The L-arginine-nitric oxide system regulates platelet aggregation in pregnancy.
OBJECTIVE
To investigate the ex vivo platelet aggregation in response to a substrate (L-arginine [L-Arg]) and a donor (sodium nitroprusside [SN]) of nitric oxide (NO) in nonpregnant women and in normotensive pregnancies.


METHODS
Platelet aggregation was studied with a dual-channel aggregometer and expressed as a percentage of light transmission. Measurements were done at baseline and after preincubation with scalar doses of L-Arg and SN. The intraplatelet L-citrulline (L-Cit) levels were measured by high-performance liquid chromatography (HPLC).


RESULTS
In both groups, the baseline aggregation values were similar for adenosine diphosphate (ADP) and collagen stimuli. Wilcoxon rank-sum testing demonstrated that in both groups the addition of L-Arg had a significant effect on aggregation: Doses of 50 to 5000 mumol decreased ADP-induced aggregation. Conversely, collagen-induced aggregation was affected only by the highest dose of L-Arg. Sodium nitroprusside administered in doses of 2.5 to 250.0 nmol decreased ADP- and collagen-induced platelet aggregation equally. ADP-induced aggregation values obtained after (SN) incubation were positively correlated with gestational age. Intraplatelet L-Cit levels showed a significant rise after the incubation with L-Arg, and this effect was negatively correlated with gestational age.


CONCLUSIONS
The L-Arg-NO system regulates platelet aggregation during pregnancy. Moreover, a physiologic reduction of platelet sensitivity to the antithrombotic effect of NO occurs.
Department of Obstetrics, University of Modena, Italy.
I
I
Neri
M
M
Marietta
F
F
Piccinini
A
A
Volpe
F
F
Facchinetti
D000244:Adenosine Diphosphate / Q000494:pharmacology; D000328:Adult; D001120:Arginine / Q000494:pharmacology*; D003094:Collagen / Q000494:pharmacology; D005260:Female; D005865:Gestational Age; D006801:Humans; D009569:Nitric Oxide / Q000378:metabolism*; D009599:Nitroprusside / Q000494:pharmacology*; D010974:Platelet Aggregation / Q000187:drug effects*; D011247:Pregnancy
D009599:Nitroprusside; D009569:Nitric Oxide; D000244:Adenosine Diphosphate; D003094:Collagen; D001120:Arginine