A Direct Comparison of Peptide Drug Delivery Systems Based on the Use of Hybrid Calcium Phosphate/Chitosan Nanoparticles versus Unmixed Calcium Phosphate or Chitosan Nanoparticles In Vitro and In Vivo

Nanocarriers provide a number of undeniable advantages that could improve the bioavailability of active agents for human, animal, and plant cells. In this study, we compared hybrid nanoparticles (HNPs) consisting of a calcium phosphate core coated with chitosan with unmixed calcium phosphate (CaP) and chitosan nanoparticles (CSNPs) as carriers of a model substrate, enalaprilat. This tripeptide analog is an inhibitor of angiotensin-converting enzyme and was chosen by its ability to lower intraocular pressure (IOP). In particular, we evaluated the physicochemical characteristics of the particles using dynamic light scattering (DLS) and scanning electron microscopy (SEM) and analyzed their ability to incorporate and release enalaprilat. HNPs exhibited the highest drug loading capacity and both HNPs and CSNPs demonstrated slow drug release. The comparison of the physiological effects of enalaprilat-loaded CaP particles, HNPs, and CSNPs in terms of their impact on IOP in rabbits revealed a clear advantage of hybrid nanoparticles over both inorganic and chitosan nanoparticles. These results could have important mechanistic implications for developing nano-based delivery systems for other medical, veterinary, and agricultural applications.

Exploration of chiral drugs as references for chiral discrimination of valsartan and voriconazole by tandem mass spectrometry

The use of mass spectrometry for chiral recognition and quantification has attracted great interest owing to its speed, sensitivity, specificity, and tolerance. However, searching for chiral selectors in chiral analyses using mass spectrometry is still problematic. In this study, chiral drugs could be applied as references for the chiral recognition and enantiomeric quantification of valsartan and voriconazole. Two novel pairs of metal-bound diastereomeric complex ions were detected by mass spectrometry, namely, nickel (II)-bound dimeric ions [NiII (2R,5S-emtricitabine) (S-valsartan)-H]+ and [NiII (2R,5S-emtricitabine) (R-valsartan)-H]+ and copper (II)-bound dimeric ions [CuII (S,S,S-enalaprilat) (2S,3R-voriconazole)-H]+ and [CuII (S,S,S-enalaprilat) (2R,3S-voriconazole)-H]+ . The resulting diastereomers were successfully identified based on the relative intensities of their characteristic fragments using tandem mass spectrometry. The logarithm of the characteristic fragment ion abundance ratio exhibited a good linear relationship with the enantiomeric excess. Density functional theory calculations were also performed to elucidate the mechanism of the structural differences observed in the MS results. This established approach proves that chiral drugs can serve as ligands for the rapid recognition and quantitative analysis of other chiral drugs without a chiral chromatographic column or complex sample pretreatment.

The Influence of Structural Variants of the CES1 Gene on the Pharmacokinetics of Enalapril, Presumably Due to Linkage Disequilibrium with the Intronic rs2244613

Variants in the CES1 gene encoding carboxylesterase 1 may affect the metabolism of enalapril to the active metabolite enalaprilat. It was shown that the A allele of rs71647871 and the C allele of rs2244613 led to a decrease in plasma enalaprilat concentrations. This study aimed to estimate the effect of structural haplotypes of CES1 containing the pseudogene CES1P1, or a hybrid of the gene and the pseudogene CES1A2, on the pharmacokinetics of enalapril. We included 286 Caucasian patients with arterial hypertension treated with enalapril. Genotyping was performed using real-time PCR and long-range PCR. Peak and trough plasma enalaprilat concentrations were lower in carriers of CES1A2. The studied haplotypes were in linkage disequilibrium with rs2244613: generally, the A allele was in the haplotype containing the CES1P1, and the C allele was in the haplotype with the CES1A2. Thus, carriers of CES1A2 have reduced CES1 activity against enalapril. Linkage disequilibrium of the haplotype containing the CES1P1 or CES1A2 with rs2244613 should be taken into account when genotyping the CES1 gene.

The design and properties of N-carboxyalkyldipeptide inhibitors of angiotensin-converting enzyme

Angiotensin-converting enzyme inhibitors promise to make important therapeutic contributions to the control of hypertension and congestive heart failure. The nonapeptide teprotide was the first of these inhibitors to be tested clinically. It was followed by orally active inhibitors, captopril in 1977 and enalapril in 1980. The latter is representative of a new design for the inhibition of metallopeptidases and is the subject of this review. The best of the N-carboxyalkyldipeptide inhibitors inhibits angiotensin-converting enzyme with a Ki of 7.6 X 10(-11) M. This compound is the most potent competitive inhibitor of a metallopeptidase yet to have been reported. The basis of this high potency is beginning to be understood and in part is considered to involve precisely arranged multiple interactions within the enzyme active site. X-ray crystallography of a thermolysin-inhibitor complex has been achieved. Assuming that similar interactions within the active site of angiotensin-converting enzyme are mechanistically probable, the authors hypothesize the binding of enalaprilat to converting enzyme as shown in Figure 24. Such interactions are consistent with kinetic studies (Section V) with the understanding that binding to the enzyme is not sensitive to the inhibitor's state of NH protonation. The reason for this surprising conclusion has not been established. Perhaps counterbalancing factors are involved in the energetics of binding or there may be compensating adjustments made in the enzyme which permit NH protonated and nonprotonated inhibitor to bind equally well. Figure 24 also summarizes present understanding of the conformation of enalaprilat when bound to angiotensin-converting enzyme. From studies on conformationally defined analogs of enalaprilat, it seems likely that the Ala-Pro segment of enalaprilat binds in a conformation that is close to a minimum energy conformer. This situation no doubt contributes to the potency of enalaprilat, since little binding energy would be needed to induce conformational changes in this part-structure of enalaprilat when it is bound to the enzyme. The phenethyl group of enalaprilat is believed to be near the alpha-hydrogen of the L-Ala residue in the enzyme-inhibitor complex. However, the synthesis of conformationally restricted analogs to establish this point has not yet been reached. The N-carboxyalkylpeptide design was developed from Wolfenden's collected product inhibitors of carboxypeptidase-A. Whether or not N-carboxyalkyldipeptides should be classified as collected product or transition state inhibitors is unclear.(ABSTRACT TRUNCATED AT 400 WORDS)

Differentiation between acute cyclosporine nephrotoxicity and acute tubular necrosis using enalaprilat renal scintigraphy in rats

RATIONALE AND OBJECTIVES

Acute cyclosporine (CsA) nephrotoxicity cannot be easily differentiated from other renal parenchymal complications, such as acute tubular necrosis (ATN), that cause renal function impairment at the early posttransplantation period. The purpose of this study was to differentiate acute CsA nephrotoxicity from ATN using enalaprilat renal scintigraphy in rats.

METHODS

Twenty-six rats were divided into 4 experimental groups: CsA group, who were treated with CsA (50 mg/kg/d) for 2 days; ATN group, who received clamping of both renal arteries for 45 minutes; vehicle group, who were treated with olive oil (1 mL/kg/d) for 2 days; and sham-operated group, who received the same surgical procedure as ATN group without clamping of renal arteries. The baseline study was performed with 300 microCi of technetium-99m diethylenetriaminepentaacetic acid and enalaprilat scintigraphy with 2 mCi of technetium-99m diethylenetriaminepentaacetic acid 5 minutes after intravenous enalaprilat injection (30 microg/kg). The changes of renogram grade and the renal function indices such as T(max), T(1/2), residual cortical activity, and mean transit time between 2 studies were analyzed. Immediately after renal scintigraphy, blood urea nitrogen and serum creatinine levels were measured and renal tissues stained by periodic acid Schiff reaction were examined in each group.

