Abstract

Angiotensin converting enzyme (ACE) inhibitors reduce the development of atherosclerosis in hypercholesterolemic animals across a wide range of species. Although the mechanism for these effects has not been well delineated, it has been assumed generally that both angiotensin II suppression and interference with the breakdown of bradykinin are involved. To determine whether angiotensin II receptor blockade provides similar effects as those observed with ACE inhibition, we examined the influence of irbesartan, an AT1 receptor antagonist, on aortic atherosclerosis in Watanabe heritable hyperlipidemic rabbits using the identical protocol that was employed in our earlier studies involving ACE inhibitors. At a dose of irbesartan (30 mg/kg/day), which was selected because it appeared to block most of the pressor effects of infused angiotensin in rabbits, no effect on atherosclerosis was observed. However, a higher dose of irbesartan (75 mg/kg/day) caused reductions in blood pressure and aortic atherosclerosis similar to those seen in earlier studies with ACE inhibitors. The decrease in aortic intimal surface involvement with irbesartan was from 38.9 ± 3.8% in controls to 24.1 ± 3.0% in the treated group (P < .01). Aortic cholesterol content was also significantly reduced in those animals (P < .02). The findings indicate that suppression of the renin-angiotensin system by AT1 receptor blockade in a genetically hypercholesterolemic rabbit model causes comparable inhibition of aortic atherosclerosis as that achieved by ACE inhibition, and that a mild reduction of blood pressure induced by both classes of agents may contribute to their antiatherosclerotic action in this model. Am J Hypertens 1999;12:28–34 © 1999 American Journal of Hypertension, Ltd.

Considerable interest has been focused on the potential role of angiotensin II (AII) in causing vascular injury and atherosclerosis. Several years ago, our laboratory demonstrated that angiotensin converting enzyme (ACE) inhibitors diminished the development of atherosclerosis in the Watanabe heritable hyperlipidemic (WHHL) rabbit, an animal that has a genetic defect in the low-density lipoprotein (LDL) receptor, which causes elevations in circulating low-density lipoproteins and early onset of atherosclerosis.1,2 Antiatherosclerotic effects of ACE inhibition were also reported subsequently in several other animal models.3,4,5,6 Furthermore, the development of fibromuscular plaques in the rat after arterial balloon-injury was diminished by ACE inhibition.7

As ACE inhibitors have dual effects in reducing conversion of angiotensin I to AII and by blocking bradykinin breakdown, the antiatherosclerotic action of these drugs could be related to either or both of these actions. In the rat carotid artery balloon injury model, studies comparing the effect of losartan, an AT1 receptor antagonist of AII, with that of ACE inhibition, alone or in combination with a bradykinin receptor antagonist, HOE140, have suggested that both the bradykinin-related effects and the inhibition of AII are important in reducing the response to this form of arterial injury.8 In the cholesterol-fed rabbit, contrasting results have been reported regarding the effects of angiotensin II blockade on lesion development. Inhibition of atherosclerosis was observed with the AT1 receptor antagonist, E-4177,9 whereas in a second study, the AT1 blocker, SC51316, had no effect.4

The current investigation was undertaken to examine the action of a new AT1 receptor antagonist, irbesartan, on atherosclerosis in the WHHL rabbit model. The pharmacology of irbesartan has been described by Cazaubon et al.10 The protocol used was essentially identical to that previously employed by us for ACE inhibitors to allow comparisons between the two drug classes. The findings indicate that AT1 receptor blockade with irbesartan in the WHHL rabbit causes a similar inhibition of atherosclerosis as that attained by ACE inhibition at doses that provide comparable lowering of blood pressure.

Materials and methods

Low-dose irbesartan (30 mg/kg/day) study

In the initial study involving a 30 mg/kg/day dose of irbesartan, 24 WHHL rabbits, which were bred within our facility, were assigned randomly to either the control or the irbesartan-treated group. The dose selected was shown in earlier studies in New Zealand white rabbits to inhibit by an average of 73% the pressor responses to intravenously administered AII (0.3 nmol) (N. Trippodo, personal communication). The irbesartan was added to the pelleted Agway Prolab High Fiber Rabbit Chow (Agway, Syracuse, NY), which also contained 4% Karo syrup to enhance the palatability of the mixture and improve adherence of the drug to the food.1 The drug was administered at 3 months of age when the animals were approximately 2.0 kg in weight and continued without interruption for 9 months. Control WHHL rabbits were handled identically except that irbesartan was omitted from the food.

