Intracoronary blockade of angiotensin-converting enzyme in humans: interaction with cardiac sympathetic neurotransmission?

Acute effects of angiotensin-converting enzyme inhibition versus angiotensin II receptor blockade on cardiac sympathetic activity in patients with heart failure

The beneficial effects of angiotensin-converting enzyme (ACE) inhibitors and angiotensin II (ANG II) receptor antagonists in patients with heart failure secondary to reduced ejection fraction (HFrEF) are felt to result from prevention of the adverse effects of ANG II on systemic afterload and renal homeostasis. However, ANG II can activate the sympathetic nervous system, and part of the beneficial effects of ACE inhibitors and ANG II antagonists may result from their ability to inhibit such activation. We examined the acute effects of the ACE inhibitor captopril (25 mg, n = 9) and the ANG II receptor antagonist losartan (50 mg, n = 10) on hemodynamics as well as total body and cardiac norepinephrine spillover in patients with chronic HFrEF. Hemodynamic and neurochemical measurements were made at baseline and at 1, 2, and 4 h after oral dosing. Administration of both drugs caused significant reductions in systemic arterial, cardiac filling, and pulmonary artery pressures (P < 0.05 vs. baseline). There was no significant difference in the magnitude of those hemodynamic effects. Plasma concentrations of ANG II were significantly decreased by captopril and increased by losartan (P < 0.05 vs. baseline for both). Total body sympathetic activity increased in response to both captopril and losartan (P < 0.05 vs. baseline for both); however, there was no change in cardiac sympathetic activity in response to either drug. The results of the present study do not support the hypothesis that the acute inhibition of the renin-angiotensin system has sympathoinhibitory effects in patients with chronic HFrEF.

Myocardial protection with enalaprilat in patients unresponsive to ischemic preconditioning during percutaneous coronary intervention

Cardioprotection due to angiotensin enzyme inhibitors is attributed, at least in part, to the inhibition of bradykinin breakdown and the preconditioning effect of the elevated endogenous bradykinin level. We have previously shown that in patients undergoing percutaneous coronary intervention, one 120-second balloon inflation is insufficient to precondition the heart. The objective of the present study was to examine whether the administration of enalaprilat to these patients results in protection. Twenty patients underwent two 120-second coronary artery occlusions separated by a reperfusion interval of 10 min. Ten patients were given 50 µg·min–1 enalaprilat in an intracoronary infusion between the balloon inflations, whereas the others received an infusion of saline. In the latter control patients, there were no significant differences in ST-segment elevation between the consecutive occlusions (peak ST: 1.61 ± 0.17 vs. 1.61 ± 0.16 mV; time to reach 0.5 mV ST elevation: 16 ± 4 vs. 22 ± 7 s; mean ST: 1.03 ± 0.12 vs. 1.02 ± 0.11 mV). In the patients who received enalaprilat before the second balloon inflation, the ST-segment elevation was significantly less pronounced and slower during the second inflation than during the first (peak ST: 1.80 ± 0.18 vs. 1.41 ± 0.19 mV; time to reach 0.5 mV ST elevation: 18 ± 4 vs. 30 ± 4 s; mean ST: 1.04 ± 0.11 vs. 0.85 ± 0.14 mV). We conclude that enalaprilat administered during percutaneous coronary intervention provides protection to patients who do not have a protective response to the initial balloon inflation.

Angiotensin II and norepinephrine release: interaction and effects on the heart

BACKGROUND

Angiotensin (Ang) II may enhance the influence of the sympathetic nervous system at various levels by facilitating norepinephrine (NE) release. We investigated whether such an interaction is evident in the human heart and whether it has an impact on left ventricular (LV) structure.