RESULTS

Blood urea nitrogen and serum creatinine levels in the CsA and ATN groups were higher than their control groups (P < 0.05). Histologic study revealed severe ischemic necrosis of tubular epithelium in ATN group, but the other groups remained with essentially normal morphology. After enalaprilat injection, renal function indices became improved in CsA group, whereas they deteriorated in ATN group. The renogram grade was decreased in CsA group and increased or unchanged in ATN group after enalaprilat injection. The T(max), residual cortical activity, and mean transit time ratio were statistically different between the 2 groups on enalaprilat study (P < 0.05).

CONCLUSIONS

These results suggest that enalaprilat renal scintigraphy could be used clinically in differentiating acute CsA nephrotoxicity from ATN after renal transplantation.

Tyrosine kinase involvement in renal arteriolar constrictor responses to angiotensin II

Experiments were performed to test the hypothesis that tyrosine kinase activity contributes to renal arteriolar contractile responses to angiotensin (Ang) II. Rats were subjected to short-term enalaprilat treatment to decrease endogenous Ang II formation before tissue was harvested for experiments with the in vitro blood-perfused juxtamedullary nephron technique. Acute surgical papillectomy was used to avoid the indirect afferent arteriolar effect of Ang II that arises through increased tubuloglomerular feedback sensitivity. Arteriolar lumen diameter responses to 1 and 10 nmol/L Ang II were monitored by videomicroscopic methods before and during treatment with various tyrphostin compounds: 100 micromol/L AG18 (broad-spectrum tyrosine kinase inhibitor), 100 nmol/L AG1478 (selective epidermal growth factor receptor tyrosine kinase inhibitor), or 100 micromol/L AG9 (inactive analog). Baseline afferent arteriolar lumen diameter averaged 23.5+/-1.2 micrometer and was not influenced by any tyrphostin. Ang II (10 nmol/L) decreased afferent diameter by 11.1+/-1.0 micrometer under untreated conditions, a response that was not altered by AG9 but significantly blunted by AG18 (34+/-9% inhibition) or AG1478 (52+/-8% inhibition). AG18 did not suppress afferent arteriolar contractile responses to membrane depolarization (20 to 55 mmol/L K(+ )bath). Efferent arteriolar baseline diameter averaged 24.1+/-0.8 micrometer and was unaltered by AG18 or AG1478; however, efferent diameter responses to 10 nmol/L Ang II were diminished 52+/-10% by AG18 and 51+/-13% by AG1478. These observations indicate that Ang II signaling in renal afferent and efferent arteriolar vascular smooth muscle is either mediated or modulated by tyrosine kinase activity, including that of the epidermal growth factor receptor tyrosine kinase.

Angiotensin-converting enzyme inhibitor-enhanced phase-contrast MR imaging to measure renal artery velocity waveforms in patients with suspected renovascular hypertension

OBJECTIVE

We investigated the usefulness of phase-contrast MR imaging to measure renal artery velocity waveforms as an adjunct to renal MR angiography. We also examined whether an angiotensin-converting enzyme (ACE) inhibitor improves the diagnostic accuracy of waveform analysis.

SUBJECTS AND METHODS

Thirty-five patients referred for MR angiography of renal arteries underwent non-breath-hold oblique sagittal velocity-encoded phase-contrast MR imaging through both renal hila (TR/TE, 24/5; flip angle, 30 degrees; signal averages, two; encoding velocity, 75 cm/sec) before and after i.v. administration of an ACE inhibitor (enalaprilat). We analyzed velocity waveforms using established Doppler sonographic criteria. A timing examination with a test bolus of gadolinium contrast material was performed to ensure optimal arterial enhancement during breath-hold gadolinium-enhanced three-dimensional gradient-echo MR angiography.

RESULTS

MR phase-contrast waveform pattern analysis was 50% (9/18) sensitive and 78% (40/51) specific for the detection of renal artery stenosis equal to or greater than 60% as shown on MR angiography. Sensitivity (67%, 12/18) and specificity (84%, 42/50) increased slightly, but not significantly, after i.v. administration of an ACE inhibitor. Also, the accuracy of quantitative criteria such as acceleration time and acceleration index did not improve after the administration of ACE inhibitor.

CONCLUSION

Renal hilar velocity waveforms, measured using non-breath-hold MR phase-contrast techniques with or without an ACE inhibitor, are insufficiently accurate to use in predicting renal artery stenosis.

Effect of angiotensin converting enzyme inhibition on the Doppler waveform in dogs with renal artery stenosis

Our objective was to investigate whether the angiotensin converting enzyme inhibitor enalaprilat improves detection of hemodynamically significant renal artery stenoses in dogs. Renal artery stenoses of 50 to 99% were surgically created unilaterally in five dogs. Doppler ultrasonographic evaluation was performed at baseline (no stenosis), after creation of the stenosis, and after the administration of enalaprilat. The resistive index increased in the nonstenotic kidney (P < 0.01) but not in the stenotic kidney after administration of enalaprilat. The difference in resistive indices between nonstenotic and stenotic kidneys increased significantly (P < 0.05) after administration of enalaprilat. Measurement of the resistive index after administration of an angiotensin converting enzyme inhibitor in humans may improve the performance of Doppler ultrasonography in detecting hemodynamically significant renal artery stenoses.

Distribution and functional significance of cardiac angiotensin converting enzyme in hypertrophied rat hearts

BACKGROUND

The intracardiac conversion rate of angiotensin (Ang) I to Ang II and the expression of angiotensin converting enzyme (ACE) mRNA are amplified in rat hearts with left ventricular hypertrophy (LVH). To examine whether the accelerated intracardiac Ang II generation in LVH is related to an induction of cardiac ACE, we studied localization and function of cardiac ACE in hypertrophied rat hearts using specific ACE inhibitors.

METHODS AND RESULTS

Cardiac ACE was localized and quantified in hearts from male Wistar rats with LVH due to chronic experimental aortic stenosis and from control rats. With the ACE inhibitor 125I-351A, a derivative of lisinopril, as a radioligand on coronal sections of LVH and control hearts, in vitro autoradiography demonstrated ACE binding in aorta, coronary arteries, atria, and ventricles of both groups. Quantitative analyses revealed that ACE density (counts per minute per cross-sectional area of tissue) was twofold higher within the myocardium of hypertrophied left ventricles compared with controls (p < 0.005). Quantitative morphometry demonstrated a modest increase in the fractional volume of myocytes as well as capillary volume without an increase in the fractional volume of endothelial cells in left ventricular tissue from aortic stenosis rats. These data suggest that an increase in endothelial cell volume per se cannot alone account for the observed doubling of ACE density and support an upregulation of ACE production in hypertrophied tissue. The role of cardiac ACE in intracardiac conversion of Ang I to Ang II and its specific inhibition was studied in isolated, isovolumic beating, buffer-perfused LVH and control hearts. Biochemical conversion rates as well as functional changes in response to 3 x 10(-7) M Ang I were examined in the absence or presence of the ACE inhibitor enalaprilat (4 x 10(-6) M). After a brief stabilization period, groups of LVH and control hearts were subjected to the following infusion protocols: 15 minutes of vehicle followed by 30 minutes of Ang I plus vehicle, 15 minutes of enalaprilat followed by 30 minutes of Ang I plus enalaprilat (enal/Ang I), or 45 minutes of vehicle only to allow comparison with a time control. Intracardiac Ang I-to-Ang II conversion rate was fourfold higher in LVH than in control hearts (p < 0.05). Infusion of enalaprilat reduced the intracardiac Ang I-to-Ang II conversion rate in LVH hearts by 70% (p < 0.05 versus Ang I). At similar levels of constant coronary flow per gram, Ang I increased coronary perfusion pressure by 23 +/- 5 mm Hg (p < 0.01 versus vehicle) in LVH hearts and by 36 +/- 10 mm Hg (p < 0.005 versus vehicle) in control hearts. When enalaprilat was infused with Ang I, the increase in perfusion pressure was limited to 5 +/- 5 mm Hg (NS versus vehicle) in LVH hearts and 12 +/- 3 mm Hg (p < 0.05 versus vehicle) in control hearts and was significantly lower than in hearts infused with Ang I only (p < 0.05 in LVH and p < 0.05 in control hearts, respectively). Systolic function was not affected by either infusion protocol. In contrast, Ang I infusion was associated with diastolic dysfunction. In LVH hearts, left ventricular end-diastolic pressure (LVEDP) increased from 10 +/- 1 mm Hg at baseline to 25 +/- 2 mm Hg at the end of the Ang I infusion (p < 0.001 versus vehicle), which was inhibited by infusion of enalaprilat. In control hearts, there was a lesser increase in LVEDP from 10 +/- 1 mm Hg to 15 +/- 1 mm Hg in response to Ang I (p < 0.05 versus LVH). Control hearts treated with enalaprilat with Ang I displayed no increase in LVEDP:

