Angiotensin I converting enzyme activity in hypertension. Relationship to blood pressure, renin-sodium profiles, and antihypertensive therapy

Additive effects of moderate dietary salt reduction and captopril in hypertension

In a randomized, cross-over study 27 patients had diastolic blood pressure of greater than or equal to 96 mmHg during four visits without treatment. Following captopril 25 mg b.i.d. nine patients' blood pressure was less than or equal to 90 mmHg. The remaining 18 were randomized into two treatment modalities, captopril and moderate dietary salt reduction, and captopril and hydrochlorothiazide 25 mg daily. Following a wash-out period the groups crossed over to the alternative treatment. At the end of the control period the average blood pressure was 151/100 +/- 12/6 mmHg recumbent and 140/91 +/- 11/7 standing, following captopril 144/94 +/- 13/5 and 132/92 +/- 12/6, respectively, with low salt diet added to captopril 140/91 +/- 12/6 and 128/89 +/- 11/6 and with hydrochlorothiazide and captopril 133/86 +/- 12/7 and 120/84 +/- 11/7 mmHg supine and erect, respectively. It is concluded that moderate dietary salt reduction, which is easily advised, will significantly potentiate the blood pressure fall following captopril treatment in moderate arterial hypertension.

Vascular angiotensin-converting enzyme expression regulates local angiotensin II

We tested the hypothesis that changes in angiotensin-converting enzyme (ACE) gene expression can regulate the rate of local vascular angiotensin II (Ang II) production. We perfused isolated rat hindlimbs with an artificial medium and infused renin and Ang I via the perfusate. Ang I and II were measured by radioimmunoassay. We then increased ACE gene expression and ACE levels in the rat aorta by producing two-kidney, one clip (2K1C) hypertension for 4 weeks. Gene expression was measured by RNAse protection assay, and ACE activity in the vessel wall was measured by the Cushman-Cheung assay. Angiotensin I infusion at 1, 10, 100, and 1000 pmol/mL led to 371 +/- 14 (+/-SEM), 3611 +/- 202, 44,828 +/- 1425, and 431,503 +/- 16,439 fmol/mL Ang II released, respectively, from the hindlimbs (r = .98, P < .001). Thus, the conversion rate did not change across four orders of magnitude, and the system was not saturable under these conditions. In 2K1C hindlimbs, Ang I infusion (0.5 pmol/mL) resulted in increased Ang II generation (157 +/- 16 versus 123 +/- 23 fmol/mL, P = .014 at minute 10) compared with controls. ACE gene expression and ACE activity were increased in 2K1C hindlimbs compared with controls (36 +/- 4 versus 17 +/- 1 mU/mg protein, P < .001). Ang II degradation in the two groups did not differ. To investigate the conversion of locally generated Ang I, we infused porcine renin (0.5 milliunits per mL) into 2K1C and control hindlimbs. Despite markedly higher Ang I release in sham-operated than in 2K1C rats (71 +/- 8 versus 37 +/- 6 pmol/mL, P = .008 at minute 12), Ang II was only moderately increased (36 +/- 3 versus 25 +/- 6 pmol/mL, P = .12 at minute 12). This difference between 2K1C rats and controls reflected a higher rate of conversion in 2K1C rats. Thus, Ang I conversion in the rat hindlimb is linear over a wide range of substrate concentrations and occurs at a fixed relationship. Nevertheless, increased ACE gene expression and ACE activity in the vessel wall lead to an increase in the conversion of Ang I to Ang II. We conclude that local ACE gene expression and ACE activity can influence the local rate of Ang II production.

Racial difference in the relationship of an angiotensin I-converting enzyme gene polymorphism to serum angiotensin I-converting enzyme activity

An insertion (I)/deletion (D) polymorphism of the angiotensin I-converting enzyme (ACE) gene that has been associated with certain cardiovascular disorders accounts for nearly half the variation in serum ACE level in white subjects. Whether a similar association of serum ACE with the I/D polymorphism occurs in other racial groups is not known. We studied the I/D polymorphism of ACE in relation to serum ACE activity in 141 white and 62 black healthy, unrelated children and adolescents (mean age, 14.7 years). The mean level of ACE activity in whites homozygous for the D allele was higher than in heterozygotes (P = .002) and in homozygotes for the I allele (P = .0001), consistent with an earlier study. In blacks, on the other hand, no significant difference in serum ACE activity between genotypes was observed. An additional finding was a significantly positive relationship between serum ACE activity and diastolic pressure (P = .009). In children and adolescents, serum ACE activity is related to the ACE gene I/D polymorphism in whites but not in blacks. The results indicate a potentially important ethnic variation in genetic regulation of serum ACE activity and the relationship of the I/D polymorphism to cardiovascular disease.

