a rat model of preeclampsia

A Rat Model of Preeclampsia

MONICA IANOSI-IRIMIE,1 HOP V. VU,1 JOY M. WHITBRED,1

CANDICE A. PRIDJIAN,1 J. D. NADIG,1

MARIAN Y. WILLIAMS,1 DENE C. WRENN,1

GABRIELLA PRIDJIAN,2 AND JULES B. PUSCHETT1

1Department of Medicine, Tulane University School of Medicine, New Orleans,

Louisiana, USA2Department of Obstetrics and Gynecology, Tulane University School of

Medicine, New Orleans, Louisiana, USA

Preeclampsia/eclampsia is a disorder of human pregnancy that continues to exactsignificant maternal morbidity and mortality and fetal wastage. Therapy of thesedisorders has not changed in over 50 years and there are no proven preventivemeasures. We describe a model of the development of a syndrome in the pregnant ratthat resembles preeclampsia, which results from the imposition of excessive volumeexpansion early in gestation. We administered desoxycorticosterone acetate (DOCA)to pregnant animals whose drinking water had been replaced with saline. Wecompared the results obtained in these animals with those resulting from the study ofcontrol, virgin animals, virgin animals receiving DOCA and saline, and normalpregnant (NP) animals. The virgin animals given DOCA and saline did not becomehypertensive. The experimental paradigm in the DOCA plus saline pregnant (PDS)animals provides many of the phenotypic characteristics of the human disorderincluding the development of hypertension, proteinuria, and intrauterine growthrestriction. In addition, the mean blood nitrite/nitrate concentration was reduced inthe PDS rats compared with their NP counterparts. We propose that this model mayprove to be useful in the study of the human condition.

Keywords hypertension, pregnancy, volume-expansion

IntroductionPreeclampsia/eclampsia is a pregnancy-specific hypertensive disorder that reflects end-

organ damage not only to the uterus, fetus, and placenta, but to other systems as well

(1, 2). These include the nervous system, the kidneys, the liver and often the coagulation

cascade (1, 2). Hypertensive disorders of pregnancy represent the second largest cause of

fetal wastage and maternal morbidity and mortality (3). Efforts to unravel the etiology of

Clinical and Experimental Hypertension, 8:605–617, 2005

Copyright D Taylor & Francis, Inc.

ISSN: 1064-1963 print / 1525-6006 online

DOI: 10.1080/10641960500298608

Received 18 November 2004; accepted 1 June 2005.Address correspondence to Jules B. Puschett, M.D., Professor and Chairman, Department of

Medicine, SL12, Tulane University School of Medicine, 1430 Tulane Ave., New Orleans, LA70112-2699, USA; E-mail: [email protected]

605

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this syndrome have been hampered by the fact that these conditions occur spontaneously

only in the human subject and rarely in the nonhuman primate (4). The senior investigator

and his colleagues have studied the role of volume expansion in the mediation of one

form of essential hypertension: that associated with expansion of the extracellular fluid

(ECF) volume (5). Since pregnancy represents a condition in which spontaneous volume

expansion (VE) of the ECF occurs (6, 7), we have turned our attention to the study of

preeclampsia as an example of VE-mediated hypertension. In the studies from this

laboratory mentioned previously (5), we performed uninephrectomy prior to the

introduction of desoxycorticosterone (DOCA) and saline. We reasoned, however, that

the burden of VE represented by pregnancy would be sufficient, without uninephrectomy,

to cause the development of hypertension.

We report in this article what the authors believe to be a reproducible rat model in

which excessive VE precipitates the development of a syndrome that resembles human

preeclampsia. It consists in the ‘‘overexpansion’’ of the pregnant rat by virtue of two

maneuvers: the administration of saline in place of drinking water; the concomitant

provision of exogenous mineralocorticoid (DOCA) to ensure the retention of the excess

sodium. Under these circumstances, the pregnant rat develops a syndrome with many of

the phenotypic characteristics of human preeclampsia. The significance of these findings

for the further study of preeclampsia in the human patient is discussed.

