Proceedings of The Physiological Society

University College Dublin (2009) Proc Physiol Soc 15, PC121

Poster Communications

Effects of systemic arterial hypertension on nitric oxide synthase activity and expression, arginase activity and lipid peroxidation in human platelets

M. B. Moss1, M. A. Siqueira1, C. G. dos Santos1, W. V. Mury1, V. B. Moss1, G. E. Mann2, T. M. Brunini1, A. Mendes Ribeiro1

1. Farmacologia e Psicobiologia, Universidade do Estado do Rio de Janeiro, Rio de Janeiro, Rio de Janeiro, Brazil. 2. Cardiovascular Division, King's College, London, United Kingdom.

Introduction: Systemic arterial hypertension (SAH) is a major independent risk factor for cardiovascular disease. The physiopathology of SAH is multifactorial, complex and remains to be elucidated. Nitric oxide (NO) is an important regulator of vascular and haemostatic functions1. The cationic amino acid L-arginine serves as the substrate for NO synthases (NOS) and arginase, an enzyme of the urea cycle. Our group has previously reported an inhibition of L-arginine transport in erythrocytes and platelets in hypertension associated with enhanced platelet aggregation2,3. Oxidative stress is involved in the pathophysiology of hypertension4. The aim of the present study was to investigate the L-arginine-NO pathway, urea cycle and oxidative stress in platelets in SAH patients. Methods: 11 hypertensive patients and 13 healthy controls matched for age and sex were included in the study. Basal NOS activity was measured by the conversion of L-[3H]-arginine into L-[3H]-citrulline. Inducible and endothelial NOS expressions were accessed by Western Blotting. Arginase activity was analyzed in platelet lysate through the conversion of [C14]-L-arginine into [C14]-urea. The level of plasma lipid peroxidation was evaluated on the basis of thiobarbituric acid reactive substances (TBARS). Mann Whitney test was used for statistical analysis and values were considered significantly different when p<0,05. Results: We provided clear evidence that the NOS activity (pmol/108 cells) was diminished in hypertensive patients compared to controls (0.09 ± 0.02 vs 0.19 ± 0.03). Platelets from SAH patients exhibited a compensatory over expression of inducible NOS (iNOS), but not endothelial NOS (eNOS), whilst intraplatelet arginase activity (pmol urea/mg protein/2h) was not affected (2.1 ± 0.1 vs 2.8 ± 0.5). There was no difference between TBARS levels (pmol/mg protein) in platelets from SAH patients (40 ± 19) and those detected in platelets from controls (21.8 ± 5). Conclusion: In conclusion, the thrombotic state observed in hypertensive patients could be explained in part by the inactivation of the L-arginine-NO pathway in platelets. Higher expression of iNOS in platelets might be a compensatory mechanism against platelet activation in hypertension. A better understanding of the mechanisms that contribute to platelet dysfunction in hypertension could provide important tools for the development of new therapies to minimize the risk of cardiovascular complications in these patients.

Where applicable, experiments conform with Society ethical requirements