(Hypertension. 1996;27:176-183.)
© 1996 American Heart Association, Inc.
Articles |
ACE Inhibition Prevents and Reverses L-NAMEExacerbated Nephrosclerosis in Spontaneously Hypertensive Rats
From the Hypertension Research Laboratories, Alton Ochsner Medical Foundation, New Orleans, La.
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Abstract |
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 Top Abstract IntroductionMethods Results Discussion References |
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Abstract Chronic nitric oxide inhibition exacerbates hypertension and nephrosclerosis in spontaneously hypertensive rats (SHRs). In this study, we determined whether angiotensin-converting enzyme (ACE) inhibition could prevent or reverse the systemic, renal, and glomerular hemodynamic alterations and the pathological changes of nephrosclerosis. Four groups of 20-week-old SHRs were studied: group 1, untreated controls; group 2, treated with N
-nitro-L-arginine methyl ester
(L-NAME, 50 mg/L for 3 weeks); group 3, L-NAME cotreated with quinapril
(3
mg·kg-1·d-1
for 3 weeks); and group 4, L-NAME for 3 weeks followed by quinapril for
3 weeks (same doses). The results of this study demonstrated that both
cotreatment (group 3) and posttreatment (group 4) with quinapril
reduced mean arterial pressure (186±9 and 192±9 mm Hg,
respectively, compared with group 2 SHRs, 221±5 mm Hg) and total
peripheral resistance index associated with significant
reductions in afferent and efferent arteriolar resistances;
nephrosclerosis pathological scores; and urinary
protein excretion (all at least P<.01). ACE inhibition also
significantly increased stroke index, single-nephron
glomerular filtration rate, and ultrafiltration coefficient
compared with the L-NAME SHRs. Most notable were the findings that
cotreatment with quinapril completely prevented the renal
glomerular hemodynamic alterations with
reduced glomerular capillary hydrostatic pressure and
efferent arteriolar resistance compared with both the untreated and the
L-NAME–treated SHRs (all at least P<.01). Posttreatment
with quinapril also reversed the glomerular injury
(subcapsular, -83%; juxtamedullary, -56%) and arteriolar
(-87%) injury scores obtained from renal biopsy specimens
(P<.005 and P<.0001, respectively). These
changes were associated with decreased periarteriolar fibronectin and
increased afferent arteriolar 
-smooth muscle actin deposition
(immunohistochemistry). These data, therefore, demonstrate that ACE
inhibition not only prevents but also reverses
L-NAME–exacerbated severe nephrosclerosis in
SHRs, as indicated by improved systemic, renal, and
glomerular hemodynamic changes,
proteinuria, and histological alterations.
Key Words: renal micropuncture • biopsy • L-NAME • rats, inbred, SHR • nephrosclerosis • proteinuria • angiotensin-converting enzyme inhibitors
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Introduction |
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TopAbstractIntroductionMethods Results Discussion References |
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Antihypertensive drug therapy has reduced morbidity and mortality from stroke, congestive heart failure, and coronary heart disease in patients with hypertension, but it has been ineffective in reducing end-stage renal disease.1 In this respect, it is unclear whether goal treatment pressures have been realistic; whether only certain antihypertensive agents can reduce or may even exacerbate the renal microcirculatory and structural involvement of hypertension; or whether the nephrosclerosis of hypertension is, in fact, irreversible. Studies that used several animal models of renal disease with hypertension have shown that renal ischemia, glomerular hypertension, and glomerular filtration were associated with leakage of protein molecules, thereby promoting glomerular sclerosis and progressive functional renal deterioration.2 3 These reports have also demonstrated renal protection using ACE inhibitors, but they all involved reduced renal mass or experimental and clinical diabetes mellitus. Often the responses were better than one would expect from the hypotensive effect of the drug alone.4 5 6 7
Recently, using aged (73-week-old) SHRs as a model of human essential hypertension, we demonstrated a natural progression of the functional and structural evidence of severe hypertensive nephrosclerosis and its reversibility after only 3 weeks of ACE inhibition therapy.8 Since it is neither possible to purchase nor practical to maintain such aged SHRs because it is extremely costly and time-consuming, we developed a similar model of naturally developing nephrosclerosis in younger (20-week-old) SHRs with 3 weeks of intervention with the NO synthase inhibitor L-NAME.9 The control and L-NAME–treated SHR groups in that study are included in the present report for the purpose of reference. The present report not only demonstrates similar reversibility of all aspects of the severe nephrosclerosis in that L-NAME SHR model within 3 weeks with the same ACE inhibitor, but we have also been able to prevent renal involvement with the simultaneous administration of ACE inhibitor with L-NAME.
