Intermedin in the Paraventricular Nucleus Attenuates Cardiac Sympathetic Afferent Reflex in Chronic Heart Failure Rats

Background and Aim

Intermedin (IMD) is a member of calcitonin/calcitonin gene-related peptide (CGRP) family together with adrenomedullin (AM) and amylin. It has a wide distribution in the central nervous system (CNS) especially in hypothalamic paraventricular nucleus (PVN). Cardiac sympathetic afferent reflex (CSAR) is enhanced in chronic heart failure (CHF) rats. The aim of this study is to determine the effect of IMD in the PVN on CSAR and its related mechanisms in CHF rats.

Methodology/Principal Findings

Rats were subjected to left descending coronary artery ligation to induce CHF or sham-operation (Sham). Renal sympathetic nerve activity (RSNA), mean arterial pressure (MAP) and heart rate (HR) were recorded. CSAR was evaluated by the RSNA and MAP responses to epicardial application of capsaicin. Acute experiments were carried out 8 weeks after coronary ligation or sham surgery under anesthesia. IMD and angiotensin II (Ang II) levels in the PVN were up-regulated in CHF rats. Bilateral PVN microinjection of IMD caused greater decreases in CSAR and the baseline RSNA and MAP in CHF rats than those in Sham rats. The decrease of CSAR caused by IMD was prevented by pretreatment with AM receptor antagonist AM22-52, but not CGRP receptor antagonist CGRP8-37. Ang II in the PVN significantly enhanced CSAR and superoxide anions level, which was inhibited by PVN pretreatment with IMD or tempol (a superoxide anions scavenger) in Sham and CHF rats.

Conclusion

IMD in the PVN inhibits CSAR via AM receptor, and attenuates the effects of Ang II on CSAR and superoxide anions level in CHF rats. PVN superoxide anions involve in the effect of IMD on attenuating Ang II-induced CSAR response.     

Inhibition of cardiac sympathetic afferent reflex and sympathetic activity by baroreceptor and vagal afferent inputs in chronic heart failure

Background

Cardiac sympathetic afferent reflex (CSAR) contributes to sympathetic activation and angiotensin II (Ang II) in paraventricular nucleus (PVN) augments the CSAR in vagotomized (VT) and baroreceptor denervated (BD) rats with chronic heart failure (CHF). This study was designed to determine whether it is true in intact (INT) rats with CHF and to determine the effects of cardiac and baroreceptor afferents on the CSAR and sympathetic activity in CHF.

Methodology/Principal Findings

Sham-operated (Sham) or coronary ligation-induced CHF rats were respectively subjected to BD+VT, VT, cardiac sympathetic denervation (CSD) or INT. Under anesthesia, renal sympathetic nerve activity (RSNA) and mean arterial pressure (MAP) were recorded, and the CSAR was evaluated by the RSNA and MAP responses to epicardial application of capsaicin. Either CSAR or the responses of RSNA, MAP and CSAR to Ang II in PVN were enhanced in CHF rats treated with BD+VT, VT or INT. Treatment with VT or BD+VT potentiated the CSAR and the CSAR responses to Ang II in both Sham and CHF rats. Treatment with CSD reversed the capsaicin-induced RSNA and MAP changes and the CSAR responses to Ang II in both Sham and CHF rats, and reduced the RSNA and MAP responses to Ang II only in CHF rats.

Conclusions

The CSAR and the CSAR responses to Ang II in PVN are enhanced in intact CHF rats. Baroreceptor and vagal afferent activities inhibit CSAR and the CSAR responses to Ang II in intact Sham and CHF rats.     

Superoxide anions in the paraventricular nucleus mediate the enhanced cardiac sympathetic afferent reflex and sympathetic activity in renovascular hypertensive rats

