Renal nerve stimulation augments effect of intraluminal angiotensin II on proximal tubule transport

The proximal tubule synthesizes and secretes angiotensin II into the lumen, where it regulates transport. Renal denervation abolishes the effect of angiotensin II on proximal tubule transport. Using in vivo microperfusion, we examined whether renal nerve stimulation modulates the effect of angiotensin II on transport. The effect of angiotensin II was assessed by measuring the decrease in volume reabsorption with the addition of 10(-4) M luminal enalaprilat. Luminal enalaprilat did not alter volume reabsorption (2.80 +/- 0.18 vs. 2.34 +/- 0.14 nl x mm(-1) x min(-1)). However, with renal nerve stimulation, enalaprilat decreased volume reabsorption (3.45 +/- 0.22 vs. 1.67 +/- 0.20 nl x mm(-1) x min(-1), P < 0.0005). The absolute and percent decrements in volume reabsorption with luminal enalaprilat were higher with renal nerve stimulation than with native innervation (1.78 +/- 0.19 vs. 0.46 +/- 0.23 nl x mm(-1) x min(-1), P < 0.02, and 51.8 +/- 5.0 vs. 14.6 +/- 7.4%, P < 0.05, respectively). Renal nerve stimulation did not alter the glomerular filtration rate or renal blood flow. Renal nerve stimulation augments the stimulatory effect of intraluminal angiotensin II. The sympathetic renal nerves modulate the proximal tubule renin-angiotensin system and thereby regulate proximal tubule transport.

Effects of intracoronary low-dose enalaprilat as an adjunct to primary percutaneous transluminal coronary angiography in acute myocardial infarction

Bradykinin accumulation is a potent cardioprotective mechanism underlying angiotensin-converting enzyme (ACE) inhibition in ischemia and/or reperfusion injury. There is, however, concern about treatment with ACE inhibitors in the very early phase of acute myocardial infarction (AMI) due to adverse systemic hemodynamic effects. We tested the hypothesis that cardiac bradykinin metabolism can be influenced by very low doses of intracoronary ACE inhibitors without harmful systemic effects in patients with AMI. Twenty-two patients with AMI in Killip classes II to III who underwent primary percutaneous transluminal coronary angiography (PTCA) were randomized to intracoronary enalaprilat (50 microg) or saline, given immediately after reopening of the infarct-related artery. Hemodynamics and electrocardiograms were monitored continuously and samples for determination of ACE activity, angiotensin II, bradykinin, kininogen, and cardiac marker proteins were collected from pulmonary arterial and central venous blood. Enalaprilat had no adverse effects on systemic hemodynamics, but rather stabilized arterial pressure and cardiac rhythm during reperfusion. Enalaprilat induced a 70% reduction of ACE activity and a significant increase of bradykinin in pulmonary arterial blood. Angiotensin II was not significantly affected by enalaprilat either in pulmonary arterial or in central venous blood. Myoglobin release was lower and the duration of reperfusion arrhythmias was significantly reduced in the enalaprilat group (p <0.05). Thus, in this pilot study, intracoronary enalaprilat infusion in the infarct-related artery is feasible in the setting of primary angioplasty and is safe and well tolerated. Effective cardiac ACE inhibition can be achieved by low-dose intracoronary enalaprilat, which primarily causes a potentiation of bradykinin.

High serum enalaprilat in chronic renal failure

BACKGROUND

Most angiotensin-converting enzyme (ACE) inhibitors and their metabolites are excreted renally and doses should hence be reduced in renal insufficiency. We studied whether the dosage of enalapril in daily clinical practice is associated with drug accumulation of enalaprilat in chronic renal failure.

METHODS

Fifty nine out-patients with plasma creatinine >150 micromol/L and chronic antihypertensive treatment with enalapril were investigated, in a cross-sectional design.

RESULTS

Median glomerular filtration rate (GFR) was 23(range 6-60) ml/minute/1.73 m2. The daily dose of enalapril was 10 (2.5-20) mg and the trough serum concentration of enalaprilat was 31.8 (<2.5-584.7)ng/ml. Ninety percent of the patients had higher serum concentrations of enalaprilat than has been reported in subjects with normal kidney function, and a marked elevation of serum enalaprilat was observed in patients with GFR <30 ml/minute. All but three patients had serum ACE activity below the reference range. The ACE genotype did not influence the results. Additional pharmacokinetic studies were done in nine patients in whom GFR was 23 (10-42)ml/minute/1.73 m2. The median clearance of enalaprilat was 28 (16-68) ml/minute and correlated linearly with GFR (r=0.86, p=0.003). Intra-subject day-to-day variation in trough concentrations was 19.7%.

CONCLUSION

Patients with chronic renal failure given small or moderately high doses of enalapril may thus have markedly elevated levels of serum enalaprilat. Whether this affords extra renoprotection, or on the contrary may inappropriately impair renal function, is not known, and should be investigated in prospective, controlled studies.