CONCLUSIONS

These observations indicate that ACE protein is increased within the myocardium of LVH hearts, extending recent findings of increased cardiac ACE activity and mRNA levels in this model of pressure-overload LVH in the rat. Blockade of the enzyme by an ACE inhibitor decreases intracardiac Ang I-to-Ang II conversion rate and prevents the functional changes of Ang I-to-Ang II activation

Enalaprilat-enhanced renography in a rat model of renovascular hypertension

The effect of rapid converting enzyme inhibition (CEI) with intravenous enalaprilat on technetium-99m-(99mTc) diethylenetriaminepentaacetic acid (DTPA) and 99mTc-dimercaptosuccinic acid (DMSA) renograms was evaluated in rats with two-kidney, one-clip renovascular hypertension. Rapid sequential DTPA renograms, performed immediately before and five minutes after enalaprilat injection (30 micrograms/kg), demonstrated a selective decrease in clipped kidney DTPA plasma clearance following CEI and no significant effect on unclipped kidney function. Pre- and post-CEI data were obtained with a single injection of DMSA by administering enalaprilat five minutes after the radiopharmaceutical. Enalaprilat slowed the rate of DMSA accumulation in clipped relative to unclipped kidneys, and reduced the clipped/unclipped kidney ratio of absolute DMSA uptake at 10 and 30 min. DTPA and DMSA were equally effective in demonstrating the CEI effect. Enalaprilat was also compared with captopril (3 mg/kg, intraperitoneally), using sequential DTPA renograms. Clipped kidney DTPA plasma clearance was reduced to an identical degree (40%) by both converting enzyme inhibitors. Clinical renographic protocols can probably be devised to take advantage of the rapid, reliable CEI of enalaprilat, thereby shortening total procedure time.

Kinetics and dynamics of enalapril in patients with liver cirrhosis

The pharmacokinetics and pharmacodynamics (blood pressure, heart rate, serum angiotensin-converting enzyme, and plasma renin activity) of enalapril and enalaprilat were studied after oral administration of enalapril maleate (10 mg) to seven biopsy-proven cirrhotic patients and to seven healthy subjects. The mean Cmax, AUC, and urinary excretion of enalapril and enalaprilat were greater and less (p less than 0.01), respectively, and mean oral clearance of enalapril was less (p less than 0.01) in the cirrhotic group than in the healthy group. However, there was no significant difference in the mean total drug (enalapril plus enalaprilat) excretion between the two groups. Blood pressure fell (p less than 0.05) only at 3 or 4 hours postdose, with no change in heart rate in the two groups. Serum angiotensin-convering enzyme (ACE) decreased (p less than 0.001) and plasma renin activity (PRA) increased (p less than 0.05) in the two groups. The magnitude of the percentage of inhibition of ACE activity was comparable between the two groups. Serum enalaprilat concentration correlated (p less than 0.001) with the percentage of inhibition of ACE activity. The results suggest that the bioactivation of enalapril to enalaprilat is considerably impaired in patients with cirrhosis but that the pharmacodynamic effects do not appear to be blunted in those patients. The mechanism and clinical implications remained unclear.

Kinin antagonist reverses converting enzyme inhibitor-stimulated vascular prostaglandin I2 synthesis

Treatment with a converting enzyme inhibitor has been shown to stimulate aortic prostaglandin I2 synthesis. We studied whether converting enzyme inhibitor-stimulated prostaglandin I2 synthesis might be mediated by kinins. Anesthetized male Sprague-Dawley rats were given a continuous 70-minute infusion of either saline or a kinin analogue antagonist, [DArg0-Hyp3-Thi5-DPhe7-Thi8]bradykinin, 8 micrograms/kg/min. After 10 minutes, rats were given an intravenous bolus of either vehicle or the converting enzyme inhibitor enalaprilat (30 micrograms/100 g body wt). After 70 minutes, aorta and renal cortical slices were harvested and incubated in vitro in buffer without drugs at pH 7.4, 37 degrees C for 60 minutes. The buffer was then sampled for measurement of 6-keto prostaglandin F1 alpha (an index of prostaglandin I2), prostaglandin E2, and renin release (angiotensin I generation) by radioimmunoassay. The aortic prostaglandin I2 from rats treated with converting enzyme inhibitor was significantly elevated (36.7 +/- 5.0 ng/mg dry wt/hr) compared with aorta from rats treated with either vehicle (25.6 +/- 2.2 ng/mg/hr), kinin antagonist (25.1 +/- 2.4 ng/mg/hr), or kinin antagonist plus converting enzyme inhibitor (23.0 +/- 2.0 ng/mg/hr), p less than 0.02. There were no differences in aortic prostaglandin E2, renin release, or prostaglandin E2 from renal cortical slices. Direct in vitro incubation of aorta with molar concentrations of converting enzyme inhibitor from 10(-9) to 10(-4) had no effect on prostaglandin I2. These results suggest that kinins may mediate the effect of converting enzyme inhibition on aortic prostaglandin I2 synthesis and thereby may account for part of the hemodynamic responses resulting from treatment using converting enzyme inhibitors.

Visual compatibility of enalaprilat with commonly used critical care medications during simulated Y-site injection

Physical incompatibility studies between an intravenous angiotensin-converting enzyme inhibitor, enalaprilat, and potentially coadministrable ICU medications have been performed. Forty-one medications and four solutions were evaluated. The medications were anesthetic/narcotics, antibiotics, an anticoagulant, a bronchodilator, electrolyte solutions, fluids, H-2 receptor blocking agents, steroids and vasoactive agents. There was no turbidity, precipitation, or color change caused by the admixing of enalaprilat with any of the 45 agents studied. This study did not take bioavailability into consideration.

Consequences of angiotensin-converting enzyme inhibitor overdose

Overdose with angiotensin-converting enzyme (ACE) inhibitors is still a relatively underreported phenomenon. We report here a case of an unintentional overdose of enalapril (100 mg) together with other medications. The patient experienced no adverse consequences. Pharmacokinetic evaluation revealed a t 1/2 for enalaprilat (prodrug) of seven hours and for enalapril at 36 hours. Based on this case report as well as others, guidelines for assessment and treatment of these patients are proposed. Management of hypotension is the primary therapeutic intervention.

An in vitro study of interactions between doxazosin and enalaprilat at vascular alpha 1-adrenoceptors

1. Isolated perfused male Sprague-Dawley rat tail artery segments were used to investigate interactions between the alpha-1-adrenoceptor antagonist, doxazosin, and the angiotensin converting enzyme (ACE) inhibitor, enalaprilat, using phenylephrine (PE) as the alpha 1-adrenoceptor agonist. 2. In concentrations of up to 10(-5) mol/L, enalaprilat had no effect on arterial responses to PE. 3. Doxazosin produced a concentration-dependent competitive alpha 1-adrenoceptor antagonism, yielding a mean pA2 value of 8.72. 4. In the continuous presence of 10(-6) mol/L enalaprilat, doxazosin with a pA2 value of 9.10 was a 2.4-fold more potent alpha 1-adrenoceptor antagonist than in the absence of enalaprilat. 5. These results are interpreted to indicate that endogenously produced angiotensin II can modulate the activity of alpha 1-adrenoceptors in vascular smooth muscle.

