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Effects of prolonged oral supplementation with L-arginine on blood pressure and nitric oxide synthesis in preeclampsia

Rytlewski K, Olszanecki R, Korbut R, Zdebski Z

European Journal of Clinical Investigation 2005 Volume 35, Issue 1, pages 32-37

Bibliography

DOI: 10.1111/j.1365-2362.2005.01445.x
PubMed: PMID 15638817
Funding: This work was supported in part by Jagiellonian University research grant no. BNS/501/KL/179/L and Polish State Committee for Scientific Research grant no. 4 PO5A 061 25. Curtis Healthcare, Poznan, Poland, provided the preparation and provision of L-arginine and placebo tablets.
Competing interests: Z.Z. served as a consultant of Curtis Healthcare, Poznan, Poland. K.R. participated as a speaker in scientific meetings organized and financed by Curtis Healthcare, Poznan, Poland.

Study snapshot

Design	Interventional, prospective, randomized, placebo-controlled trial, L-arginine added to standard hypotensive therapy.
Model	Pregnant women with preeclampsia (ACOG criteria), 20+ weeks' gestation, normotensive in first trimester, no chronic hypertension, singleton pregnancies; smokers and those with chronic illness excluded.
Sample	61 completed (L-arginine n=30, placebo n=31); 83 initially enrolled.
Intervention	Oral L-arginine 3 g/day (Curtis Healthcare) or placebo, as adjunct to standard hypotensive therapy (dihydralazine, methyldopa, IV magnesium sulphate).
Duration	3 weeks of treatment, with a 1-week reduced-nitrate diet before and after; overall hypotensive treatment continued to 36th week of pregnancy.
Endpoints	Systolic, diastolic, and mean arterial blood pressure (SBP, DBP, MAP); 24-h urinary nitrate/nitrite (NOx) excretion; Plasma NOx concentration; Plasma amino acid levels: L-arginine, L-citrulline, L-ornithine, ADMA+SDMA, L-NMMA; Urine protein excretion

What the study showed, in plain terms

Preeclampsia is a pregnancy complication marked by high blood pressure and protein in the urine, and it is linked to poor function of the blood vessel lining (the endothelium). One reason for this may be reduced production of nitric oxide, a molecule made from the amino acid L-arginine that helps blood vessels relax. This study tested whether adding oral L-arginine to standard blood pressure treatment could help.

Sixty-one women with preeclampsia took either 3 grams of L-arginine or a placebo every day for three weeks, in addition to their usual blood pressure medication. After three weeks, the women taking L-arginine had meaningfully lower systolic, diastolic, and mean arterial blood pressure than the placebo group.

The L-arginine group also excreted significantly more nitric oxide breakdown products (nitrate and nitrite) in their urine over 24 hours, and had higher blood levels of L-citrulline, a byproduct made when the body converts L-arginine into nitric oxide. These findings support the idea that the blood pressure benefit came from increased nitric oxide production, rather than simply raising blood arginine levels, which stayed unchanged.

Key findings

After 3 weeks, SBP was significantly lower with L-arginine vs. placebo (134.2 ± 2.9 vs. 143.1 ± 2.8 mmHg), as were DBP (81.6 ± 1.7 vs. 86.5 ± 0.9 mmHg) and MAP (101.8 ± 1.5 vs. 108.0 ± 1.2 mmHg), all P < 0.01.
24-h urinary NOx excretion was significantly elevated in the L-arginine group vs. placebo after treatment (0.162 ± 0.045 vs. 0.07 ± 0.0098 µmol/µmol creatinine, P < 0.05), with no difference between groups at baseline.
Plasma L-citrulline rose significantly with L-arginine treatment (30.0 ± 13 vs. 18.9 ± 11 µmol/L in placebo, P < 0.05), consistent with increased conversion of L-arginine to nitric oxide.
Plasma NOx tended to be higher in the L-arginine group but did not reach statistical significance; plasma concentrations of L-arginine, L-ornithine, and methylated arginines (ADMA+SDMA, L-NMMA) were not significantly altered by treatment.
No adverse effects attributable to L-arginine were observed or reported, and urine protein excretion did not differ between groups (3.32 ± 2.8 vs. 3.18 ± 3.74 g/24h, NS).

What this study can and cannot tell us

All patients also received standard hypotensive drugs (dihydralazine, methyldopa) and IV magnesium sulphate, and doses of these drugs were adjusted during the study based on blood pressure response; this makes it difficult to fully isolate the blood pressure effect of L-arginine alone from co-administered antihypertensive therapy.

The authors disclose a competing interest: Curtis Healthcare, the manufacturer that supplied the L-arginine and placebo tablets, also compensated two authors (as a consultant and as a paid speaker). This is a commercial sponsorship relationship relevant to interpreting the results.

Urine and plasma NOx measurements reflect whole-body nitric oxide production and cannot pinpoint the vascular endothelium specifically as the source. Plasma NOx itself did not differ significantly between groups, so the strongest biochemical signal came from urinary excretion and L-citrulline, not from a direct plasma NO measure.

This study does not report maternal or neonatal clinical outcomes (e.g., gestational age at delivery, birth weight); the authors reference improved fetal/infant outcomes as unpublished data elsewhere. Findings are specific to a 3 g/day oral dose over 3 weeks in preeclamptic women already on hypotensive therapy and should not be generalized to other doses, durations, or populations.