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Original Research: Lead Article

Effect of l-Arginine Therapy on the Glomerular Injury of Preeclampsia

A Randomized Controlled Trial

Hladunewich, M A. MD; Derby, G C. RN, BSN; Lafayette, R A. MD; Blouch, K L. BA; Druzin, M L. MD; Myers, B D. MD

Author Information
doi: 10.1097/01.AOG.0000207637.01824.fe
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The main site of renal injury in preeclampsia is the glomerular endothelial cell.1 Glomerular dysfunction is characterized by depression of the glomerular filtration rate (GFR), proteinuria, and hypertension. In animal studies, evidence points to a prominent role for nitric oxide in the low renovascular resistance and glomerular hyperfiltration that attend the gravid state.2,3 Normal pregnancy in the rat is accompanied by increased production of nitric oxide and its second messenger cyclic guanosine 3′5′ monophosphate (cGMP).3 There is a parallel increase in renal expression of constitutive nitric oxide synthase, the enzyme that generates nitric oxide from arginine.3 In the pregnant rat, an infusion of NG-nitro-l-arginine methyl ester (l-NAME), an exogenous inhibitor of nitric oxide synthase, has been shown to replicate some of the hemodynamic features of the syndrome of preeclampsia.4,5 Another model of preeclampsia is one in which a chronic reduction of uterine perfusion pressure in the pregnant rat is associated with elevated mean arterial pressure, proteinuria, and renal insufficiency.6 An associated deficiency of nitric oxide has been demonstrated. In humans, evidence to support the role of nitric oxide deficiency in the pathogenesis of preeclampsia has been conflicting. Consistent findings, however, have been the demonstration of elevated circulating levels of asymmetric dimethyl arginine, an endogenous inhibitor to nitric oxide synthase, along with lower levels of arginine, the substrate for nitric oxide production.7–10

In a recent animal study, l-arginine supplementation significantly reduced mean arterial pressure in the reduction of uterine perfusion pressure model of preeclampsia.6 In another animal study, l-arginine supplementation reversed the adverse effects of l-NAME on pregnancy by attenuating hypertension and by significantly decreasing proteinuria and the proportion of injured glomeruli.11 To date, studies of the use of l-arginine supplementation to treat women with preeclampsia have been small or uncontrolled and have only assessed blood pressure as a primary outcome measure.12–14 We report a single-center, double-masked, randomized, placebo-controlled trial of l-arginine supplementation for the treatment of preeclampsia, in which precise physiologic techniques were used to assess glomerular dysfunction in addition to blood pressure.

MATERIALS AND METHODS

Women selected for the study had preeclampsia that was diagnosed in the second half of pregnancy.15,16 All participants were patients admitted to Stanford University Medical Center. Inclusion criteria were 1) an elevation of blood pressure to levels in excess of 140 systolic over 90 diastolic, and 2) proteinuria determined by a urine dipstick value of 2+ or greater, or quantitated at 0.5 g or more either per gram creatinine or in a 24-hour urine collection. Women with a history of underlying renal disease defined as a pre-pregnancy azotemia (serum creatinine ≥ 1.2 mg/dL) or proteinuria were excluded. Forty-five women consented to participate in a double-masked, randomized, placebo-controlled trial of l-arginine therapy that was approved by the Institutional Review Board at Stanford University. Healthy gravid women provided control values for the prepartum and postpartum values of interest. These women were randomly selected from the obstetric ward or responded to advertisements posted throughout the hospital. Recruitment began in January of 2000 and was completed in December of 2003.