In vitro characterization of human intact erythrocytes loaded by enalaprilat

In vitro characteristics of the human erythrocytes loaded by enalaprilat have been evaluated. Erythrocytes obtained from a healthy volunteer were loaded by enalaprilat using the hypotonic preswelling method, and the loading parameters, drug-release kinetics, hematological indices, particle size distribution, scanning electron microscopy view, osmotic and turbulence fragilities, and deformability of the resulting carrier cells were determined along with the sham encapsulated and unloaded cells. Carrier erythrocytes, having acceptable loading parameters, released their drug content according to zero-order kinetics. Mean corpuscular hemoglobin and mean corpuscular hemoglobin content values of the cells decreased, particle size dispersion increased, the cells transformed to cup-form, the erythrocytes became more fragile against osmotic pressure and turbulent flow, and, finally, the deformability of the cells decreased significantly upon drug loading.

Inhibition of serum angiotensin-converting enzyme in rabbits after intravenous administration of enalaprilat-loaded intact erythrocytes

Encapsulation of drugs in intact erythrocytes, because of the profound characteristics of these natural microspheres, has gained considerable attention in recent years. In this study, the inhibition time courses of serum angiotensin-converting enzyme (ACE) activity after intravenous administration of enalaprilat encapsulated in intact erythrocytes was evaluated and compared with free drug, in a rabbit model. Three groups of animals each received free drug, drug-loaded erythrocytes or sham-encapsulated erythrocytes. Serum ACE activity was determined in each case using the synthetic substrate hippuryl-histidyl-leucine and quantitation of the hippuric acid released by a developed and validated HPLC method. The serum ACE inhibition profiles in the three groups showed that the encapsulated drug inhibited the serum ACE more slowly, more efficiently, over a considerably longer time and in a more reproducible manner, than the free drug or sham-encapsulated erythrocytes. We conclude that the erythrocytes can serve as efficacious slow-release drug carriers for enalaprilat in circulation.

Treatment of chronic hypertension with intravenous enalaprilat and transdermal clonidine

We report an 11-year-old boy with hypertension and chronic intestinal pseudo-obstruction, which renders him totally dependent on parenteral nutrition and prevents the use of oral medications. Here we report the feasibility of utilizing chronic i.v. enalaprilat and transdermal clonidine on a chronic basis to control hypertension. Over the last 10 months, the patient's hypertension has been well controlled by 1.25 mg i.v. enalaprilat every 8 h and a 0.2-mg clonidine patch every 6 days, with no apparent side-effects. There are no reports of i.v. enalaprilat usage exceeding 3 weeks' duration. Therefore we believe that it is possible to effect reasonable management of chronic hypertension with the use of chronic i.v. enalaprilat and transdermal clonidine therapy.

Evaluation of hypotonic preswelling method for encapsulation of enalaprilat in intact human erythrocytes

The hypotonic preswelling method for encapsulation of drugs in intact human erythrocytes was evaluated using enalaprilat as a model peptide-like drug. Several process variables, including volume, concentration, pH, and method of addition of drug solution, type of erythrocyte-suspending medium, temperature, initial packed density of erythrocytes, and individual process steps, were exploited with respect to their effects on the loading parameters (i.e., loaded amount, efficiency of entrapment, and cell recovery). In addition, the probable mechanism by which the erythrocytes were loaded by enalaprilat at the point of lysis was shown to be a simple concentration gradient-based diffusion through membrane openings occurring on hemolysis. Finally, the adopted method was validated, and the results showed a considerable degree of reproducibility and recovery for the entire loading procedure.

Differentiated response of the sympathetic nervous system to angiotensin-converting enzyme inhibition in hypertension

Hypertension with renal artery stenosis is associated with both an activated renin-angiotensin system and elevated sympathetic activity. Therefore, in this condition it may be favorable to use a therapeutic modality that does not reflexly increase heart rate, renin secretion, and sympathetic nervous activity. The purpose of the present study was to assess overall, renal, and muscle sympathetic activity after short-term administration of an angiotensin-converting enzyme inhibitor (enalaprilat) and a nonspecific vasodilator (dihydralazine) to hypertensive patients with renal artery stenosis. Forty-eight patients undergoing a clinical investigation for renovascular hypertension were included in the study. An isotope dilution technique for assessing norepinephrine spillover was used to estimate overall and bilateral renal sympathetic nerve activity. In 11 patients simultaneous intraneural recordings of efferent muscle sympathetic nerve activity were performed. Thirty minutes after dihydralazine administration, mean arterial pressure fell by 15%, whereas plasma angiotensin II, muscle sympathetic nerve activity, heart rate, and total body norepinephrine spillover increased (P<0.05 for all). In contrast, after enalaprilat administration a fall in arterial pressure similar to that for dihydralazine was followed by decreased angiotensin II levels and unchanged muscle sympathetic nerve activity, heart rate, and total body norepinephrine spillover, whereas renal norepinephrine spillover increased by 44% (P<0.05). Acute blood pressure reduction by an angiotensin-converting enzyme inhibitor provokes a differentiated sympathetic response in patients with hypertension and renal artery stenosis, inasmuch that overall and muscle sympathetic reflex activation are blunted, whereas the reflex renal sympathetic response to blood pressure reduction is preserved.