The role of platelets in essential hypertension

Recent research is helping us understand the complex interactions that occur between platelets and their environment. The several intracellular events that occur during platelet activation are being identified as ar their effects on other platelets, the endothelium and coagulation factors. Heightened platelet activation is seen early in essential hypertension and probably plays an important role in the initiation and progression of atherosclerosis and the disorders associated with it. This review identifies some of the changes in platelet structure and function in essential hypertension and their role in the pathogenesis of hypertensive vascular disease.

Response of serum angiotensin converting enzyme, plasma renin activity and plasma aldosterone to conventional dialysis in patients on chronic haemodialysis

The aim of this study was to examine serum angiotensin converting enzyme (SACE) activity and the renin-angiotensin-aldosterone system in patients on chronic haemodialysis during one routine dialysis session. Fourteen patients (8 men and 6 women; mean age 51.9 +/- 17 years) with end stage renal disease, receiving regular haemodialysis treatment for an average of 6 months, were studied. The patients were dialysed for 4 hours three times a week using cellulose membranes (cuprophan). After an overnight fast blood samples were taken from the patients before and after the haemodialysis session. Serum and plasma were separated and stored at -20 degrees C until assayed for SACE, plasma renin activity (PRA) and plasma aldosterone (PA). For comparison, SACE, PRA and PA were also measured in 8 patients after renal allotransplantation and on treatment with cyclosporin A (5 men, 3 women; mean age 38.9 +/- 12.3 years) and in 19 healthy subjects (13 men, 6 women; mean age 38.9 +/- 12.3 years). SACE levels in patients with chronic renal failure and on haemodialysis (17.55 +/- 9.03 nmol/ml/min) and in patients with renal transplantation (18.12 +/- 3.92) were significantly higher than those of the healthy subjects (9.27 +/- 1.67) (p < 0.0001, respectively). At the end of the dialysis session SACE levels in patients with chronic renal failure (14.9 +/- 7.19) did not increase in respect to pre-dialysis levels (17.55 +/- 9.03; p = 0.132). PRA and PA values increased after the dialysis session (p < 0.026 and p < 0.044, respectively). Correlation of SACE with PRA and PA was not demonstrated before or after the dialysis session. In patients with chronic renal failure and on haemodialysis our findings suggest that a disarrangement exists between the circulatory components of the reninangiotensin-aldosterone system before and after the dialysis session.

Angiotensin-converting enzyme gene polymorphism has no influence on the circulating renin-angiotensin-aldosterone system or blood pressure in normotensive subjects

BACKGROUND

Angiotensin-converting enzyme (ACE) is involved in the metabolism of two major vasoactive peptides, converting angiotensin (Ang) I into Ang II and inactivating bradykinin. An insertion/deletion (I/D) polymorphism is present in the 16th intron of the ACE gene and is strongly associated with plasma and cellular ACE levels. Contrasting with the lack of relation between ACE gene polymorphism and blood pressure level, a large case-control study has shown that the deletion marker allele of the ACE gene was associated with an increased risk of myocardial infarction. The pathophysiological link between ACE gene polymorphism and cardiovascular events remains hypothetical. One hypothesis is that this polymorphism influences Ang II and bradykinin concentrations in the peripheral and/or local circulations through its effects on ACE levels in plasma and endothelial cells. The aim of this study was to investigate the effect of the ACE gene I/D polymorphism on blood pressure, plasma active renin, and aldosterone regulation in normal subjects.