After obtaining patient consent, we commenced a baseline evaluation that included urine for albumin-to-creatinine (A/C) ratio and a serum sample for creatinine, uric acid, liver function, and a platelet count. A serum l-arginine level was determined before the initiation of treatment. In addition, serum levels were determined for nitric oxide, cGMP, endothelin-1, and asymmetric dimethyl arginine. Patients were enrolled upon presentation to the hospital. However, a large part of the trial was subsequently conducted under outpatient conditions after delivery. As a result, control of the nitrogen content in the diet was not feasible. The systolic, diastolic, and mean arterial pressure before the initiation of magnesium sulfate therapy was documented.

l-Arginine (n = 22) or placebo therapy (n = 23) was initiated after the baseline evaluation of preeclampsia. The medication was randomized and assigned by pharmacy personnel. The randomization procedure involved a set of computer-generated random numbers, each attached to a specified treatment. Pharmacy personnel assigned patients using this predetermined algorithm ensuring roughly equal distribution of patients to both study arms. The study subjects, medical team and all other involved study personnel remained masked throughout the duration of the study. In a minority of patients (15/45), therapy or placebo was administered for more than 1 day before delivery. Of these, 8 of the 22 members of the l-arginine group received therapy for a median of 6 days before delivery (range 3–17) and 7 of the 23 members of the placebo group received this intervention for a median of 8 days (range 1–21). The remaining majority of cases (30/45) presented late in pregnancy or with preeclampsia of sufficient severity to serve as an indication for prompt termination of pregnancy. In these cases, l-arginine was initiated within the 24 hours before delivery (n = 10) or immediately after delivery (n = 5). The corresponding numbers of patients in whom placebo was initiated immediately before or after delivery was 13 and 2, respectively. In those patients terminated by cesarean delivery, treatment was given intravenously until postoperative recovery of bowel motility permitted oral therapy.

l-Arginine (or placebo) was administered orally (3.5 g every 6 hours), or intravenously (10 g every 8 hours) when medications could not be taken orally. Treatment was continued in the postpartum period and patients underwent a full study of renal function and circulating levels of vasoactive substances on the third and 10th postpartum days. All 45 subjects completed three postpartum days of therapy and underwent the postpartum day 3 study. In addition, 19 members of the l-arginine group and 20 members of the placebo group completed a full 9 postpartum days of therapy and returned to the General Clinical Research Center for a final evaluation on postpartum day 10. The study nurse closely followed all patients and performed a pill count on postpartum day 10 to ensure compliance.

In addition to the assessment of hypertension, albuminuria and serum levels of creatinine and vasoactive hormones, the GFR and renal plasma flow were determined on postpartum days 3 and 10. The healthy subjects completing a normal pregnancy provided control values for all of the determinations performed in the experimental preeclampsia groups with one exception. This was the evaluation of GFR and renal plasma flow on postpartum day 3 because most women completing a normal uncomplicated pregnancy are discharged from hospital on postpartum day 3. The formal study of renal function was conducted in 22 women from the gravid control group on the 10th postpartum day.

Mean arterial pressure was determined by Dinamap (Johnson & Johnson, Tampa, FL). Urinary clearances of inulin and para-amino hippurate were used to determine GFR and renal plasma flow, respectively.1 Both the GFR and renal plasma flow were adjusted for body surface area (BSA) using the pre-pregnancy weight as reported by the patient and confirmed by review of the medical record of the first obstetric visit. Renal blood flow was calculated by dividing renal plasma flow by (1 − hematocrit), and renovascular resistance was derived by dividing mean arterial pressure by the renal blood flow.

Patient charts were reviewed in detail to determine doses and duration of therapy for magnesium sulfate and all antihypertensive agents. Liver function tests, platelet counts, serum uric acid levels, and cord blood gases were noted when available. Documented fetal outcomes included gestational age, weight expressed as the percent variation from the 50th percentile for a given gestational age, 1− and 5-minute Apgar scores, and Score for Neonatal Acute Physiology.17 We also recorded the duration of stay in the neonatal intensive care unit, vasopressor therapy, mechanical ventilation, continuous positive pressure ventilation, and Fio2 in excess of 30%.

The mean arterial pressure, GFR, and urinary A/C ratio served as primary outcome measures of resolution of the glomerular injury of preeclampsia. Secondary outcome measures included perturbations in vasoactive hormone levels, renal plasma flow, additional laboratory markers characteristic of progression to severe preeclampsia as defined by the American College of Obstetricians and Gynecologists18 including liver function tests and platelet counts, and the aforementioned fetal outcomes.