Plasma concentration of irbesartan was measured in 11 of the WHHL rabbits treated with 30 mg/kg/day for 1 to 4 months. Assays were performed at Bristol-Myers Squibb using solid-phase extraction followed by HPLC fluorescence. Plasma irbesartan in these animals averaged 127.5 ± 62.8 ng/mL.

Systolic blood pressure and heart rate were measured noninvasively at monthly intervals using a tail cuff plethysmograph with photoelectric cell detector as described previously.1 Serum cholesterol was measured at monthly intervals on blood samples obtained from the central ear artery after overnight fasting.1

All animals were killed with pentobarbital (100 mg/kg intravenous) at the end of the 9-month treatment period. The tissues were fixed by whole body perfusion with 10% acetate-buffered formalin.1 The aorta was removed, cleaned free of adventitia, and maintained in formalin. Aortic surface involvement by atherosclerosis was determined on photographs of the intimal surface that were projected onto a digitizing tablet (model SD 402E, Wacom Technology, Inc., Vancouver, WA).2 The total area and lesion areas were traced and quantitated using the National Institutes of Health IMAGE 1.49 processor with an analysis program for the Macintosh computer (Apple, Cuppertino, CA). Cholesterol content of the different aortic regions was assayed as described previously.1

High-dose irbesartan (75 mg/kg/day) study

Because of the failure of the 30 mg/kg/day dose of irbesartan to inhibit the development of atherosclerosis (see Results), a separate trial was instituted using a larger dose. This decision was based on the possibility that the degree of AT1 receptor inhibition in the vasculature with the 30-mg dose was incomplete or otherwise inadequate to influence atherosclerosis. In addition, because our studies with ACE inhibitors had suggested that blood pressure lowering might be involved in their antiatherogenic action,11 we used a dose of irbesartan that produced a 15- to 20-mm Hg average reduction in systolic blood pressure, as was seen in the studies with ACE inhibitors. The 75 mg/kg/day irbesartan dose was selected from studies in which doses ranging from 50 to 150 mg/kg/day were administered over a 1- to 3-week period in a separate group of WHHL rabbits.

Twenty-two WHHL rabbits were assigned randomly to either control or drug-treated groups. Except for differences in drug dosage, the protocol used was identical to that described for the lower-dose studies.

Statistical analyses of data on body weight, serum cholesterol, blood pressure, and heart rate were made by two-way ANOVA with correction for repeated measures using the SAS program (SAS Institute, Inc., Cary, NC). The values of aortic surface atherosclerosis were analyzed by the Wilcoxon rank sum test. Aortic cholesterol levels were analyzed by the Student's t test for independent measures.

Results

Low-dose irbesartan study

Clinical data

No significant differences in blood pressure, heart rate, or serum cholesterol concentration were present between control and irbesartan-treated animals (Figure 1). During the final 3 months of the study, body weight was significantly less in treated than in control rabbits, though not during earlier periods.

Graphs of the effects of irbesartan 30 mg/kg body wt/day on body weight (A), serum cholesterol (B), systolic blood pressure (C), and heart rate (D) in Watanabe heritable hyperlipidemic rabbits.

Aortic atherosclerosis

Irbesartan had no significant effect on aortic surface involvement by atherosclerosis in either the total aorta or in the individual regions (Table 1). Aortic cholesterol content also did not differ significantly between the two groups (Table 2).

Table 1

EFFECTS OF IRBESARTAN (30 MG/KG/DAY) ON AORTIC SURFACE ATHEROSCLEROSIS IN WATANABE HERITABLE HYPERLIPIDEMIC RABBITS

Aortic Region Control (% intimal surface) Irbesartan (% intimal surface) 
Total aorta 42.17 ± 3.28 34.33 ± 4.06 
Ascending and arch 89.67 ± 3.21 82.42 ± 3.73 
Descending thoracic 36.17 ± 6.32 23.92 ± 5.85 
Abdominal 27.50 ± 2.67 22.33 ± 2.66 
Aortic Region Control (% intimal surface) Irbesartan (% intimal surface) 
Total aorta 42.17 ± 3.28 34.33 ± 4.06 
Ascending and arch 89.67 ± 3.21 82.42 ± 3.73 
Descending thoracic 36.17 ± 6.32 23.92 ± 5.85 
Abdominal 27.50 ± 2.67 22.33 ± 2.66 

Values represent the mean ± SE for 12 animals in each group.

