Captopril in the management of hypertension with renal artery stenosis: its long-term effect as a predictor of surgical outcome

The action of salt and captopril on blood pressure in mice with genetic hypertension

OBJECTIVE

Does captopril lower blood pressure in genetically hypertensive, normotensive and hypotensive mice under normal and salt-loaded conditions?

DESIGN AND METHODS

Groups of inbred mice that were genetically hypertensive, normotensive or hypotensive were given one of the following treatments: (a) captopril in drinking water for 7 days; controls were given water. (b) 0.85% saline to drink for up to 14 days; controls were given water. (c) Water or saline followed by captopril/water or captopril/saline for 7 days. (d) In hypotensive mice only, 0.85% saline, 0.85% saline plus captopril, water or captopril in water. Systolic blood pressures (SBP) were measured by a computerized tail-cuff sphygmomanometer. Results were compared by analysis of variance (ANOVA).

RESULTS

Captopril lowered SBP in all strains of mice. When saline was given with captopril, the fall in SBP was slower but the final SBP level was similar to that of mice given captopril in water. Hypotensive mice showed a transient rise in SBP on saline, which was abolished by concurrent treatment with captopril.

CONCLUSION

Captopril lowers blood pressure in hypertensive, normotensive and hypotensive mice. Salt-loading retards the captopril-induced fall in SBP, but the final level of SBP achieved is similar to that in mice given captopril with water. The BPL1 strain of mouse was slightly salt-sensitive, and this was abolished by captopril.

Current concepts in renovascular hypertension

Renovascular disease represents an important dimension of hypertension. Although estimates vary regarding the exact prevalence of renovascular hypertension, it is being diagnosed with increasing frequency because of refined criteria for the workup and the availability of sensitive diagnostic tests. Two major pathologic entities--atherosclerosis and fibromuscular dysplasia--account for most cases of renovascular hypertension. Once the diagnosis and clinical significance of renal artery stenosis in a hypertensive patient are established, appropriate and specific therapy should be considered. The goal is not only to treat hypertension, but to preserve and restore renal function. Although antihypertensive drug therapy may lower the blood pressure, reperfusion of the kidney (surgical, angioplasty) is a desirable long-term objective in the management of patients with renovascular hypertension. With careful selection of therapeutic choices, we are now able to render optimal care to patients with renovascular hypertension.

Angiotensin-converting enzyme inhibitors: a comparative review

The chemistry, pharmacology, pharmacokinetics, adverse effects, and dosages of the three currently available angiotensin-converting enzyme (ACE) inhibitors are reviewed. This class of agents effectively inhibits the conversion of angiotensin I to the active vasoconstrictor angiotensin II, a hormone that also promotes, via aldosterone stimulation, increased sodium and water retention. The ACE inhibitors, therefore, are capable of lowering blood pressure primarily by promoting vasodilatation and reducing intravascular fluid volume. Captopril, the first orally active, commercially available ACE inhibitor, is a sulfhydryl-containing compound. Captopril was followed by the introduction of enalapril and lisinopril, two non-sulfhydryl ACE inhibitors. The pharmacokinetic profiles of these three ACE inhibitors differ. Captopril has rapid onset with relatively short duration of action, whereas enalapril and lisinopril have slower onset and relatively long duration of action. Captopril is an active ACE inhibitor in its orally absorbable parent form. In contrast, enalapril must be deesterified in the liver to the metabolite enalaprilat in order to inhibit the converting enzyme; this accounts for its delayed onset of action. Lisinopril does not require metabolic activation to be effective; however, a slow and incomplete absorption pattern explains the delay in onset of activity. Captopril and its disulfide metabolites are primarily excreted in the urine with minor elimination in the feces. Approximately two-thirds of an administered enalapril dose is excreted in the urine as both the parent drug and the metabolite enalaprilat; the remainder of these two substances are excreted in the feces. Lisinopril does not undergo measurable metabolism and approximately one-third is excreted unchanged in the urine with the remaining parent drug being excreted in the feces. The ACE inhibitors lower systemic vascular resistance with a resultant decrease in blood pressure. Their efficacy is comparable to diuretics and beta-blockers in treating patients with mild, moderate, or severe essential and renovascular hypertension. In those patients with severe congestive heart failure (CHF) the ACE inhibitors produce a reduction in systemic vascular resistance, blood pressure, pulmonary capillary wedge pressure, and pulmonary artery pressure. These drugs may produce improvement in cardiac output and stroke volume and, with chronic administration, may promote regression of left ventricular hypertrophy. The antihypertensive effects of the ACE inhibitors are enhanced when these agents are combined with a diuretic. Captopril and enalapril have been shown to be of particular benefits as adjunctive therapy in patients with congestive heart failure, both in terms of subjective improvement of patient symptoms, and in improving overall hemodynamic status.(ABSTRACT TRUNCATED AT 400 WORDS)