In small trials of l-arginine supplementation in pregnant women, no adverse outcomes have been reported to date.12,19,20 Nevertheless, a daily checklist was completed to record the presence of reversible side effects that have been reported by 1–10% of subjects receiving l-arginine including headache, nausea, vomiting, and numbness. Although l-arginine toxicity has not been reported in neonates, all newborns were monitored for the theoretical possibility that l-arginine could potentiate hypotension in the preterm infant and necessitate the institution of vasopressor agents.

We have previously described in detail our methods for the determination of inulin, para amino hippuric acid, creatinine, and albumin in plasma and urine.1,21 All serum samples for assays of vasoactive peptides were collected in ethylenediaminetetraacetic acid. Serum l-arginine was assayed by high-pressure liquid chromatography using a modification of the method developed by Gopalakrishnan.22 Because we encountered a matrix effect resulting in only 80% recovery of l-arginine when serum samples contained protein, we prepared the standards with 6% bovine serum albumin. The mean recovery calculated from the standard BSA curve was 96% ± 2%. Serum asymmetric dimethyl arginine was also assayed by high-pressure liquid chromatography23 in aliquots, both unspiked and spiked with 0.5 μM/L asymmetric dimethyl arginine. The mean recovery of asymmetric dimethyl arginine in the spiked samples was 100% ± 13%. Endothelin was extracted from 3-mL aliquots of urine and plasma using Waters Sep-Pak C18 cartridges with 0.1% triflouroacetic acid in acetonitrile. Dried extracts were reconstituted in 250 μL buffer and analyzed by radioimmunoassay using rabbit anti-human, porcine endothelin-1 (#RAS6901, Peninsula Laboratories, Belmont, CA), and 125I porcine endothelin-1 (#IM223, Amersham Biosciences, Piscataway, NJ). Plasma cGMP was measured using a 3H radioimmunoassay kit (#TRK500, Amersham Pharmacia Biosciences, Piscataway, NJ). Nitric oxide levels were measured using a modification of the method described by Navarro-Gonzales et al.24 Ten thousand MW cutoff filters (Amicon Ultra-4) were used for plasma deproteinization and 1 g cadmium beads (#NB88, Oxford Biomedical Research, Oxford, MI) were used to reduce nitrate to nitrite. The Griess assay for nitrite was performed on a microtiter plate with the resulting color read at 540 nm.

For continuous variables, either a t test or the Wilcoxon rank-sum test was used to assess the significance of differences observed between the placebo group and the recipients of l-arginine supplementation. An analysis of variance or the Kruskal-Wallis test was used to assess for significant differences among the placebo, l-arginine, and gravid control groups. Paired testing was used to assess changes over time. Either the Tukey Kramer test or the Bonferroni test was used to make the respective post hoc comparisons. The Fisher exact test was used to compare proportions. Results are presented as either mean and standard deviation or median (95% CI). Assuming a standard deviation of 10 mm Hg, which was approximated from a previously studied pilot group of women with preeclampsia,1 the study was powered to detect a 10-mm Hg difference in mean arterial pressure (α .05, β .20) between the study groups.

RESULTS

Baseline characteristics of the preeclamptic subjects randomized to receive l-arginine or placebo, and corresponding characteristics of healthy gravid controls, are provided in Table 1. Each preeclamptic group differed significantly from healthy controls in that gestational age was lower, whereas mean arterial pressure, serum creatinine level, and the urinary A/C ratio were each substantially elevated. The placebo and l-arginine preeclamptic groups were well matched with respect to gestational age (34.4 ± 3.7 versus 34.7 ± 4.0 weeks), mean arterial pressure (123 ± 9 versus 126 ± 9 mm Hg), and serum creatinine (0.73 ± 0.19 versus 0.77 ± 0.22 mg/dL), respectively. Patients randomized to l-arginine, however, had heavier albuminuria than the placebo group, as judged by a median A/C ratio of 2,089 (562–3,067) versus 764 (362–1,551) mg/g, respectively. Although this difference did not meet statistical significance, the treatment group did have a significantly lower serum albumin at 2.2 ± 0.5 versus 2.5 ± 0.3 g/dL, respectively (P < .05).