METHODS AND RESULTS

Twenty-four normotensive male volunteers homozygous for the ACE I/D polymorphism (12 DD and 12 II) received a renin inhibitor infusion (remikiren 0.1 mg.kg-1.h-1 for 130 minutes) to suppress endogenous Ang I and Ang II production. Forty minutes after initiating the remikiren infusion, an exogenous Ang I infusion was begun and increased gradually every 15 minutes from 1 to 10 ng.kg-1.min-1. Median (range) plasma ACE levels (mU/mL) were 39 (32 to 57) and 24 (12 to 30) in the DD and II groups, respectively. Remikiren suppressed plasma Ang I and Ang II, increased plasma active renin (from 23 +/- 12 to 154 +/- 161 pg/mL), decreased plasma aldosterone (from 106 +/- 42 to 82 +/- 33 pg/mL), and slightly decreased diastolic blood pressure (from -2.4 +/- 2.7 mm Hg). The blood pressure and hormonal responses to Ang I infusion after renin inhibition and the slope of the rise in plasma Ang II with increasing Ang I dose were identical in both groups, as was the plasma Ang I/Ang II ratio before (DD, 2.09 +/- 1.04; II, 2.59 +/- 0.76) and after (DD, 0.15 +/- 0.13; II, 0.09 +/- 0.03) combined renin inhibitor and Ang I infusion.

CONCLUSIONS

Despite its association with a major difference in plasma ACE levels, the ACE I/D polymorphism did not influence the Ang II and plasma aldosterone production, plasma active renin decrease, or diastolic blood pressure increase induced by exogenous Ang I infusion, suggesting that ACE has no limiting influence on systemic Ang II generation and effects under these experimental conditions.

Serum angiotensin converting enzyme activity and plasma renin activity in experimental models of rats

1. Serum angiotensin converting enzyme activity (ACEA) and plasma renin activity (PRA) were determined in rats under different experimental conditions such as: nephrotic syndrome (NS), bilateral nephrectomy (BN), renovascular hypertension (RH), dehydration (DEH), anaesthesia (AN), low sodium diet (LSD) and high sodium diet (HSD), and injection with propranolol (PRO) and isoprenaline (ISO). 2. PRA increased in LSD, AN, NS, RH, DEH and IPT groups, and decreased in HSD, BN, and PRO groups. Serum ACEA did not change in RH, HSD, IPT, DEH, AN, and PRO groups, increased in NS group, and decreased in LSD and BN groups. 3. Serum ACEA changed in the opposite direction to PRA only in the LSD group. This finding suggests that ACE may limit the full expression of the renin-angiotensin system in the LSD group, but not in the other groups.

Lisinopril in elderly patients with hypertension. Long term effects on renal and metabolic function

The efficacy and tolerability of lisinopril administered once daily were evaluated in a 12-week open study of 60 elderly patients aged between 65 and 85 years (mean 75 years) with essential hypertension. Mean sitting blood pressure was reduced from 190/106 +/- 6.3/1.3mm Hg (mean +/- SEM) at entry to 162/89 +/- 5.5/0.9 mm Hg after 12 weeks of treatment (p less than 0.001). There was no significant alteration in heart rate, and no occurrence of postural hypotension. The median daily dose of lisinopril was 20mg (range 5 to 40 mg) and only 4 patients required the addition of a diuretic. Mean glomerular filtration rate (GFR) at entry was 61.6 +/- 3.4 ml/min and was unchanged after 12 weeks of therapy. 25 patients continued to receive treatment for 1 year, and 20 of these completed 2 years of treatment. Control of blood pressure was maintained, and heart rate, biochemical parameters and GFR remained unaltered throughout the study. Renal function was preserved and renal blood flow, measured in a group of 14 patients, was significantly increased (p less than 0.025) at the end of the first year after treatment with lisinopril. Thus, in the elderly, lisinopril was well tolerated and highly effective in lowering blood pressure, and renal function was maintained.

Changes in plasma ACE activity during the development and reversal of one-kidney, one clip hypertension in rats

Plasma angiotensin converting enzyme (ACE) activity was studied during the development and the reversal of one-kidney, one clip (1K1C) renal hypertension in rats (RHR). Plasma ACE activity was measured in RHR 1 (n = 11), 3 (n = 8), 6 (n = 12), 14 (n = 7), and 80-120 days (n = 17) after clipping. Plasma ACE activity (nmol/min/ml) was elevated (p less than 0.05) in chronic RHR (80-120 days; mean arterial pressure, MAP: 216 +/- 9 mmHg), being 142 +/- 14 (n = 17) vs. 100 +/- 3.2 (n = 20) for normotensive control rats (MAP: 116 +/- 3 mmHg), whereas no significant differences were observed at earlier times. Overactivity of the renin-angiotensin system (RAS) was demonstrated indirectly by the reduction of MAP (greater than 15 mmHg) in response to captopril (10 mg/kg, i.v.) only during the first 3 days after clipping and in chronic severely hypertensive rats. In another experiment, ACE activity in chronic RHR was measured serially before and 1, 6 and 24 hours after unclipping. Serial measurements of plasma ACE showed a progressive decrease from 145 +/- 26 to 122 +/- 21, 24 hours after unclipping (n = 7, p less than 0.05, paired Student t-test) when MAP was reduced from 204 +/- 15 to 113 +/- 7 mmHg. There was essentially no change during 24 hours from the initial values of RHR-sham (MAP: 206 +/- 5 mmHg, ACE: 140 +/- 19, n = 8) and normal rats-sham (MAP: 115 +/- 2 mmHg, ACE: 96 +/- 3, n = 6). These data provide further evidence that chronic renal hypertension is associated with important changes in the metabolism of vasoactive peptides.