Long-term prognosis of surgical treatment of renovascular hypertension

During the period 1974-1986, 71 patients were operated on for renovascular hypertension. Forty-eight patients had atherosclerotic disease and 23 patients had fibromuscular dysplasia. There was no operative mortality. Fourteen patients died during the follow-up, 12 of them from cardiovascular causes. The 57 surviving patients were reexamined with a mean follow-up of 7 years. The relative cumulative 5- and 10-year survival rates in all patients were 79% and 55%, respectively. At follow-up, seven (19%) of the atherosclerotic patients were classified as cured, 22 (59%) as improved and eight (22%) as failures. In the patients with fibromuscular dysplasia, 12 (60%) were normotensive without medication, and six (30%) were improved. The relative 5-year survival rates in these aetiological groups were 73% and 90%, respectively. Only complete cure of hypertension by surgery predicted a good outcome, whereas very similar survival curves were found in the improved and failed groups. This could be due to a higher incidence of target organ changes before surgery in the latter groups. A positive blood pressure response to long-term converting-enzyme inhibition correlated well with the response to surgery. Renal venous renin studies correctly predicted long-term outcome of surgery in 78% of the patients studied, but require careful preparation of the patients and interpretation of results.

Angiotensin converting enzyme inhibitors. II. Clinical use

Since their introduction in clinical practice in 1980, ACE inhibitors have been found useful in the treatment of hypertension and CHF. In hypertension, they are effective as monotherapy in 40% to 50% of the patients, and in combination with diuretics or calcium antagonists, they are effective in up to 85% of the patients. They are well tolerated, are not associated with depression, impotence, bronchospasm or metabolic derangements such as hypokalemia, hyperuricemia or hyperglycemia, and do not have adverse effects on the quality of life. As a result, they are preferred in hypertensive patients with CHF, left ventricular dysfunction, mental depression, older age, coronary artery disease, metabolic disorders, chronic destructive pulmonary disease, and peripheral vascular disease. In CHF they cause long-lasting hemodynamic and symptomatic improvement, improve exercise tolerance, and may lower mortality in certain patient subsets. Evolving new indications for ACE inhibitors include the diagnosis of renovascular hypertension, the prediction of surgical success, the treatment of scleroderma renal crisis, the reduction of proteinuria, renal protection, cardioprotection, the improvement of arterial compliance, in Bartter's syndrome and idiopathic edema, etc. ACE inhibitors are usually well tolerated but in some instances they may cause class-specific side effects such as hypotension; usually reversible azotemia or renal failure, especially in patients with renal artery stenosis or with CHF with low blood pressure; cough; angioedema; and hyperkalemia. Differences among ACE inhibitors are emerging and include chemical class (e.g., zinc ligand), biotransformation, potency, pharmacokinetics, prodrugs, tissue effects, additional pharmacologic properties, and drug interactions.

Lisinopril: a new angiotensin-converting enzyme inhibitor

Lisinopril is a new, nonsulfhydryl angiotensin-converting enzyme inhibitor approved for the treatment of hypertension. After oral administration, 25-29 percent of the dose is absorbed intact; biotransformation is not required for pharmacological activity. Onset of action occurs one to two hours after administration, with effects still present 24 hours later. The major route of elimination is through renal excretion and an elimination half-life of 12.6 hours has been reported in normotensive individuals. In patients with impaired renal function (creatinine clearance less than or equal to 30 ml/min) a longer half-life and accumulation have been observed. Lisinopril 20-80 mg/d has been shown to be as effective as hydrochlorothiazide, nifedipine, and beta-blocking agents in the treatment of essential hypertension. Its efficacy in renovascular hypertension has also been demonstrated. In congestive heart failure (CHF) doses of 2.5-20 mg/d appear to provide hemodynamic effects comparable to those of captopril. Dizziness and cough have been the most frequently reported side effects; rash and proteinuria have also been reported in a small number of patients. Interactions with diuretics, potassium supplements, and possibly with nonsteroidal antiinflammatory agents may occur. Lisinopril appears to be similar in efficacy to other antihypertensive agents in the treatment of essential hypertension and to captopril in the treatment of CHF. Whether lisinopril is safer or more effective than captopril or enalapril in the treatment of hypertension or CHF requires further investigation. Prolonged duration of action of lisinopril allows once daily dosing, unlike captopril for which dosing is required every 8-12 hours or enalapril which may necessitate twice daily dosing.