An enhanced cardiac sympathetic afferent reflex (CSAR) is involved in the sympathetic activation in renovascular hypertension. The present study was designed to determine the role of superoxide anions in the paraventricular nucleus (PVN) in mediating the enhanced CSAR and sympathetic activity in renovascular hypertension in the two-kidney, one-clip (2K1C) model. Sinoaortic denervation and vagotomy were carried out, and renal sympathetic nerve activity (RSNA) and mean arterial pressure (MAP) were recorded under anesthesia. The CSAR was evaluated by the response of RSNA to the epicardial application of capsaicin. Superoxide anion levels and NAD(P)H oxidase activity in the PVN increased in 2K1C rats and were much higher in 2K1C rats than in sham-operated (sham) rats after the epicardial application of capsaicin or PVN microinjection of ANG II. In both 2K1C and sham rats, PVN microinjection of the superoxide anion scavenger tempol or the NAD(P)H oxidase inhibitor apocynin abolished the CSAR, whereas the SOD inhibitor diethyldithiocarbamic acid (DETC) potentiated the CSAR. Tempol and apocynin decreased but DETC increased baseline RSNA and MAP. ANG II in the PVN caused larger responses of the CSAR, baseline RSNA, and baseline MAP in 2K1C rats than in sham rats. The effects of ANG II were abolished by pretreatment with tempol or apocynin in both 2K1C and sham rats and augmented by DETC in the PVN in 2K1C rats. These results indicate that superoxide anions in the PVN mediate the CSAR and the effects of ANG II in the PVN. Increased superoxide anions in the PVN contribute to the enhanced CSAR and sympathetic activity in renovascular hypertension.     

Hydrogen Sulfide in Paraventricular Nucleus Enhances Sympathetic Activity and Cardiac Sympathetic Afferent Reflex in Chronic Heart Failure Rats

Background

Intracerebroventricular infusion of NaHS, a hydrogen sulfide (H₂S) donor, increased mean arterial pressure (MAP). This study was designed to determine the roles of H₂S in the paraventricular nucleus (PVN) in modulating sympathetic activity and cardiac sympathetic afferent reflex (CSAR) in chronic heart failure (CHF).

Methodology/Principal Findings

CHF was induced by left descending coronary artery ligation in rats. Renal sympathetic nerve activity (RSNA) and MAP were recorded under anesthesia. CSAR was evaluated by the RSNA and MAP responses to epicardial application of capsaicin. PVN microinjection of low doses of a H₂S donor, GYY4137 (0.01 and 0.1 nmol), had no significant effects on RSNA, MAP and CSAR. High doses of GYY4137 (1, 2 and 4 nmol) increased baseline RSNA, MAP and heart rate (HR), and enhanced CSAR. The effects were greater in CHF rats than sham-operated rats. A cystathionine-β-synthase (CBS) inhibitor, hydroxylamine (HA) in PVN had no significant effect on the RSNA, MAP and CSAR. CBS activity and H₂S level in the PVN were decreased in CHF rats. No significant difference in CBS level in PVN was found between sham-operated rats and CHF rats. Stimulation of cardiac sympathetic afferents with capsaicin decreased CBS activity and H₂S level in the PVN in both sham-operated rats and CHF rats.

Conclusions

Exogenous H₂S in PVN increases RSNA, MAP and HR, and enhances CSAR. The effects are greater in CHF rats than those in sham-operated rats. Endogenous H₂S in PVN is not responsible for the sympathetic activation and enhanced CSAR in CHF rats.     

Angiotensin-(1–7) in Paraventricular Nucleus Modulates Sympathetic Activity and Cardiac Sympathetic Afferent Reflex in Renovascular Hypertensive Rats

Background

Excessive sympathetic activity contributes to the pathogenesis and progression of hypertension. Enhanced cardiac sympathetic afferent reflex (CSAR) is involved in sympathetic activation. This study was designed to determine the roles of angiotensin (Ang)-(1–7) in paraventricular nucleus (PVN) in modulating sympathetic activity and CSAR and its signal pathway in renovascular hypertension.

Methodology/Principal Findings

Renovascular hypertension was induced with two-kidney, one-clip method. Renal sympathetic nerve activity (RSNA) and mean arterial pressure (MAP) were recorded in sinoaortic-denervated and cervical-vagotomized rats with anesthesia. CSAR was evaluated with the RSNA and MAP responses to epicardial application of capsaicin. PVN microinjection of Ang-(1–7) and cAMP analogue db-cAMP caused greater increases in RSNA and MAP, and enhancement in CSAR in hypertensive rats than in sham-operated rats, while Mas receptor antagonist A-779 produced opposite effects. There was no significant difference in the angiotensin-converting enzyme 2 (ACE2) activity and Ang-(1–7) level in the PVN between sham-operated rats and hypertensive rats, but the Mas receptor protein expression in the PVN was increased in hypertensive rats. The effects of Ang-(1–7) were abolished by A-779, adenylyl cyclase inhibitor SQ22536 or protein kinase A (PKA) inhibitor Rp-cAMP. SQ22536 or Rp-cAMP reduced RSNA and MAP in hypertensive rats, and attenuated the CSAR in both sham-operated and hypertensive rats.