Materials and Methods

Animal Preparation

Female Sprague-Dawley rats (200–250 g) (Harlan, Indianapolis, IN, USA) were allowed

free access to standard rat chow and tap water. They were maintained on a 12:12 hr

light:dark cycle and acclimatized for 1 week prior to being studied. Animal care was

conducted in accordance with institutional guidelines. The animals were mated with male

Sprague-Dawley rats weighing 275–300 g. Pregnancy was confirmed by the presence of

vaginal plugs or by examination of vaginal smears (1 day of pregnancy). The pregnant

females were then isolated from the males.

The animals were randomly divided into 4 groups: Group 1: control (C), nonpregnant

animals ( n = 14); group 2: DOCA + saline (DS) animals ( n = 8); nonpregnant animals

were injected initially with 12.5 mg of DOCA intraperitoneally in a depot form, followed

by 6.5 mg on a weekly basis. Their drinking water was replaced with 0.9% saline. Group

3: normal pregnant (NP) animals were given tap water ad libitum ( n = 13). Group 4:

pregnant, + DOCA + saline (PDS) animals ( n = 13) were injected initially with 12.5 mg

of DOCA intraperitoneally in a depot form (before mating), followed by 6.5 mg on a

weekly basis. Their drinking water was replaced with 0.9% saline. All 4 groups were

maintained on normal rat chow (Lab Diet 5001 Laboratory Rodent Diet).

Systolic blood pressure by the tail-cuff method (IITC Inc., LifeScience Instruments,

model 59). For each systolic blood pressure (BP) value reported, an average of 3–4

readings were performed when the BP had stabilized. The measurements were obtained at

3 different time points: T0 = before any treatment was started (followed by the initial

DOCA injection); T1 = when the animals were 7–10 days pregnant; T2 = when the

animals were 14–17 days pregnant. For the virgin animals, comparable time periods

were utilized.

At 18–19 days of pregnancy, 24-hr urine was collected in the absence of food (this

was done to eliminate contamination of the urinary protein determination by any fallen

food particles). Each animal was housed separately in a metabolic cage. Simultaneously,

M. Ianosi-Irimie et al.606

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blood was drawn from the ophthalmic venous plexus. At 20 days of pregnancy, the

animals were euthanized by exposing them to carbon dioxide in a Perspex chamber. The

pregnant uterus and the kidneys were harvested for further analyses. The number of the

fetuses and the total litter weight were noted. Kidney cortex and medullary tissue were

separated and utilized for SDS-PAGE electrophoresis and Western blot analyses.

Urine and Blood Analyses

The 24-hr protein excretion was measured using the pyrogallol red method (Total Protein

Kit, Micro Pyrogallol Red Method, Sigma). A Beckman Creatinine Analyser 2 and the

creatinine reagent kit (the picric acid method) (Beckman Coulter) were used for

creatinine determinations in blood and urine. Nitrite/nitrate (NO) measurements in sera

and in 24-hr urines were performed using the nitric oxide colorimetric assay (Roche

Diagnostics Gmbh) based on the method with sulfanilamide and N- (-naphtyl)–

ethylenediamine. Hematocrit was measured using an Autocrit Ultra 3 centrifuge.

Tissue Preparation

The kidneys were excised, dissected, and washed in ice-cold saline buffered with 1 mM

Tris-HEPES (pH = 7.5) before removal of the cortex and medulla of the kidneys. The

kidney cortex was separated from the medulla and used for Western determinations. The

tissue was homogenized in a (10-fold, w/v) solution (50 mM mannitol buffered with

2 mM tris-HEPES), in washed sea sand (Fisher S25). Cell lysate samples were taken after

the kidney tissue had been centrifuged at 1000 � g to pellet sand and cell debris. After

extraction, aliquots were stored in a �80�C freezer.

Protein assays were performed employing a Pierce BCA assay kit utilizing bovine

albumin standards and measured with a plate reader with a 562 nm filter.