Renal perfusion and function. The implications of converting enzyme inhibition

Because the kidney is both the source of circulating renin and the final determinant of the state of sodium balance, which in turn defines responsiveness to angiotensin II, one might have anticipated substantial interest in the impact of converting enzyme inhibitors on the kidney when these agents were developed. The lessons learned about the role of the renin-angiotensin system in normal renal perfusion and function, and possible disorders of control that contribute to disease in patients with essential hypertension, renovascular hypertension, and chronic progressive renal parenchymal disease are reviewed. In each case, the lessons here have important implications for the clinical application of converting enzyme inhibition.

Angiotensin-converting enzyme inhibitors

There is convincing evidence that ACE inhibitors, alone or in combination with a diuretic, effectively lower blood pressure in patients with all grades of essential or renovascular hypertension and that they are of particular benefit as adjunctive therapy in patients with congestive heart failure. The hemodynamic, hormonal and clinical effects of the presently available ACE inhibitors, captopril and enalapril, are comparable and their side effect profiles are extremely favorable. One important difference between the two oral ACE inhibitors, however, is their pharmacokinetics; enalapril's action is slower to begin and is of longer duration. Compared with other agents, ACE inhibitors offer important advantages, among them an improved feeling of well being. It is, therefore, expected that ACE inhibitors will gain greater acceptance by patients and physicians in the future.

The renin-angiotensin systems

The renin-angiotensin systems are important regulators of cardiovascular homeostasis and participate in a variety of pathological conditions. Recent advances have not only clarified the functioning of the systemic renin cascade but have also indicated the importance of the generation of angiotensin in tissues.

Ramipril for hypertension secondary to renal artery stenosis. Changes in blood pressure, the renin-angiotensin system and total and divided renal function

The converting enzyme inhibitor, ramipril, 20 mg once daily, was given to 3 hypertensive patients with unilateral renovascular disease. At 1 month, 24 hours after the last dose of ramipril, blood pressure, plasma angiotensin II and converting enzyme activity remained low, and active renin and angiotensin I high. There was no tendency for converting enzyme inhibition to be overcome during 1 month of ramipril therapy. Ramipril caused slight increases in serum potassium and urea, no change in serum creatinine and no consistent changes in the renal vein renin ratio. Ramipril caused little change in renal plasma flow on the stenotic side, but filtration fraction was reduced in 2 patients. There was no serious deterioration in total or individual glomerular filtration rate during ramipril therapy. The drug was well tolerated and there were no serious side effects. Ramipril, given once daily, is likely to be effective in controlling hypertension with renal artery stenosis.

The clinical use of angiotensin converting enzyme inhibitors in hypertension and cardiac failure

The renin-angiotensin system has a range of physiological actions concerned with the control of the circulation. Angiotensin II has both an immediate and a delayed pressor effect, it stimulates the secretion of aldosterone and antidiuretic hormone, promotes thirst, stimulates the sympathetic nervous system at various sites while inhibiting vagal tone, and has a range of direct effects on the kidney. Several aspects of this range of actions can become deranged in a number of forms of hypertension as well as in congestive cardiac failure. Hence much effort has been directed in recent years to the development of agents designed to interfere with the renin-angiotensin system and to apply these clinically in the treatment of hypertension and congestive cardiac failure. Orally active converting enzyme inhibitors are of proven benefit not only in renovascular hypertension, but also, when combined with loop diuretics, in the treatment of intractable hypertension as well as, both alone and in combination with thiazide diuretics, in the treatment of essential hypertension. In congestive cardiac failure controlled trials have shown that converting enzyme inhibitors can improve exercise tolerance while diminishing lassitude, correct potassium deficiency and limit ventricular arrhythmias. Energetic efforts are being made to develop orally active inhibitors of the enzyme renin itself, since these would be more specific in action than the presently available and very successful converting enzyme inhibitors.