Conclusions

Ang-(1–7) in the PVN increases RSNA and MAP and enhances the CSAR, which is mediated by Mas receptors. Endogenous Ang-(1–7) and Mas receptors contribute to the enhanced sympathetic outflow and CSAR in renovascular hypertension. A cAMP-PKA pathway is involved in the effects of Ang-(1–7) in the PVN.     

Angiotensin II and Angiotensin-(1-7) in Paraventricular Nucleus Modulate Cardiac Sympathetic Afferent Reflex in Renovascular Hypertensive Rats

Background

The enhanced cardiac sympathetic afferent reflex (CSAR) is involved in the sympathetic activation that contributes to the pathogenesis and progression of hypertension. Activation of AT₁ receptors by angiotension (Ang) II in the paraventricular nucleus (PVN) augments the enhanced CSAR and sympathetic outflow in hypertension. The present study is designed to determine whether Ang-(1-7) in PVN plays the similar roles as Ang II and the interaction between Ang-(1-7) and Ang II on CSAR in renovascular hypertension.

Methodology/Principal Findings

The two-kidney, one-clip (2K1C) method was used to induce renovascular hypertension. The CSAR was evaluated by the renal sympathetic nerve activity (RSNA) and mean arterial pressure (MAP) responses to epicardial application of capsaicin in sinoaortic-denervated and cervical-vagotomized rats with urethane and α-chloralose anesthesia. Either Ang II or Ang-(1-7) in PVN caused greater increases in RSNA and MAP, and enhancement in CSAR in 2K1C rats than in sham-operated (Sham) rats. Mas receptor antagonist A-779 and AT₁ receptor antagonist losartan induced opposite effects to Ang-(1-7) or Ang II respectively in 2K1C rats, but losartan had no effects in Sham rats. Losartan but not the A-779 abolished the effects of Ang II, while A-779 but not the losartan blocked the effects of Ang-(1-7). PVN pretreatment with Ang-(1-7) dose-dependently augmented the RSNA, MAP, and CSAR responses to the Ang II in 2K1C rats. Ang II level, AT₁ receptor and Mas receptor protein expression in PVN increased in 2K1C rats compared with Sham rats but Ang-(1-7) level did not.

Conclusions

Ang-(1-7) in PVN is as effective as Ang II in enhancing the CSAR and increasing sympathetic outflow and both endogenous Ang-(1-7) and Ang II in PVN contribute to the enhanced CSAR and sympathetic outflow in renovascular hypertension. Ang-(1-7) in PVN potentiates the effects of Ang II in renovascular hypertension.     

Involvement of enhanced cardiac sympathetic afferent reflex in sympathetic activation in early stage of diabetes

Cardiac sympathetic afferent reflex (CSAR) is involved in sympathetic activation. The present study was designed to investigate the contribution of enhanced CSAR to sympathetic activation in the early stage of diabetes and the involvement of AT(1) receptors in the paraventricular nucleus (PVN). Diabetes was induced by a single intravenous injection of streptozotocin in rats. Acute experiments were carried out under anesthesia after 3 wk. The CSAR was evaluated by the responses of renal sympathetic nerve activity (RSNA) and mean arterial pressure (MAP) to epicardial application of capsaicin or bradykinin. Sympathetic activity and CSAR were enhanced in diabetic rats. Plasma norepinephrine and angiotensin II were increased, but the transient receptor potential vanilloid 1 (TRPV1) in the left ventricle wall was not significantly increased in diabetic rats. Pericardial injection of resiniferatoxin to desensitize cardiac afferents or PVN microinjection of lidocaine attenuated the CSAR and decreased the RSNA and MAP in diabetic rats. The AT(1) receptor expression in the PVN increased in diabetic rats. Angiotensin II in the PVN caused greater increases in the RSNA and MAP and enhancement in the CSAR in diabetic rats, which were abolished by the losartan pretreatment. Losartan decreased the RSNA and MAP and attenuated the CSAR in diabetic rats but not in control rats. These results indicate that the CSAR is enhanced in the early stage of diabetic rats, which contributes to the sympathetic activation. AT(1) receptors in the PVN are involved in the enhanced CSAR in diabetic rats.     