METHODS AND RESULTS

Ang I and Ang II concentrations were determined in arterial and coronary sinus (CS) plasma samples in a group of normotensive (n = 10) and hypertensive (n = 18) subjects. Total systemic and cardiac NE spillover was measured using isotope dilution methodology and LV structure by echocardiography. Arterial and CS concentrations of Ang I and Ang II were similar in both groups (Ang II CS, 5.8 +/- 4.0 versus 3.7 +/- 3.1 fmol/ml; P = not significant), as was the Ang II/Ang I ratio (CS, 0.56 +/- 0.17 versus 0.54 +/- 0.22 fmol/fmol; P = not significant). Total systemic (223 +/- 145 versus 374 +/- 149 ng/min; P < 0.05) and cardiac NE spillover (11.7 +/- 6.3 versus 19.4 +/- 10.5 ng/min; P < 0.05) were increased in hypertensive patients, as was LV mass index (LVMI) (86.7 +/- 14.7 versus 117.2 +/- 19.4 g/m; P < 0.001). LVMI correlated with cardiac NE spillover (r = 0.47; P < 0.02). No correlation was evident between CS Ang II and cardiac NE spillover (r = 0.001; P = not significant) or LVMI (r = -0.20; P = not significant). Arterial Ang II tended to correlate with total systemic NE spillover (r = 0.34; P = 0.081). When hypertensive subjects were divided into two groups with either high or low CS Ang II concentration, cardiac NE spillover and LVMI did not differ between the two groups.

CONCLUSION

These findings suggest a growth-promoting effect of increased cardiac sympathetic tone on cardiomyocytes in hypertensive patients, but do not support the notion of a significant role of Ang II for norepinephrine release and LV hypertrophy in the hypertensive human heart.

Long-term outcome in relation to renal sympathetic activity in patients with chronic heart failure

AIMS

Although cardiac sympathetic activation is associated with adverse outcome in patients with chronic heart failure (CHF), the influence of renal sympathetic activity on outcome is unknown. We assessed the hypothesis that renal noradrenaline (NA) spillover is a predictor of the combined endpoint of all-cause mortality and heart transplantation in CHF.

METHODS AND RESULTS

Sixty-one patients with CHF, New York Heart Association (NYHA) I-IV (66% NYHA III-IV), and left ventricular ejection fraction (LVEF) 26+/-9% (mean+/-SD) were studied with cardiac and renal catheterizations at baseline and followed for 5.5+/-3.7 years (median 5.5 years, range 12 days to 11.6 years). Nineteen deaths and 13 cases of heart transplantation were registered. Only renal NA spillover above median, 1.19 (interquartile range 0.77-1.43) nmol/min, was independently associated with an increased relative risk (RR) of the combined endpoint (RR 3.1, 95% CI 1.2-7.6, P=0.01) in a model also including total body NA spillover, LVEF, glomerular filtration rate (GFR), renal blood flow, cardiac index, aetiology, and age.

CONCLUSION

Renal noradrenergic activation has a strong negative predictive value on outcome independent of overall sympathetic activity, GFR, and LVEF. These findings suggest that treatment regimens that further reduce renal noradrenergic stimulation could be advantageous by improving survival in patients with CHF.

Sympathetic augmentation in hypertension: role of nerve firing, norepinephrine reuptake, and Angiotensin neuromodulation

There is growing evidence that essential hypertension is commonly neurogenic and is initiated and sustained by sympathetic nervous system overactivity. Potential mechanisms include increased central sympathetic outflow, altered norepinephrine (NE) neuronal reuptake, diminished arterial baroreflex dampening of sympathetic nerve traffic, and sympathetic neuromodulation by angiotensin II. To address this issue, we used microneurography and radiotracer dilution methodology to measure regional sympathetic activity in 22 hypertensive patients and 11 normotensive control subjects. The NE transport inhibitor desipramine was infused to directly assess the potential role of impaired neuronal NE reuptake. To evaluate possible angiotensin sympathetic neuromodulation, the relation of arterial and coronary sinus plasma concentrations of angiotensin II to sympathetic activity was investigated. Hypertensive patients displayed increased muscle sympathetic nerve activity and elevated total systemic, cardiac, and renal NE spillover. Cardiac neuronal NE reuptake was decreased in hypertensive subjects. In response to desipramine, both the reduction of fractional transcardiac 3[H]NE extraction and the increase in cardiac NE spillover were less pronounced in hypertensive patients. DNA sequencing analysis of the NE transporter gene revealed no mutations that could account for reduced transporter activity. Arterial baroreflex control of sympathetic nerve traffic was not diminished in hypertensive subjects. Angiotensin II plasma concentrations were similar in both groups and were not related to indexes of sympathetic activation. Increased rates of sympathetic nerve firing and reduced neuronal NE reuptake both contribute to sympathetic activation in hypertension, whereas a role for dampened arterial baroreflex restraint on sympathetic nerve traffic and a peripheral neuromodulating influence of angiotensin II appear to be excluded.