Insertion-deletion polymorphism of the ACE gene modulates reversibility of endothelial dysfunction with ACE inhibition

BACKGROUND

The aim of this study was to examine whether angiotensin-converting enzyme (ACE) inhibition improves coronary endothelial dysfunction in patients with atherosclerosis and its risk factors and whether this was related to the ACE insertion-deletion (I/D) polymorphism.

METHODS AND RESULTS

In 56 patients with atherosclerosis or its risk factors, we studied endothelium-dependent responses with acetylcholine and endothelium-independent function with sodium nitroprusside, before and after ACE inhibition with enalaprilat. Enalaprilat did not alter either resting coronary tone or vasodilation with sodium nitroprusside. However, it potentiated the coronary microvascular and epicardial responses with acetylcholine; coronary blood flow increased from 82+/-7 to 90+/-8 mL/min (P=0.05) after enalaprilat. Patients with depressed endothelial function (P<0.001) and those with ACE DD or ID genotypes (P=0.002) but not those homozygous for the I allele had the greatest improvement by multivariate analysis. Similarly, acetylcholine-mediated epicardial vasomotion improved in segments that initially constricted (endothelial dysfunction): from -10.1+/-1% to -1.4+/-2% (P<0.001) after enalaprilat. No augmentation was observed in segments that dilated (normal endothelial dysfunction) with acetylcholine. Patients with the D allele, hypercholesterolemia, and smokers (all P<0.05) had greater improvement.

CONCLUSIONS

Acute ACE inhibition improves coronary epicardial and microvascular endothelium-dependent vasomotion in patients with atherosclerosis or its risk factors who have endothelial dysfunction and presence of the D allele.

Dissociation between ACE activity and autonomic response to ACE inhibition in patients with heart failure

BACKGROUND

Administration of angiotensin-converting enzyme (ACE) inhibitors to patients with congestive heart failure has been shown to increase parasympathetic tone as indicated by increases in high-frequency heart rate variability. The mechanism for this effect, including its relation to changes in baroreflex activity, blood pressure variability, and suppression of ACE activity, remains undefined. This study was designed to test the relation of these variables, which may govern changes in autonomic activity, to the previously described increase in parasympathetic tone.

METHODS

Seven patients with heart failure received a 3-hour infusion of the ACE inhibitor enalaprilat. Hemodynamic variables and parameters of heart rate and blood pressure variability, baroreflex gain derived from the interaction of heart rate and blood pressure variability, and serum ACE activity were measured during and after the infusion. Measures of heart rate and blood pressure variability were also compared against a historic control group.

RESULTS

Serum ACE activity was significantly suppressed throughout and after enalaprilat infusion. Hemodynamic measures did not change other than a small decline in right atrial and pulmonary capillary wedge pressures. Parasympathetic tone showed an initial significant increase with a peak at 2 hours but then declined below baseline 8 hours after initiation of enalaprilat infusion. Sympathetically influenced low-frequency heart rate variability was significantly increased above baseline in the enalaprilat treatment group 8 hours after initiation of the infusion. Baroreflex gain showed a significant trend to an increase with the maximum value coinciding with the peak in parasympathetic tone. There was no change in blood pressure variability in the enalaprilat group and no change in baroreflex gain, heart rate variability, or blood pressure variability in the control group.

CONCLUSIONS

Parasympathetic tone and baroreflex gain increased with parenteral administration of an ACE inhibitor but subsequently decreased below baseline values despite continued suppression of serum ACE activity. The dissociation between ACE suppression and autonomic response to ACE inhibition indicates that enzyme systems not reflected by plasma ACE activity or independent from the classic pathways of angiotensin formation contribute to the regulation of the autonomic response to ACE inhibition in patients with heart failure. The absence of significant change in hemodynamic variables or in blood pressure variability indicates that these autonomic changes are not an indirect reflex response to ACE inhibitor-induced vasodilation or hemodynamic baroreceptor stimulation.