Effects of converting enzyme inhibition on split renal function in renovascular hypertension

The effects of captopril on effective renal plasma flow and glomerular filtration rate were studied using a noninvasive radioisotopic method on individual kidneys in eight patients with renovascular hypertension and 12 patients with essential hypertension with various renin levels. Four patients with renovascular hypertension had unilateral while three had bilateral renal artery stenosis. The effective renal plasma flow and glomerular filtration rate were determined by using 131I-iodohippurate sodium and 99mTc-diethylenetriamine pentaacetic acid, respectively. Glomerular filtration rate and effective renal plasma flow were significantly reduced in the stenotic kidneys of patients with renovascular hypertension compared with values in nonstenotic kidneys (p less than 0.01). Treatment with captopril, 37.5 to 75 mg/day for 1 to 48 weeks, further reduced the glomerular filtration rate only in stenotic kidneys, and effective renal plasma flow increased in both kidney types. In two of the three renal hypertensive patients with bilateral renal artery stenosis, captopril produced a reversible azotemia that was unrelated to the fall in blood pressure, as evidenced by the lack of azotemia seen after a moderate blood pressure reduction induced by other antihypertensive medications. These results indicate that endogenous angiotensin II is essential in maintaining the glomerular filtration rate in stenotic kidneys and suggest that a reduction in glomerular filtration rate during captopril administration could indicate the presence of renal artery stenosis.

Use of the converting enzyme inhibitor enalapril in renovascular hypertension. Effect on blood pressure, renal function, and the renin-angiotensin-aldosterone system

Thirteen patients were entered into a protocol to assess the safety and efficacy of enalapril (MK 421), 5 to 20 mg b.i.d., and hydrochlorothiazide, 50 to 100 mg daily, for the treatment of renovascular hypertension. Specifically monitored were the effects of therapy on blood pressure and pulse, renal function, and the renin-angiotensin-aldosterone axis. Enalapril and hydrochlorothiazide therapy produced excellent control of blood pressure with no adverse side effects. After approximately 8 weeks of therapy, renal vascular resistance was decreased and no adverse effects on glomerular filtration rate or renal blood flow were noted, except in one patient with a functional unilateral stenotic kidney. Patients receiving enalapril and hydrochlorothiazide showed stimulation of plasma renin activity and suppression of plasma angiotensin II, although the initial degree of suppression was not sustained in all patients during prolonged therapy. Although plasma aldosterone concentration was initially suppressed, the degree of suppression was not sustained. Nine patients have been followed for an additional 6 months; none have experienced further progression of renal disease, as assessed by repeated measurements of glomerular filtration and effective renal plasma flow. These results suggest that combined enalapril and hydrochlorothiazide therapy is safe and effective in the medical management of renovascular hypertension and that blood pressure control may be achieved in the absence of sustained interruption of the renin-angiotensin-aldosterone system.

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)

[Angiotensin-converting enzyme inhibition: direct and indirect mechanisms]

The introduction of angiotensin-converting-enzyme (ACE)-inhibitors into the analysis of the renin-angiotensin system (RAS) had broadened our knowledge of the integral role of renin and the kidney in circulatory homeostasis and has provided a pathophysiologically based concept for the treatment of hypertension. When the RAS is activated, as it is when sodium is restricted, the renal blood supply shows the most striking vasodilatation among vascular beds assessed after ACE-inhibition. Sodium excretion rises, there is a fall in blood-pressure, and plasma concentrations of angiotensin II (AII) and aldosterone are reduced. Conversely, with sodium loading the hemodynamic and hormonal effects of ACE-inhibitors are small. In 50-60% of normal or high-renin patients with essential hypertension ACE-inhibitors induce a potentiated acute renal response: renal blood flow and sodium excretion increase more than they do in the remainder of the hypertensives or in normal subjects. The responders of the hypertensive patients fail to increase renal blood flow or to enhance renal vascular responsiveness to infused AII when they shift from a low to a high sodium intake. The altered renal response of these "sodium-sensitive" hypertensives could be related to local activity of the RAS which is insufficiently suppressed by sodium loading. ACE-inhibition reverses this failure of the renal blood supply to respond to sodium loading. Kidneys of spontaneously hypertensive rats and the renin-rich kidney of Goldblatt-hypertensive rats show an increased tubulo glomerular (TG) feedback response as compared to normal kidneys. The change in TG-feedback response might be expected to contribute to the inability of the hypertensive kidney to respond adequately to sodium loading. ACE-inhibition reduces TG-feedback sensitivity. In renal artery stenosis glomerular capillary pressure tends to be maintained by an AII mediated rise in postglomerular resistance. Suppression of AII by ACE-inhibition reduces efferent vascular tone and thus filtration rate. There is a potential for interaction of ACE-inhibitors with the kallikrein and prostaglandin pathways as well as with the sympathetic nervous system and endogenous opioids. This may modify the renal and blood pressure responses to these compounds.

