Myocardial Interstitial Norepinephrine Levels Research Articles

Interstitial norepinephrine levels and local electrophysiological properties of the myocardium during sympathetic nerve activation

Cardiac sympathetic innervation originates mainly in the left and right stellate ganglia. The efferent and afferent fibers of the left stellate ganglion (LSG) predominantly innervate the left ventricle (LV), whereas the fibers of the right stellate ganglion (RSG) innervate the right ventricle. The major neurotransmitter, norepinephrine, shortens ventricular action potential duration (APD) and increases contractility. Activation recovery interval (ARI) can serve as a surrogate for APD in both animal models and patients. However, the linkage between myocardial interstitial norepinephrine levels and ARI during stimulation of left and right stellate ganglion remains unclear. In six anesthetized pigs, interstitial norepinephrine concentrations and ARIs were measured in the perfusion areas of the left anterior descending coronary artery. LV pressure and volume were recorded by a 5Fr Millar conductance catheter. LSG stimulation significantly shortened ARI (28%) and increased systemic blood pressure (SBP, 43%), LV dP/dtmax (200%), and interstitial norepinephrine (110%) with a mild change in heart rate (13%). RSG stimulation also significantly shortened ARI (100%) and increased SBP (63%), heart rate (80%), dP/dtmax (300%), and interstitial norepinephrine (120%). We conclude that both LSG and RSG play an important role in regulating LV function and local sympathetic nerve activity.

Cilnidipine, an N+L-Type Dihydropyridine Ca Channel Blocker, Suppresses the Occurrence of Ischemia/Reperfusion Arrhythmia in a Rabbit Model of Myocardial Infarction

Dihydropyridine Ca channel blockers are widely prescribed for the treatment of hypertension and coronary artery diseases, but it remains unknown whether these agents protect against arrhythmias. We investigated whether cilnidipine, an N+L-type Ca channel blocker, reduces the incidences of ventricular premature beats (VPBs) and, if so, via what mechanisms. Japanese white rabbits underwent 30 min of ischemia and 48 h of reperfusion. Cilnidipine (0.5 or 1.0 microg/kg/min, i.v.) or saline (i.v.) was administered from 30 min before ischemia to 30 min after reperfusion. Electrocardiogram and blood pressure were monitored and the incidences of VPBs were measured. At 48 h after reperfusion, myocardial infarct was measured. Myocardial interstitial noradrenaline levels were determined before, during and after 30 min of ischemia with cilnidipine (0.5 and 1.0 microg/kg/min) or saline. The incidences of VPBs during ischemia and reperfusion were significantly attenuated in the cilnidipine 0.5 group (15.6 +/- 3.1 and 6.8 +/- 1.9 beats/30 min) and in the cilnidipine 1.0 group (10.4 +/- 4.9 and 3.5 +/- 1.0 beats/30 min) compared to the control group (27.2 +/- 4.5 and 24.2 +/- 3.1 beats/30 min), respectively. Myocardial interstitial noradrenaline levels were significantly reduced in the cilnidipine 0.5 and 1.0 groups compared to the control group during ischemia and reperfusion. The antiarrhythmic effect of cilnidipine may be related to the attenuation of cardiac sympathetic nerve activity. This finding may provide new insight into therapeutic strategies for hypertensive patients with ventricular arrhythmias.

Cilnidipine, a N+L-type dihydropyridine ca channel blocker, suppresses the occurrence of ventricular premature arrythmia during ischemia and reperfusion in rabbits