Functional importance of angiotensin-converting enzyme-dependent in situ angiotensin II generation in the human forearm

To assess the importance for vasoconstriction of in situ angiotensin (Ang) II generation, as opposed to Ang II delivery via the circulation, we determined forearm vasoconstriction in response to Ang I (0.1 to 10 ng. kg(-1). min(-1)) and Ang II (0.1 to 5 ng. kg(-1). min(-1)) in 14 normotensive male volunteers (age 18 to 67 years). Changes in forearm blood flow (FBF) were registered with venous occlusion plethysmography. Arterial and venous blood samples were collected under steady-state conditions to quantify forearm fractional Ang I-to-II conversion. Ang I and II exerted the same maximal effect (mean+/-SEM 71+/-4% and 75+/-4% decrease in FBF, respectively), with similar potencies (mean EC(50) [range] 5.6 [0.30 to 12.0] nmol/L for Ang I and 3.6 [0.37 to 7.1] nmol/L for Ang II). Forearm fractional Ang I-to-II conversion was 36% (range 18% to 57%). The angiotensin-converting enzyme (ACE) inhibitor enalaprilat (80 ng. kg(-1). min(-1)) inhibited the contractile effects of Ang I and reduced fractional conversion to 1% (0.1% to 8%), thereby excluding a role for Ang I-to-II converting enzymes other than ACE (eg, chymase). The Ang II type 1 receptor antagonist losartan (3 mg. kg(-1). min(-1)) inhibited the vasoconstrictor effects of Ang II. In conclusion, the similar potencies of Ang I and II in the forearm, combined with the fact that only one third of arterially delivered Ang I is converted to Ang II, suggest that in situ-generated Ang II is more important for vasoconstriction than circulating Ang II. Local Ang II generation in the forearm depends on ACE exclusively and results in vasoconstriction via Ang II type 1 receptors.

Timed inhibition of the renin-angiotensin system suppresses the rise in blood pressure upon awakening in spontaneously hypertensive rats

In this study we investigated whether timed administration of drugs that inhibit the renin-angiotensin system can be used to blunt the rise in blood pressure that occurs during the transition from the resting to the active period of the day. For this purpose we compared in spontaneously hypertensive rats (SHR) the antihypertensive efficacy of the angiotensin converting enzyme (ACE) inhibitors captopril (doses: 3, 10, and 30 mg/ kg/6 h) and enalaprilat (0.3 mg/kg/6 h), and the AT1-receptor antagonist losartan (10 mg/kg/6 h) at two different treatment regimens. The antihypertensive drugs were given as a continuous 6-h infusion either during the transition from the dark to light period (DL) or that from the light to dark period (LD) for 5 consecutive days. For all agents, the average 24-h reduction of blood pressure was comparable for the LD or DL treatment regimen. However, the dynamics of the antihypertensive response were markedly different. The increase in blood pressure at awakening could be blunted much more effectively by the LD than DL treatment regimen. Furthermore, as indicated by the trough:peak ratios, blood pressure profiles were flatter with the LD than with the DL regimen. Thus, in SHR, 24-h rhythms of blood pressure can be modulated by timed administration of ACE inhibitors and losartan, such that the early morning rise in blood pressure is suppressed.

Bolus versus continuous low dose of enalaprilat in congestive heart failure with acute refractory decompensation

The first dose of angiotensin-converting enzyme (ACE) inhibitors may trigger a considerable fall of blood pressure in chronic heart failure. The response may be dose-related. To determine hemodynamic and systemic oxygenation effects of low-dose enalaprilat, we administered intravenous enalaprilat (0.004 mg/kg) as bolus (group B) or continuous 1-hour infusion (group C) in 20 patients with congestive heart failure due to ischemic heart disease with acute decompensation refractory to inotropic, vasodilator and diuretic therapy. Hemodynamic and systemic oxygenation variables were recorded at baseline (+0 min), +30, +60, +120, +180, and +360 min after the start of intervention. Mean arterial pressure (MAP) (p < 0. 001), mean pulmonary artery pressure (MPAP) (p < 0.001), pulmonary artery occlusion pressure (PAOP) (p < 0.001), oxygen extraction ratio (ER) (p < 0.026) decreased regardless of enalaprilat application. Compared to group B, there was in group C prolonged decrease of MAP, MPAP, PAOP, ER and increase of pulmonary artery oxyhemoglobin saturation in regard to baseline values. Cardiac index, heart rate, central venous pressure and oxygen consumption index did not change. A low dose of intravenous enalaprilat (0.004 mg/kg) can be used to safely improve hemodynamics and systemic oxygenation in congestive heart failure due to ischemic heart disease with acute refractory decompensation.

[Sublingual nitroglycerin or intravenous enalaprilat in preclinical treatment of hypertensive patients with pulmonary edema]