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Methods |
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TopAbstractIntroductionMethods Results Discussion References |
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Male 17-week-old SHRs (Charles River Laboratories, Wilmington, Mass) were housed in plastic cages and maintained in a temperature- and light-controlled room. Throughout the study, the rats had free access to standard rat chow (Ralston-Purina). All experiments had been approved by our institutional animal care committee.
Protocol
All surgical procedures were performed under sterile
conditions with pentobarbital (10 mg/kg IP) anesthesia for
renal biopsy or with inactin (100 mg/kg IP; Byk-Gulden) for the
hemodynamic and micropuncture studies. The rats (290 to
330 g body weight) were divided into four experimental groups: group 1
(control, n=10) rats were given the standard vehicle, tap water, alone;
and group 2 (L-NAME, n=12) rats were administered L-NAME (Sigma
Chemical Co) in drinking water (50 mg/L) for 3 weeks. These two SHR
groups were the subject of our earlier study9 and are
included in this report so that they may serve as a frame of reference
for the evaluation of the subsequent two groups, described as follows:
group 3 (L-NAME plus the ACE inhibitor quinapril,
3
mg·kg-1·d-1,
by gastric gavage for 3 weeks; n=8) and group 4 (L-NAME, then the ACE
inhibitor; n=9) rats that were administered the same dose
of L-NAME in drinking water for 3 weeks followed by a 3-week course of
treatment with quinapril (the same dose as in group 3) after the L-NAME
was discontinued. The dose of L-NAME (Sigma) was arrived at in an
earlier study9 that demonstrated its effectiveness in
mimicking the naturally occurring and severe
nephrosclerosis in the 73-week-old SHRs, manifested
by its associated clinical, physiological, and
pathological changes.8
The drinking water with L-NAME was changed daily to quantify the precisely measured dose of L-NAME, volume intake, and urinary volume. Thus, this volume intake permitted a daily L-NAME dose of 7.6±0.7 mg/kg body wt. Quinapril (3 mg/kg) was initiated only after repeated measurements of daily UProtV were obtained, after which it was administered daily for 3 weeks by gastric gavage when measurements of daily UProtV were repeated. Thus, the ACE inhibition therapy of groups 3 and 4 was for a 3-week period, although the latter SHR group was 3 weeks older at the conclusion of this study because of the prior 3-week intervention with L-NAME. The selection of a 3-week period of treatment with the ACE inhibitor was chosen because, in our previous studies, this 3-week period was shown to be of sufficient duration to reduce arterial pressure and to reverse LV hypertrophy and the renal histopathological lesions as well as the associated systemic, renal, and glomerular hemodynamic alterations.8 10 11 12 To determine the histological effects of quinapril treatment in group 4, open renal biopsy was performed under pentobarbital anesthesia through a midline abdominal incision under sterile conditions after the 3-week intervention with L-NAME. In that procedure, a small portion of the lower pole of the right kidney was removed surgically, and bleeding was controlled by gelfoam application.7 Renal tissue from the same rat was also examined from the autopsy specimen obtained 3 weeks later, after quinapril treatment, which permitted comparison of both renal histological findings in each rat. The 24-hour UProtV was measured before the renal micropuncture study by the method of Lowry et al,13 and the 24-hour UNaV was also determined with a Beckman Astra 8 flame photometer.