Table 2

Effects of Irbesartan (30 MG/KG/DAY) on Aortic Cholesterol Content in Watanabe Heritable Hyperlipidemic Rabbits

Aortic Region Control (mg/g wet weight) Irbesartan (mg/g wet weight) 
Ascending and arch 46.97 ± 2.30 48.79 ± 3.09 
Descending thoracic 22.63 ± 3.87 19.43 ± 4.52 
Abdominal 15.20 ± 1.60 14.02 ± 1.75 
Aortic Region Control (mg/g wet weight) Irbesartan (mg/g wet weight) 
Ascending and arch 46.97 ± 2.30 48.79 ± 3.09 
Descending thoracic 22.63 ± 3.87 19.43 ± 4.52 
Abdominal 15.20 ± 1.60 14.02 ± 1.75 

Values represent the mean ± SE for 12 animals in each group.

High-dose irbesartan study

Heart rate and serum cholesterol were comparable in the two groups throughout the study (Figure 2). Body weights were significantly lower in treated than control rabbits during the final 5 months of the trial, but the animals tolerated the drug well, and no evidence of drug toxicity was apparent with either dose of irbesartan.

Graphs of the effects of irbesartan 75 mg/kg body wt/day on body weight (A), serum cholesterol (B), systolic blood pressure (C), and heart rate (D) in Watanabe heritable hyperlipidemic rabbits.

Systolic blood pressure levels were significantly less in the irbesartan high-dose group than in controls (Figure 2). They generally averaged between 100 and 115 mm Hg in controls during the study whereas treated rabbits averaged between 90 and 95 mm Hg.

Aortic atherosclerosis

Atherosclerotic involvement of the aortic surface was significantly less in treated than in control animals (Table 3). The differences were highly significant (P < .01) for total aorta, ascending aorta, and arch and descending thoracic aorta, although the differences for abdominal aorta were of borderline statistical significance (P = .07).

Table 3

Effects of Irbesartan (75 MG/KG/DAY) on aortic Surface Atherosclerosis in Watanabe Heritable Hyperlipidemic Rabbit

 Control (% intimal surface) Irbesartan (% intimal surface) 
Total aorta 38.9 ± 3.8 24.1 ± 3.0* 
Ascending & arch 92.9 ± 1.9 72.0 ± 2.4* 
Descending thoracic 29.2 ± 6.9 11.1 ± 4.1* 
Abdominal 17.5 ± 2.4 11.7 ± 2.6 
 Control (% intimal surface) Irbesartan (% intimal surface) 
Total aorta 38.9 ± 3.8 24.1 ± 3.0* 
Ascending & arch 92.9 ± 1.9 72.0 ± 2.4* 
Descending thoracic 29.2 ± 6.9 11.1 ± 4.1* 
Abdominal 17.5 ± 2.4 11.7 ± 2.6 

Values represent the means ± SE for 11 animals in each group.

*

P < .01.

Cholesterol content in total aorta averaged 36% less in the irbesartan-treated group than in the controls (P < .02) (Table 4). Cholesterol levels were also lower in individual regions of the aorta in the irbesartan 75 mg/kg group, although the differences achieved statistical significance only in the ascending aorta and arch.

Table 4

Effects of Irbesartan (75 MG/KG/DAY) on Aortic Cholesterol Content in Watanabe Heritable Hyperlipidemic Rabbits

 Control (mg/g wet wt) Irbesartan (mg/g/wet wt) 
Total aorta 26.6 ± 2.9 17.0 ± 2.9* 
Ascending and arch 59.1 ± 3.1 46.6 ± 3.6 
Descending thoracic 16.9 ± 4.1 10.3 ± 3.8 
Abdominal 14.1 ± 1.9 11.2 ± 2.0 
 Control (mg/g wet wt) Irbesartan (mg/g/wet wt) 
Total aorta 26.6 ± 2.9 17.0 ± 2.9* 
Ascending and arch 59.1 ± 3.1 46.6 ± 3.6 
Descending thoracic 16.9 ± 4.1 10.3 ± 3.8 
Abdominal 14.1 ± 1.9 11.2 ± 2.0 

Values represent the means ± SE for 11 animals in each group.

*

P < .02;

P < .03.