In a prospectively designed randomized study, we compared the efficacy of sublingual nitroglycerine and intravenous enalaprilat in the out-of-hospital treatment of 46 hypertensive patients with pulmonary edema (defined as rales over both lungs and systolic blood pressure > 200 mm Hg and diastolic blood pressure > 100 mg). The out-of-hospital treatment consists of oxygen (6 Ll/min) via a face mask, furosemide 80 mg i.v., opioids 10 mg s.c., and either sublingual nitroglycerine (n = 23; initial dose: 0.8 mg; repetitive application of 0.8 mg every 10 min until a cumulative dose of 3.2 mg) or intravenous enalaprilat (initial dose: 2.5 mg; repetitive application of 2.5 mg every 30 min until a cumulative dose of 10 mg). The aim of the antihypertensive treatment was a reduction of systolic blood pressure below 160 mm Hg and diastolic blood pressure below 90 mm Hg until admission to the emergency department. In the emergency room, an arterial and venous blood sample was taken to determine the respiratory (pO2, pCO2) and metabolic status (pH value; base-excess; serum lactate) of the patient. Successful antihypertensive treatment was observed in 13/23 (57%) patients of the enalaprilat group and 15/23 (65%) patients of the nitroglycerine group (p = 0.54). Systolic and diastolic blood pressure on admission were similar in both treatment groups (systolic RR: enalaprilat: 179 [31] mm Hg; nitroglycerine: 184 [38] mm Hg; p = 0.59; diastolic RR: enalaprilat: 96 [14] mm Hg; nitroglycerine: 101 [14] mm Hg; p = 0.12). No significant differences were observed between the enalaprilat and the nitroglycerine groups concerning respiratory and metabolic parameters on admission (pO2: 67 [15] vs. 64 [17] mm Hg; p = 0.50; pCO2: 46 [9] vs. 47 [13]; p = 0.75; pH value: 7.27 [0.12] vs. 7.27 [0.09]; p = 0.98; BE: -4.2 [3.7] vs. -5.7 [4.1]; p = 0.23; lactate: 4.2 [3.3] vs. 4.2 [2.7]; p = 0.98). Intravenous enalaprilat did not exhibit any advantage compared to nitroglycerine in terms of blood pressure reduction or respiratory and metabolic parameters on admission to the emergency room. We conclude that enalaprilat is no substitute for nitroglycerine in the out-of-hospital treatment of hypertensive patients with pulmonary edema.

Inhibition of angiotensin-converting enzyme in human hand veins

Conversion of angiotensin I to angiotensin II likely occurs in human veins, supporting the existence of endothelial angiotensin-converting enzyme (ACE) activity in these vessels. Using the dorsal hand vein technique, we investigated the effects of 2 ACE inhibitors, captopril (single oral dose of 6.25 mg) and enalaprilat (local infusion of 1 microgram/min), on venous responsiveness in healthy subjects. Orally administered captopril induced a marked decrease in angiotensin I- but not angiotensin II-induced venoconstriction. This blunted response persisted for at least 4 hours. Enalaprilat and captopril increased the sensitivity to bradykinin, decreasing the dose producing half-maximal response (ED50) of bradykinin 18-fold and 5-fold, respectively, without changing the maximal venodilatory response. These results confirm that there is substantial rapid metabolism of angiotensin I in human veins and suggest that a single dose of locally infused angiotensin I can be used with the dorsal hand vein technique to assess the time-course effect of vascular ACE inhibition after oral administration. Our findings also extend previous in vitro observations in human veins by showing that these agents potentiate the venodilatory effects of bradykinin in vivo.

The effect of i.v. enalaprilat in chronically treated hypertensive patients during cardiac surgery

BACKGROUND

Angiotensin-converting enzyme (ACE) inhibitors are well established as long-term antihypertensives and have also been proved useful in hypertensive emergencies. Therefore, we investigated whether intraoperative i.v. enalaprilat may reduce the incidence of perioperative hypertensive reactions in coronary artery bypass grafting (CABG).

METHODS

Thirty-eight male patients chronically treated for arterial hypertension and scheduled for CABG randomly and double-blindly received either enalaprilat 30 micrograms.kg-1 or NaCl 0.9% at the time of skin incision. Intraoperatively, increases of mean arterial pressure (MAP) > 85 mmHg or > 80 mmHg during cardiopulmonary bypass (CPB) were treated by an urapidil bolus. The total intraoperative amount of urapidil was documented for both groups. Systemic and pulmonary hemodynamics as well as the plasma levels of epinephrine, norepinephrine, arginine vasopressin and renin were measured intraoperatively and up to 2 h after admission to the intensive care unit.

RESULTS

Mean arterial pressure, cardiac index and systemic vascular resistance did not differ between the enalaprilat and the control group. Renin plasma levels significantly increased after infusion of enalaprilat and did not change in the placebo group. Catecholamine and arginine vasopressin plasma levels increased significantly during CPB and remained high in the postoperative period without any intergroup difference. The same amount of urapidil had to be given in the two groups to maintain MAP below the defined limit.

CONCLUSION

We conclude that infusing 30 micrograms.kg-1 enalaprilat in patients chronically treated for arterial hypertension does not prevent hypertensive reactions during CABG.

Beneficial effects of angiotensin-converting enzyme inhibitors during acute revascularization

BACKGROUND

This experimental study was undertaken to determine whether using angiotensin-converting enzyme inhibitors during surgical revascularization of acutely ischemic myocardium would improve wall motion and limit infarct size.