In addition, in a preliminary study for this report (and as a control group for group 4), we studied four untreated SHRs that were given L-NAME for 3 weeks and thereafter only tap water instead of quinapril for 3 weeks. Four other SHRs died during this post–L-NAME period without further study. This preliminary work was done to determine whether the L-NAME–induced changes reversed themselves spontaneously during a 3-week (non–L-NAME) period in SHRs. Pollock et al14 had reported earlier, in normotensive rats, that blood pressure returned to normal when L-NAME was discontinued. However, in our preliminary study, the findings in the SHRs were not similar to those in the normal rats. Thus, LV hypertrophy (LV index, 3.36 mg/g); cardiac (reduced CI, 245 mL·min-1·kg-1; SI, 0.69 mL per beat per square meter) and renal (reduced GFR of 0.74 mL/min and elevated renal vascular resistance of 147 mm Hg·mL-1·min-1) dysfunction; and the severe nephrosclerosis were not different from those findings obtained at the conclusion of 3 weeks of L-NAME, although their MAP (208 mm Hg) was slightly lower. Histologically, in this group, the pathological changes of nephrosclerosis were similar to those findings obtained in untreated 73-week-old SHRs8 or the younger SHRs that were treated with L-NAME for 3 weeks (group 2).9 Thus, they were all characterized by severe glomerular sclerosis and lesser glomerular thrombosis, marked glomerular ischemic changes, and tubulointerstitial changes. Therefore, L-NAME hypertensive nephrosclerosis in the SHRs did not reverse naturally during the 3-week period after L-NAME withdrawal.
Micropuncture
All rats were deprived of food overnight before
the renal
hemodynamic and micropuncture studies, although they
were allowed free access to water. They were anesthetized with
inactin and then placed on a heating pad to maintain rectal temperature
at 37°C throughout the study. After a tracheostomy, a polyethylene
catheter (PE-50) was inserted into the abdominal aorta through the
right femoral artery to permit blood sampling and measurement of MAP
and heart rate. The right carotid artery and right jugular vein were
also cannulated with PE-50 catheters for determination of cardiac
output with a thermocouple microprobe connected to a thermodilution
device (Cardiotherm 500, Columbus Instrument) that was calibrated
twice, at the beginning and end of each study.9 Cardiac
output was calculated by use of a conversion factor that depended on
the injected volume and intravascular catheter length; it was then
normalized for body weight and expressed as CI in
mL·min-1·kg-1.
Pressures were measured with Gould-Statham transducers (model P23 Db,
Statham Instruments) connected to a multichannel polygraph (Sensor
Medics R612, Beckman Instruments Inc).
The left kidney was exposed through a ventral midline abdominal incision. Its ureter was catheterized, and the kidney was immobilized and prepared for micropuncture as described previously.8 9 10 The renal surface was illuminated and bathed in 0.9% NaCl at 34°C to 36°C. The left femoral vein was used for [3H]methoxyinulin (850 µCi/mL) infusion at a rate of 0.1 mL·100 g body wt-1·h-1, and the right femoral vein was also cannulated with PE-50 polyethylene tubing for infusion of a saline solution containing 5.6% p-aminohippurate (Merck Sharp & Dohme) at a rate of 0.2 mL·100 g body wt-1·h-1 for the initial 45 to 60 minutes of the procedure and then at a rate of 0.1 mL·100 g body wt-1·h-1 for maintenance infusion.
After physiological equilibration, urine was
collected over two 30-minute periods, and blood samples were drawn at
the midpoint of each period. Simultaneously, the following
micropuncture measurements were made: (1) efferent
glomerular arteriolar blood was withdrawn by direct
puncture of two or three superficially located "star vessels";
(2) precisely timed (90-second) samples of fluid were collected from
four to six selected superficial proximal tubules for determination of
SNGFR; and (3) PE, PT, and SFP
were measured directly by a servo-null system (Instrumentation for
Physiology & Medicine). The PT and PE
measurements were obtained from proximal convoluted tubules and the
star vessels, respectively. Because the SHR glomerular
capillaries are not superficial in the renal location, PG
was calculated from the sum of the SFP and the systemic
A. The PE, PT, and
SFP measurements were made three times, and their averages were
determined.