The effect of local angiotensin converting enzyme inhibition on the action of atrial natriuretic peptide in the human forearm

It has been suggested that angiotensin converting enzyme (ACE) may play a role in the metabolism of atrial natriuretic peptide (ANP), and that ANP may interfere with angiotensin-induced vasoconstriction. This has been investigated within the forearm vascular bed during local ANP infusion and ACE inhibition. Six normotensive volunteers were studied, each on two occasions. On both occasions, after saline infusion, volunteers were given initially a 20 min infusion of ANP at 0.1 microgram/min via the brachial artery. This was followed, after 20 min, by a second infusion of ANP at the same dose, co-infused with enalaprilat (5 micrograms/min) on one occasion, and placebo (saline) on the other (in random order). Forearm blood flow was measured using venous occlusion plethysmography with mercury-in-silastic strain gauges. Blood flow in the cannulated arm increased significantly during the first ANP infusion; by 52 +/- 15% before placebo (P less than 0.05), and by 41 +/- 8% before enalaprilat (P less than 0.005). This increase was similar with the second ANP infusion during co-infusion of either placebo (40 +/- 10%) or enalaprilat (45 +/- 11%). Enalaprilat did not affect the half-life of vasodilatation produced by ANP (t1/2 = 5 min). These studies in healthy subjects demonstrate no effect of local ACE inhibition on resting blood flow, or on the vasodilatation produced by ANP in the human forearm, and provide no evidence of a role of ACE in the metabolism of ANP in this vascular bed.

ACE-inhibitor-induced enhancement of spontaneous and IgE-mediated histamine release from mast cells and basophilic leukocytes and the modulatory effect of capsaicin sensitive nerves

Frequently reported adverse inflammatory skin and airway reactions have been reported in subjects being medicated with angiotensin converting enzyme (ACE)-inhibitors. Intradermally evoked wheal and flare reactions to ovalbumin, capsaicin and bradykinin, in ovalbumin sensitized guinea pigs, was previously demonstrated to be enhanced by pretreatment with the ACE-inhibitor MK 422 (the active parent diacid of enalapril). In vitro results from this study demonstrate that the ACE-inhibitor MK 422 degranulated guinea pig lung and skin mast cells as well as human basophils, and enhanced allergen-evoked histamine release. Local capsaicin pretreatment in vivo of guinea pig skin decreased spontaneous and allergen-triggered release of histamine in vitro from skin mast cells. No clear enhancing effect of MK 422 was seen on the allergen-triggered histamine release in vitro from capsaicin pretreated skin, and the spontaneous release was unaffected by the ACE-inhibitor. The allergen-triggered wheal and flare reaction in ovalbumin sensitized guinea pigs was potentiated by MK 422 and the late phase reaction of the inflammatory response was especially augmented. Capsaicin pretreatment of the guinea pigs abolished this late phase reaction as well as the inflammatory enhancing effect of MK 422. Our in vitro results from capsaicin pretreated skin indicate that the reduced inflammatory response in vivo in capsaicin pretreated skin is due not only to capsaicin induced depletion of neuropeptides from sensory nerves, but also to secondary degranulation of mast cells by one or more of these peptides.

High-affinity binding of the converting enzyme inhibitor, ramiprilat, to isolated human glomeruli

Evidence for effects of angiotensin converting enzyme (ACE) on isolated human glomeruli was provided using specific binding of tritium-labeled ramiprilat, a potent inhibitor of ACE. [3H]ramiprilat bound to isolated glomeruli, depending on time and temperature, displaying a KD of 3.8 nmol/L and a Bmax of 853 fmol/mg protein. Specific binding represented more than 90% of total binding. Dissociation occurred rapidly after dilution of the sample with incubation buffer or after addition of an excess of unlabeled inhibitor. Binding of [3H]ramiprilat was also inhibited by increasing concentrations of enalaprilat, another ACE inhibitor. ACE is a zinc-containing enzyme. Addition of EGTA to the assay, which chelates zinc ions, completely prevented binding. This was reversed by divalent Zn2+ and Ca2+ ions, but not by magnesium. Binding of [3H]ramiprilat to isolated glomeruli was maximal at pH 8, which also is optimal for ACE activity. The binding of [3H]ramiprilat to isolated human glomeruli is specific, and resembles the characteristics which have been found earlier for enzyme activity of ACE. Thus, binding of [3H]ramiprilat to isolated glomeruli can be assumed to be directed to ACE.

Inhibition of serotonin release by bombesin-like peptides in rat hypothalamus in vitro

We investigated the activity of bombesin (BN), neuromedin-C (NM-C) and neuromedin-B (NM-B) on serotonin (5-HT) release and reuptake in rat hypothalamus (HYP) in vitro. BN and NM-C but not NM-B (all 1 microM) decreased K+ evoked 3H-5-HT release from superfused HYP slices by 25%. Bacitracin (BCN, 2 micrograms/ml), a nonspecific peptidase inhibitor, reversed the inhibitory effect of BN on K+ evoked 3H-5-HT release. Phosphoramidon (PAN, 10 microM) an endopeptidase 24.11 inhibitor, abolished the inhibitory effect of BN, but not NM-C, on K+ evoked 3H-5-HT release. The peptidyl dipeptidase A inhibitor enalaprilat (ENP, 10 microM), enhanced both BN and NM-C inhibition of 3H-5-HT release. Bestatin (BST, 10 microM) had no effect on BN or NM-C inhibitory activity on 3H-5-HT release. Neither BN, NM-C nor NM-B affected reuptake of 3H-5-HT into HYP synaptosomes alone or in combination with any of the peptidase inhibitors, nor did these peptides alter the ability of fluoxetine to inhibit 3H-5-HT uptake. These data suggest: a) that BN-like peptides may alter neurotransmission in the HYP by acting presynaptically on the 5-HT release mechanism; b) a similarity in the structural requirements for the BN induced inhibition of 5-HT release and BN evoked thermoregulatory disturbances; and c) that peptidases may selectively augment or reduce pharmacologic activity of BN-like peptides upon CNS administration.

Regulation of regional vascular tone: the role of angiotensin conversion in human forearm resistance vessels

Inhibition of the action of endothelially-located angiotensin converting enzyme (ACE) in blood vessels of the human forearm was studied using enalaprilat, the active metabolite of the prodrug enalapril. In a dose of 5 micrograms/min enalaprilat inhibits arteriolar vasoconstriction in response to angiotensin I (Ang I) and enhances vasodilation in response to bradykinin. At this dose enalaprilat had no effect on resting forearm blood flow, or on the reduction in forearm blood flow in response to application of lower body negative pressure, in subjects with normal sodium intake. Following sodium depletion, however, enalaprilat produced an increase in resting forearm blood flow compared with the response in the same subjects under normal-sodium conditions. It appears that local ACE within forearm resistance vessels of healthy volunteers is unlikely to play an important role in regulation of local vascular tone in the sodium-replete state. However, in sodium-depleted subjects, and perhaps also in other circumstances where circulating concentrations of Ang I are elevated, local ACE may significantly affect vascular tone.

Pharmacokinetics of lisinopril, enalapril and enalaprilat in renal failure: effects of haemodialysis

1. Lisinopril and enalapril were administered as 2.5 mg single doses and as eight single daily 2.5 mg doses to separate groups of six patients with chronic renal failure. Patients were receiving regular haemodialysis. 2. In the absence of haemodialysis, the decline in plasma concentrations of lisinopril and enalaprilat was extremely slow and plasma concentrations were generally high. 3. Haemodialysis had large effects on plasma concentrations of lisinopril and enalaprilat. A 4 h period reduced plasma concentrations of both drugs by around one-half and often by significantly more than this. Even 1 or 2 h of haemodialysis had significant effects. 4. Haemodialysis plasma clearance was similar for both drugs with mean values of the order of 40 ml min-1. Clearance did not markedly differ when measured after 1, 2 or 4 h of haemodialysis or after single or multiple doses of lisinopril or enalapril. 5. The design of dosage regimens of both lisinopril and enalapril for patients with severe renal impairment or chronic renal failure should take into consideration the use and effects of haemodialysis.