Discussion

These studies demonstrate that the AT1 receptor antagonist irbesartan, when used at a dose that reduces blood pressure, inhibits the development of atherosclerosis in the WHHL rabbit. The degree of reduction of atherosclerosis was remarkably similar to that observed with either captopril or trandolapril. With irbesartan (75 mg/kg), the total aortic surface involvement was decreased by an average of 38%, whereas in the prior studies with captopril1 and trandolapril,2 the reductions averaged 36% and 37%, respectively.

The 30 mg/kg dose of irbesartan, which failed to lower blood pressure, was adequate to inhibit most of the pressor effect of infused AII. This dose also produced steady-state plasma concentrations of irbesartan nearly 75 times higher than that reported to inhibit the contractile effects of AII on rabbit aorta or to block AII-induced proliferation of cultured smooth muscle cells.10 In view of recent reports that AT1 receptor mRNA levels are elevated in atherosclerotic aorta of hypercholesterolemic rabbits,9 and that macrophages in atherosclerotic plaques are a rich source of AII and ACE,12 perhaps a higher dose of irbesartan may be required to inhibit atherosclerosis than that needed to affect certain other vascular actions of AII.

AII has been shown experimentally to have a broad range of effects that can induce or be associated with arterial injury. These include an increase in superoxide (O2) anion production, stimulation of arterial smooth muscle proliferation, reduction of endothelium-dependent arterial relaxation, increased monocyte adherence to endothelium, enhanced release of endothelin-1 from arterial tissue, inhibition of plasminogen activation, and stimulation of lipoxygenase production by macrophages with an increase in the capacity of macrophages to oxidize low-density lipoproteins.13,14,15,16,17,18 AII, through its effect on the AT1 receptor, has been reported to increase the activity of NADH/NADPH oxidase, the major source of superoxide (O2) production in arterial tissue studied both in vitro19 and in vivo.13 By reducing superoxide anion production, AT1 receptor inhibition could also diminish inactivation of nitric oxide.

Bradykinin enhancement by ACE inhibition also may lead to increases in nitric oxide (NO) by stimulation of cGMP. Augmentation of synthesis of NO in cholesterol-fed rabbits by increase in dietary intake of L-arginine has been shown to diminish atherosclerosis,20 whereas inhibition of NO synthesis promotes the disease.21 The observation that AT1 receptor blockade can cause an inhibition of aortic atherosclerosis similar to that induced by ACE inhibition does not rule out the potential importance of bradykinin and nitric oxide in the antiatherosclerotic effects of ACE inhibitors.

We have observed previously that doses of the ACE inhibitor trandolapril, which caused marked reductions in serum and arterial ACE activities but which did not lower blood pressure in the WHHL rabbit, also did not inhibit atherosclerosis.11 In previously published studies on the effects of other antihypertensive drugs in the WHHL rabbit, the calcium antagonists nifedipine22 and verapamil,23 and the β-blocker propranolol,24 all failed to inhibit atherosclerosis in this model.

Hemodynamic and mechanical factors appear to affect nitric oxide production and release by endothelial cells. Flow-mediated vasodilation is accompanied by increase in nitric oxide release.25 Mechanical stimuli associated with uniform laminar shear stress (or low shear stress) can cause potentially favorable upregulation of endothelial nitric oxide synthase as well as of superoxide dismutase and cyclooxygenase-2, whereas turbulent shear stress may cause opposite changes.26 In addition, it has been reported that increase in shear stress may reduce endothelial cell ACE expression.27 Whether AII suppression, through blood pressure or other hemodynamic effects, can cause beneficial effects on endothelial function and protection against atherosclerosis remains to be determined.

The clinical significance of the current findings is unclear. No specific data are available concerning the influence of either ACE inhibitor or AII receptor blockade on atherosclerosis in humans. Several clinical studies have demonstrated that ACE inhibitors reduce the rate of recurrence of myocardial infarction in patients with left ventricular dysfunction.28,29,30 A recent study comparing the effects of losartan and captopril in patients with heart failure suggests that losartan also may have cardioprotective value.31 Whether such actions are in any way related to inhibiting plaque formation or reducing the risk of plaque rupture is unknown. We hope that the large number of clinical studies that are currently in progress will provide some important insights into these issues.

We thank Dr. James Powell of Bristol-Myers Squibb for the assay of the plasma irbesartan samples and for his helpful suggestions.