The tubular fluid, urine, and plasma samples were counted
for
[3H]inulin radioactivity by placement in 10-mL
scintillation vials (Bio-Safe II) for counting in a
ß-scintillation counter, which allowed calculation of SNGFR, GFR,
and ERPF. These measurements permit calculation of A and
E, RA and RE, and
the glomerular capillary Kf. At the
termination of each study, blood was drawn for measurement of serum
creatinine and uric acid concentrations by a 747-100
Analyzer (Boehringer Mannheim/Hitachi).
Renal Morphology
Light microscopy was performed after
completion of each
micropuncture study. Kidneys, heart, and thoracic aorta were removed,
weighed, and fixed in 10% neutral buffered formalin. Two midcoronal
slices of the right kidney, 2 to 3 mm thick, were embedded in paraffin
after conventional processing. Sections (3 µm thick) were stained
with hematoxylin-eosin and by the periodic acid–Schiff reaction.
Sections obtained from the left kidney were stained with
hematoxylin-eosin, periodic acid–Schiff, periodic
acid–methenamine–silver, and phosphotungstic
acid–hematoxylin for specific staining of extracellular matrix,
fibrin, and collagen. Grading of GIS and of AIS was performed as
previously described.8 9 GIS was graded from 0 to
3+, in
which 0 was no injury, 1+ was injury of up to one third (
1/3) of the
glomerulus, 2+ was one third to two thirds glomerular
injury, and 3+ was injury of more than two thirds (
2/3) of
glomerular involvement. The AIS was also graded from 0 to
3+, in which 0 was no injury at all, 1+ demonstrated hyalinosis of
the
arteriolar wall up to 50% of the mural circumference, 2+ demonstrated
hyalinosis between 50% and 100% of the wall circumference but without
luminal narrowing, and 3+ was complete mural hyalinosis with luminal
encroachment. The overall nephrosclerosis score was
calculated by adding the GIS and AIS for each rat. These scores were
obtained by independent study by two investigators, and scoring of all
tissue was conducted in a blinded manner.
For immunohistochemistry,
immunostaining of the
sections of each group was carried out with the streptavidin/biotin
immunoperoxidase method (LSAB kit, DAKO) after deparaffinization.
Antibodies used for immunohistochemical analysis were as
follows: anti–-SMA was detected with murine monoclonal antibody 1A4
(DAKO) diluted 1:50, and fibronectin with mouse monoclonal antibody
NCL-FIB (Novocastra, Vector) diluted 1:100.
Statistical Analysis
One-way ANOVA, followed by
Duncan's multiple range test,
was performed for between-group significance, and linear regression
analysis was used to examine for correlation between CI and
micropuncture data and between CI and morphological
data.15 16 All data are expressed as mean±SEM.
A
probability level of <5% was considered to be of statistical
significance.
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Results |
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TopAbstractIntroductionMethods Results Discussion References |
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Body and Organ Weights
Body weight was greater in group 4 rats, no doubt because of their additional 3 weeks in age, but this was associated with decreased LV and aortic indexes. Otherwise, the body and organ weight data were not significantly different among the other three groups (Table 1
).
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Systemic, Cardiac, and Whole-Kidney
Hemodynamics
L-NAME treatment of group 2 significantly increased MAP,
TPRI, and renal vascular resistance index and reduced CI, SI, ERPF, and
GFR (Table 2).9 Cotreatment with L-NAME and
quinapril (group 3) significantly prevented the L-NAME–induced
increases in MAP, TPRI, renal vascular resistance index, and the
reductions of CI, SI, ERPF, and GFR (Table 2). Furthermore,
when
quinapril was administered after the 3-week L-NAME period
(group 4), the increases in MAP, TPRI, and SI and the decreases in GFR
were reversed significantly; heart rate decreased, although ERPF and CI
remained unchanged (Table 2). Finally, there was a direct
correlation
between the changes in CI and ERPF (r=.558;
P<.005).