Age-related changes in angiotensin II-stimulated proximal tubule fluid reabsorption in the spontaneously hypertensive rat

The development of hypertension in the spontaneously hypertensive rat (SHR) up to 8 weeks of age involves sodium retention with reduced fractional sodium excretion. Since angiotensin II (Ang II) directly stimulates proximal tubular sodium transport, we investigated age-related changes in proximal reabsorption (Jv), using shrinking split-drop micropuncture before and after enalaprilat in SHR at 5, 7 and 12 weeks of age and in age-matched Wistar-Kyoto rats (WKY). Control values for Jv were higher in the SHR than in WKY at 5 weeks, but lower at 7 and 12 weeks, consistent with an early phase of sodium retention. Enalaprilat reduced mean Jv by approximately 15% in all WKY groups, indicating the extent of Ang II-stimulated transport. In the SHR there was an age-dependent reduction in the effect of enalaprilat on Jv, and by 12 weeks no Ang II stimulation could be detected. Age-related changes in proximal tubular reabsorption could contribute to sodium retention in the young SHR and may reflect a more general pattern of inherited transport defects.

Effect of intravenous enalaprilat in moderate and severe systemic hypertension

The antihypertensive effect and tolerability of enalaprilat, an intravenously administered angiotensin converting enzyme inhibitor, was studied in 65 patients with moderate or severe hypertension. In this randomized, double-blind study, enalaprilat was compared with placebo in 42 (22 enalaprilat, 20 placebo) moderate hypertensive (diastolic blood pressure [BP] 100 to 114 mm Hg) patients. It was compared with furosemide in 23 (12 enalaprilat, 11 furosemide) severe hypertensive (diastolic BP 115 to 130 mm Hg) patients. Enalaprilat (1.25 or 5.0 mg), placebo (5% dextrose) or furosemide (40 or 80 mg) was given every 6 hours intravenously up to 48 hours. In the moderate hypertension stratum, the mean supine diastolic BP was significantly (p less than or equal to 0.01) reduced from baseline at all timepoints in the enalaprilat group. These diastolic BP reductions were significantly (p less than or equal to 0.01) greater in the enalaprilat group than the placebo at 1 to 24 hours (-12 vs -4 mm Hg), with 59% of the patients responding to enalaprilat compared with 30% of the patients responding to placebo. An even greater reduction (p less than or equal to 0.01) was seen at 25 to 48 hours (-14 vs -7 mm Hg, with 73% enalaprilat vs 58% placebo responders). Significant (p less than or equal to 0.01) reductions in mean, supine systolic BP were also seen at 1 to 24 hours (-22 vs -2 mm Hg) and 25 to 48 hours (-24 vs -8 mm Hg) during the 48 hours of the double-blind treatment phase in the enalaprilat group compared with placebo.(ABSTRACT TRUNCATED AT 250 WORDS)

Resistance to blockade by saralasin of effect of ACE inhibitors in conscious sodium-restricted dog

Comparison of the effect of captopril and enalaprilat was made on mean systemic arterial blood pressure (BP), renal blood flow (RBF), and renal vascular resistance (RVR) of conscious sodium-replete and sodium-restricted dogs (plasma renin activity = 6.66 ng angiotensin I.ml-1.h-1). BP was decreased by -8 +/- 2 mmHg and RBF was increased by 34 +/- 12 ml/min with captopril given intravenously and by -5 +/- 2 mmHg and 28 +/- 7 ml/min with enalaprilat in sodium-replete dogs. The respective changes in BP and RBF in sodium-restricted dogs were -29 +/- 2 mmHg and 62 +/- 12 ml/min with captopril and -25 +/- 6 mmHg and 53 +/- 18 ml/min with enalaprilat. Saralasin infused intra-arterially to the kidney significantly blocked the increase in RBF seen after angiotensin-converting enzyme (ACE) inhibition in sodium-replete dogs, and reduced the increase in RBF in sodium-restricted dogs, but the latter effect was not statistically significant. A more moderate increase in plasma renin activity was established in another group of sodium-restricted dogs, and saralasin was administered intravenously instead of intra-arterially. Enalaprilat increased RBF in these dogs in the presence of a saralasin blockade (42 +/- 7 ml/min), and this effect was not significantly changed by prior administration of indomethacin (28 +/- 6 ml/min). The results suggest that blockade of the influence of the renin-angiotensin system and possibly another vasodilator mechanism, such as kinin potentiation, account for the increase in RBF after ACE inhibition in the low-sodium state.

Pharmacological profiles of CS-622, a novel angiotensin converting enzyme inhibitor

CS-622 is a prodrug type ACE inhibitor with a thiazepin ring. Its active form, CS-622 diacid, was slightly more potent than enalaprilat in inhibiting ACE isolated from rabbit lung. The inhibitory potency of CS-622 diacid on isolated rat aorta was 3 times that of enalaprilat. The inhibitory action of enalaprilat was abolished quickly by washing the aortic strip with drug-free solution, whereas that of CS-622 diacid was abolished only slowly. This difference suggests that CS-622 diacid binds to vascular ACE more firmly than enalaprilat. By oral administration, CS-622 was 3 times more potent than enalapril, and its onset of action was faster than that of enalapril, suggesting that the conversion of CS-622 to its active diacid occurs faster than the conversion of enalapril. Although CS-622 diacid was only slightly more potent than enalaprilat by intravenous administration, it had a longer duration than enalaprilat. Elimination of renal excretory function potentiated the action of captopril but not that of CS-622, suggesting that unlike captopril, only a small portion of CS-622 is excreted through the kidney.

Angiotensin influences on tubuloglomerular feedback mechanism in hypertensive rats

The tubuloglomerular feedback (TGF) mechanism was evaluated in the nonclipped kidney of Goldblatt hypertensive rats from both stop flow pressure (SFP) and single nephron glomerular filtration rate (SNGFR) responses to step increases in late proximal perfusion rate from 0 to 40 nl/min. During control conditions, increases in late proximal perfusion rate produced flow dependent decreases in SFP and SNGFR with maximal values of 10.2 +/- 1.0 mm Hg and 12.9 +/- 2.5 nl/min, values similar to those obtained in normal rats. During ACE inhibition (MK 422; 0.6 mg/kg/hr), arterial pressure decreased from 168 +/- 8 to 137 +/- 7 mm Hg and there was a marked attenuation in the magnitude of SFP feedback responses (delta = 2.5 +/- 0.3 mm Hg). SNGFR feedback responses, however, were not significantly impaired. Direct decreases in renal arterial pressure reduced control SFP but SFP feedback responses were maintained, indicating that the attenuated SFP feedback responses during ACE inhibition were not due to decreased arterial pressure. Superimposed infusion of angiotensin II during ACE inhibition partially restored SFP feedback responses. In contrast, norepinephrine infusion did not result in a similar restoration of SFP feedback sensitivity. These results indicate that the nonclipped kidney of Goldblatt hypertensive rats has an intact TGF mechanism as assessed from SFP and SNGFR feedback responses. Furthermore, ACE inhibition attenuates SFP but not SNGFR feedback responses, and systemic angiotensin II infusions can restore SFP feedback responsiveness towards normal.

