Renal vascular responses to renin inhibition with zankiren in men

Effects of Direct Renin Blockade on Renal & Systemic Hemodynamics and on RAAS Activity, in Weight Excess and Hypertension: A Randomized Clinical Trial

Aim

The combination of weight excess and hypertension significantly contributes to cardiovascular risk and progressive kidney damage. An unfavorable renal hemodynamic profile is thought to contribute to this increased risk and may be ameliorated by direct renin inhibition (DRI). The aim of this trial was to assess the effect of DRI on renal and systemic hemodynamics and on RAAS activity, in men with weight excess and hypertension.

Methods

A randomized, double-blind, cross-over clinical trial to determine the effect of DRI (aliskiren 300 mg/day), with angiotensin converting enzyme inhibition (ACEi; ramipril 10 mg/day) as a positive control, on renal and systemic hemodynamics, and on RAAS activity (n = 15).

Results

Mean (SEM) Glomerular filtration rate (101 (5) mL/min/1.73m²) remained unaffected by DRI or ACEi. Effective renal plasma flow (ERPF; 301 (14) mL/min/1.73m²) was increased in response to DRI (320 (14) mL/min/1.73m², P = 0.012) and ACEi (317 (15) mL/min/1.73m², P = 0.045). Filtration fraction (FF; 34 (0.8)%) was reduced by DRI only (32 (0.7)%, P = 0.044). Mean arterial pressure (109 (2) mmHg) was reduced by DRI (101 (2) mmHg, P = 0.008) and ACEi (103 (3) mmHg, P = 0.037). RAAS activity was reduced by DRI and ACEi. Albuminuria (20 [9–42] mg/d) was reduced by DRI only (12 [5–28] mg/d, P = 0.030).

Conclusions

In men with weight excess and hypertension, DRI and ACEi improved renal and systemic hemodynamics. Both DRI and ACEi reduced RAAS activity. Thus, DRI provides effective treatment in weight excess and hypertension.

Trial Registration

Dutch trial register, registration number: 2532 www.trialregister.nl

Renin inhibitors and cardiovascular and renal protection: an endless quest?

Renin-angiotensin system (RAS) blockade with angiotensin-converting enzyme (ACE) inhibitors or angiotensin receptor blockers (ARBs) has become a major therapeutic approach in medicine since the end of the 1970's. Although these molecules were the first RAS blockers to be developed, it would have been physiologically and pharmacologically more pertinent to selectively inhibit renin itself. Indeed, the reaction between renin and its unique substrate, angiotensinogen, is the highly regulated and rate-limiting step of the RAS. The development of direct renin inhibitors (DRI) has been a slow and complex process and the synthesis of the first orally active DRI, aliskiren, was only achieved in the 2000's. Its pharmacological profile in patients with hypertension, diabetic nephropathy or heart failure, in addition to experimental evidence, suggests that aliskiren may be of value for the management of cardiovascular and renal diseases. However, the long-term, randomized, placebo-controlled, morbidity/mortality trial, ALTITUDE, which included 8,600 patients with type 2 diabetes, proteinuria and a high cardiovascular risk already treated with ACE inhibitors or ARBs was terminated in December 2011 because of futility and an increased incidence of serious adverse events in the aliskiren 300 mg arm. Other long-term studies are still ongoing to demonstrate the safety and efficacy of aliskiren to reduce cardiovascular morbidity and mortality in patients with heart failure and in elderly individuals (≥65 years) with systolic blood pressure of 130 to 159 mmHg, no overt cardiovascular disease, and a high cardiovascular risk profile. In the meantime, according to the European Medicines Agency recommendations, aliskiren should not be prescribed to diabetic patients in combination with ACE inhibitors or ARBs.

Entry-into-humans study with a new direct renin inhibitor

PURPOSE

To evaluate the pharmacokinetics, pharmacodynamics, safety, and tolerability of escalating single oral doses of ACT-077825, a novel orally active renin inhibitor, in healthy male subjects.

METHODS

In this single-center, double-blind, placebo- and active-controlled (with enalapril) randomized study, 70 subjects received a single dose of ACT-077825 (1-1,000 mg), placebo, or enalapril 20 mg under fasted conditions. The main pharmacokinetic endpoints were area under the plasma ACT-077825 concentration-time curve from time zero to infinity and the terminal half-life (t(1/2)). The pharmacodynamic endpoints included immunoactive active renin (iAR) plasma concentrations and plasma renin activity (PRA). Standard laboratory and safety data were collected.