Background: Ca channel blockers are widely prescribed for the treatment of hypertension and coronary artery diseases. However, it is still unknown whether dihydropyridine Ca channel blockers are protective against arrythmias. We investigated whether cilnidipine, a N+L-type Ca channel blocker reduces the incidence of ventricular premature arrythmia during ischemia and reperfusion. Methods and Results: Forty Japanese white rabbits underwent 30 min ischemia and 30 min reperfusion. Cilnidipine (0.5 or 1.0 microgram/kg/min, i.v.), nifedipine (3.0 microgram/kg/min, i.v.) or saline was continuously during ischemia and reperfusion. Electrocardiogram and blood pressure were monitored and the incidences of ventricular premature beats (VPBs) during ischemia and reperfusion were measured. In other 21 rabbits, myocardial interstitial noradrenaline levels were determined before, during and after 30 min of ischemia with cilnidipine (1.0 microgram/kg/min, n = 7), nifedipine (3.0 microgram/kg/min, n = 7) or saline (n = 7) using a microdialysis technique. The incidences of VPBs during ischemia and during reperfusion were significantly attenuated in the cilnidipine 0.5 and 1.0 groups but not in the nifedipine group compared to the control group. Myocardial interstitial noradrenaline levels were significantly reduced in the cilnidipine 1.0 group but not in the nifedipine group compared to the control. Conclusion: Cilnidipine but not nifedipine attenuates the incidence of ventricular premature beats during ischemia and reperfusion and this effect may be related to decreased cardiac sympathetic nerve activity in rabbits.

Contribution of catechol-O-methyltransferase to changes in myocardial interstitial norepinephrine levels during ischemia and reperfusion

Contribution of catechol-O-methyltransferase to changes in myocardial interstitial norepinephrine levels during ischemia and reperfusion

Cardioprotection in pigs by exogenous norepinephrine but not by cerebral ischemia-induced release of endogenous norepinephrine.

Endogenous norepinephrine release induced by cerebral ischemia may lead to small areas of necrosis in normal hearts. Conversely, norepinephrine may be one of the mediators that limit myocardial infarct size by ischemic preconditioning. Because brief ischemia in kidneys or skeletal muscle limits infarct size produced by coronary artery occlusion, we investigated whether cardiac norepinephrine release during transient cerebral ischemia also elicits remote myocardial preconditioning. Forty-one crossbred pigs of either sex were assigned to 1 of 7 experimental groups, of which in 6 groups myocardial infarct size was determined after a 60-minute coronary occlusion and 120 minutes of reperfusion. One group served as control (no pretreatment), while the other groups were pretreated with either cerebral ischemia or an intracoronary infusion of norepinephrine. In 10 anesthetized control pigs, infarct size was 84+/-3% (mean+/-SEM) of the area at risk after a 60-minute coronary occlusion and 120 minutes of reperfusion. Intracoronary infusion of 0.03 nmol/kg. min(-)(1) norepinephrine for 10 minutes before coronary occlusion did not affect infarct size (80+/-3%; n=6), whereas infusion of 0.12 nmol/kg. min(-)(1) limited infarct size (65+/-2%; n=7; P:<0.05). Neither 10-minute (n=5) nor 30-minute (n=6) cerebral ischemia produced by elevation of intracranial pressure before coronary occlusion affected infarct size (83+/-4% and 82+/-3%, respectively). Myocardial interstitial norepinephrine levels tripled during cerebral ischemia and during low-dose norepinephrine but increased 10-fold during high-dose norepinephrine. Norepinephrine levels increased progressively up to 500-fold in the area at risk during the 60-minute coronary occlusion, independent of the pretreatment, while norepinephrine levels remained unchanged in adjacent nonischemic myocardium and arterial plasma. Cerebral ischemia preceding a coronary occlusion did not modify infarct size, which is likely related to the modest increase in myocardial norepinephrine levels during cerebral ischemia. The infarct size limitation by high-dose exogenous norepinephrine is not associated with blunting of the ischemia-induced increase in myocardial interstitial norepinephrine levels.

Protective effect of imidaprilat, an angiotensin-converting enzyme inhibitor on OH generation in rat myocardium