Electrophoresis and Protein Transfer

Proteins of interest were resolved by SDS-PAGE electrophoresis according to the method

of Laemmli (8). Cell lysate samples were prepared in Novex LDS sample buffer

(Invitrogen, Carlsbad, CA, USA) and were loaded on 7% tris-acetate NuPAGE gels

(Invitrogen) using NuPAGE tris-acetate SDS running buffer. The proteins were then

transferred to a 0.2 mm nitrocellulose membrane (Biorad) using NuPAGE transfer buffer

(Invitrogen NP0006).

Immunologic Studies

Once the proteins were transferred, the membranes were stained with Ponceau S Solution

(Sigma P-7170). The upper part of the membrane was used for endothelial nitric oxide

synthase (eNOS) determination and the bottom for b-actin controls. Western analyses

were performed using commercially available monoclonal antibodies to eNOS/NOS

Type III (BD Transduction Laboratories). The membranes were blocked for 1 hr in

blocking buffer (PBS), 0.5% Tween-20, and 5% milk powder at room temperature. The

membranes were then briefly rinsed in wash solution (PBS, 0.5% Tween-20) and then

incubated with the anti-eNOS antibody (1:500) or with mouse monoclonal anti-b-actin

antibody (1:5000 mouse monoclonal Clone AC-15, Sigma A-5441) for another hour. The

membranes were then washed and incubated with a 1:2500 dilution of a horseradish

peroxidase-conjugated goat antimouse IgG secondary antibody (Kirkegaard and Perry

Laboratories, Gaithersburg, MD, USA) for 60 min, followed by another wash. The

chemiluminescent detection was performed using ECL Western blotting detection

607Rat Model of Preeclampsia

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reagents (Amersham Biosciences). Resulting autoradiographs were quantified by

scanning and employing QuantiScan software (Biosoft, Ferguson, MO, USA). The

results were obtained after normalizing for b-actin.

Statistical analyses were performed using SPSS 11.5 for Windows: univariate

analyses of variance (tests of between-subjects effects) as well as Student’s t-test (when

comparing only two groups). p < 0.05 was considered statistically significant.

Results

Blood Pressure and Hematocrit

Changes in systolic BP (as measured via the tail cuff method) in the 4 groups of animals

are shown in Figure 1. The PDS group showed a significant rise in systolic BP when

compared with each of the NP, C and DS groups as early as 7–10 days into pregnancy.

The NP group showed a trend toward a decrease in systolic BP as pregnancy progressed,

most evident at days 14–17 of pregnancy. The nonpregnant groups did not show any

changes in BP over a similar time period. The BP values at T2 were: C: 109 ± 9 mmHg;

DS: 106 ± 9 mmHg; NP: 80 ± 4.8 mmHg; PDS: 130.8 ± 9.7 mmHg (data are expressed

as means ± standard deviation). Statistical analyses at T2 showed that the effect of

treatment (DOCA and saline) was significantly different when one compares its effects

on pregnant versus nonpregnant animals ( p < 0.05).

To provide some estimate of changes in the intravascular and extravascular ECF

compartments, we measured the hematocrits in the C, NP, and PDS rats. The mean value

of 0.43 ± 0.03 for the PDS group was statistically significantly different from those for

the NP group (0.38 ± 0.05, p = 0.04) and for the C animals (0.51 ± 0.02, p < 0.01).

Furthermore, C differed from NP ( p < 0.001).

Weight Gain

Increases in weight after 20 days of pregnancy and at comparable time periods in the

nonpregnant animals are presented in Figure 2. The mean values (± SE) for weight gain

in each of the 4 groups are: C: 39.1 ± 13.6 g; DS: 53.9 ± 9.8 g; NP: 92 ± 21.4 g; and

Figure 1. Systolic blood pressure values in pregnant and nonpregnant rats. Values are

means ± SD; n = number of rats. T0 = day 0 of the experiment (prior to any experimental

maneuvers); T1 = days 7–10 of pregnancy; and T2 = days 14–17 of pregnancy. C = control,

virgin animals; DS = virgin animals receiving DOCA and saline; NP = normal pregnant animals;

PDS = pregnant animals receiving DOCA and saline. PDS is different from C, DS, and NP at T1

and T2, p < 0.05. NP is different from C and DS at T2, p < 0.05.


