNA and MAP of the right carotid artery were simultaneously recorded with a PowerLab data acquisition system. Apelin and APJ mRNA and proteins in the PVN were measured with real-time PCR and Western blot in WKY rats and SHR, respectively. Plasma AVP and norepinephrine levels were measured with ELISA method in WKY rats and SHR. Atrial natriuretic peptide (ANP) and beta-myosin heavy chain (β-MHC) mRNA expressions in the myocardium were measured with real-time PCR.Results1. There were no significant differences in body weight and HR between WKY rats and SHR, but the left ventricular weight (LVW), ratio of LVW to body weight, SBP and MAP were significantly increased in SHR.2. Apelin-13 and APJ mRNA and protein levels in the PVN were greatly increased in SHR.3. Microinjection of apelin-13 into the PVN caused greater increases in the RSNA and MAP in SHR than those in WKY rats in a dose-related manner. Microinjection of an APJ antagonist F13A into the PVN significantly reduced the RSNA and MAP in SHR, but not in WKY rats.4. The sympatho-excitatory and pressor effects of apelin-13 in both WKY rats and SHR were abolished by the pretreatment with F13A. Microinjection of losartan into the PVN failed to inhibit the responses induced by apelin-13.5. Intravenous infusion of AAVP, HEX or AAVP+HEX significantly reduced baseline RSNA and MAP in SHR. Losartan significantly reduced baseline MAP, but had no significantly effect on baseline RSNA in SHR.6. Compared with intravenous infusion of saline, AAVP significantly attenuated the apelin-13-induced sympatho-excitatory effect and pressor effect, while HEX caused much greater attenuation in the sympatho-excitatory effect and pressor effect of apelin-13 in SHR. HEX+AAVP completely abolished the effects apelin-13. Intravenous infusion of losartan had no significant effects on the RSNA and MAP responses to apelin-13 in SHR.7. Microinjection of apelin-13 into the PVN increased plasma NE and AVP levels in both WKY rats and SHR, while F13 A significantly reduced plasma NE and AVP levels only in SHR.8. Unilateral perfusion of apelin-13 into the PVN with micro-osmotic pump induced persistent hypertension in normal conscious WKY rats. The perfusion of apelin-13 increased the plasma NE and AVP levels, and promoted the ANP and β-MHC mRNA expressions in the myocardium. However, apelin-13 had no significant effects on the heart rate, left ventricular weight (LVW) and the ratio of LVM to body weight.Conclusions1. The up-regulation of apelin and APJ in the PVN contribute to the sympathetic activation and hypertension in SHR.2. APJ in the PVN, independent of the activation of ATi receptors, mediates the effect of Apelin-13 in the PVN.3. Sympathetic activation plays a primary role and AVP release plays a secondary role in the apelin-13-induced pressor response in SHR.4. Persistent activation of APJ with exogenous apelin-13 in the PVN in normal conscious WKY rats induces hypertension and cardiac hypertrophy..Part 2NMDAR and non-NMDAR in the PVN are involved in the apelin-13-induced sympathetic nervous system overactivity in spontaneously hypertensive ratsBackgroundOur recent study has shown that the up-regulation of apelin and APJ in the PVN contribute to the sympathetic activation and hypertension in SHR. Apelin-13 and APJ activation in the PVN contribute to hypertension via sympathetic excitation and AVP release in SHR. It is known that microinjection of glutamate or N-methyl-D-aspartate (NMDA) into the PVN increases RSNA and mean arterial pressure (MAP) in conscious or anesthetized rats. Both NMDA receptors (NMDAR) and non-NMDAR play roles in the tonic control of sympathetic outflow and blood pressure, and NMDAR in the PVN contributes more in the tonic roles than the non-NMDAR in normal rats. There are two glutamatergic pressor pathways in the PVN:one sympathetic pathway that is mediated by NMDA receptors and a vasopressinergic pathway that is mediated by non-NMDA receptors. However, it is unknown whether the NMDAR and non-NMDAR in the PVN mediate the effects of apelin-13 on sympathetic activity and blood pressure. The present study was designed to determine whether ionotropic glutamate receptors in the PVN are involved in the effects of apelin-13 in SHR.Objective1. To determine whether ionotropic glutamate receptors in the PVN are involved in the effects of apelin-13 in SHR.MethodsExperiments were carried out in 13-week-old male WKY rats and SHR purchased from Vital River Laboratory Animal Technology Co. Ltd (Beijing, China). The rats were housed on a 12-hour light/dark cycle in a temperature-controlled room with standard chow and tap water ad libitum. Systolic blood pressure (SBP) of tail artery was measured in a conscious state with a non-invasive computerized tail-cuff system. Acute experiments were carried out under anesthesia. The coordinates for PVN were determined in a stereotaxie instrument according to the Paxinos and Watson rat atlas. All the drugs are bilaterally microinjected into PVN. RSNA and MAP of the right carotid artery were simultaneously recorded with a PowerLab data acquisition system. Plasma AVP level was measured with ELISA method in SHR.Results1. Microinjection of AP5, CNQX, or AP5+CNQX into the PVN reduced baseline RSNA and MAP in SHR.2. Compared with the PVN pretreatment with saline, AP5, CNQX, or AP5+CNQX greatly attenuated the RSNA response to apelin-13, but moderately attenuated the MAP response to apelin-13 in SHR.3. Pretreatment with microinjection of AP5, CNQX or AP5+CNQX had no significant effects on the plasma AVP response to apelin-13 in SHR.ConclusionsBoth NMDAR and non-NMDAR in the PVN are involved in the apelin-13-induced sympathetic activation rather than AVP release. |
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