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Glomerular Dynamics
At the superficial nephron glomerular
dynamic level,
the L-NAME group (group 2) demonstrated decreased SNPF, SNGFR,
PT, and Kf and increased
RA, RE, and SFP, but 
P and
PG remained unchanged (Table 3).9 This
unchanged PG was
associated with a reduced SNPF and an intense RA increase
with a lesser RE increase (Table 3; Fig
1).
Cotreatment with L-NAME and quinapril (group 3) significantly prevented
the foregoing L-NAME–induced changes in whole kidney, single nephron,
and glomerular dynamic functions. Furthermore, the P and
PG were significantly reduced and associated with a
decreased SFP and RE (compared with the control untreated
SHRs; Table 3 and Fig 1). However, when
quinapril treatment followed
L-NAME administration (group 4), SNPF was not significantly changed
during the 3-week quinapril period compared with the L-NAME treatment
group (group 2) (Table 3). Other glomerular dynamic
alterations (including SNGFR, PT, SFP, P,
PG, RA, RE,
and Kf) were reversibly changed after that
3-week period of quinapril treatment.
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P<.01,
P<.05 vs percent changes of group 2.
UProtV and other
indexes were increased significantly by
L-NAME (Table 4), but both treatment groups receiving
quinapril (groups 3 and 4) demonstrated significantly reduced protein
excretion compared with the untreated SHRs (group 1) or the SHR group
treated only with L-NAME (group 2) (Table 4;
P<.01).
Furthermore, there was a direct correlation between UProtV
and nephrosclerosis score (see below)
(r=.550, P<.001). UNaV, increased by
L-NAME (Table 4; P<.05), still remained increased
despite
the reduced MAP and UProtV after the 3 weeks of
quinapril (group 4). There was no difference in UNaV
between the untreated SHRs and those given L-NAME
simultaneously with quinapril (group 3). It was also of
interest that serum creatinine and uric acid concentrations
were increased significantly by L-NAME (group 2), and the uric acid
concentrations were reduced by quinapril (in both groups 3 and 4), with
the creatinine level remaining unchanged (Table 3
).
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Renal Morphological Findings
The morphological appearance of
glomeruli and interstitium
remained entirely normal or displayed only a few minor alterations of
the afferent arterioles in the 20-week-old control SHRs (group 1;
Fig 2A). However, the glomeruli of the L-NAME–treated
SHRs (group 2) exhibited a diffuse increase in mesangial
matrix with minimal evidence of cellular proliferation (Fig
2B).9 L-NAME cotreatment with quinapril (group 3;
Fig 2C)
displayed only minimal histological alterations. The
frequency of segmental glomerular lesions was reduced by
58%, a value significantly less severe than that seen in the
L-NAME–treated SHRs (group 2). However, two rats of this group did
develop severe glomerulosclerosis with
mesangiolysis or an increased mesangial matrix that was
similar to that in the L-NAME–treated SHRs (group 2). Afferent
arteriolar alterations in all rats were reduced by 77% (average),
significantly less than that in the untreated group 1 SHRs
(P<.05; Table 4). The tubule and interstitial
alterations were virtually absent in the group 3 rats.
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Despite the
unchanged ERPF and PG, all rats in the
group receiving quinapril after L-NAME administration (group 4)
demonstrated reversible changes within 3 weeks in the segmental
glomerular and arteriolar lesions (Fig 2D) compared with
the renal biopsy lesions from the same rats after only 3 weeks of
L-NAME (Fig 3). The glomeruli (obtained by renal biopsy
after week 3) showed severe nephrosclerotic lesions that were similar
in severity to the lesions observed in the L-NAME–treated SHRs (group
2). However, on autopsy, the glomeruli after week 6 (after quinapril
treatment; group 4) showed only minimal structural alterations and only
irregularity of the capillary loops with adhesions to Bowman's capsule
(Fig 2D). In addition, there were only occasional glomeruli
that
demonstrated sclerosis within the interstitium and also shunt glomeruli
associated with interstitial fibrosis, tubular atrophy, and
inflammatory cell infiltration.