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PDS: 77.4 ± 25.9 g. As expected, the weight gain in the nonpregnant groups was less

than that seen in each of the two pregnant groups ( p < 0.01 in each case). The difference

in the weight gain in the PDS animals, which was less than that noted in the NP group

( p < 0.05), can be attributed to the smaller litters observed in the PDS group.

Fetal Parameters

Because rats have multiple gestation pregnancies, we considered the total litter weight

and the total number of fetuses as relevant indicators of fetal growth. These data are

presented in Table 1. They show a decrease in the fetal number as well as the total weight

of the litter for the PDS group compared with the NP group ( p < 0.05).

Urinary Protein Excretion

The PDS group (9 ± 4.5 mg/24 h) showed a significant increase in protein excretion

when compared with the NP group (5.0 ± 2.0) ( p < 0.05) (Figure 3). Also, the pregnant

Table 1Fetal parameters at day 20 of pregnancy

Animal group NP ( n = 11) PDS ( n = 10)

Number of fetuses 12.4 ± 4.4 7.5 ± 6.1*

Total litter weight 50.7 ± 7.2 gm 37.8 ± 14.9* gm

Values are means ± SD; n = number of rats. NP = normal pregnant animals; PDS = pregnantanimals receiving DOCA and saline.

*There was a statistically significant difference between the two groups ( p < 0.05).

Figure 2. Weight gain pattern at 20 days of gestation. Values are means ± SD obtained at 20 days

of gestation in NP and PDS rats and at comparable time periods in virgin rats (C, DS). C = control,

nonpregnant animals; DS = nonpregnant animals receiving DOCA and saline; NP = normal

pregnant animals; PDS = pregnant animals receiving DOCA and saline. xWeight gain in the

pregnant animals exceeded that in both nonpregnant groups ( p < 0.05). *The weight gain in the NP

animals exceeded that in the PDS rats ( p < 0.05).


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groups had a statistically significantly higher protein excretion when compared with the

nonpregnant groups: C: 3.1 ± 1 mg/24 h; DS: 3.1 ± 1.3 m/24 h ( p < 0.05).

Creatinine Values

Creatinine values (Table 2) in blood were lower in the pregnant animals (NP and PDS)

compared with the C and DS rats ( p < 0.01 for each group), most likely as a result of

hemodilution, which is characteristic of pregnancy. However, the DS animals also

showed a decreased level of creatinine ( p < 0.05), suggesting that the treatment (DOCA

and saline) had a different effect on pregnant versus nonpregnant animals ( p < 0.05).

There were no significant differences between the creatinine clearance values in the

2 groups of pregnant animals (NP and PDS) or between the 2 nonpregnant groups of

animals (C and DS). The higher values in the NP and PDS groups ( p < 0.05) most likely

represented the effects of pregnancy.

Figure 3. Urinary protein excretion in pregnant and virgin animals. The values are the means ± SD

obtained on day 19 of pregnancy and at comparable time periods in the nonpregnant rats;

n = number of rats. C = control, nonpregnant animals; DS = nonpregnant animals receiving

DOCA and saline; NP = normal pregnant animals; PDS = pregnant animals receiving DOCA and

saline. xUrinary protein excretion in both groups of pregnant animals exceeded those in the virgin

rats ( p < 0.05). *Protein excretion in the PDS animals exceeded that in the NP rats ( p < 0.05).

Table 2Serum creatinine concentrations and creatinine clearance data

Animal group C ( n = 14) DS ( n = 7) NP ( n = 13) PDS ( n = 10)

Serum (mg/dl) 0.71 ± 0.13 0.54 ± 0.05* 0.58 ± 0.07* 0.58 ± 0.07*

Clearance (ml/min) 0.99 ± 0.20 1.11 ± 0.18 1.60 ± 0.64** 1.65 ± 1.02**

Data were obtained at the 19th day of pregnancy and at comparable time periods in virgin rats.Values are means ± SD; n = number of rats.