Melanocortin 4 Receptors in the Paraventricular Nucleus Modulate the Adipose Afferent Reflex in Rat

Background and Aim

Paraventricular nucleus (PVN) of hypothalamus is an important central component in modulating adipose afferent reflex (AAR). Melanocortin receptors (MC3/4Rs) expressions are found in the hypothalamic PVN. This study was designed to determine the roles of MC3/4Rs in the PVN in modulating the AAR and its downstream signaling pathway in normal rats.

Methodology/Principal Findings

Renal sympathetic nerve activity (RSNA) and mean arterial pressure (MAP) were recorded in anaesthetized rats. AAR was evaluated using RSNA and MAP responses to capsaicin injection into the inguinal white adipose tissue (iWAT). Microinjection of the MC3/4R agonist melanotan II (MTII) into the PVN enhanced the AAR. The MC3/4R antagonist SHU9119 or MC4R antagonist HS024 attenuated the AAR and abolished MTII-induced AAR response. The adenylate cyclase (AC) inhibitor SQ22536 or the protein kinase A (PKA) inhibitor Rp-cAMP attenuated the AAR and the effect of MTII on the AAR was abolished by pretreatment with SQ22536 or Rp-cAMP in the PVN. Furthermore, both PVN microinjection of MTII and iWAT injection of capsaicin increased the cAMP level in the PVN. SHU9119 in the PVN abolished the increase in cAMP level which induced by iWAT injection of capsaicin.

Conclusion

The activation of MC4Rs rather than MC3Rs enhances the AAR, and a cAMP-PKA pathway is involved in the effects of MC4Rs in the PVN.     

ANG II in the paraventricular nucleus potentiates the cardiac sympathetic afferent reflex in rats with heart failure.

Chronic heart failure (CHF) is characterized by sympathoexcitation, and the cardiac sympathetic afferent reflex (CSAR) is a sympathoexcitatory reflex. Our previous studies have shown that the CSAR was enhanced in CHF. In addition, central angiotensin II (ANG II) is an important modulator of this reflex. This study was performed to determine whether the CSAR evoked by stimulation of cardiac sympathetic afferent nerves (CSAN) in rats with coronary ligation-induced CHF is enhanced by ANG II in the paraventricular nucleus (PVN). Under alpha-chloralose and urethane anesthesia, renal sympathetic nerve activity (RSNA) was recorded. The RSNA responses to electrical stimulation (5, 10, 20, and 30 Hz) of the CSAN were evaluated. Bilateral microinjection of the AT1-receptor antagonist losartan (50 nmol) into the PVN had no significant effects in the sham group, but it abolished the enhanced RSNA response to stimulation in the CHF group. Unilateral microinjection of three doses of ANG II (0.03, 0.3, and 3 nmol) into the PVN resulted in dose-related increases in the RSNA responses to stimulation. Although ANG II also potentiated the RSNA response to electrical stimulation in sham rats, the RSNA responses to stimulation after ANG II into the PVN in rats with CHF were much greater than in sham rats. The effects of ANG II were prevented by pretreatment with losartan into the PVN in CHF rats. These results suggest that the central gain of the CSAR is enhanced in rats with coronary ligation-induced CHF and that ANG II in the PVN augments the CSAR evoked by CSAN, which is mediated by the central angiotensin AT1 receptors in rats with CHF.     

Cardiac sympathetic afferent stimulation augments the arterial chemoreceptor reflex in anesthetized rats.