References

1.
Chobanian
AV
,
Haudenschild
CC
,
Nickerson
C
,
Drago
R
:
Anti-atherogenic effect of captopril in the Watanabe heritable hyperlipidemic rabbit
.
Hypertension
 
1990
;
1
:
327
331
.
2.
Chobanian
AV
,
Haudenschild
CC
,
Nickerson
C
,
Hope
S
:
Trandolapril inhibits atherosclerosis in the Watanabe Heritable Hyperlipidemic Rabbit
.
Hypertension
 
1992
;
20
:
473
477
.
3.
Aberg
G
,
Ferrer
P
:
Effects of captopril on atherosclerosis in cynomolgus monkeys
.
J Cardiovasc Pharmacol
 
1990
;
15
:
S65
S72
.
4.
Schuh
JR
,
Blehmn
DJ
,
Friedrich
GE
et al.  
Differential effects of renin-angiotensin blockade on atherogenesis in cholesterol-fed rabbits
.
J Clin Invest
 
1993
;
91
:
1453
1458
.
5.
Charpiot
P
,
Rolland
Ph
,
Friggi
A
et al.  
ACE inhibition with perindopril and atherogenesis-induced structural and functional changes in minipig arteries
.
Arterioscler Thromb
 
1993
;
13
:
1125
1138
.
6.
Kowala
MC
,
Grove
RI
,
Aberg
G
:
Inhibitors of angiotensin-converting enzyme decrease early atherosclerosis in hyperlipidemic hamsters. Fosinopril reduces plasma cholesterol and captopril inhibits macrophage-foam cell accumulation independently of blood pressure and plasma lipids
.
Atherosclerosis
 
1994
;
108
:
61
72
.
7.
Powell
JS
,
Clozel
J-P
,
Muller
RKM
et al.  
Inhibitors of angiotensin-converting enzyme prevent myointimal proliferation after vascular injury
.
Science
 
1989
;
245
:
186
188
.
8.
Farhy
RD
,
Carretero
OA
,
Ho
K
,
Scili
AG
:
Role of kinins and nitric oxide in the effects of angiotensin converting enzyme inhibitors on neointima formation
.
Circ Res
 
1993
;
72
:
1202
1210
.
9.
Sugano
M
,
Makino
N
,
Yanaga
T
:
The effects of renin-angiotensin system inhibition on aortic cholesterol content in cholesterol-fed rabbits
.
Atherosclerosis
 
1996
;
127
:
123
129
.
10.
Cazaubon
C
,
Gougat
J
,
Bousquet
F
et al.  
Pharmacologic characterization of SR 47436, a new nonpeptide AT1 subtype angiotensin II receptor antagonist
.
J Pharmacol Exp Ther
 
1993
;
265
:
826
834
.
11.
Chobanian
AV
,
Hope
S
,
Brecher
P
:
Dissociation between antiatherosclerotic effect of trandolapril and suppression of serum and aortic angiotensin-converting enzyme activity in the Watanabe Heritable Hyperlipidemic rabbit
.
Hypertension
 
1995
;
25
:
1306
1310
.
12.
Diet
F
,
Pratt
RE
,
Berry
GJ
et al.  
Increased accumulation of tissue ACE in human atherosclerotic coronary artery disease
.
Circulation
 
1996
;
94
:
2756
2767
.
13.
Rajagopalan
S
,
Kurz
S
,
Münzel
T
et al.  
Angiotensin II mediated hypertension in the rat increases vascular superoxide production via membrane NADH/NADPH oxidase activation: contribution to alterations of vasomotor tone
.
J Clin Invest
 
1996
;
97
:
1916
1923
.
14.
Naftilan
A
,
Pratt
R
,
Dzau
V
:
Induction of c-fos, c-myc and PDGF A-chain gene expressions by angiotensin II in cultured vascular smooth muscle cells
.
J Clin Invest
 
1989
;
83
:
1419
1424
.
15.
Capers
QIV
,
Alexander
RW
,
Taylor
WR
:
Vascular MCP-1 mRNA is upregulated in experimental hypertension
.
Hypertension
 
1996
;
28
:
516
.(abst)
16.
Hahn
AW
,
Resink
TJ
,
Scott-Burden
T
et al.  
Stimulation of endothelin mRNA and secretion in rat vascular smooth muscle cells: a novel autocrine function
.
Cell Regul
 