C = control, nonpregnant animals; DS = nonpregnant animals receiving DOCA and saline;NP = normal pregnant animals; PDS = pregnant animals receiving DOCA and saline.

*The NP, PDS, and DS groups are different from C, p < 0.05.**NP and PDS are different from C and DS, p < 0.05.


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Nitrite/Nitrate (NO) Studies

Table 3 shows a decreased NO concentration in blood for the PDS group. Those animals

with the highest blood pressures had the lowest blood NO values and vice-versa. In

contrast, nonpregnant animals receiving the same treatment did not develop hypertension

or decreased NO concentration in blood. Statistical analyses showed that pregnancy

( p < 0.01) as well as DOCA and saline treatment ( p < 0.05) had a significant effect on

blood NO concentration.

Table 3Nitrite/nitrate concentration in blood and urine and urinary sodium excretion in the

4 groups of animals studied

Animal group C ( n = 14) DS ( n + 7) NP ( n = 13) PDS ( n = 10)

Serum NO (mM/L) 22.7 ± 5.4 18.8 ± 3.2 42.4 ± 8.4 35.2 ± 8.6*

Urine (nM NO/mg

creatinine)

37.5 ± 13.8 106.7 ± 56.8** 36.6 ± 18.9 104.6 ± 36.7**

Urinary sodium

excretion (mmol/24 h)

0.3 ± 0.05 3.4 ± 2.9+ 0.3 ± 0.2 3.5 ± 2.9+

Values are means ± SD. NO = nitrite/nitrate; n = number of rats; C = control, nonpregnantanimals; DS = nonpregnant animals receiving DOCA and saline; NP = normal pregnant animals;PDS = pregnant animals receiving DOCA and saline.

Statistical analyses: *NP vs. PDS, p < 0.05; **DS vs. C and PDS vs. NP: p < 0.01; +DS vs. Cand PDS vs. NP, p < 0.0001.

Figure 4. Western blots for eNOS and b-actin from kidney tissue. There were no differences

between C, NP, and PDS rats (a) or between C and PDS rats (b). C = control, nonpregnant animals;

NP = normal pregnant animals; PDS = pregnant animals receiving DOCA and saline.


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The 24-hr urinary NO excretion was increased in the PDS and DS groups compared

with the normal pregnant and control groups, respectively ( p < 0.01). These observations

correlated with the degree of sodium excretion. Thus, the PDS and DS animals excreted

several times the amount of sodium as did the NP and C rats, respectively ( p < 0.001, in

each case).

We performed eNOS Western analyses on kidney cortical tissue. Representative

Westerns of eNOS expression in these tissues are shown in Figure 4a and 4b. After

quantifying the Westerns from both experiments and normalizing to b-actin, there were

no differences in eNOS expression between the 4 groups.

The kidneys of 5 PDS and 5 NP animals were examined histologicaly. No

abnormalities were found in the kidneys of the NP rats. In 1 of the 5 PDS animals, there

was evidence of arteriolar fibrinoid necrosis. Renal tubular proteinosis also was noted.

DiscussionStandardized diagnostic terminology and categorization of hypertensive disorders in

pregnancy have developed over the past several years (1, 3, 9). This effort has allowed

physicians and scientists to separate dissimilar conditions, all of which result in

hypertension during pregnancy. The failure of these distinguishing characteristics to be

applied to the various syndromes of hypertension in pregnancy in the past has contributed

to the confusion in the literature regarding pathogenetic mechanisms of, and therapeutic

stratagems in, hypertension in pregnancy (1, 2). According to currently accepted guide-

lines, preeclampsia is diagnosed when new-onset hypertension supervenes after 20 weeks

of gestation and is associated with significant, persistent proteinuria (9). Although

excessive edema is often a concomitant, it is not invariable (1, 10). A phenomenon

frequently associated with preeclampsia is intrauterine growth restriction (IUGR) that

manifests as low birth weight and fetal loss. These features were demonstrated by the

preeclamptic rat model described in this article.

For at least two decades, it has been suggested that preeclampsia is not a single

disorder but a consequence of more than one pathogenetic mechanism (11, 12). Both fetal

and maternal factors have been proposed as important in the etiopathogenesis (11).