Table 1
Table 1:
Prerandomization Baseline Patient Characteristics

Circulating baseline levels of vasoactive substances related to the l-arginine–nitric oxide system are illustrated in Figure 1 and summarized in Table 2. Median plasma nitric oxide differed significantly from the gravid controls only in the placebo group of preeclamptic subjects (32 versus 41 μM, respectively). In keeping with nitric oxide deficiency in preeclampsia, the median circulating levels of the nitric oxide synthase inhibitor, asymmetric dimethyl arginine were significantly elevated to 0.65 μM/L in both placebo- and l-arginine–treated preeclamptic groups compared with only 0.53 μM/L in gravid controls (Fig. 1, Table 2). Paradoxically, median circulating levels of cGMP in the placebo and l-arginine treated preeclamptic groups were significantly elevated (7.6 and 6.9 pmol/mL) above corresponding healthy gravid control levels (4.0 pmol/mL) (Fig. 1, Table 2). Finally, there was also an excess of circulating levels endothelin in each preeclamptic group compared with healthy gravid controls (Fig. 1, Table 2). Of note, none of the prerandomization circulating levels summarized in Figure 1 and Table 2 differed significantly between the placebo- and l-arginine–treated groups, indicating that they were also well-matched for the prevailing levels of these endothelial vasoactive substances.

Fig. 1.
Fig. 1.:
Box plots comparing the predelivery serum hormone levels in the control (dotted bar), placebo (diagonal lines bar), and l-arginine groups (white bar), respectively, including nitric oxide (A), asymmetric dimethyl arginine (ADMA, B), cyclic guanosine 3′5′ monophosphate (cGMP, C), and endothelin (D). *P < .05 compared with the control group.Hladunewich. l-Arginine Therapy for Preeclampsia. Obstet Gynecol 2006.
Table 2
Table 2:
Serum Vasoactive Hormone Levels

Pretreatment serum l-arginine levels were similar at baseline in the placebo and l-arginine–treated groups, 62 (42–77) versus 54 (52–62) μM/L, respectively, and not different from the corresponding healthy gravid control level of 62 (51–63) μM/L (Table 2). l-Arginine therapy was associated with doubling of the prevailing serum l-arginine level to 110 (93–129) μM/L on postpartum day 3 (Table 2). The postpartum day 3 level increased significantly to 91 (75–101) μM/L in the placebo-treated group from the predelivery value, but remained significantly less than the corresponding value for the arginine-treated group (Table 2).

l-Arginine therapy did not hasten recovery from preeclampsia, however. Mean arterial pressure, although below predelivery levels on postpartum day 3, remained substantially elevated above the gravid control level of 79 ± 7 mm Hg at 103 ± 12 and 102 ± 12 mm Hg in the placebo- and l-arginine–treated groups, respectively (Tables 1 and 3). Corresponding levels on postpartum day 10 were 81 ± 8 versus 96 ± 11 and 98 ± 14 mm Hg, with the latter preeclamptic levels continuing to exceed healthy postpartum control levels significantly (Table 3). Similar elevations above gravid control levels were observed for systolic and diastolic arterial pressures in the preeclamptic groups, but these were not significantly different between the treatment and placebo groups (Table 3). There were also no differences between groups in the use or dosage of magnesium sulfate, or in the number or dosage of antihypertensive agents used during the postpartum period.

Table 3
Table 3:
Trial Outcome Measures

Serum creatinine levels on postpartum day 3 declined below predelivery levels in both the placebo and l-arginine–treated groups, but remained similarly elevated above the corresponding gravid control value, 0.63 ± 0.17 and 0.61 ± 0.21 versus 0.49 ± 0.11 mg/dL, respectively (Tables 1 and 3). No significant differences remained by postpartum day 10.