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Immunoreactive Renal -SMA and
Fibronectin
Immunoreactive fibronectin deposition was increased in the
surrounding area of injured afferent arterioles and interlobular
arteries in association with fibrinoid necrosis and the onionskin
appearance of severe nephrosclerosis in the
L-NAME–treated SHRs (group 2). Furthermore, staining for fibronectin
was increased in the interstitium (Fig 4, upper right).
However, in control untreated group 1 (Fig 4, upper left) and
cotreated
L-NAME and quinapril SHRs (group 3), fibronectin was deposited
minimally in the periarteriolar adventitia of the afferent arterioles,
and there was no staining in the interstitium. In the group receiving
quinapril after L-NAME (group 4), fibronectin deposition was
decreased in the adventitia of afferent arterioles and interlobular
arteries, which was associated with a decreased AIS compared with group
2.
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In control SHRs (group 1; Fig 4, lower left), the
-SMA
staining was localized to the afferent arterioles and to the
interlobular arterial smooth muscular cells; similar
staining was demonstrated in group 3. By contrast, in group 2 (Fig
4,
lower right), this -SMA staining was reduced in the injured afferent
arterioles, with fibrinoid degeneration. The decreased afferent
arteriolar -SMA staining in the L-NAME SHRs was reversed
significantly by quinapril (group 4). Hence, immunoreactive fibronectin
and -SMA depositions were evident in afferent arterioles and
associated with an increased AIS.
Glomerular and Arteriolar Injury
Scores
Quantitative histological severity grading
revealed more severe GIS and AIS (P<.01, Table 4)
in the
L-NAME SHRs (group 2) than the untreated SHRs (group 1). Quinapril
cotreatment (group 3) significantly reduced the severity scoring of the
cortical glomerular lesions. The GIS of L-NAME SHRs that
were later treated with quinapril (group 4) also demonstrated a
significant reduction in the subcapsular glomeruli; however, the
juxtamedullary glomerular GIS remained unchanged. The AIS
was also reduced significantly in both quinapril-treated groups
(groups 3 and 4) than in the L-NAME SHRs (group 2). Thus, the overall
nephrosclerosis score (GIS+AIS) was significantly
greater in the L-NAME SHRs than the untreated SHRs (P<.01),
and this score was reduced significantly by both quinapril treatment
protocols (P<.01).
Finally, there was a strongly positive
correlation between the
glomerular and arteriolar injury indexes
(r=.744, P<.0005). Moreover, direct correlations
were also demonstrated between nephrosclerosis score
and RA (r=.680, P<.0005),
RE (r=.649, P<.0005), SFP
(r=.552, P<.001), P (r=.630,
P<.0005), and PG (r=.548,
P<.001), and there were indirect correlations between
nephrosclerosis score and SNPF
(r=-.544, P<.001) and SNGFR
(r=-.581, P<.0005). These important
pathophysiological correlations demonstrated a
strong and close relation between the degree of renal ischemia
and the pathological evidence of nephrosclerosis.