RESULTS

Of the few adverse events reported, diarrhea and headache were the most frequent. The pharmacokinetics of ACT-077825 were dose-proportional in the dose range 100 to 1,000 mg. Terminal t(1/2), best characterized following a dose of 1,000 mg, was 41.6 h and t(max) 4-5 h post-dose. ACT-077825 dose-dependently increased iAR and decreased PRA, effects that were associated with a decrease in blood pressure at 1,000 mg, similar to following treatment with enalapril.

CONCLUSION

The results provide evidence that ACT-077825, with a pharmacokinetic profile consistent with a once-a-day dosing regimen, may represent an effective antihypertensive agent and pave the way toward a multiple-ascending dose study.

Renal and cardio-protective effects of direct renin inhibition: a systematic literature review

BACKGROUND

Blockade of the renin-angiotensin-aldosterone system (RAAS) at its rate-limiting step by means of renin inhibition has led to the development of direct renin inhibitors (DRIs). Given the renal and cardioprotective effects of RAAS blockade by angiotensin-converting enzyme inhibitors and angiotensin-receptor blockers, DRIs may increase the armamentarium for further organ protection. Over the last two decades the effects of DRIs on biomarkers for renal and cardiovascular disease have been investigated. This systematic review aims to delineate the effects of DRIs on surrogate markers of renal and cardiovascular function.

METHODS

MEDLINE and previous systematic reviews were searched for articles reported between 1980 and 2008. A standardized dataset was extracted from articles describing the effects of DRIs on markers of renal and cardiac damage and hard outcomes.

RESULTS

Fifty-two articles were included. Blood pressure reductions were generally insufficient using early generation DRIs. However, recent DRIs have greater blood pressure-lowering effects. Preclinical and clinical studies showed profound effects of DRIs on markers of renal function, including clear increases in renal plasma flow and reductions in albuminuria. These effects were observed either alone or in combination with other RAAS inhibitors and suggest potential large renal protective benefit. DRIs improved hemodynamic cardiovascular parameters, such as total peripheral resistance, arterial pressure and left ventricular mass index, to a similar extent as those observed with other RAAS inhibitors. Furthermore, addition of DRIs to optimal heart failure treatment resulted in further reductions in B-type natriuretic peptide.

CONCLUSIONS

Evidence from preclinical and clinical studies suggests that DRIs may have renal and cardiovascular effects beyond their ability to lower blood pressure. Results of ongoing hard outcome trials are awaited to definitively assess the renal and cardio-protective effects of these agents.

Direct renin inhibitors: ONTARGET for success?

Direct renin inhibitors are the first new class of antihypertensive to emerge since angiotensin II receptor blockers. We discuss their reno- and cardioprotective potential, based on extrapolation from animal models and phase three trials that are currently ongoing. This paper reviews the potential benefits of direct renin inhibitors (DRIs), the only new anti-hypertensive class developed in the last decade, as compared to pre-existing classes of drug inhibiting more downstream, such as Angiotensin Converting Enzyme inhibitors (ACEI), Angiotensin 2 Receptor Blockers (ARBS).

Renin inhibition with aliskiren

1. Initial attempts to inhibit renin in humans have faced numerous difficulties. Molecular modelling and X-ray crystallography of the active site of renin have led to the development of new orally active renin inhibitors, such as aliskiren. 2. Aliskiren has a low bioavailability (between 2.6 and 5.0%) compensated by its high potency to inhibit renin (IC50: 0.6 nmol/L) and a long plasma half-life (23-36 h), which makes it suitable for once-daily dosing. 3. The once-daily administration of aliskiren to hypertensive patients lowers BP as strongly as standard doses of established angiotensin II type 1 (AT1) receptor blockers (losartan, valsartan, irbesartan), hydrochlorothiazide, angiotensin converting enzyme inhibitors (ramipril and lisinopril) or long acting calcium channel blockers (amlodipine). In combination therapy, aliskiren further decreases blood pressure when combined with either hydrochlorothiazide, amlodipine, irbesartan or ramipril. 4. The biochemical consequences of renin inhibition differ from those of angiotensin I-converting enzyme (ACE) inhibition and Ang II antagonism, particularly in terms of angiotensin profiles and interactions with the bradykinin-nitric oxide-cyclic guanosine monophosphate pathway and possibly the (pro)renin receptor. 5. Blockade of the renin angiotensin system (RAS) with ACE inhibitors, AT1 receptor blockers or a combination of these drugs has become one of the most successful therapeutic approaches in medicine. However, it remains unclear how to optimize RAS blockade to maximize cardiovascular and renal benefits. In this context, renin inhibition to render the RAS fully quiescent is a new possibility requiring further study.