Chronic heart failure (CHF) is well known to be associated with both an enhanced chemoreceptor reflex and an augmented cardiac "sympathetic afferent reflex" (CSAR). The augmentation of the CSAR may play an important role in the enhanced chemoreceptor reflex in the CHF state because the same central areas are involved in the sympathetic outputs of both reflexes. We determined whether chemical and electrical stimulation of the CSAR augments chemoreceptor reflex function in normal rats. Under anesthesia, renal sympathetic nerve activity (RSNA) and mean arterial pressure (MAP) were recorded. The chemoreceptor reflex was tested by unilateral intra-carotid artery bolus injection of potassium cyanide (KCN) and nicotine. We found that 1) left ventricular epicardial application of capsaicin increased the pressor responses and the RSNA responses to chemoreflex activation induced by both KCN and nicotine; 2) when the central end of the left cardiac sympathetic nerve was electrically stimulated, both the pressor and the RSNA responses to chemoreflex activation induced by KCN were increased; 3) pretreatment with intracerebroventricular injection of losartan (500 nmol) completely prevented the enhanced chemoreceptor reflex induced by electrical stimulation of the cardiac sympathetic nerve; and 4) bilateral microinjection of losartan (250 pmol) into the nucleus tractus solitarii (NTS) completely abolished the enhanced chemoreceptor reflex by epicardial application of capsaicin. These results suggest that both the chemical and electrical stimulation of the CSAR augments chemoreceptor reflex and that central ANG II, specially located in the NTS, plays a major role in these reflex interactions.     

Chronic endothelin-1 blockade reduces sympathetic nerve activity in rabbits with heart failure

Endothelin-1 (ET-1) is elevated in chronic heart failure (CHF). In this study, we determined the effects of chronic ET-1 blockade on renal sympathetic nerve activity (RSNA) in conscious rabbits with pacing-induced CHF. Rabbits were chronically paced at 320--340 beats/min for 3--4 wk until clinical and hemodynamic signs of CHF were present. Resting RSNA and arterial baroreflex control of RSNA were determined. Responses were determined before and after the ET-1 antagonist L-754,142 (a combined ET(A) and ET(B) receptor antagonist, n = 5) was administered by osmotic minipump infusion (0.5 mg. kg(-1) x h(-1) for 48 h). In addition, five rabbits with CHF were treated with the specific ET(A) receptor antagonist BQ-123. Baseline RSNA (expressed as a percentage of the maximum nerve activity during sodium nitroprusside infusion) was significantly higher (58.3 +/- 4.9 vs. 27.0 +/- 1.0, P < 0.001), whereas baroreflex sensitivity was significantly lower in rabbits with CHF compared with control (3.09 +/- 0.19 vs. 6.04 +/- 0.73, P < 0.001). L-754,142 caused a time-dependent reduction in arterial pressure and RSNA in rabbits with CHF. In addition, BQ-123 caused a reduction in resting RSNA. For both compounds, RSNA returned to near control levels 24 h after removal of the minipump. These data suggest that ET-1 contributes to sympathoexcitation in the CHF state. Enhancement of arterial baroreflex sensitivity may further contribute to sympathoinhibition after ET-1 blockade in heart failure.     

Microinjection of ANG II into paraventricular nucleus enhances cardiac sympathetic afferent reflex in rats

The aims of present study were to determine whether angiotensin II (ANG II) in the paraventricular nucleus (PVN) is involved in the central integration of the cardiac sympathetic afferent reflex and whether this effect is mediated by the ANG type 1 (AT(1)) receptor. While the animals were under alpha-chloralose and urethane anesthesia, mean arterial pressure, heart rate, and renal sympathetic nerve activity (RSNA) were recorded in sinoaortic-denervated and cervical-vagotomized rats. A cannula was inserted into the left PVN for microinjection of ANG II. The cardiac sympathetic afferent reflex was tested by electrical stimulation (5, 10, 20, and 30 Hz in 10 V and 1 ms) of the afferent cardiac sympathetic nerves or epicardial application of bradykinin (BK) (0.04 and 0.4 microg in 2 microl). Microinjection of ANG II (0.03, 0.3, and 3 nmol) into the PVN resulted in dose-related increases in the RSNA responses to electrical stimulation. The percent change of RSNA response to 20- and 30-Hz stimulation increased significantly at the highest dose of ANG II (3 nmol). The effects of ANG II were prevented by pretreatment with losartan (50 nmol) into the PVN. Microinjection of ANG II (0.3 nmol) into the PVN significantly enhanced the RSNA responses to epicardial application of BK, which was abolished by pretreatment with losartan (50 nmol) into the PVN. These results suggest that exogenous ANG II in the PVN augments the cardiac sympathetic afferent reflex evoked by both electrical stimulation of cardiac sympathetic afferent nerves and epicardial application of BK. These central effects of ANG II are mediated by AT(1) receptors.     