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Discussion |
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TopAbstractIntroductionMethods Results Discussion References |
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The effects of the ACE inhibitor quinapril on intrarenal hemodynamics in rats with cardiac failure and in young and aged SHRs have been reported earlier from our laboratory,8 10 11 but the effects on intrarenal hemodynamics, proteinuria, and histopathology are still unclear in the young SHRs with chronic NO synthase inhibition.17 We therefore designed the present study with two purposes in mind: to determine whether a similar length of ACE inhibition treatment prevents or reverses the whole-kidney and glomerular dynamic alterations of nephrosclerosis as well as the pathological changes associated with prolonged blockade of NO synthase in young SHRs. The data presented demonstrate convincingly that ACE inhibition almost totally prevented the damage induced by L-NAME and that it also significantly reversed those effects within only a 3-week treatment period. These prevention and reversal changes applied to clinical and functional (ie, proteinuria and serum uric acid concentration) indexes, although serum creatinine concentration remained unchanged during the 3-week treatment period with the ACE inhibitor. One possible explanation for the unchanged serum creatinine level despite an improved GFR is that the treatment period of 3 weeks was not sufficiently long. However, the reversible changes of serum uric acid concentration by the ACE inhibitor were most likely related to functional changes associated with the increase in renal blood flow.18 19
In an earlier study involving 73-week-old SHRs with naturally developing nephrosclerosis, we demonstrated that quinapril also decreased PG, RA, and RE, increased SNPF, and decreased glomerular and arteriolar injury scores within a 3-week treatment period.8 The responses of the 20-week-old SHRs used in the present report that were cotreated with L-NAME and quinapril (group 3) are consistent with that earlier study.8 Thus, RA and PG were significantly reduced by quinapril, suggesting that the clinical, hemodynamic, glomerular dynamic, and histological damage of L-NAME–induced nephrosclerosis in the younger SHRs can be prevented by ACE inhibition. These changes were confirmed by the striking pathophysiological changes that clearly indicated renal prevention. Moreover, when the quinapril was administered after L-NAME (group 4), these same clinical, hemodynamic, glomerular dynamic, and histological alterations revealed at least partial reversal of these alterations within the same 3-week period. To be sure, there were some differences between groups 3 and 4 with respect to the functional glomerular dynamics and pathological changes in response to the ACE inhibitor: ACE inhibition (group 3) completely prevented the effects of L-NAME, whereas ACE inhibitor after L-NAME (group 4) did not fully reverse these changes. As indicated above, these differences may reflect the brief treatment period (only 3 weeks) in group 4, which was already damaged by L-NAME. Nevertheless, even during this brief period, some significant functional and structural improvements were demonstrated.
In our earlier study of 20-week-old SHRs, MAP and RA
were elevated, but the PG (53±1 mm Hg) and RE
were normal.10 These younger rats demonstrated only
minimal pathological changes that were manifested by hyaline deposition
and increased media wall thickness of the afferent arterioles, and
there was no evidence of glomerular sclerosis (similar to
the changes in group 1). In that earlier study, ACE inhibition with
quinapril subsequently reduced PG and the
glomerular arteriolar resistances.11 In other
reports, cilazapril, captopril, perindopril, and other ACE
inhibitors also diminished intrarenal and mesenteric
arteriolar hypertrophy and glomerular damage in
young SHRs20 given DOCA salt,21 in
one-kidney, one clip Goldblatt hypertensive rats,22
and in subtotally nephrectomized rats.7 However, until
recently, little information was known concerning the renal effects of
ACE inhibitors in chronic NO inhibited models. Arnal et
al23 reported that chronic adaptations to NO synthase
inhibition were not uniform in normotensive rats. Specifically, 
25%
of their rats treated with L-NAME developed cardiac
hypertrophy and increased PRA, whereas their remaining rats
did not. In another report, L-NAME–treated SHRs demonstrated increased
PRA, severely elevated arterial pressure, and a high
mortality that they attributed to developed
nephrosclerosis.24 In yet another model
of chronic renal failure, using subtotal nephrectomy with L-NAME (with
dosing schedule and duration of treatment similar to our present
study), Fujihara et al25 produced severe
glomerulosclerosis and arterial
pressure elevation but without a changed PRA. Hence, the
physiological responses to chronic NO synthase
blockade do not appear to be uniform in all studies and may be related
to the experimental models used and the alterations induced
pathophysiologically.
The most intriguing observation of our present study is that treatment with quinapril prevented the rise in arterial pressure and the pathophysiological renal alterations provoked by the inhibition of NO synthesis induced by L-NAME. It is important to recognize that even though MAP was not fully normalized, quinapril prevented not only the systemic and local hemodynamic changes but also the renal histological alterations and the proteinuria induced by inhibited NO synthesis. Quinapril inhibits the degradation of bradykinin as well as angiotensin II generation, and it produces endothelium-dependent relaxation involving the stimulation of NO release mediated through the bradykinin B2 receptor or by certain prostaglandins.26 27 28 29 30 31 32 The vascular protective capacity of NO is attributed not only to its vasodilator action but also to its antimitotic, antiproliferative, and antiplatelet properties,27 which probably contribute to the overall effects of ACE inhibition on vascular smooth muscle.28 Thus, our study does not provide the precise mode of action subserved by ACE inhibition in these L-NAME SHRs.