Renin inhibitors: optimal strategy for renal protection

Diabetic nephropathy and hypertension are the major causes of chronic kidney disease. The renin system plays a key role in the control of blood pressure (BP), as well as in the regulation of renal and adrenal function. Chronic activation of the renin system can lead to organ damage, particularly renal damage; increasing evidence indicates that suppression of the renin system can provide renal protection. Despite the use of angiotensin-converting enzyme inhibitors (ACEIs) and angiotensin II receptor blockers (ARBs), the renin system is not completely suppressed. The direct renin inhibitors (DRIs) provide suppression of the entire renin system at the rate-limiting step. Studies in humans with early DRIs indicated potential renoprotective effects, but these agents failed in clinical development due to poor oral bioavailability. Aliskiren is a new orally active DRI with proven BP-lowering effects. Animal studies indicate that aliskiren may provide renal protection, and data from human studies are anticipated.

Oral renin inhibitors

Use of drugs that inhibit the renin-angiotensin system is an effective way to intervene in the pathogenesis of cardiovascular and renal disorders. The idea of blocking the renin system at its origin by inhibition of renin has existed for more than 30 years. Renin inhibition suppresses the generation of the active peptide angiotensin II. The first generation of orally active renin inhibitors were never used clinically because of low bioavailability and weak blood-pressure-lowering activity. At present, aliskiren is the first non-peptide orally active renin inhibitor to progress to phase-III clinical trials. It might become the first renin inhibitor with indications for the treatment of hypertension and cardiovascular and renal disorders. Novel compounds with improved oral bioavailability, specificity, and efficacy are now in preclinical development. This Review summarises the development of oral renin inhibitors and their pharmacokinetic and pharmacodynamic properties, with a focus on aliskiren.

Renin inhibition

PURPOSE OF REVIEW

Initial attempts to inhibit renin in humans have faced numerous difficulties. Molecular modeling and X-ray crystallography of the active site of renin have led to the development of new orally active renin inhibitors, such as aliskiren. Recent preclinical and clinical data suggest that this drug may be of value for treating patients with cardiovascular and renal disorders.

RECENT FINDINGS

The once-daily administration of aliskiren to hypertensive patients lowers blood pressure as strongly as, or more strongly than, standard doses of established angiotensin II type 1 receptor blockers. It further decreases blood pressure in combination with hydrochlorothiazide. The biochemical consequences of renin inhibition differ from those of angiotensin I-converting enzyme inhibition and angiotensin II antagonism, particularly in terms of angiotensin profiles and interactions with the bradykinin-nitric oxide-cGMP pathway and possibly the (pro)renin receptor.

SUMMARY

Blockade of the renin-angiotensin system with angiotensin I-converting enzyme inhibitors, angiotensin II type 1 receptor blockers or a combination of these drugs has become one of the most successful therapeutic approaches in medicine. It remains unclear, however, as to how to optimize the renin-angiotensin system blockade to maximize cardiovascular and renal benefits. In this context, renin inhibition to render the renin-angiotensin system fully quiescent is a new possibility requiring further study.

Renin Inhibition: What Are the Therapeutic Opportunities?

Blockade of the renin-angiotensin system with angiotensin-converting enzyme inhibitors or angiotensin receptor blockers has become a crucial element in cardiovascular and renal medicine. This review evaluates the potential of renin inhibition as an adjunct to therapies that depend on renin system interruption.

Angiotensin receptor blockers in diabetic nephropathy

Where shall we place angiotensin receptor blockers in the scheme of the prevention of diabetic nephropathy? Only the results of a large, randomized double-blind trial with a comparable and appropriate alternative would prove therapeutic efficacy. The results of several trials with angiotensin-converting enzyme (ACE) inhibitors have proven them to be the standard of care for diabetics and their kidneys. As reviewed in this article, the results of three large such clinical trials have recently been completed with angiotensin receptor blockers in patients with type 2 diabetes mellitus. Initial results appear favorable. However, whether angiotensin blockers have more to offer than ACE inhibitors is still speculative. The renin-angiotensin system plays an important role in the pathogenesis of diabetic nephropathy. Since alternative pathways to ACE have been uncovered in the formation of angiotensin II, inhibition at the final end point would provide favored blockade. Because angiotensin receptor blockers do provide this specific blockade, they offer far more promise than ACE inhibitors.