Diagnosis of unilateral renovascular hypertension: comparative effect of intravenous enalaprilat and oral captopril

The effectiveness of 2 angiotensin converting enzyme inhibitors, intravenous enalaprilat and oral captopril, in stimulating renin secretion was compared in 47 hypertensive patients with suspected renovascular hypertension. Both inhibitors were more effective stimuli to renin secretion than head-up tilting of the patient. In patients with unilateral renovascular hypertension single doses of angiotensin converting enzyme inhibitors increased the renal venous renin ratio compared to the recumbent ratio. This therapy reduced the number of false negative studies more effectively than head-up tilting and was tolerated better. Contralateral suppression of renin in the unaffected kidney, an important ancillary diagnostic marker of unilateral renovascular hypertension, was preserved. No false positive studies owing to the use of angiotensin converting enzyme inhibitors acutely were apparent. Mean arterial pressure decreased by 5 minutes with intravenous enalaprilat and by 20 minutes with oral captopril, and it continued to decrease gradually for at least 2 hours. No significant syncopal symptoms were observed with either inhibitor. Plasma renin activity increased by 5 and 15 minutes with enalaprilat and captopril, respectively. Plasma aldosterone levels decreased by 10 minutes with enalaprilat and by 30 minutes with captopril, and these changes increased in magnitude during the 2 hours of observation. To achieve the maximum diagnostic effectiveness from the renal venous renin ratio, single dose angiotensin converting enzyme inhibitors warrant consideration for routine use. Intravenous enalaprilat may be preferable because of certain achievement of an effective blood level.

Suppression of in vitro granulocytopoiesis by captopril and penicillamine

The mechanisms underlying drug-induced neutropenia are poorly characterized. We have examined the mechanism of suppression of granulocytopoiesis by captopril and penicillamine using human and canine bone marrow cells in an in vitro culture system. Addition of captopril caused no significant change in granulocyte-macrophage colony formation at concentrations up to 30 micrograms/ml. In the presence of CuSO4 (1-3 micrograms/ml), however, captopril caused significant inhibition of colony growth (p less than 0.05). Penicillamine, another agent associated with neutropenia and, like captopril, having a reactive thiol group, also inhibited colony formation in the presence of copper. Chemical congeners of captopril lacking a reactive thiol group and enalaprilic acid, an alternative angiotensin-converting enzyme (ACE) inhibitor, failed to show inhibition, suggesting that the thiol group and not ACE inhibition was responsible. Analysis of day-7 colonies (98% neutrophilic) and day-21 colonies (37% neutrophilic, 30% macrophagic, 27% eosinophilic, and 6% mixed) showed that neutrophil-containing colonies, but not nonneutrophilic colonies were inhibited by the addition of captopril plus copper. Catalase totally reversed the inhibition of colony formation caused by these agents. Direct measurement of oxygen consumption in the presence of captopril showed marked enhancement with the addition of CuSO4 and a 48% reduction in the presence of added catalase. These data indicate that drugs with a reactive thiol group can interact with copper to generate H2O2, which can be toxic to neutrophilic progenitor cells. We postulate that this may be an important mechanism for drug-associated neutropenia and a general mechanism for drug-induced marrow cell injury.

Tubuloglomerular feedback-dependent influence of angiotensin II on the kidney in rats

To examine the modulatory role of angiotensin II on the tubuloglomerular feedback (TGF) mechanism, TGF responses were assessed during control conditions, converting enzyme inhibition (CEI; MK 422, 0.6 mg/kg.hr) and during continued CEI with the replacement of angiotensin II. TGF responses were assessed from stop flow pressure (SFP) feedback responses obtained during step increases in the late proximal perfusion rate from 0-40 nl/min. SFP values in the absence of perfusion were used to estimate glomerular pressure (GP) under conditions where the influence of the TGF mechanism should be at a minimum. During CEI, the arterial pressure decreased from 124 +/- 3 to 106 +/- 3 mmHg and the estimated GP decreased from 53 +/- 1.4 to 49 +/- 0.8 mmHg. There was a marked attenuation in the magnitude of SFP feedback responses from 11.0 +/- 1.3 to 2.7 +/- 0.6 mmHg. TGF feedback responses, however, were restored towards normal during superimposed angiotensin II infusion (7.7 +/- 0.9 mmHg). These results indicate that converting enzyme inhibition decreases the effects of angiotensin II on the kidney through TGF dependent mechanism.

Angiotensin-converting enzyme inhibitors. Mercaptan, carboxyalkyl dipeptide, and phosphinic acid inhibitors incorporating 4-substituted prolines

Analogues of captopril, enalaprilat, and the phosphinic acid [hydroxy(4-phenylbutyl)phosphinyl]acetyl]-L-proline incorporating 4-substituted proline derivatives have been synthesized and evaluated as inhibitors of angiotensin-converting enzyme (ACE) in vitro and in vivo. The 4-substituted prolines, incorporating alkyl, aryl, alkoxy, aryloxy, alkylthio, and arylthio substituents were prepared from derivatives of 4-hydroxy- and 4-ketoproline. In general, analogues of all three classes of inhibitors with hydrophobic substituents on proline were more potent in vitro than the corresponding unsubstituted proline compounds. 4-Substituted analogues of captopril showed greater potency and duration of action than the parent compound as inhibitors of the angiotensin I induced pressor response in normotensive rats. The S-benzoyl derivative of cis-4-(phenylthio)captopril, zofenopril, was found to be one of the most potent compounds of this class and is now being evaluated clinically as an antihypertensive agent. In the phosphinic acid series, the 4-ethylenethioketal and trans-4-cyclohexyl derivatives were found to be the most potent compounds in vitro and in vivo. A prodrug of the latter compound, fosinopril, is also being evaluated in clinical trials.

Effects of an alpha-2 adrenoceptor agonist on angiotensin converting enzyme inhibitor-induced hypotension and potentiated allergen-evoked inflammatory skin responses

Angiotensin converting enzyme (ACE) inhibitors have been demonstrated to possess proinflammatory properties. Persistent cough and increased broncho-obstruction have been reported frequently in hypertensive subjects on ACE inhibitor therapy. We have studied the effect of an alpha-2 adrenoceptor agonist, clonidine, on MK 422 (active parent diacid of enalapril)-induced hypotension and potentiated inflammatory skin responses in ovalbumin-sensitized guinea pigs. Clonidine was found to abolish dose-dependently MK 422-potentiated ovalbumin-evoked inflammatory dermal responses and it possesses additive hypotensive effects when combined with the ACE inhibitor. It would therefore be interesting to evaluate further alpha-2 adrenoceptor agonists and ACE inhibitors in a combination therapy in humans when single drug antihypertensive therapy of the drugs is insufficient.

Differential renal handling of angiotensin-converting enzyme inhibitors enalaprilat and lisinopril in rats

Enalaprilat, the active metabolite of enalapril, and its lysine analogue lisinopril are potent nonsulfhydryl angiotensin-converting enzyme inhibitors. Earlier studies from our laboratories demonstrated that neither drug is significantly metabolized, and both are almost exclusively eliminated by renal excretion. This report compares the renal excretory mechanisms for these structurally related compounds in the rat. After an iv, 1-mg/kg dose, ratios of renal clearance (CLR) of unbound drug to glomerular filtration rate (GFR) for enalaprilat and lisinopril were 2.72 +/- 0.70 and 1.01 +/- 0.18, respectively, suggesting that enalaprilat, but not lisinopril, was actively secreted by the kidneys. Treatment with probenecid and p-aminohippuric acid, potent competitive inhibitors for the renal anionic transport system, caused a profound decrease in the renal clearance of enalaprilat to the level of GFR. The CLR/fu.GFR, where fu is the unbound fraction, became 1.10 +/- 0.09 and 1.25 +/- 0.25, respectively. These results and the fact that quinine, a potent inhibitor for the cationic transport system, had little effect on the renal clearance of enalaprilat indicated that enalaprilat is secreted by the organic anion transport system. On the other hand, probenecid, p-aminohippuric acid, and quinine had no effect on the renal clearance of lisinopril, suggesting that lisinopril is eliminated exclusively by glomerular filtration.