Diagnostic aspects of angiotensin converting enzyme in pulmonary sarcoidosis

Angiotensin converting enzyme (ACE) has been measured in 102 biopsy-proven sarcoid patients, 70 patients diagnosed by clinical and radiological methods and 74 nonsarcoid patients as controls. The distributions of the various groups have been examined, and the effects of stage of disease, disease activity and prednisone treatment have been evaluated. Receiver operating characteristic (ROC) curves have been established for ACE, and the appropriateness of various statistical procedures is discussed. We have not discerned any effect of stage of sarcoidosis or of extent of disease activity on ACE values. The ROC curves suggest an upper limit of normal of about 50 U/L for our assay, and a sensitivity of 63% and specificity of 93%, yielding predictive values of 93% for a positive result and 74% for a negative result, with a likelihood ratio of 3.6. The results are discussed in the context of other work on ACE and in relation to the more invasive procedures of bronchoalveolar lavage and Gallium scan.

Pharmacology of angiotensin converting enzyme inhibitors. A review

Two angiotensin converting enzyme inhibitors are currently available for clinical use. Captopril, a sulfhydryl-containing compound, is a direct acting enzyme inhibitor. Enalapril is a non-sulfhydryl pro-drug that requires enzymatic conversion to enalaprilic acid, a potent angiotensin converting enzyme inhibitor. Both drugs lower blood pressure, suppress blood pressure response to angiotensin I infusion, and elevate plasma renin activity. Enalapril bioavailability is unaffected by food, whereas captopril availability is suppressed by food. Dose adjustments are necessary for patients with congestive heart failure and renal failure.

Adverse reactions with angiotensin converting enzyme (ACE) inhibitors

Teprotide, a nonapeptide isolated from the venom of a Brazilian pit viper, Bothrops jararaca, was the first angiotensin converting enzyme (ACE) inhibitor to be discovered and tested. It was found to be an effective, non-toxic antihypertensive agent as well as an afterload-reducing agent for patients with congestive heart failure (CHF). The primary activity of teprotide resulted from blockade of the angiotensin I converting enzyme--the pivotal step in the renin-angiotensin-aldosterone system (RAAS), and consequent reductions in angiotensin II levels. There was limited clinical testing for teprotide because of: its scarcity; the need for parenteral administration; and the subsequent discovery and synthesis of captopril, the first orally active angiotensin converting enzyme inhibitor. Captopril is the prototype oral angiotensin converting enzyme inhibitor and has been extensively studied since the initiation of formal studies in 1976. Perhaps one of the most closely researched drugs in modern times, the experience with captopril now includes more than 12,000 patients studied in formalized trials and over 4,000,000 patients treated world-wide by physicians for hypertension and congestive heart failure. Enalapril (MK421) is the first of what appears to be a growing number of analogues which are structurally and pharmacodynamically different from captopril; yet, they possess the same capacity for inhibiting the activity of angiotensin converting enzyme. The side effect profile of enalapril (and presumably future) angiotensin converting enzyme inhibitors appears to be similar to captopril, though clearly more experience is needed with newer agents. The initial use of captopril was troubled by a relatively high incidence of side effects which will form the focus of this discussion. Partially the result of incomplete pharmacokinetic information, captopril was administered in early studies at dosages now recognised to be far in excess of those necessary for drug action. In addition, dosages were given without regard for deficiencies of renal function, now known to be the main excretory route of captopril. The population of those patients studied frequently had chronic, treatment-resistant hypertension, often associated with concomitant end-organ disease (especially renal disease); and many additional factors further complicating the clinical setting, e.g. a relatively high incidence of collagen vascular disease and immunosuppressive treatments.(ABSTRACT TRUNCATED AT 400 WORDS)