Resistance to captopril in hypertension of coarctation of the aorta

Two patients with hypertension due to coarctation of the aorta were treated for 12 weeks with captopril at increasing doses. After an immediate response, resistance developed to captopril, which was associated with restoration of initially elevated renin and plasma aldosterone levels. Lack of hypertension control may be related to long-term reappearance of mechanisms which lead to excessive renin stimulation.

A dose-response study of HOE 498, a new non-sulphydryl converting enzyme inhibitor, on blood pressure, pulse rate and the renin-angiotensin-aldosterone system in normal man

The effect of different oral doses of HOE 498, a new non-sulphydryl containing converting enzyme inhibitor, was investigated in a double-blind, placebo-controlled study in normotensive volunteers. Dose-related reductions in serum converting enzyme activity, plasma angiotensin II and aldosterone were seen, greater at 4 h than at 12 h after drug ingestion. Converse dose-related increases in blood angiotensin I and plasma active renin concentration occurred. Falls of angiotensin II were as great with 20 mg as with 50 mg of HOE 498, although the effect was more prolonged with 50 mg. The reductions in concentrations of plasma angiotensin II and serum converting enzyme activity and the increases in plasma renin concentration were correlated with the concentration of HOE 498 - diacid in plasma. Dose-related falls in both supine and erect blood pressure were maximal 2-3.5 h after dosing. Pulse rate increased marginally but insignificantly in the supine; slightly and significantly in the upright position, concomitantly with the blood pressure reduction at all doses of active drug. We conclude that effects of single doses of HOE 498 on the renin-angiotensin system are maximal within 4 h, but are still apparent after 24 h. Thus it is likely that once daily administration will be adequate for treatment of high blood pressure in patients.

Enalapril in treatment of hypertension with renal artery stenosis. Changes in blood pressure, renin, angiotensin I and II, renal function, and body composition

The converting enzyme inhibitor enalapril, in single daily doses of 10 to 40 mg, was given to 20 hypertensive patients with renal artery stenosis. The decrease in blood pressure six hours after the first dose of enalapril was significantly related to the pretreatment plasma concentrations of active renin and angiotensin II, and to the concurrent decrease in angiotensin II. Blood pressure decreased further with continued treatment; the long-term decrease was not significantly related to pretreatment plasma renin or angiotensin II levels. At three months, 24 hours after the last dose of enalapril, blood pressure, plasma angiotensin II, and converting enzyme activity remained low, and active renin and angiotensin I high; six hours after dosing, angiotensin II had, however, decreased further. The increase in active renin during long-term treatment was proportionately greater than the increase in angiotensin I; this probably reflects the diminution in renin substrate that occurs with converting enzyme inhibition. Long-term enalapril treatment increased renin secretion by more than 10-fold, and renal venous and peripheral plasma renin concentration by more than 20-fold; however, the mean renal venous renin ratio was not changed. Enalapril caused a reduction in effective renal plasma flow via the affected kidney but a marked and consistent increase on the contralateral side, where renal vascular resistance decreased. The overall increase in effective renal plasma flow was significantly related to the decrease in angiotensin II. Overall glomerular filtration rate was lowered, and serum creatinine and urea increased. Enalapril alone caused a long-term reduction in exchangeable sodium, with slight but distinct increases in serum potassium. In five patients with bilateral renal artery lesions, enalapril given alone for three months did not cause renal function to deteriorate. Enalapril was well tolerated and provided effective long-term control of hypertension; only two of the 20 patients studied required concomitant diuretic treatment.