Renal effects of atrial natriuretic factor during control of the renin-angiotensin system in anesthetized dogs

The contribution of the renin-angiotensin system to the natriuretic responses to intrarenal infusions of 1, 5, 25, and 125 pmol/kg/min synthetic rat atrial natriuretic peptide 101-126 was determined in one-kidney anesthetized dogs. In vehicle-treated dogs, atrial natriuretic peptide 101-126 increased fractional sodium excretion from 1.8 +/- 0.6% to a peak response of 5.1 +/- 0.9% during infusion of 25 pmol/kg/min. The peptide progressively decreased mean arterial pressure from 110 +/- 5 to 94 +/- 4 mm Hg, renal vascular resistance from 0.40 +/- 0.02 to 0.30 +/- 0.02 mm Hg/ml/min, and arterial plasma renin activity from 4.3 +/- 1.6 to 3.1 +/- 0.8 ng/ml/hr. When the renin-angiotensin system was blocked by 3 mg/kg i.v. enalaprilat, baseline pressure fell to 86 +/- 4 mm Hg, and subsequent infusions of atrial natriuretic peptide 101-126 did not affect fractional sodium excretion. The decreases in blood pressure (from 86 +/- 4 to 76 +/- 4 mm Hg) and in renal vascular resistance (from 0.27 +/- 0.03 to 0.23 +/- 0.02 mm Hg/ml/min) were also ameliorated compared with the control responses. Intravenous infusion of 2.5 ng/kg/min angiotensin II restored mean arterial pressure and potentiated the natriuretic and renal vascular responses to atrial natriuretic peptide 101-126. In two additional groups of anesthetized dogs, enalaprilat did not produce the profound hypotension and did not affect the natriuretic responses to atrial natriuretic peptide 101-126. When renal vascular resistance was elevated by intrarenal infusion of angiotensin II in enalaprilat-treated dogs, the natriuretic response was improved.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of a kinin antagonist on the acute antihypertensive activity of enalaprilat in severe hypertension

The purpose of this study was to assess the role of kinins in the acute antihypertensive effect of the converting enzyme inhibitor (CEI) enalaprilat in rats with severe hypertension induced by aortic ligation between both renal arteries. For this study, we used a bradykinin analogue, D-Arg-Arg-Pro-Hyp-Gly-Thi-Ser-DPhe-Thi-Arg-TFA, with in vivo antagonistic properties. Hypertensive rats were infused intra-aortically for 15 minutes with either saline (30 microliters/min) or the kinin antagonist (40 micrograms/kg/min). Five minutes after the infusion was begun, a bolus injection of enalaprilat (60 micrograms/kg) was given. The blood pressure of the saline-infused animals decreased 48 +/- 6 mm Hg (from 180 +/- 7 to 132 +/- 7 mm Hg), while that of the rats treated with the antagonist decreased only 21 +/- 4 mm Hg (from 175 +/- 3 to 154 +/- 3 mm Hg). The difference between both decrements was significant (p less than 0.01). In another group of hypertensive animals (n = 9), we measured kinin concentration in plasma from arterial blood before and after administration of CEI (41 +/- 10 vs 68 +/- 20 pg/ml, respectively; NS). These results are consistent with the hypothesis that kinins play a role in the acute antihypertensive effect of CEIs in rats with severe hypertension. However, since arterial blood kinin concentrations were not increased significantly after CEI administration, the effect of the CEI may be due to an increase in tissue kinins, which could act as autacoids regulating vascular resistance.

Converting enzyme activity and angiotensin metabolism in the dog brainstem

The concentrations of angiotensin converting enzyme (ACE) activity, norepinephrine, and serotonin were measured in microdissected regions of the dog's brainstem and spinal cord. In addition, we determined the in vitro metabolism of 125I-angiotensin I (Ang I) in homogenates of the same brain punch regions. High ACE-specific activity was found in the monoamine-containing regions of the brainstem and in the intermediolateral column of the spinal cord. In brainstem homogenates 125I-Ang I was metabolized to angiotensin II (Ang-[1-8]) and the N-terminal heptapeptide Ang-(1-7). In the presence of MK 422 (50 microM), Ang-(1-7) was still generated, while the production of Ang-(1-8) was inhibited. This study revealed the presence of high ACE activity in monoamine regions of dog brainstem and spinal cord, and showed that the metabolite Ang-(1-7) is the major product generated from Ang I in the presence and absence of ACE inhibition.

The ventrolateral medulla. A new site of action of the renin-angiotensin system

High-affinity binding sites for angiotensin II (Ang II) in the ventrolateral medulla suggest that Ang II may act at cell groups that are known to modulate blood pressure. This hypothesis was investigated by the topical application of angiotensin I (Ang I), Ang II, the Ang II antagonist [Sar1, Thr8]Ang II, and the Ang I converting enzyme inhibitor MK 422 to a restricted region of the ventral medullary surface known as the glycine-sensitive area. Both Ang I (100 pmol) and Ang II (100 pmol) produced significant (p less than 0.01) increases in blood pressure (+20 +/- 4 and +31 +/- 5 mm Hg, respectively) that were associated with no change in heart rate. Furthermore, the relationship between the peak increases in blood pressure and Ang II was dose-dependent. Blockade of endogenous Ang II by [Sar1, Thr8]Ang II (13 nmol) produced a significant decrease in baseline blood pressure (-8 +/- 1 mm Hg; p less than 0.001). Similarly, topical application of MK 422 prevented the pressor effect of Ang I. Taken together, these experiments indicate that at least some components of the renin-angiotensin system exist in the ventrolateral medulla and they may modulate vasomotor outflow.

Direct myocardial and coronary effects of enalaprilat in patients with dilated cardiomyopathy: assessment by a bilateral intracoronary infusion technique

Angiotensin II elicits contractile responses in the coronary arteries and myocardial tissue, which suggests that blockade of the renin-angiotensin system by specific agents should lead to both coronary vasodilation and an alteration of left ventricular inotropism. The present work was designed to delineate--independently from its systemic effects--the intrinsic actions of an angiotensin converting-enzyme inhibitor on the coronary circulation and left ventricular function. To minimize peripheral effects, a bilateral intracoronary infusion of enalaprilat (0.05 mg.min-1, 1 ml.min-1 in each coronary artery) was performed in 16 patients with dilated cardiomyopathy. All patients had normal coronary arteriograms. In 12 patients (group I) the intracoronary infusion of enalaprilat resulted in minimal peripheral changes, with a 5% reduction in the mean aortic pressure (p less than .05) and no significant alteration in indexes of preload, i.e., left ventricular end-diastolic pressure and volume, or of afterload, i.e., left ventricular end-systolic stress and systemic resistances. Myocardial oxygen consumption was also unaffected by the intracoronary infusion of enalaprilat. Coronary vasodilation was demonstrated by a significant elevation of coronary sinus blood flow (+19%, from 181 +/- 73 to 214 +/- 79 ml.min-1, p less than .001) and a reduction of coronary resistance (-18%, from 0.51 +/- 0.17 to 0.41 +/- 0.15 mm Hg.ml-1.min, p less than .001), with a parallel increase in coronary sinus oxygen content and pressure (both p less than .05). Oxygen extraction by the myocardium was reduced (p less than .01).(ABSTRACT TRUNCATED AT 250 WORDS)

Individual responses to converting enzyme inhibitors and calcium antagonists

This study was designed to assess whether the acute blood pressure response of an individual hypertensive patient to a calcium antagonist or an angiotensin converting enzyme (ACE) inhibitor is a good predictor of the long-term efficacy of these drug classes in this particular patient. The concept that good responses to ACE inhibitors and calcium antagonists may be mutually exclusive was also tested. Sixteen patients were included in a randomized crossover trial of enalapril, 20 mg daily, and diltiazem, 120 mg daily, for 6 weeks each. Blood pressure was measured by ambulatory blood pressure recording. During the washout phase, the acute effect of nifedipine, 10 mg p.o., and enalaprilat, 5 mg i.v., was evaluated. Nifedipine and enalaprilat reduced blood pressure equally well. The long-term blood pressure reduction induced by enalapril and diltiazem was similar. The acute blood pressure response to a given drug was not a good predictor of the result obtained with long-term therapy. No age dependency of the antihypertensive effect of either drug class was apparent. There was no evidence that a good response to one drug excluded a similarly good response to the other.