Is there a future for renin inhibitors?

Pharmacological interruption of the renin-angiotensin system is possible at three major sites, the angiotensin-converting enzyme (ACE), the AT1 receptor and at the interaction of renin with its substrate, angiotensinogen. Skeggs and his associates in 1957 argued logically but without prognostic accuracy that 'since renin is the initial and rate-limiting substance in the renin-angiotensin system, it would seem that the renin inhibition approach would be the most likely to succeed'. In fact, the development of agents that act at all three levels has enjoyed substantial success, yet renin inhibition, which showed early progress in studies in humans, has languished. Our task in this essay is to review the reasons for the slow evolution of renin inhibition and to discuss the potential of such agents in modern pharmacotherapy. All of the structure-action relationships have involved variation on the original peptide structure. The possibility that alternative approaches based on x-ray crystallography and reconstruction of the structure of the active site would lead to novel agents, appears not to have been explored systematically. This opportunity is all the more attractive because renin is one of the few targets that is actually soluble and amenable to x-ray crystallographic studies. At the moment, it appears that all renin inhibitor development programs have been closed, although hints periodically reappear to indicate that one company or another is pursuing a novel agent. The decision to close programs seems to have reflected not the therapeutic potential of renin inhibitors, but rather the cost of their synthesis, continuing problems with bioavailability and the remarkable success of the competitor class--the AngII antagonists. We believe that the potential of renin inhibition in human therapy has been under estimated and still shows substantial promise.

Renal hemodynamic and hormonal responses to the angiotensin II antagonist candesartan

The development of very specific blockers for the angiotensin II type 1 (AT(1)) receptor made it possible to examine the contribution of angiotensin II to normal control mechanisms and disease with a specificity beyond what ACE inhibitors could provide. In the present study, we explored the contribution of angiotensin II to 2 renal mechanisms: renal hemodynamics and the short feedback loop, in which angiotensin II acts as a determinant of renin release. To make that comparison, we studied healthy volunteers in balance on a 10-mmol sodium intake to activate the renin system. Our goal was to compare the relation between the dose of candesartan, an AT(1) receptor blocker, and the renal hemodynamic and hormonal responses. A second goal was to ascertain the relation between time after candesartan administration and the peak response. Twelve healthy subjects (mean age 33+/-2.3 years) in low-sodium balance were administered candesartan in 4-, 8-, 16-, and 32-mg doses. Candesartan produced a dose-related increase in renal plasma flow, with the maximum vasodilator response at 16 mg (142+/-13 mL. min(-1). 1.73 m(-2)) occurring during the first 4 hours after the dose. Likewise, candesartan caused a dose-related rise in plasma renin activity, with 32 mg as the dose producing the greatest response at 4 and 24 hours after administration. The peak plasma renin activity achieved in this study (15.3+/-1.6 ng. L(-1). s(-1); 55.0+/-5.6 ng angiotensin I. mL(-1). h(-1)) was found at the 4- to 8-hour interval after dosing in a subset of subjects (n=5) who received the 16-mg dose 4 hours earlier than the other subjects. On the basis of the difference in the relation between dose and response and the relationship between time after drug administration and response, the determinants of the renal hemodynamic and hormonal response can be said to differ. The remarkable rise in plasma renin activity after candesartan is substantially larger than that in earlier studies with ACE inhibition, providing additional evidence for non-ACE-dependent angiotensin II generation in the kidney.

Renal and systemic effects of continued treatment with renin inhibitor remikiren in hypertensive patients with normal and impaired renal function

BACKGROUND

Remikiren is an orally active renin inhibitor with established antihypertensive efficacy. As a single dose it induces renal vasodilatation, suggesting specific renal actions. Data on the renal effects of continued treatment by renin inhibition are not available, either in subjects with normal, or in subjects with impaired renal function.

METHODS

The effect of 8 days of treatment with remikiren 600 mg o.i.d. on blood pressure, renal haemodynamics, and proteinuria was studied in 14 hypertensive patients with normal or impaired renal function.The study was conducted on an ambulatory in-hospital basis and was designed in a single-blind, longitudinal order.