Endothelin-dependent vasoconstriction in human uterine artery: application to preeclampsia

Background

Reduced uteroplacental perfusion, the initiating event in preeclampsia, is associated with enhanced endothelin-1 (ET-1) production which feeds the vasoconstriction of uterine artery. Whether the treatments of preeclampsia were effective on ET-1 induced contraction and could reverse placental ischemia is the question addressed in this study. We investigated the effect of antihypertensive drugs used in preeclampsia and of ET receptor antagonists on the contractile response to ET-1 on human uterine arteries.

Methodology/Principal Findings

Experiments were performed, ex vivo, on human uterine artery samples obtained after hysterectomy. We studied variations in isometric tension of arterial rings in response to the vasoconstrictor ET-1 and evaluated the effects of various vasodilators and ET-receptor antagonists on this response. Among antihypertensive drugs, only dihydropyridines were effective in blocking and reversing the ET-1 contractile response. Their efficiency, independent of the concentration of ET-1, was only partial. Hydralazine, alpha-methyldopa and labetalol had no effect on ET-1 induced contraction which is mediated by both ET_A and ET_B receptors in uterine artery. ET receptors antagonists, BQ-123 and BQ-788, slightly reduced the amplitude of the response to ET-1. Combination of both antagonists was more efficient, but it was not possible to reverse the maximal ET-1-induced contraction with antagonists used alone or in combination.

Conclusion

Pharmacological drugs currently used in the context of preeclampsia, do not reverse ET-1 induced contraction. Only dihydropyridines, which partially relax uterine artery previously contracted with ET-1, might offer interesting perspectives to improve placental perfusion.     

GABA in Paraventricular Nucleus Regulates Adipose Afferent Reflex in Rats

Background

Chemical stimulation of white adipose tissue (WAT) induces adipose afferent reflex (AAR), and thereby causes a general sympathetic activation. Paraventricular nucleus (PVN) is important in control of sympathetic outflow. This study was designed to investigate the role of γ-aminobutyric acid (GABA) in PVN in regulating the AAR.

Methodology/Principal Findings

Experiments were carried out in anesthetized rats. Renal sympathetic nerve activity (RSNA) and mean arterial pressure (MAP) were continuously recorded. AAR was evaluated by the RSNA and MAP responses to electrical stimulation of the right epididymal WAT (eWAT) afferent nerve. Electrical stimulation of eWAT afferent nerve increase RSNA. Bilateral microinjection of the GABA_A receptor agonist isoguvacine or the GABA_B receptor agonist baclofen attenuated the AAR. The effect of isoguvacine on the AAR was greater than that of baclofen. The GABA_A receptor antagonist gabazine enhanced the AAR, while the GABA_B receptor antagonist CGP-35348 had no significant effect on the AAR. Bilateral PVN microinjection of vigabatrin, a selective GABA-transaminase inhibitor, to increase endogenous GABA levels in the PVN abolished the AAR. The inhibitory effect of vigabatrin on the AAR was attenuated by the pretreatment with gabazine or CGP-35348. Pretreatment with combined gabazine and CGP-35348 abolished the effects of vigabatrin.

Conclusions

Activation of GABA_A or GABA_B receptors in the PVN inhibits the AAR. Blockade of GABA_A receptors in the PVN enhances the AAR. Endogenous GABA in the PVN plays an important role in regulating the AAR.     

Modulation by endothelin-1 of spontaneous activity and membrane currents of atrioventricular node myocytes from the rabbit heart

Background

The atrioventricular node (AVN) is a key component of the cardiac pacemaker-conduction system. Although it is known that receptors for the peptide hormone endothelin-1 (ET-1) are expressed in the AVN, there is very little information available on the modulatory effects of ET-1 on AVN electrophysiology. This study characterises for the first time acute modulatory effects of ET-1 on AVN cellular electrophysiology.

Methods

Electrophysiological experiments were conducted in which recordings were made from rabbit isolated AVN cells at 35–37°C using the whole-cell patch clamp recording technique.