Regional cerebral blood flow during acute left ventricular failure in the dog: effect of converting enzyme inhibition

Regional cerebral blood flow (rCBF) was studied in anesthetized dogs subjected to acute left ventricular failure and its treatment with enalaprilat (MK-422). When failure was induced a reduction in rCBF paralleling the reduction in systemic blood pressure was observed. After treatment rCBF did not change in spite of further blood pressure reduction. The results are explained by changes in vascular resistance of larger cerebral arteries. Vasoconstriction in these vessels during failure was counteracted by enalaprilat through reduction in circulating angiotensin II.

A possible drug interaction between rifampicin and enalapril

When a 35-year-old man with essential hypertension was treated with antibiotics for brucellosis his blood pressure rose significantly. While all other treatment was kept constant rifampicin was discontinued. On rechallenge rifampicin did not alter serum concentrations of enalapril or the area under the curve (AUC) between 0 and 7 h, but it did reduce the AUC of the active metabolite enalaprilat by 31%. These observations suggest that there may be an interaction between rifampicin and enalapril, causing reduced hypotensive efficacy of enalapril. The mechanism of such an interaction merits further study, but it could be due to enhanced renal clearance of enalaprilat.

Brachial artery hemodynamic response to acute converting enzyme inhibition by enalaprilat in essential hypertension

To assess the vascular involvement of renin-angiotensin system inhibition in human hypertension, acute effects of intravenous enalaprilat on brachial artery diameter, blood flow, and blood velocity were investigated in hypertensive patients by pulsed Doppler technique and compared with effects of saline vehicle. Compared with saline vehicle, enalaprilat reduced blood pressure (P less than 0.001) and increased brachial arterial diameter (P less than 0.01) and brachial blood flow (P less than 0.01). Enalaprilat effect on arterial pulse pressure was dependent on preinjection pulse pressure (r = -0.76; P less than 0.001), but its effect on mean blood pressure was not dependent on preinjection mean blood pressure. On the other hand, enalaprilat effect on arterial blood flow was negatively correlated with preinjection blood pressure (r = -0.64; P less than 0.02). The findings point to different responses of large and small arteries to intravenous enalaprilat.

Effects of spiraprilic acid, an angiotensin converting enzyme inhibitor, on large artery compliance in anesthetized dogs

The present study examined the actions of spiraprilic acid, a new non-sulfhydryl angiotensin converting enzyme (ACE) inhibitor upon aortic compliance (AC) in anesthetized dogs. Enalaprilic acid was examined for comparative purposes. AC was determined via sonomicrometric determination of the ratio of aortic systolic-diastolic diameter (mm) and arterial pulse pressure (mmHg). One AC unit (ACU) equals 10(-3) mm/mmHg. In non-thiazide pretreated animals, spiraprilic acid (1 mg/kg i.v.), caused a sustained hypotensive response of 21 +/- 3 mmHg (P less than .05). At the same time, aortic systolic and diastolic dimensions were reduced from basal values of 8.17 +/- 0.45 and 7.95 +/- 0.40 mm by 0.19 +/- 0.07 (P less than .05) and 0.29 +/- 0.10 mm (P less than .05), respectively. The aortic systolic-diastolic dimension rose significantly by 0.10 +/- 0.01 mm. Since pulse pressure was unchanged, AC rose from a basal value of 4.6 +/- 0.8 ACU by 1.7 +/- .3 ACU (P less than .05). Similar effects were observed with enalaprilic acid. In dogs pretreated orally with 5 mg/kg hydrochlorothiazide (HCTZ) twice daily for 3 days, spiraprilic and enalaprilic acids caused slightly greater falls in blood pressure (34 +/- 7 and 30 +/- 4 mmHg, respectively) than in nonpretreated dogs. However, the onset of the hypotension effect was more rapid for both ACE inhibitors in HCTZ-pretreated dogs. Effects of spiraprilic and enalaprilic acid upon aortic dimensions were similar to those observed in non-HCTZ pretreated animals. The data illustrate that the ACE inhibitors spiraprilic and enalaprilic acids not only lower blood pressure but also enhance large artery compliance.

Antihypertensive effect of a renin inhibitor in marmosets with a segmental renal infarction

Hypertension was induced in marmosets by ligating the minor branch of one renal artery. The blood pressure (BP), measured by a tail-cuff method, increased to hypertensive levels within 4-5 weeks and the maximum increases occurred after 4-15 weeks (BP, mean +/- s.e.m. was 120 +/- 3 and 152 +/- 6 mmHg before and 10 weeks after ligation, respectively; n = 9). There was a small increase in plasma renin activity (PRA) after 2 weeks, but PRA decreased thereafter and there was no correlation between PRA and BP. The renin inhibitor CGP 29,287 (Ciba-Geigy Ltd., Basle, Switzerland, synthesized by D.B. Rinker and P. Bühlmayer; 1 mg/kg i.p.) and the angiotensin converting enzyme (ACE) inhibitor, enalaprilat (Merck Sharp and Dohme, USA.; 2 mg/kg i.p.), lowered the BP of the hypertensive marmosets to normotensive levels. These results indicate that although PRA is not elevated in this primate model of hypertension, BP is dependent on the activity of the renin-angiotensin system.

Electronic spectroscopy of cobalt angiotensin converting enzyme and its inhibitor complexes

Zinc, the catalytically essential metal of angiotensin converting enzyme (ACE), has been replaced by cobalt(II) to give an active, chromophoric enzyme that is spectroscopically responsive to inhibitor binding. Visible absorption spectroscopy and magnetic circular dichroic spectropolarimetry have been used to characterize the catalytic metal binding site in both the cobalt enzyme and in several enzyme-inhibitor complexes. The visible absorption spectrum of cobalt ACE exhibits a single broad maximum (525 nm) of relatively low absorptivity (epsilon = 75 M-1 cm-1). In contrast, the spectra of enzyme-inhibitor complexes display more clearly defined maxima at longer wavelengths (525-637 nm) and of markedly higher absorptivities (130-560 M-1 cm-1). The large spectral response indicates that changes in the cobalt ion coordination sphere occur on inhibitor binding. Magnetic circular dichroic spectropolarimetry has shown that the metal coordination geometry in the inhibitor complexes is tetrahedral and of higher symmetry than in cobalt ACE alone. The presence of sulfur----cobalt charge-transfer bands in both the visible absorption and magnetic circular dichroic spectra of the cobalt ACE-Captopril complex confirm direct ligation of the thiol group of the inhibitor to the active-site metal.

Hepatic extraction of renin: quantitation and characterization in the isolated perfused rat liver

Since the liver is thought to be the major organ for the metabolism of renin, the rate-limiting enzyme in the renin-angiotensin cascade, we examined the kinetics and regulation of renin extraction by the isolated perfused rat liver. Partially purified, hog kidney renin was continuously infused into isolated rat livers perfused in a nonrecirculating manner with serum-free medium. Concentrations of renin in the portal and hepatic veins were measured by radioimmunoassay and first-pass hepatic extraction calculated. In livers from normal rats, steady-state, first-pass hepatic extraction of porcine renin ranged from 12.3 +/- 0.9 to 25.5 +/- 3.9% of the infused dose; at high renin infusion rates, hepatic extraction was saturable. Administration of captopril, a converting enzyme inhibitor, decreased hepatic extraction of renin by approximately 60%; enalaprilat, another converting enzyme inhibitor, had no effect. First-pass hepatic extraction of renin was also inhibited by the bile acid, taurocholate, in a dose-dependent manner. However, bilateral nephrectomy, which reduced endogenous plasma renin activity to unmeasurable levels, had no significant effect on hepatic extraction of renin by livers isolated from nephrectomized rats. These results demonstrate directly that the liver extracts renin in a dose-dependent and saturable manner, although the precise mechanism of uptake remains to be determined.