The corresponding postpartum GFR values also did not differ significantly between the two preeclamptic groups on either postpartum day 3 or postpartum day 10 (Table 3). The GFR averaged 118 ± 37 and 111 ± 29 mL · min−1 · 1.73 m−2 in the placebo-treated and l-arginine–treated groups on postpartum day 3. For reference, the GFR in a previously studied and published group of healthy gravid controls on postpartum day 1 was significantly higher at 149 ± 33 mL · min−1 · 1.73 m−2 (P < .05).21 By postpartum day 10, however, the normal control level had fallen to 125 ± 29 mL · min−1 · 1.73 m−2. The postpartum day 10 GFR values in each treatment group were no longer significantly different from the gravid control value, but tended to be lower by approximately 20 mL/min on average (Table 3).

Renal plasma flow was also not significantly different between the placebo and l-arginine groups on either postpartum day 3 or 10 (Table 3). As was the case for GFR, a declining disparity between the preeclamptic and gravid control values by postpartum 10 resulted in only a nonsignificant trend toward depressed renal plasma flow in placebo and l-arginine groups as compared with the corresponding gravid control value (respectively 444 ± 123 and 479 ± 112 versus 513 ± 109 mL · min−1 · 1.73 m−2) (Table 3). Elevation of renovascular resistance in the preeclamptic groups versus gravid controls was significant on postpartum day 10, however. There were no corresponding differences between the placebo and l-arginine–treated preeclamptic groups on either postpartum day 3 or postpartum day 10 and no significant trend for decreased renovascular resistance between evaluations in either group (Table 3).

The predelivery disparity in albuminuria between the treated and placebo groups persisted on postpartum days 3 and 10 (Tables 1 and 3). However, the level of the A/C ratio declined progressively and proportionately during the postpartum period by approximately 50% on day 3 and by 60–70% on postpartum day 10 (Fig. 2, Table 3). Noteworthy is that median A/C in the healthy gravid controls was in the microalbuminuric range (median value 101 mg/g) on postpartum day 3, and remained above the predelivery values on postpartum day 10 (21 versus 7 mg/g, P < .05; Tables 1 and 3). We infer that these elevated postpartum levels reflect contamination of urine by lochia, especially on postpartum day 3, rather than a true increase in albuminuria. The implication of such postpartum contamination is that the values reported for the A/C ratio in the treated and placebo groups with preeclampsia, in the present study, are likely to be spuriously high, particularly on postpartum day 3. Nevertheless, the similar rate of A/C decline during the postpartum period of observation in the two groups is likely dominated by true albuminuria and suggests a similar rate of improvement. The heavier albuminuria in the treated than placebo group was accompanied by a significant depression of serum albumin in predelivery and postpartum day 3 samples (Tables 1 and 3). The difference between the treated groups was no longer statistically significant by postpartum day 10. Of note, serum albumin was below the normal, nongravid range in our healthy gravid controls, likely reflecting the hemodilution that accompanies healthy pregnancy.25 The albuminuria in the placebo group was too modest to lead to a significant reduction in serum albumin below gravid control levels, although a trend toward such reduction is clearly evident (Table 3). The significant reduction of serum albumin below normal control levels at all three times of sampling in the l-arginine–treated group with preeclampsia attests to a magnitude of proteinuria near to or in the nephrotic range.

Fig. 2.
Fig. 2.:
Predelivery and postpartum days 3 and 10 median albumin to creatinine ratios in the placebo and l-arginine groups. P < .05 versus the predelivery value for a corresponding group; P < .05 versus the postpartum day 3 value for a corresponding group.Hladunewich. l-Arginine Therapy for Preeclampsia. Obstet Gynecol 2006.