Results

Application of ET-1 (10 nM) to spontaneously active AVN cells led rapidly (within ∼13 s) to membrane potential hyperpolarisation and cessation of spontaneous action potentials (APs). This effect was prevented by pre-application of the ET_A receptor inhibitor BQ-123 (1 µM) and was not mimicked by the ET_B receptor agonist IRL-1620 (300 nM). In whole-cell voltage-clamp experiments, ET-1 partially inhibited L-type calcium current (I_Ca,L) and rapid delayed rectifier K⁺ current (I_Kr), whilst it transiently activated the hyperpolarisation-activated current (I_f) at voltages negative to the pacemaking range, and activated an inwardly rectifying current that was inhibited by both tertiapin-Q (300 nM) and Ba²⁺ ions (2 mM); each of these effects was sensitive to ET_A receptor inhibition. In cells exposed to tertiapin-Q, ET-1 application did not produce membrane potential hyperpolarisation or immediate cessation of spontaneous activity; instead, there was a progressive decline in AP amplitude and depolarisation of maximum diastolic potential.

Conclusions

Acutely applied ET-1 exerts a direct modulatory effect on AVN cell electrophysiology. The dominant effect of ET-1 in this study was activation of a tertiapin-Q sensitive inwardly rectifying K⁺ current via ET_A receptors, which led rapidly to cell quiescence.     

延髓头端腹外侧区一氧化氮与慢性心力衰竭大鼠心交感传入反射的关系

为观察延髓头端腹外侧区(rostral ventrolateral medulla,RVLM)一氧化氮(NO)在慢性心力衰竭(chronic heartfailure,CHF)大鼠增强的心交感传入反射(cardiac sympathetic afferent reflex,CSAR)中的作用,实验在去压力感受器神经支配的结扎冠状动脉诱发的CHF大鼠和假手术SD大鼠进行,记录电刺激心交感传入神经中枢端前后的血压和肾交感神经活动(renal sympathetic nerve activity,RSNA)变化以评价CSAR.结果显示:(1)CHF大鼠的CSAR显著增强;(2)RVLM微量注射NO合酶(NOS)抑制剂MeTC增强对照组大鼠的CSAR但对CHF大鼠的CSAR无显著影响;(3)RVLM微量注射NO供体S-nitroso-N-acetyl-penicillamine(SNAP)抑制CHF大鼠增强的CSAR;(4)S-methyl-L-thiocitmline(MeTC)仅增强对照组大鼠基础水平的RSNA,而SNAP抑制对照组和CHF大鼠基础水平的RSNA.结果表明RVLM中内源性NO的减少是导致CHF大鼠CSAR增强的重要机制之.     

延髓头端腹外侧区一氧化氮与慢性心力衰竭大鼠心交感传入反射物的关系

为观察延髓头端腹外侧区(rostral ventrolateral medulla,RVLM)一氧化氮(N0)在慢性心力衰竭(chronic heart failure,CHF)大鼠增强的心交感传入反射(cardiac sympathetic afferent reflex,CSAR)中的作用,实验在去压力感受器神经支配的结扎冠状动脉诱发的CHF大鼠和假手术SD大鼠进行,记录电刺激心交感传入神经中枢端前后的血压和肾交感神经活动(renal sympathetic nerve activity,RSNA)变化以评价CSAR。结果显示：(1)CHF大鼠的CSAR显著增强;(2)RVLM微量注射NO合酶(NOS)抑制剂MeTC增强对照组大鼠的CSAR但对CHF大鼠的CSAR无显著影响;(3)RVLM微量注射NO供体S-nitroso-N-acetyl-penicillamine(SNAP)抑制CHF大鼠增强的CSAR;(4)S-methyl-L-thioeitruline（MeTC)仅增强对照组大鼠基础水平的RSNA,而SNAP抑制对照组和CHF大鼠基础水平的RSNA。结果表明RVLM中内源性NO的减少是导致CHF大鼠CSAR增强的重要机制之一。     

PVN lesions prevent the endothelin 1-induced increase in arterial pressure and vasopressin

Endothelin (ET) acts within the central nervous system to increase arterial pressure and arginine vasopressin (AVP) secretion. This study assessed the role of the paraventricular nuclei (PVN) in these actions. Intracerebroventricular ET-1 (10 pmol) or the ET(A) antagonist BQ-123 (40 nmol) was administered in conscious intact or sinoaortic-denervated (SAD) Long-Evans rats with sham or bilateral electrolytic lesions of the magnocellular region of the PVN. Baseline values did not differ among groups, and artificial cerebrospinal fluid (CSF) induced no significant changes. In sham-lesioned rats, ET-1 increased mean arterial pressure (MAP) 15.9 +/- 1.3 mmHg in intact and 22.3 +/- 2.7 mmHg in SAD (P < 0.001 ET-1 vs. CSF) rats. PVN lesions abolished the rise in MAP: -0.1 +/- 2.8 mmHg in intact and 0.0 +/- 2.9 mmHg in SAD. AVP increased in only in the sham-lesioned SAD group 8.6 +/- 3.5 pg/ml (P < 0.001 ET-1 vs. CSF). BQ-123 blocked the responses. Thus the integrity of the PVN is required for intracerebroventricularly administered ET-1 to exert pressor and AVP secretory effects.     