Renal hemodynamics in essential and renovascular hypertension. Influence of captopril

Among vascular beds, that of the kidney is especially responsive to angiotensin II, perhaps a reflection of the fact that the renin-angiotensin axis is normally a volume-control rather than a pressure-control system. The dose of angiotensin required to induce renal vasoconstriction in a normal subject receiving a typical, liberal sodium intake, for example, is about an order of magnitude lower than that required to induce a pressor response. Indeed, compelling arguments can be made for a local, intrarenal role as angiotensin's first action in phylogeny, with additional cardiovascular and endocrine responses arising later. In patients with essential hypertension, in whom renal vascular tone is commonly increased, converting enzyme inhibitors such as teprotide and captopril induce a potentiated acute renal vascular response: renal blood flow increases more than it does in normal subjects. The result is a consistent, early increase in sodium excretion and an occasional increase in glomerular filtration rate. Reduced aldosterone release consequent to the block of angiotensin II formation also contributes to the natriuresis and results in positive potassium balance. With long-term therapy, renal function tends to be very well maintained. In renal artery stenosis the situation is more complex: as perfusion pressure distal to the stenosis falls, typically afferent arteriolar dilatation exists and glomerular capillary pressure tends to be maintained by an increase in postglomerular resistance. To the extent that this increase is angiotensin-mediated, suppression of angiotensin formation with captopril can reduce glomerular capillary pressure and thus filtration rate. This is well tolerated in the patient with unilateral stenosis and a healthy contralateral kidney, but can provoke renal failure when the stenosis is bilateral or involves a solitary kidney. The available evidence suggests that the converting enzyme inhibitor's influence on the kidney primarily reflects reduced angiotensin II formation, although reduced kinin degradation or increased prostaglandin synthesis may also have an influence. Whatever the mechanism responsible for the renal response, there are compelling reasons for suspecting that the salutary action of captopril on the kidney makes a substantial contribution to its over-all efficacy in the treatment of hypertension.

Enalapril in the treatment of hypertension with renal artery stenosis

The converting enzyme inhibitor enalapril, in single daily doses of 10-40 mg, was given to 20 hypertensive patients with renal artery stenosis. The blood pressure fall six hours after the first dose of enalapril was significantly related to the pretreatment plasma concentrations of active renin and angiotensin II and to the concurrent fall in angiotensin II. Blood pressure fell further with continued treatment; the long term fall was not significantly related to pretreatment plasma renin or angiotensin II concentrations. At three months, 24 hours after the last dose of enalapril, blood pressure, plasma angiotensin II, and converting enzyme activity remained low and active renin and angiotensin I high; six hours after dosing, angiotensin II had, however, fallen further. The rise in active renin during long term treatment was proportionally greater than the rise in angiotensin I; this probably reflects the fall in renin substrate that occurs with converting enzyme inhibition. Enalapril alone caused reduction in exchangeable sodium, with distinct increases in serum potassium, creatinine, and urea. Enalapril was well tolerated and controlled hypertension effectively long term; only two of the 20 patients required concomitant diuretic treatment.

Long-term converting-enzyme inhibition as a guide to surgical curability of hypertension associated with renovascular disease

Converting-enzyme inhibition as a guide to the hypotensive response to be expected from surgery was evaluated in 27 hypertensive patients with renovascular disease. Blood pressure averaged 163 +/- 5/102 +/- 2 mm Hg (mean +/- standard error of the mean) during converting-enzyme inhibition with captopril, 518 +/- 29 mg daily for 2.8 +/- 0.3 months, and stabilized at a similar level of 165 +/- 4/104 +/- 3 mm Hg during 5.0 +/- 0.6 months of postoperative follow-up, when no medication was administered. Postoperative pressure, both systolic (r = +0.53; p = 0.004) and diastolic (r = +0.55; p = 0.003), was correlated with blood pressure during converting-enzyme inhibition. In addition, multiple regression analysis identified systolic pressure during converting-enzyme inhibition as the only significant (p less than 0.01) predictor of postoperative systolic pressure. Diastolic pressure during converting-enzyme inhibition (p less than 0.05) in conjunction with circulating renin (p less than 0.05) and renin suppression from the contralateral kidney (p less than 0.01) explained up to 53% of the postoperative diastolic pressure. Therefore, blood pressure during long-term converting-enzyme inhibition may be useful as a predictor of the postoperative blood pressure in hypertensive patients with renovascular disease.