Despite l-arginine supplementation, there was a trend for serum nitric oxide and cGMP to decline below predelivery levels on both postpartum days 3 and 10 in the treated group (Table 2). Furthermore, postpartum levels of nitric oxide and cGMP in the l-arginine group were not different from corresponding values in the placebo group (Table 2). Endothelin and asymmetric dimethyl arginine levels in serum were also not different in the treated and placebo groups on postpartum days 3 and 10 (Table 2). The former tended to decline, whereas the latter increased progressively during the postpartum period. Of note, the serum levels of nitric oxide, asymmetric dimethyl arginine, and endothelin in both preeclamptic groups were not different from corresponding gravid control levels on postpartum days 3 and 10 (Table 2). However, serum cGMP remained elevated above the gravid control levels on postpartum day 3 (Table 2), but this difference was no longer evident in either placebo or treated groups on postpartum day 10 (Table 2).

Because the primary goal of any therapy for preeclampsia is prolongation of the pregnancy and improved outcome for mother and baby, we assessed laboratory abnormalities including liver function tests and platelet counts, which indicate progression toward the severe preeclampsia syndrome as defined by the American College of Obstetricians and Gynecologists.18 We also assessed neonatal outcomes in the subgroup of women presenting with severe preeclampsia at less than 37 weeks gestation. The subgroup analysis included 15 women in each group. Although the difference did not meet statistical significance (P = .35), gestation was prolonged in the treatment group by 7 ± 8 days compared with 4 ± 8 days in the placebo group. This likely reflects no women progressing toward severe preeclampsia as defined by a doubling of serum transaminase levels and a drop in platelet count to less than 1003/mm3 in the treatment group compared to 4 in the placebo group (P = .032). Neonatal outcomes are displayed in Table 4. Despite trends toward improved outcomes including fewer hours of vasopressor use, mechanical ventilation, continuous positive airway pressure, and high-dose oxygen in the neonates that received l-arginine supplementation, none of the neonatal outcomes reached statistical significance. We did not detect any adverse events secondary to the treatment in either the women or the neonates.

Table 4
Table 4:
Neonatal Outcomes

DISCUSSION

Impaired synthesis of nitric oxide has been hypothesized to underlie preeclampsia. Evidence supporting this hypothesis has included depressed levels of nitric oxide in serum,26 elevation of asymmetric dimethyl arginine levels, an endogenous inhibitor of nitric oxide synthetase,23,27 and low levels of l-arginine, the substrate for nitric oxide production.10 Moreover, 2 experimental models of preeclampsia in rats, those following either infusion of l-NAME or chronic reduction of uterine artery perfusion pressure, have been shown to respond to l-arginine therapy, as judged by resolution of hypertension, proteinuria, and glomerular endothelial injury.6,11

Evaluation of our preeclamptic subjects at baseline has provided only ambiguous evidence to support impairment of nitric oxide synthesis, however. Although we observed reduction of nitric oxide serum levels in our placebo group, this was not the case in our treatment group. The ambiguity of these contrasting findings is likely related to our inability to control our subjects’ dietary content of nitrate. Further, in contrast to earlier reports,10 we did not observe significant depression of plasma l-arginine in our preeclamptic groups. Also, rather than depression of cGMP in preeclamptic plasma, we found this second messenger of nitric oxide to be elevated, a finding that is likely attributable to the enhanced release of atrial natriuretic peptide that accompanies preeclampsia.28 Finally although we did confirm that asymmetric dimethyl arginine is elevated in preeclampsia, therapy with l-arginine in large doses failed to accelerate the rate of resolution of hypertension, albuminuria, and GFR depression, relative to that observed in placebo-treated patients during the puerperium.