Abstract We used a flexibly mounted microdialysis technique to the hearts of rats and examined the protective effect of imidaprilat, an angiotensin-converting enzyme (ACE) inhibitor, on the production of hydroxyl free radical (⋅OH) generation. A microdialysis probe was implanted into the left ventricular myocardium, and dialysate norepinephrine (NE) concentrations were measured as an index of myocardial interstitial NE levels. Sodium salicylate in Ringer’s solution (0.5 nmol/μl/min) was directly infused through a microdialysis probe to detect the generation of ⋅OH reflected by the formation of dihydroxybenzoic acid (DHBA) in rat myocardium. When tyramine (1 mM) was directly infused through the microdialysis probe, the level of NE significantly increased in the dialysate and the level of NE increased by 128±43%. Imidaprilat (5, 25 and 50 μM) decreased the level of tyramine (1 mM)-induced NE in a concentration-dependent manner. Tyramine clearly produced an increase in ⋅OH formation. In the presence of imidaprilat (50 μM), tyramine failed to increase both 2,3- and 2,5-dihydroxylation. Therefore, the effects of imidaprilat on the ⋅OH generation in the sympathetic nerve blockaded hearts by reserpine treatment were not observed. Moreover, to examine the effect of imidaprilat on ⋅OH formation by ischemia/reperfusion of the myocardium, the heart was subjected to myocardial ischemia for 15 min by occlusion of the left anterior descending coronary artery. When the heart was reperfused, elevation of NE and 2,3- and 2,5-DHBA in imidaprilat (50 μM)-pretreated animals was not observed in the heart dialysate. Imidaprilat 2.5 mg/kg i.p. pretreatment at 5 h before coronary occlusion significantly blunted the rise of serum creatine phosphokinase and improved the electrocardiogram 2 h after coronary occlusion. These results suggest that imidaprilat, an ACE inhibitor, is associated with cardioprotective effect due to the suppression of NE-induced ⋅OH generation.

Protective effect of imidaprilat, an angiotensin-converting enzyme inhibitor on ⋅OH generation in rat myocardium

We used a flexibly mounted microdialysis technique to the hearts of rats and examined the protective effect of imidaprilat, an angiotensin-converting enzyme (ACE) inhibitor, on the production of hydroxyl free radical ( ⋅OH) generation. A microdialysis probe was implanted into the left ventricular myocardium, and dialysate norepinephrine (NE) concentrations were measured as an index of myocardial interstitial NE levels. Sodium salicylate in Ringer’s solution (0.5 nmol/μl/min) was directly infused through a microdialysis probe to detect the generation of ⋅OH reflected by the formation of dihydroxybenzoic acid (DHBA) in rat myocardium. When tyramine (1 mM) was directly infused through the microdialysis probe, the level of NE significantly increased in the dialysate and the level of NE increased by 128±43%. Imidaprilat (5, 25 and 50 μM) decreased the level of tyramine (1 mM)-induced NE in a concentration-dependent manner. Tyramine clearly produced an increase in ⋅OH formation. In the presence of imidaprilat (50 μM), tyramine failed to increase both 2,3- and 2,5-dihydroxylation. Therefore, the effects of imidaprilat on the ⋅OH generation in the sympathetic nerve blockaded hearts by reserpine treatment were not observed. Moreover, to examine the effect of imidaprilat on ⋅OH formation by ischemia/reperfusion of the myocardium, the heart was subjected to myocardial ischemia for 15 min by occlusion of the left anterior descending coronary artery. When the heart was reperfused, elevation of NE and 2,3- and 2,5-DHBA in imidaprilat (50 μM)-pretreated animals was not observed in the heart dialysate. Imidaprilat 2.5 mg/kg i.p. pretreatment at 5 h before coronary occlusion significantly blunted the rise of serum creatine phosphokinase and improved the electrocardiogram 2 h after coronary occlusion. These results suggest that imidaprilat, an ACE inhibitor, is associated with cardioprotective effect due to the suppression of NE-induced ⋅OH generation.

A new, concise dialysis approach to assessment of cardiac sympathetic nerve terminal abnormalities.

We applied a dialysis technique to the hearts of anesthetized cats and examined whether the concentration of dialysate norepinephrine (NE) reflected NE disposition at the cardiac sympathetic nerve terminals. Dialysis probes were implanted in the left ventricular wall, and dialysate NE concentrations were measured as an index of myocardial interstitial NE levels. Stimulation of stellate ganglia significantly increased dialysate NE responses that were suppressed by local administration of an NE-releasing inhibitor (omega-conotoxin GVIA, 10 microM). Increments in basal dialysate NE levels were correlated with concentrations of a locally administered neuronal uptake blocker (desipramine; 1, 10, and 100 microM). Desipramine (100 microM) augmented stimulation-induced dialysate NE responses. Local administration of a neuronal vesicle uptake blocker (reserpine, 1 and 10 microM) did not alter dialysate NE levels but increased dialysate dihydroxyphenylglycol levels. An NE-releasing amine (tyramine, 100 microg/ml) was locally administered to examine NE storage capacity at the nerve terminal. The tyramine-induced NE-releasing response was completely abolished by pretreatment with reserpine (1 mg/kg i.p.). Thus cardiac dialysis with local administration of a pharmacological tool offers a new, concise approach to assessment of neuronal NE release, uptake, vesicle uptake, and storage capacity by cardiac sympathetic nerve terminals.

