Proceedings of The Physiological Society

University of Oxford (2011) Proc Physiol Soc 23, PC59

Poster Communications

Nitric oxide production and platelet function in obese adults

N. R. Pereira1, T. M. Brunini1, C. Matsuura1,3, M. M. Siqueira1, W. M. Vianna1, A. Mendes-Ribeiro1,2

1. Pharmacology, Universidade do Estado do Rio de Janeiro, Rio de Janeiro, Rio de Janeiro, Brazil. 2. Escola de Educa

Introduction: Obesity is associated with an elevated risk of cardiovascular morbidity and mortality due to atherothrombotic events (1). Nitric oxide is produced through the conversion of the semi-essential cationic amino acid L-arginine into L-citrulline and NO in a reaction catalyzed by a family of NO synthases (NOS)(2). The biological effects of NO are mainly mediated through cyclic guanosine monophosphate (cGMP), which regulates vascular smooth muscle relaxation, inhibits platelet aggregation and adhesion and induces platelet disaggregation (2). L-arginine is also a substrate for arginase, which competes with NOS for L-arginine (3). Methods: Eleven patients classified as obese according to the National Health Institute - NHI (body mass index > 30 kg/m2) (4), recruited from the Pedro Ernesto Hospital, and eleven age-matched healthy controls were included in the study. The Pedro Ernesto Hospital Ethical Committee approved this study (2488 - CEP/HUPE), and informed consent was obtained from each participant. L-[3H]-arginine influx (1-50 µM) was measured over 5 min and L-leucine (10 mM) was used to resolve total L-arginine transport in platelets into system y+L and transport with diffusion kinetics. Basal NOS activity was determined by the conversion of L-[3H]-arginine to L-[3H]-citrulline. cGMP content was determined in washed platelets at baseline using a commercial ELISA method. Platelet aggregation was evaluated in platelet rich plasma (PRP) by optical densitometry. L-arginine concentration in plasma was measured through the high-performance liquid chromatography (HPLC) method. Arginase activity was determined by the conversion of L-[14C]-arginine to [14C]-urea. Statistical significance was assessed by the Student t-Test, with p <0.05. Results: Total L-[3H]-arginine transport (35.57 ± 4.04 vs 61.88 ± 7.47 pmol/109cells/min, n=11) and transport by y+L system (17.36 ± 2.36 vs 33.37 ± 6.48 pmol/109cells/min, n=11), NOS activity (0.065 ± 0.009 vs 0.101 ± 0.012 pmol/108 cells/min, n=8) and basal cGMP levels (0.31 ± 0.02 vs 0.50 ± 0.07 pmol/108 cells, n=9) were reduced in platelets. In this context, there was increased platelet aggregation (89.63 ± 8.73 X 76.67 ± 14.27%, n=9) in obese adults compared to control. On the other hand, plasma levels of L-arginine (67.0 ± 9.3 X 70.1 ± 14.7 μM/L, n=7) and arginase activity (0.061 ± 0.007 X 0.08 ± 0.01 pmol urea/mg protein/2h, n=10) were unaltered. Conclusion: The dysfunction of L-arginine-NO-cGMP signalling observed in platelets of obese patients may contribute to cardiovascular events in these patients.

Where applicable, experiments conform with Society ethical requirements