In contrast to the animal literature, but in keeping with the present findings, l-arginine supplementation has not consistently conferred significant benefit in women with pregnancies complicated by preeclampsia. In a recently reported study, 30 women with preeclampsia were randomized to receive either 4 g l-arginine 3 times a day for 5 days or placebo.12 No reduction of diastolic blood pressure was demonstrated. In another small study, 20 g l-arginine was infused into 9 women with preeclampsia and 10 healthy gravid controls.14 However, this study also failed to demonstrate a decrease in blood pressure in either group despite increased serum cGMP levels.14 To date, only 1 study has demonstrated a blood-pressure–lowering effect secondary to l-arginine supplementation.13 In this study, 17 women with preeclampsia and 12 women with an uncomplicated pregnancy were given 30 g l-arginine supplementation intravenously. Both groups experienced a significant decrease in systolic blood pressure. However, the decline was transient in women with preeclampsia, returning to baseline values 30 minutes after the infusion was discontinued. This finding calls into question the clinical utility of such large doses, which have been documented to result in side effects.29 The dose we used in this trial is estimated to boost intake to approximately 250% of what is consumed in a normal diet, and increases plasma arginine levels by a factor of 2.30 Demonstrated biologic actions of such therapy have included decreased platelet aggregation and monocyte adhesiveness and increased forearm blood flow.31–33 However, it remains a possibility that the dose administered in this trial was inadequate.

Not only did l-arginine not exert an antihypertensive effect in our preeclamptic subjects, but it also failed to influence glomerular hemodynamics on postpartum day 3 and 10, as judged by an absence of augmentation of the depressed levels of both GFR and renal plasma flow compared to the placebo-treated group (Table 2). Although not statistically significant, our treatment and placebo groups were mismatched in that the former had heavy, near-nephrotic–range albuminuria, whereas subjects randomized to our placebo group had only moderate albuminuria. It is attractive to hypothesize that a benefit due to arginine therapy was masked by this discrepancy and that, in fact, the women in the arginine group were more severely affected. However, there was also no clear acceleration of the rate at which albuminuria resolved during the postpartum period of observation. Further, given that the magnitude of albuminuria is not predicative of either maternal or fetal outcome,34,35 we submit that there is no compelling reason to design a new and much larger trial to better match the treatment and placebo groups for the magnitude of albuminuria.

Although the present study assessed blood pressure and glomerular function as primary outcome measures, perhaps the most clinically relevant question is whether gestation can be prolonged and neonatal outcome improved by l-arginine supplementation. In our study, there was a trend to prolonged gestation in the l-arginine group compared with the placebo group (7 versus 4 days). This was associated with fewer women exhibiting thrombocytopenia below 1003/mm,3 and doubling of their serum transaminase levels. In the randomized placebo-controlled trial that preceded our study, a similar trend emerged with a nonsignificant increase in time to gestation in the group that received l-arginine supplementation (12 versus 9 days).12 In both our study and the smaller randomized placebo-controlled trial that preceded it, too few neonates required intensive care to provide meaningful data.12 Given that serum arginine levels increased in all groups in the postpartum period and the fact that arginine transporters have been found on the placenta,36,37 it may be that arginine is important for fetal development. A larger study is required to determine if a prolongation of gestational age with improved maternal and neonatal outcomes can be achieved with l-arginine supplementation.

In light of new insights into the pathophysiology of preeclampsia, the lack of benefit of l-arginine supplementation perhaps is not surprising. Other pathophysiologic abnormalities and therefore potential therapeutic targets have now been identified. One such abnormality is the presence of autoantibodies capable of activating the angiotensin II AT1 receptor that correlate with the hypertension, appearing at approximately 20 weeks gestation and waning by 6 week postpartum.38 Another is the presence of a placental, soluble fms-like tyrosine kinase (sFlt1–1) in women with preeclampsia.39 This tyrosine kinase is hypothesized to cause maternal endothelial dysfunction, resulting in proteinuria and GFR depression by inhibiting the action of vascular endothelial growth factor and placental growth factor.39

We conclude that 1) our study has not provided conclusive evidence for either l-arginine or nitric oxide deficiency in preeclampsia, 2) l-arginine supplementation in the dosage given failed to accelerate recovery by the 10th postpartum day, and 3) further study of l-arginine supplementation may be warranted to determine whether an ensuing prolongation of gestation in preeclampsia reduces neonatal morbidity and mortality.

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