RESULTS

Remikiren induced a significant peak fall in mean arterial pressure of 11.2+/-0.8%, with corresponding trough values of -6+/-0.8%. This fall was somewhat more pronounced in the patients with renal function impairment (-13.3 vs -9.6%; P<0.01). Glomerular filtration rate remained stable, whereas effective renal plasma flow increased from 301+/-35 to 330+/-36 ml/min/1.73 m(2) (P<0.05). Filtration fraction and renal vascular resistance fell by 10+/-2% and 15+/-2% respectively (both P<0.01). Remikiren induced a cumulated sodium loss of -82+/-22 mmol and a positive potassium balance of 49+/-9 mmol (both P<0.01). During remikiren, proteinuria fell by 27% (range -18 to -38%; P<0.01) in the patients with overt proteinuria at onset (n=6). In the remainder of the patients albuminuria fell by 20% (range -1 to -61%, P<0.05). No side-effects were observed.

CONCLUSIONS

Continued treatment with remikiren induced a sustained fall in blood pressure, renal vasodilatation, negative sodium balance, and a reduction in glomerular protein leakage. These data are consistent with a renoprotective potential of renin inhibition.

Implications of species difference for clinical investigation: studies on the renin-angiotensin system

The justification for clinical investigation has its roots in the fact that physiological mechanisms and disease pathogenesis in animal models replicate mechanisms and pathogenesis in humans only in part. In the case of the renin-angiotensin system, there is species variation in the anatomic distribution of the renin-angiotensin system, in the active site of the renin enzyme, and in the structure of angiotensin and the AT(1) receptor. The conversion of angiotensin I (Ang I) to angiotensin II (Ang II) may prove to be the most important aspect of species variation. In plasma, all the conversion occurs through a single enzyme, angiotensin-converting enzyme (ACE), and species variation in structure and function have not been reported. Non-ACE-dependent pathways, which occur only at the tissue level, show unambiguous, striking species variation. Specifically, chymase, the most important enzyme responsible for non-ACE conversion of Ang I to Ang II, shows striking species variation. In humans and a number of species, including the hamster, quantitatively important chymase-independent Ang II formation from Ang I occurs in the heart, arteries, and kidney. In rats and rabbits, on the other hand, chymase differs, is not active in the conversion of Ang I to Ang II, and indeed is involved in Ang II degradation. Consequently, one would anticipate that blockade of the system at the ACE step would be equivalent to that at the Ang II receptor in the rat. This has been widely reported. In humans, on the other hand, one would anticipate that the AT(1) receptor blockers will be more effective than ACE inhibitors. Again, preliminary evidence favors this possibility. The implications for therapeutics are clear.

Pathways for angiotensin II generation in intact human tissue: evidence from comparative pharmacological interruption of the renin system

Multiple lines of evidence have suggested that alternative pathways to the angiotensin-converting enzyme (ACE) exists for angiotensin II (Ang II) generation in the heart, large arteries, and the kidney. In vitro studies in intact tissues, homogenates, or membrane isolates from the heart and large arteries have repeatedly demonstrated such pathways, but the issue remains unresolved because the approaches used have not made it possible to extrapolate from the in vitro to the in vivo situation. For our in vivo model, we studied young and healthy human volunteers, for the most part white and male; when these subjects achieved balance on a low salt diet to activate the renin system, the response of renal perfusion to pharmacological interruption of the renin system was studied. With this approach, we studied the renal vasodilator response to 3 ACE inhibitors, 2 renin inhibitors, and 2 Ang II antagonists at the top of their respective dose-response relationships. When these studies were initiated, our premise was that a kinin-dependent mechanism contributed to the renal hemodynamic response to ACE inhibition; therefore, the renal vasodilator response to ACE inhibition would exceed the alternatives. To our surprise, both renin inhibitors and both Ang II antagonists that were studied induced a renal vasodilator response of 140 to 150 mL/min/1.73 m2, approximately 50% larger than the maximal renal hemodynamic response to ACE inhibition, which was 90 to 100 mL/min/1.73 m2. In light of the data from in vitro systems, our findings indicate that in the intact human kidney, virtually all Ang II generation is renin-dependent but at least 40% of Ang I is converted to Ang II by pathways other than ACE, presumably a chymase, although other enzyme pathways exist. Preliminary data indicate that the non-ACE pathway may be substantially larger in disease states such as diabetes mellitus. One implication of the studies is that at the tissue level, Ang II antagonists have much greater potential for blocking the renin-angiotensin system than does ACE inhibition-with implications for therapeutics.