Stimuli of Sensory-Motor Nerves Terminate Arterial Contractile Effects of Endothelin-1 by CGRP and Dissociation of ET-1/ETA-Receptor Complexes

Background

Endothelin-1 (ET-1), a long-acting paracrine mediator, is implicated in cardiovascular diseases but clinical trials with ET-receptor antagonists were not successful in some areas. We tested whether the quasi-irreversible receptor-binding of ET-1 (i) limits reversing effects of the antagonists and (ii) can be selectively dissociated by an endogenous counterbalancing mechanism.

Methodology/Principal findings

In isolated rat mesenteric resistance arteries, ET_A-antagonists, endothelium-derived relaxing factors and synthetic vasodilators transiently reduced contractile effects of ET-1 but did not prevent persistent effects of the peptide. Stimuli of peri-vascular vasodilator sensory-motor nerves such as capsaicin not only reduced but also terminated long-lasting effects of ET-1. This was prevented by CGRP-receptor antagonists and was mimicked by exogenous calcitonin gene-related peptide (CGRP). Using 2-photon laser scanning microscopy in vital intact arteries, capsaicin and CGRP, but not ET_A-antagonism, were observed to promote dissociation of pre-existing ET-1/ET_A-receptor complexes.

Conclusions

Irreversible binding and activation of ET_A-receptors by ET-1 (i) occur at an antagonist-insensitive site of the receptor and (ii) are selectively terminated by endogenously released CGRP. Hence, natural stimuli of sensory-motor nerves that stimulate release of endogenous CGRP can be considered for therapy of diseases involving ET-1.     

ET-1-induced bronchoconstriction is mediated via ETB receptor in mice

Nagase, Takahide, Tomoko Aoki, Teruaki Oka, YoshinosukeFukuchi, and Yasuyoshi Ouchi. ET-1-induced bronchoconstriction ismediated via ET_B receptor in mice.J. Appl. Physiol. 83(1): 46-51, 1997.Endothelin (ET)-1 is one of the most potent agonists of airwaysmooth muscle and can act via two different ET receptor subtypes, i.e.,ET_A andET_B. To determine the effects ofET-1 on in vivo pulmonary function and which ET receptors are involved in murine lungs, we investigated 1)the effects of ET and sarafotoxin S6c (S6c), a selectiveET_B agonist, on pulmonary functionand 2) the effects of BQ-123 andBQ-788, specific ET_A- andET_B-receptor antagonists, onET-1-induced bronchoconstriction. ICR mice were anesthetized and mechanically ventilated (frequency = 2.5 Hz, tidalvolume = 8 ml/kg, positive end-expiratory pressure = 3 cmH₂O). Intravenous ET-1, ET-2,and ET-3 increased lung resistance similarly and equipotently, whereasS6c elicited a greater degree of bronchoconstriction. Mice were thenpretreated with saline (Sal), BQ-123 (0.2, 1, and 5 mg/kg), or BQ-788(0.2, 1, and 5 mg/kg) before administration of ET-1(10⁷ mol/kg iv). No dose ofBQ-123 blocked ET-1-induced constriction, whereas pretreatment witheach dose of BQ-788 significantly inhibited ET-1-induced responses.There were significant differences in morphometrically assessed airwayconstriction between Sal and BQ-788 and between BQ-123 and BQ-788,whereas no significant difference was observed between Sal and BQ-123.There were no significant morphometric differences in the airway wallarea among the three groups. These observations suggest that theET_B- but notET_A-receptor subtype may mediatethe changes in murine pulmonary function in response to ET-1. Inaddition, the ET_B-receptorantagonist reduces ET-1-induced airway narrowing by affecting airwaysmooth muscle contraction in mice.