Effects of locally administered desipramine on myocardial interstitial norepinephrine levels

We investigated whether locally administered neuronal uptake blockade with desipramine (DMI) modified basal myocardial interstitial norepinephrine (NE) levels and stimulation-induced NE responses. Using the dialysis technique, dialysates were sampled from the midwall of the left ventricle in anesthetized cats. Dialysate NE concentrations, as an index of myocardial interstitial NE level, were measured by high performance liquid chromatography. Through the dialysis probe, local administration of DMI (10 −4 mol/l) increased the dialysate NE level from 24.6±12.2 to 127.8±37.4 and from 11.9±5.4 to 64.9±28.7 pg/ml regardless of whether stellate ganglia were intact or transected. The arterial pressure and heart rate responses to electrical stimulation of the stellate ganglia were not altered by DMI. Control nerve stimulation increased dialysate NE concentrations to 214.5±100.0 and 57.5±22.0 pg/ml at 5 Hz and 2 Hz, respectively. During local administration of DMI, nerve stimulation-induced NE response increased to 997.5±202.0 at 5 Hz and to 436.0±68.5 pg/ml at 2 Hz. We conclude that local administration of DMI caused marked rises in basal myocardial interstitial NE concentrations and responses to cardiac sympathetic activation.

Elevated myocardial interstitial norepinephrine concentration contributes to the regulation of Na +,K +-ATPase in heart failure

Myocardial Na +,K −-ATPase is reduced in congestive heart failure. To study the regulation of Na +,K +-ATPase in congestive heart failure, we performed Western and Northern blot analyses of ventricular myocardium of dogs with pacing-induced congestive heart failure and chronic norepinephrine infusion, using isoform-specific antibodies and cDNA probes. Congestive heart failure and norepinephrine infusion caused similar increases in myocardial interstitial norepinephrine concentration and reductions of myocardial Na +,K +-ATPase α 3-subunit protein, but differed in their effects on myocardial Na +,K +-ATPase α 3-subunit gene expression. Chronic norepinephrine infusion produced no changes in the steady-state mRNA level for the α 3-subunit of Na +,K +-ATPase, suggesting that the changes in Na +,K +-ATPase protein were induced via a post-transcriptional mechanism. In contrast, down-regulation of the Na +,K +-ATPase α 3-subunit in the failing heart was accompanied by a decreased α 3-subunit mRNA level, indicating the presence of a transcriptional event. The α 1-subunit protein content and mRNA level were not affected by either norepinephrine infusion or rapid ventricular pacing. We conclude that, while elevated myocardial interstitial norepinephrine levels may contribute substantially to the down-regulation of the Na +,K +-ATPase α 3-subunit in the failing myocardium, additional regulatory factors are responsible for the decreased myocardial α 3-subunit mRNA expression in congestive heart failure.

Regional myocardial interstitial norepinephrine kinetics during coronary occlusion and reperfusion.