METHODS

Twenty pigs underwent 90 minutes of occlusion of the second and third diagonal arteries followed by 45 minutes of cardioplegic arrest and 180 minutes of reperfusion. In 10 animals, the angiotensin-converting enzyme inhibitor enalaprilat (0.05 mg/kg) was infused intravenously during coronary occlusion; 10 other animals received no angiotensin-converting enzyme inhibitors. Ischemic damage was assessed by the number of cardioversions required for ventricular tachycardia or fibrillation; wall motion scores using echocardiography (4=normal to -1=dyskinesia); and infarct size using histochemical staining. Epicardial coronary artery vasomotor function was assessed using standard organ chamber methodology.

RESULTS

Enalaprilat-treated hearts had the least amount of ventricular irritability (0.84+/-0.24 versus 2.77+/-0.22 cardioversions; p < 0.01), the best recovery of wall motion score (3.20+/-0.15 versus 1.52+/-0.07; p < 0.0001), and the lowest infarct size (22.6%+/-1.4% versus 37.7%+/-3.0%; p < 0.001). Endothelium-independent relaxation was preserved in all hearts; however, endothelium-dependent relaxation was impaired in both groups.

CONCLUSIONS

Angiotensin-converting enzyme inhibitors reduce myocardial damage during surgical revascularization of acutely ischemic myocardium.

Combined effects of angiotensin converting enzyme inhibition and angiotensin II receptor antagonism in conscious pigs with congestive heart failure

OBJECTIVE

The goal of this study was to determine if the hemodynamic effects of the combined administration of an angiotensin converting enzyme (ACE) inhibitor and angiotensin II type 1 (AT1) receptor antagonist are greater than those produced by either of these agents administered individually during heart failure.

METHODS

Ten farm pigs were chronically instrumented with aortic, left atrial and right atrial catheters, a left ventricular (LV) pressure gauge, LV dimension crystals, coronary occluders, an ascending aortic flow probe and pacing leads. Heart failure was induced by serial myocardial infarctions followed by repeated rapid ventricular pacing.

RESULTS

Heart failure was manifested by significant (p < 0.01) decreases in LV dP/dt (-38 +/- 5%, from 2943 +/- 107 mmHg/s) and cardiac output (-27 +/- 4%, from 4.1 +/- 0.2 l/min) and increases in left atrial pressure (+18 +/- 1 mmHg, from 4 +/- 1 mmHg) and total peripheral resistance (TPR)(+40 +/- 8%, from 23 +/- 2 mmHg/l/min). The effects of an ACE inhibitor (enalaprilat) and an AT1 receptor antagonist (L-158,809), administered in maximally effective doses, either individually or concomitantly, were examined on different days in conscious pigs with heart failure. There were no differences in any of the baseline hemodynamic measurements among the groups studied. Thirty minutes after administration, enalaprilat (4 mg/kg i.v.) increased (p < 0.05) cardiac output by 8 +/- 2% and reduced (p < 0.05) mean arterial pressure and TPR by 5 +/- 1 and 12 +/- 1%, respectively, while the changes in LV dP/dt (0 +/- 2%), LV fractional shortening (+4 +/- 3%) and heart rate (+1 +/- 1%) were not statistically significant. Similarly, L-158,809 (4 mg/kg, i.v.) increased cardiac output by 9 +/- 2% and reduced mean arterial pressure and TPR by 4 +/- 1 and 11 +/- 3%, respectively, while the changes in LV dP/dt (+3 +/- 3%), LV fractional shortening (+3 +/- 1%) and heart rate (0 +/- 1%) were not significant. However, enalaprilat (1 mg/kg, i.v.) and L-158,809 (1 mg/kg, i.v.), administered concomitantly, reduced TPR by 21 +/- 3%, an effect greater (p < 0.05) than when either of these agents was administered individually at a dose of 4 mg/kg, i.v. The changes in mean arterial pressure (-9 +/- 2%), cardiac output (+15 +/- 4%) and LV fractional shortening (+11 +/- 3%) also tended to be greater with concomitant administration. In addition, in a sequential dosing protocol, when L-158,809 (1 mg/kg, i.v.) was administered 30 min after enalaprilat (1 mg/kg, i.v.), TPR was reduced by 20 +/- 4% compared to only a 6 +/- 3% reduction (p < 0.05) when the enalaprilat was followed 30 min later by a second dose of enalaprilat (1 mg/kg, i.v.). The changes in mean arterial pressure and cardiac output for the combined treatment group also tended to be greater than those for the group given two sequential doses of enalaprilat.

CONCLUSION

In conscious pigs with heart failure, the combined vasodilatory effects of an ACE inhibitor and AT1 receptor antagonist are greater than those produced when only one of these agents is administered, suggesting that independent mechanisms of ACE inhibition and AT1 receptor antagonism could be partly responsible for the improved vascular dynamics during heart failure.