Renal hemodynamic response to an angiotensin II antagonist, eprosartan, in healthy men

In view of the vasodilator potential of angiotensin-converting enzyme (ACE) inhibition via prostaglandins and kinins, we asked why renin inhibition induces a larger renal vasodilator response than ACE inhibitors in healthy humans in earlier studies. One possibility was that there was a more complete blockade of the renin system, which could also be achieved by an angiotensin II antagonist, eprosartan. We measured the hormonal and renal hemodynamic responses to eprosartan doses, from 10 to 400 mg in 9 healthy young men in balance on a 10-mmol/d sodium intake. The threshold eprosartan dose to influence renal perfusion was <10 mg, and the 100-mg dose induced a near-maximal vasodilator response of 135+/-19.7 mL x min(-1) x 1.73 m2. When the dose was increased to 400 mg, there was a modest additional increase of 147+/-57 mL x min(-1) x 1.73 m(-2). A highly significant dose-related fall in arterial blood pressure occurred (r=-.97; P<.001), with no indication of a maximal response at 400 mg. In 6 additional subjects, we compared responses to eprosartan on a high salt and a low salt diet. The renal response to 200 mg eprosartan on a high salt diet, 26.0+/-6.6 mL x min(-1) x 1.73 m(-2), was significantly less than that seen with the low salt diet (P<.001). There was no renal partial agonist angiotensin-like effect of eprosartan. Eprosartan reduced sharply the pressor, renal vascular, and hormonal responses to exogenous angiotensin II. The renal vasodilator response to the angiotensin II antagonist eprosartan closely resembles responses to renin inhibition and exceeds previously reported responses to ACE inhibitors. Thus, eprosartan probably exerted its effect via the angiotensin receptor. More complete blockade of the renin system can be achieved by pharmacological interruption at this level, a finding that could have therapeutic implications.

Renal circulation and blockade of the renin-angiotensin system. Is angiotensin-converting enzyme inhibition the last word?

The mechanism by which angiotensin-converting enzyme (ACE) inhibition influences renal perfusion and function has assumed growing importance as alternatives for blocking the system have emerged. Neither renin inhibitors nor angiotensin II (Ang II) antagonists are likely to trigger responses similar to ACE inhibitor-induced involvement of kinins, prostaglandins, or nitric oxide. Several observations suggest species variation in the contribution of these pathways to the renal response to ACE inhibition. In humans, recent investigation suggests that virtually all of the renal response is due to a fall in Ang II formation. Perhaps most persuasive is the surprising observation that the renal hemodynamic response to renin inhibitors exceeds by more than 50% the response to ACE inhibition in healthy humans. To the extent that kinins or prostaglandins contribute to the renal response to ACE inhibition, one would anticipate a smaller response to renin inhibition. Possible explanations include an unanticipated additional action of renin inhibitors, better tissue penetration of these highly lipophilic agents, or more effective blockade of Ang II formation through an action at the rate-limiting step or non-ACE-dependent Ang II generation. Substantial evidence favors the latter two possibilities. Whatever the explanation, these observations raise the intriguing possibility that the undoubted therapeutic efficacy of ACE inhibition in renal injury, documented most rigorously for type I diabetes mellitus, might be exceeded with the newer classes of agent.

Renin inhibition

Modification of the renin-angiotensin-aldosterone system by renin inhibitors may be an alternative to angiotensin-converting enzyme inhibitors in the treatment of cardiovascular disease. The development of clinically useful renin inhibitors has been hampered by a variety of pharmacologic problems, most notably the poor oral bioavailability of these peptide-related compounds. Peptidomimetic renin inhibitors that have been stabilized to enzymatic degradation in conjunction with optimizing physical characteristics amenable to intestinal absorption offer the greatest promise to date. Studies in animal models demonstrate that renin inhibitors are capable of reducing both systolic and diastolic blood pressures without causing reflex tachycardia. The response appears to be sustained with chronic administration. The beneficial cardiovascular effects of these compounds have been confirmed in the few studies conducted in patients with hypertension and in those with congestive heart failure. Further development of renin inhibitors is warranted.