Exogenous angiotensin II does not facilitate norepinephrine release in the heart

Studies on the effect of angiotensin II on norepinephrine release from sympathetic nerve terminals through stimulation of presynaptic angiotensin II type 1 receptors are equivocal. Furthermore, evidence that angiotensin II activates the cardiac sympathetic nervous system in vivo is scarce or indirect. In the intact porcine heart, we investigated whether angiotensin II increases norepinephrine concentrations in the myocardial interstitial fluid (NE(MIF)) under basal conditions and during sympathetic activation and whether it enhances exocytotic and nonexocytotic ischemia-induced norepinephrine release. In 27 anesthetized pigs, NE(MIF) was measured in the left ventricular myocardium using the microdialysis technique. Local infusion of angiotensin II into the left anterior descending coronary artery (LAD) at consecutive rates of 0.05, 0.5, and 5 ng/kg per minute did not affect NE(MIF), LAD flow, left ventricular dP/dt(max), and arterial pressure despite large increments in coronary arterial and venous angiotensin II concentrations. In the presence of neuronal reuptake inhibition and alpha-adrenergic receptor blockade, left stellate ganglion stimulation increased NE(MIF) from 2.7+/-0.3 to 7.3+/-1.2 before, and from 2.3+/-0.4 to 6.9+/-1.3 nmol/L during, infusion of 0.5 ng/kg per minute angiotensin II. Sixty minutes of 70% LAD flow reduction caused a progressive increase in NE(MIF) from 0.9+/-0.1 to 16+/-6 nmol/L, which was not enhanced by concomitant infusion of 0.5 ng/kg per minute angiotensin II. In conclusion, we did not observe any facilitation of cardiac norepinephrine release by angiotensin II under basal conditions and during either physiological (ganglion stimulation) or pathophysiological (acute ischemia) sympathetic activation. Hence, angiotensin II is not a local mediator of cardiac sympathetic activity in the in vivo porcine heart.

Direct interaction between the sympathetic and renin-angiotensin system in myocardial tissue: a microdialysis study in anaesthetised rats

It has been suggested that local activation of the renin-angiotensin system is involved in early stages of myocardial pathophysiology. To date, there is increasing evidence for interactions between the renin-angiotensin system and the sympathetic nervous system; consequently, local sympathetic activation may also be involved in this. Microdialysis has great potential in the direct investigation of neurohormonal interactions. Therefore, the present study employs microdialysis to study the local effects of exogenous angiotensin II on the interstitial norepinephrine concentration of the normally innervated left ventricle of the anaesthetised rat. The present study investigates the effect of increasing dosages of exogenous angiotensin II on local interstitial norepinephrine. Furthermore, a single dose of losartan was infused on top of the highest dose of angiotensin II, in order to study possible involvement of angiotensin II type 1 (AT1) receptors. Both infusion and sampling were carried out locally, via the microdialysis probes. Concomitantly, circulating norepinephrine levels, heart rate and respiratory rate were monitored to evaluate physiologic stability of the preparation throughout the experiment. Time controls consisted of rats that were perfused with only a Ringer's solution. Angiotensin II induced a dose dependent increase in norepinephrine that was significantly reduced by losartan. Norepinephrine levels in both plasma (infusion experiment and time controls) and the left ventricular wall (time controls) remained stable throughout the experiment, just as heart rate and respiratory rate did. This study for the first time employs microdialysis to demonstrate direct interaction between the sympathetic nervous system and the renin-angiotensin system in the rat left ventricle. The data strongly suggest that AT1 receptors are involved in this interaction, since selective AT1 receptor blockade with losartan significantly reduced the angiotensin II induced norepinephrine concentration.