Furthermore, multiple pathogenetic processes have been suggested to explain the

difference between mild, moderate, and severe disease (10). Additionally, it is likely that

early-onset preeclampsia is often more severe than that developing in late pregnancy (12)

and may represent a different disease process.

Should the paradigm presented here be applicable to the human condition, we

suggest that it is a model of mild-to-moderate preeclampsia, the pathogenesis of

which may be different from that of severe preeclampsia/eclampsia. Thus, our ani-

mals showed no evidence of a lesion in the kidney said to be characteristic of this

disorder, glomerular endotheliosis (10, 13). The (latter) finding is not invariable in

preeclampsia (14) and might only be present in severe disease (10). However, as

described in some (mild) cases of preeclampsia (10), we did detect evidence of renal

tubular proteinosis.

In recent years, a number of investigators have concentrated upon evaluating the

primacy of reduced uteroplacental blood flow as a major determinant of the

pathophysiology of this disorder. This hypothesis, originated more than 30 years ago

(15), has formed the basis for a number of more recent investigations (16, 17). Because

preeclampsia/eclampsia occur spontaneously only in human pregnant patients and

possibly in certain rare instances, in nonhuman primates (2, 14), its study has been


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difficult. Thus, with the possible exception of a recently reported genetic form of the

disease in mice (18), no completely satisfactory small animal model heretofore has been

developed that addresses the issue of the early events in preeclampsia.

Interestingly, a recently reported study in which 1.8% NaCl was administered to

pregnant rats has produced a syndrome resembling human preeclampsia (19). Based upon

the observations provided in this article, we propose, but cannot prove at this point, that

excessive volume expansion in patients with a genetic or acquired defect in sodium

excretion (see below) results in a mild-to-moderate form of preeclampsia that is

simulated by the rat model presented in this report. This model has many (but not all) of

the phenotypic characteristics of the human condition. Thus, the pregnant animals treated

with saline and DOCA developed significant hypertension, while normal pregnant

animals showed a decline in blood pressure (Figure 1), much like that occurring during

normal human pregnancy (1).

As in preeclamptic women, PDS rats developed a marked increase in urinary protein

excretion that significantly exceeded that seen in normal pregnant animals (Figure 3).

When DOCA and salt were administered to nonpregnant animals, hypertension did not

occur nor did proteinuria (Figures 1 and 3). Thus, the changes we have reported are

specific to the pregnant circumstance.

IUGR, as adjudged by pup number and total uterine weight, was a routinely observed

phenomenon in our ‘‘preeclamptic’’ rats (Figure 2 and Table 1). We chose a pregnant rat

model in which excessive expansion of the ECF volume is accomplished by

administering a salt surfeit in the form of 0.9% saline replacing the drinking water. To

simulate a postulated defect in sodium excretion in some forms of human preeclampsia,

we administered DOCA, thus attempting to ensure failure of the experimental animal to

fully excrete the added sodium load. Examination of our data indicates that there was a

lower pup survival and decreased uterine weight in animals that received DOCA and

saline than in NP animals.

Patients are automatically classified as having severe preeclampsia if they exhibit

IUGR, even if they demonstrate rather modest elevations in blood pressure and/or less

than major increments over normal in protein excretion (10). Yet it is clear that some

preeclamptic patients with even modest elevations in blood pressure will give birth to low

birth weight infants and to stillborns (20, 21). We suggest, therefore, that the finding of

IUGR in animals without other serious stigmata seen in human preeclampsia (platelet

dysfunction, glomerulosis, etc.) does not militate against the utility of this animal model

in the study of mild-to-moderate forms of the human disease (22). Indeed, some

investigators have reported that preeclamptic patients often deliver high birth weight

infants (23). Again, these apparent discrepancies could result from the heterogeneity of

etiologies of the preeclamptic syndrome (11, 24).