We investigated myocardial interstitial norepinephrine kinetics in both the ischemic and nonischemic regions during reperfusion after 40 min of coronary occlusion in anesthetized cats. By use of a cardiac dialysis technique, dialysate norepinephrine contents from both regions were monitored as an index of myocardial interstitial norepinephrine levels. For vehicle perfusate (n = 8), the accumulated dialysate norepinephrine level in the postischemic region decreased from 3,010 +/- 923 pg/ml at 30-40 min of occlusion to 957 +/- 178 pg/ml at 0-10 min of reperfusion and returned to near control level at 30-40 min of reperfusion. After 40 min of reperfusion, there were no significant differences in tyramine (100 micrograms/ml, norepinephrine-releasing sympathomimetic amine)-induced norepinephrine release between both regions. For perfusate containing 100 microM desipramine (neural uptake inhibitor, n = 6), at 0-10 min of reperfusion, the dialysate norepinephrine in the postischemic region did not significantly decrease. The dialysate norepinephrine then returned to near preocclusion level at 30-40 min of reperfusion. These data suggest that reperfusion rapidly returns accumulated myocardial norepinephrine to the preischemic level and neuronal norepinephrine uptake greatly contributes to this return in the early phase of reperfusion. Forty minutes of coronary occlusion cause neither norepinephrine exhaustion nor irreversible impairment of norepinephrine uptake function in nerve terminals.

Routine high-performance liquid chromatographic determination of myocardial interstitial norepinephrine

The present study describes a high-performance liquid chromatographic-electrochemical detection (HPLC-ED) system for routine measurement of the low levels of norepinephrine (NE) found in the myocardial interstitial space. In this system, an in vivo detection limit of 100 fg in a 50-μl injection was achieved for NE. Using cardiac dialysis technique, 20-μl dialysates were sampled from the myocardial interstitial space at 2-min intervals. The basal dialysate NE concentrations was 16.6 ± 4.0 pg/ml. This low detection limit allowed the dialysate NE concentration to be monitored for dysfunction of the cardiac sympathetic nerve terminal. This system offers a new possibility for routine analysis of myocardial interstitial NE levels.

Increase in myocardial interstitial norepinephrine during a short period of coronary occlusion

The neurally intact in vivo beating hearts of cats were used to examine the influence of a short period of coronary occlusion on regional myocardial norepinephrine levels. Using a cardiac dialysis technique, dialysate norepinephrine levels were measured as an index of myocardial interstitial norepinephrine levels, and the left anterior descending coronary artery was occluded for 10 min. In anesthetized cats, 10 min occlusion increased the dialysate norepinephrine level in the ischemic region but not in the non-ischemic region. To investigate the influence of neuronal norepinephrine uptake on occlusion-induced dialysate norepinephrine response, a neuronal uptake inhibitor (desipramine) was locally administered to both regions with the dialysis perfusate. In the ischemic region, 10 min occlusion significantly increased the dialysate norepinephrine level from the control level in the presence of desipramine. We concluded that 10 min coronary occlusion was associated with an increase in the myocardial interstitial norepinephrine level in the ischemic region. This increase in the early phase of ischemia was not attributed to attenuation of neuronal norepinephrine uptake function.

Differential regional responses of myocardial interstitial noradrenaline levels to coronary occlusion

The aim was to investigate the influence of coronary occlusion on myocardial interstitial noradrenaline levels in the ischaemic and non-ischaemic regions, using the dialysis technique. In nine anaesthetised cats, regional ischaemia was produced by occlusion of the left anterior descending coronary artery for 90 min. Using the dialysis technique, dialysates were sampled from both the ischaemic region and the nonischaemic left circumflex coronary artery region. Dialysate noradrenaline concentrations, as an index of myocardial interstitial noradrenaline content, were measured by high performance liquid chromatography. Myocardial blood flows in the ischaemic and non-ischaemic regions were measured by the hydrogen clearance method. In the non-ischaemic region, neither myocardial blood flow nor dialysate noradrenaline concentration showed significant change. In the ischaemic region, myocardial blood flow decreased significantly, from 117(SEM 12) at control to 23(3) ml.min-1 x 100 g-1, and dialysate noradrenaline concentration increased significantly, from 56.8(4.5) pg.ml-1 at control to 528.8(155.4) pg.ml-1 at 0-30 min of occlusion, 4212.0(1447.7) pg.ml-1 at 30-60 min, and 4179.8(1668.5) pg.ml-1 at 60-90 min. At 0-30 min of the reperfusion period, dialysate noradrenaline concentration in the postischaemic region decreased significantly to 420.2(152.1) pg.ml-1. Coronary occlusion increased myocardial interstitial noradrenaline levels in the ischaemic region, but not in the non-ischaemic region.