Glomerular thrombosis frequently occurred in the afferent
arteriolar branching capillaries (Fig 5) of
L-NAME SHR nephrosclerosis (group 2) that are
associated with increased mesangial matrix and
endothelial cells despite an unchanged PG.
Other studies with chronic NO synthase inhibition in normotensive rats
have also reported the relation between glomerular
sclerosis and increased PG without associated
glomerular
thrombosis.25 33 34 35 36
These
PG and pathological changes with NO inhibition might be
considered to be inconsistent with the concept of Baylis et
al.33 The SHRs in our study, however, did not demonstrate
an increased PG.9 The normal PG
that we found in the L-NAME SHRs could be explained by the reduction in
whole-kidney renal blood flow that was associated with a reduction
in SNPF and an exacerbation of severely elevated RA that
was more intense than the RE increase. However, we recently
reported that when a thiazide diuretic was added to L-NAME,
RE increased even more, despite a further reduction in
SNPF, which then resulted in an increased
PG.37 However, Raij and
coworkers38 also reported that NO synthase inhibition with
L-NAME in normotensive rats resulted in diffuse glomerular
thrombosis after lipopolysaccharide administration.
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It is not known why glomerular thrombosis occurs in SHRs treated chronically with L-NAME without associated glomerular hypertension. However, it has been suggested that intraglomerular tumor necrosis factor, interleukin-1, and platelet-activating factor released locally (by either activated mesangial cells or blood-borne macrophages) can induce endothelial synthesis of tissue factor and plasminogen inactivator.39 Therefore, it would appear that, under these circumstances, the local release of NO associated with ACE inhibition may be important in preventing glomerular thrombosis. Moreover, the precise mechanisms whereby ACE inhibition prevents or reverses the severe hypertensive nephropathy in L-NAME SHRs remain to be elucidated. In support of ascribing these to renin-angiotensin mechanisms, local or systemic, is the prevention of angiotensin II synthesis as well as the more recent finding that thiazide cotreated with L-NAME exacerbates the glomerulopathy.37 Further support may be offered by recent observations that demonstrated in vitro that angiotensin promoted intravascular thrombosis.40 Thus, it was of great interest to see that cotreatment or posttreatment with ACE inhibitors either prevented or significantly reversed the intravascular thrombosis associated with L-NAME. However, until studies are reported with an angiotensin II receptor antagonist or with a bradykinin or prostaglandin antagonist, the role of the kinins or prostaglandins cannot be separated from the effects of angiotensin II.
In summary, chronic ACE inhibition with quinapril prevented as well as
reversed the systemic, whole-kidney and glomerular
dynamic and pathological alterations that resulted from 3 weeks of
L-NAME intervention. These changes occurred even though
arterial pressure RA and RE were
not always normalized. Quinapril therefore protected and reversed the
nephrosclerosis and afferent arteriolar injuries in
SHRs that were associated with increased fibronectin and decreased
-SMA deposition induced by chronic L-NAME treatment.
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Selected Abbreviations and Acronyms |
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Acknowledgments |
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This study was supported by funds from the Hypertension Research Trust Fund, Alton Ochsner Medical Foundation. We also acknowledge the Parke-Davis Research Laboratories for their generous gift of quinapril. We deeply appreciate the valuable technical assistance and support of Drs Gordon B. McFarland and Gladden W. Willis of our Departments of Orthopedic Surgery and Pathology.
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Footnotes |
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Reprint requests to Edward D. Frohlich, MD, Vice President for Academic Affairs, Alton Ochsner Medical Foundation, 1516 Jefferson Hwy, New Orleans, LA 70121.
This manuscript from Alton Ochsner Medical Foundation was sent to Theodore Kotchen, MD, Consulting Editor, for review by expert referees, for editorial decision, and for final disposition.
Received September 7, 1995; first decision October 19, 1995; accepted November 29, 1995.
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