Nitric oxide has a very short plasma half-life (a few seconds), and consequently its

concentration in plasma or serum is difficult to measure. Therefore, most studies utilize

methodology to examine its metabolic end products, nitrite and nitrate, as surrogates, as

has been the case in urine. The evanescent nature of its appearance in plasma, as well as

other problems with the estimation of the NO system (see below), may have led to the

considerable controversy over its activity in normal pregnancy and in preeclampsia.

Elevated plasma levels of NO have been reported in human preeclampsia by some

workers (25–29) and either no change (30–33) or an actual decrement by others

(34–36). We noted a decreased NO concentration in blood in our PDS group of animals

compared with normal pregnant rats. However, there were no alterations in eNOS in our

animals. Novak et al. have reported recently no differences in eNOS expression between


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virgin and midterm pregnant rats in kidney inner medulla, outer medulla, or cortex (37).

Placental NO synthase activity also has been reported to be reduced in preeclampsia (38).

The rather sizable increase in urinary NO excretion seen in our ‘‘preeclamptic’’ rats

(Table 3) also is not compatible with other animal models of this disorder in which NOS

inhibition has resulted in a hypertensive state in pregnancy (39, 40). However, models of

hypertension in pregnancy produced by chronic reductions in uterine perfusion pressure

have shown no differences in urinary NO excretion from those determined in control

pregnant rats (41). We did note a correlation, however, between the amount of sodium

excreted and the level of urinary NO excretion. This relationship has been reported

previously (42). Furthermore, as has long been suspected, and mentioned earlier in this

report, preeclampsia is likely multifactorial in pathogenesis (1, 2, 11, 12). Accordingly,

the pathophysiology of the hypertension in the animal model presented in this

communication may not include a major role for NO. Alternatively, modification in

the NO system in the smooth muscle of the arteriole may be the final arbiter of the status

of vascular resistance (43). This function may not correlate with either plasma or urinary

NO measurement. Finally, a more important and accurate measure of the involvement of

eNOS may be reflected by the phosphorylation status rather than the amount of eNOS

protein as determined by Western blot analysis (44, 45).

Pathologic and histologic features of preeclampsia have been reported to be

consistent in some cases and quite variable in others (16, 46). Thus, IUGR has been

regularly reported as has reduced viability and increased morbidity and mortality of the

fetus (1, 2, 10). The number of pups in our ‘‘preeclamptic’’ rats was significantly reduced

compared with those derived from animals undergoing normal pregnancy (Table 1).

Histologic renal abnormalities were rare in our ‘‘preeclamptic’’ rats.

ConclusionWe have developed a rodent model of preeclampsia. The pathogenetic process includes

excessive expansion of the ECF volume. The cause of the redistribution of the excess

fluid (and salt) from the intravascular to the extravascular compartment of the

extracellular space is not clear. We suspect, as originally suggested by Graves et al.

(47, 48), this may be due to the release of a circulating factor or factors initiated by the

ECF volume expansion. We propose that some pregnant patients who develop

preeclampsia have a defect in sodium transport that does not become manifest until

the ECF VE represented by pregnancy occurs. Defective sodium excretion also has been

postulated as a pathogenetic mechanism for patients with VE-mediated essential

hypertension (49). Phenotypically, the rat model presented in this report reproduces many

of the characteristics of the preeclamptic human patient. In human preclamptic

pregnancy, hypertension, proteinuria, and IUGR are regularly evident. We propose that

the use of the rat paradigm of preeclampsia reported here may allow the more direct study

of the human disorder utilizing the small animal. We hope this will speed the process by

which prevention and effective treatment of this syndrome can be established. Of course,

whether or not these findings in the experimental animal have relevance to the human

disorder remains to be determined.

AcknowledgmentsThe authors thank Ida Hennington for the production of this manuscript. Portions of this

work were supported by a research grant from Dialysis Clinic, Inc., and by the Louisiana

Board of Regents Millennium Trust Health Excellence Fund (2001-2006)-07. Dr. Puschett


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is a member of the Tulane Hypertension and Renal Center of Excellence. We thank Dr.

Will Robichaux, Department of Pathology, Tulane University School of Medicine, for his

review of the pathologic slides of the uteri of our animals.

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a rat model of preeclampsia

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