Evaluation of antiarrhythmic activity of captopril and enalaprilat in experimental cardiac arrhythmias in rabbits. Part II

The influence of 21-day administration of captopril and enalaprilat on barium chloride and adrenaline-induced experimental arrhythmias was assessed. The experiments were performed on rabbits. Arrhythmias were evoked by two alternative arrhythmogen doses. The patterns of disturbances, their frequency and duration were evaluated on the basis of ECG examination. Antiarrhythmic properties of angiotensin converting enzyme inhibitors administered for 21 days were also compared with their effects after single administration. The results were subjected to statistic analysis. On the basis of the obtained results we were able to establish that repeated administration of enalaprilat decreases the frequency of barium chloride- and adrenaline-induced arrhythmias. Repeated administration of captopril and enalaprilat shortened the duration of adrenaline- and barium chloride-induced arrhythmias. Long-term enalaprilat administration was much more effective in preventing arrhythmias than its single dose, it also proved to be more efficient than either single or repeated administration of captopril.

Enalaprilat improves gut perfusion in critically injured patients

Inadequate splanchnic perfusion, detected as a low gastric intramucosal pH (pHi), in the face of normal systemic perfusion predicts an increased risk for multiple organ failure after trauma. Although the exact etiology of this low pHi is unknown, angiotensin II is thought to be an important regulator of gut perfusion during and after resuscitation from shock. The purpose of this study is to determine whether enalaprilat, an angiotensin-converting enzyme inhibitor, improves gut perfusion in critically injured patients. To test this hypothesis, 18 trauma patients monitored with a nasogastric tonometer and a pulmonary artery catheter were enrolled in a prospective study. A single dose of enalaprilat, .625 mg, was given as an i.v. bolus or a 4 h infusion following systemic resuscitation. Pre- and postdrug tonometric and hemodynamic data, including cardiac index, mean arterial pressure, right ventricular end-diastolic volume index, systemic vascular resistance index, and oxygen transport variables were compared using the paired t test. Results demonstrate that pHi was significantly improved after 4 h (7.13 +/- .04 to 7.19 +/- .03, p = .03) and after 24 h compared with baseline (7.14 +/- .04 to 7.25 +/- .04, p = .04). Overall, pHi increased in 12 of 18 patients. No significant differences were observed in any of the studied hemodynamic or systemic perfusion variables including mean arterial pressure (92 +/- 4 to 87 +/- 4, p = .24) and oxygen delivery (669 +/- 33 to 675 +/- 32, p = .82). In examining the determinants of pHi, the intramucosal-arterial PCO2 difference was improved after enalaprilat administration (27 +/- 6 to 17 +/- 3 mmHg, p = .04) while no difference was observed in arterial bicarbonate (19.5 +/- .7 to 19.7 +/- .8, p = .90). Additionally, the change in pHi observed with enalaprilat correlated with predrug intramucosal-arterial PCO2 difference (r = .74, r2 = .55, p = .0005). These results demonstrate that enalaprilat improves gut perfusion as measured by gastric tonometry in critically injured patients, and that this effect appears to be independent of changes in systemic perfusion.

Sympathetic functions in NG-nitro-L-arginine-methyl-ester-induced hypertension: modulation by the renin-angiotensin system

BACKGROUND

Nitric oxide and angiotensin II have been shown to attenuate cardiac beta-adrenergic inotropism.

OBJECTIVE

To study sympathetic presynaptic and post-synaptic functions after chronic nitric oxide synthesis blockade with NG-nitro-L-arginine-methyl-ester (L-NAME, for 40 days) in association with renin-angiotensin system blockade (during the last 12 days) in order to evaluate the possible physiological interactions between these systems.

METHODS

Haemodynamic parameters in conscious rats were assessed. Release of noradrenaline from isolated atria and cardiac beta-adrenergic-adenylyl cyclase pathway in rats of sham-treated and L-NAME-treated groups, with or without losartan or enalaprilat treatment, were assessed.

RESULTS

L-NAME-treated rats developed a time-dependent increase in blood pressure associated with increased plasma adrenaline levels whereas plasma noradrenaline and cardiac catecholamine levels were similar to those in sham-treated rats. Field-stimulated release of noradrenaline, cardiac beta-adrenoceptor density and affinity and isoproterenol-stimulated formation of cyclic AMP were similar in sham and L-NAME-treated rats. However, Gpp(NH)p, NaF and forskolin-stimulated adenylyl cyclase activity were greater in L-NAME rats although Gs and Gi protein levels were similar in sham-treated and L-NAME-treated rats. Losartan and enalaprilat treatments exerted equipotent angiotensin-pressor response blockade and hypotensive effects whereas catecholamine levels were not altered. Interestingly, only losartan treatment acted to reduce the increased Gs-adenylyl cyclase activity in L-NAME rats, without alteration of G protein levels.

CONCLUSIONS

The nitric oxide synthase blockade-induced hypertension seems to be associated with increased adrenal-medullary system and renin-angiotensin system activities. The increased Gs-adenylyl cyclase activity after chronic inhibition of formation of nitric oxide suggests that nitric oxide plays a modulatory role in formation of cyclic AMP, to which angiotensin II seems to contribute through an angiotensin II type 1 receptor-mediated mechanism.