1990
.
649
659
.
17.
Kerins
DM
,
Hao
Q
,
Vaughan
D
:
Angiotensin induction of pai-1 expression in endothelial cells is mediated by the hexapeptide angiotensin IV
.
J Clin Invest
 
1995
;
96
:
2515
2520
.
18.
Scheidegger
KJ
,
Butler
S
,
Witztum
JL
:
Angiotensin II increases macrophage-mediated modification of low density lipoprotein via a lipoxygenase-dependent pathway
.
J Biol Chem
 
1997
;
272
:
21609
21615
.
19.
Griendling
KK
,
Minieri
CA
,
Ollerenshaw
JD
,
Alexander
RW
:
Angiotensin II stimulates NADH and NADPH oxidase activity in cultured vascular smooth muscle cells
.
Circ Res
 
1994
;
74
:
1141
1149
.
20.
Cooke
JP
,
Singer
AH
,
Tsao
P
et al.  
Antiatherogenic effects of L-arginine in the hypercholesterolemic rabbit
.
J Clin Invest
 
1992
;
90
:
1168
1172
.
21.
Cayatte
AJ
,
Palacino
JJ
,
Horten
K
,
Cohen
RA
:
Chronic inhibition of nitric oxide accelerates neointima foam cell accumulation and impairs endothelial function in hypercholesterolemic rabbits
.
Arterioscler Thromb
 
1994
;
14
:
753
759
.
22.
Van Niekerk
JLM
,
Hendriks
T
,
Deboer
HHM
,
Van’t Laar
A
:
Does nifedipine suppress atherogenesis in WHHL rabbits?
.
Atherosclerosis
 
1984
;
53
:
91
98
.
23.
Tilton
GD
,
Buja
LM
,
Bilheimer
DW
et al.  
Failure of a slow channel calcium antagonist, verapamil, to retard atherosclerosis in the Watanabe heritable hyperlipidemic rabbit: an animal model of familial hypercholesterolemia
.
J Am Coll Cardiol
 
1985
;
6
:
141
144
.
24.
Lichtenstein
AH
,
Drago
R
,
Nickerson
C
et al.  
The effect of propranolol on atherogenesis in the Watanabe heritable hyperlipidemic rabbit
.
J Vasc Med Biol
 
1989
;
1
:
248
254
.
25.
Cooke
JP
,
Stamler
J
,
Andon
N
et al.  
Flow stimulates endothelial cells to release a nitrovasodilator that is potentiated by reduced thiol
.
Am J Physiol
 
1990
;
259
:
H804
H812
.
26.
Topper
JN
,
Cai
J
,
Falb
D
,
Gimbrone
MA
Jr
:
Identification of vascular endothelial genes differentially responsive to fluid mechanical stimuli: cyclooxygenase-2, manganese superoxide dismutase and endothelial cell nitric oxide synthase are selectively up-regulated by steady laminar shear stress
.
Proc Natl Acad Sci USA
 
1996
;
93
:
10417
10422
.
27.
Rieder
MJ
,
Carmona
R
,
Krieger
JE
et al.  
Suppression of angiotensin-converting enzyme expression and activity by shear stress
.
Hypertension
 
1997
;
80
:
312
319
.
28.
The SOLVD Investigators
Effect of enalapril on mortality and the development of heart failure in asymptomatic patients with reduced left ventricular ejection fractions
.
N Engl J Med
 
1992
;
327
:
685
691
.
29.
Pfeffer
MA
,
Braunwald
E
,
Moye
LA
et al.  
Effect of captopril on mortality and morbidity in patients with left ventricular dysfunction after myocardial infarction
.
N Engl J Med
 
1992
;
327
:
669
677
.
30.
Acute Infarction Ramipril Efficacy (AIRE) Study Investigators
Effect of ramipril on mortality and morbidity of survivors of acute myocardial infarction with clinical evidence of heart failure
.
Lancet
 
1993
;
342
:
821
828
.
31.
Pitt
B
,
Segal
R
,
Martinez
FA
, et al.  , on behalf of ELITE Study Investigators Randomised trial of losartan versus captopril in patients over 65 with heart failure (Evaluation of Losartan in the Elderly Study, ELITE). Lancet
1997
;
349
:
747
752
.

Author notes

*
This research was supported by a grant from Bristol-Myers Squibb and by National Institutes of Health grant HL 55001 (Hypertension Specialized Center of Research).