Short-term ACE inhibition has no effect on sodium and water excretion during PEEP ventilation

The short-term effect of intravenous (i.v.) angiotensin converting enzyme (ACE) inhibitor enalaprilat in 10 critically ill patients, being ventilated with positive end-expiratory pressure (PEEP), on sodium and water excretion was investigated. Mean arterial pressure (MAP) decreased. Heart rate and central venous pressure (CVP) did not change. Glomerular filtration rate (GFR), urine volume (V) and sodium excretion (UNaV) decreased in two patients with reduced MAP. GFR, V and UNaV increased in two patients with decreased MAP. No relation between changes in MAP and excretion was observed in six patients. ACE decreased in all patients. Plasma renin activity increased, aldosterone decreased, while atrial natriuretic peptide as well as antidiuretic hormone did not change. Enalaprilat did not facilitate sodium and water excretion during ventilation with PEEP. Decreased MAP indicates that the investigated patients were very dependent on their renin-angiotensin system to maintain systemic perfusion pressure. Base-line MAP and CVP values were no predictors of haemodynamic and excretory changes following acute ACE inhibition.

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

The present study was designed to identify an interaction between the renin-angiotensin system and noradrenergic transmission in the human heart. It is still under debate whether angiotensin II facilitates noradrenaline release in the heart. Clinical studies of congestive heart failure, involving systemic angiotensin-converting enzyme (ACE) inhibitor administration, have indicated anti-adrenergic effects, without giving a clear mechanistic picture. The influence on cardiac sympathetic transmission by local intracardiac administration of an ACE inhibitor has not been determined. Seven angina patients with normal left ventricular function, who underwent control coronary angiography after successful percutaneous transluminal coronary angioplasty were studied. Baseline measurements of haemodynamics and total and cardiac noradrenaline spillover were followed by handgrip exercise in the absence and presence of intracoronary enalaprilat infusion (0.05 mg min-1, 1 mL min-1). Baseline total body and cardiac noradrenaline spillover remained unchanged following intracoronary enalaprilat infusion, being 3745 +/- 349 and 3896 +/- 257 pmol min-1, and 148 +/- 56 and 149 +/- 55 pmol min-1, before and after drug administration, respectively. Mean arterial pressure, peripheral plasma renin activity and angiotensin II levels were also unaffected by enalaprilat infusion. During handgrip exercise procedures, both total body and cardiac noradrenaline spillover increased substantially, showing no reduction in the presence of intracardiac enalaprilat. Direct administration of the ACE inhibitor enalaprilat to the human heart failed to attenuate cardiac sympathetic drive during baseline conditions or following cardiac adrenergic activation by handgrip exercise. Thus, in the non-failing heart, without chronic adrenergic activation, no angiotensin II-facilitated effect on cardiac noradrenaline spillover could be detected.

Improvement in endothelial function by angiotensin converting enzyme inhibition in insulin-dependent diabetes mellitus

We postulated that nitric oxide (NO)-mediated endothelial function would be improved by acute and short-term treatment with an angiotensin converting enzyme (ACE) inhibitor in patients with type I diabetes mellitus, in whom endothelial function is depressed. Nine type I diabetic patients and eight healthy subjects underwent forearm blood flow measurement using strain gauge plethysmography during intraarterial infusion of incremental doses of endothelium-dependent (acetylcholine [ACh]) and endothelium-independent (sodium nitroprusside [SNP]) vasodilators. Pretreatment ACh responses were depressed in diabetic patients relative to the normal subjects (P < 0.05). No difference between the groups was evident in response to SNP. Acute ACE inhibition (with intrabrachial enalaprilat) enhanced ACh responses in the diabetic patients (P < 0.005), with a further improvement evident after 1 mo of oral therapy with enalapril (P < 0.001) when ACh responses were normalized. ACE inhibition did not affect SNP responses. We conclude that acute administration of the ACE inhibitor, enalaprilat, enhances NO-mediated endothelial function in type I diabetic patients, with further improvement evident after 4 wk of enalapril therapy.

Effect of central endogenous angiotensin II on sympathetic activation induced by hypoxia

This study examined the possible contribution of the brain renin-angiotensin system on the sympathetic activation induced by hypoxia in conscious rabbits. Blood pressure (BP), heart rate (HR) and renal sympathetic nerve activity (RSNA) were recorded under conditions of normoxia and hypoxia (10% O2 + 3% CO2) before and after fourth ventricular administration of either losartan (10 micrograms in 25 microliters), enalaprilat (500 ng in 25 microliters) or Ringer's (25 microliters). Hypoxia increased the RSNA by 113% and slightly decreased HR without changing BP. It also increased the variability of BP or HR in the 0.2-0.4 Hz frequency domain. Losartan and enalaprilat did not change the resting BP or HR but elevated the RSNA increase seen during hypoxia. Our results suggest that central angiotensin is involved in mediating response to chemoreceptor activation.