Abstract: Effect of water-immersion restraint stress on the nitric oxide production in rat platelets FENG Hao-lou1，CUI Yu-ying2, WEI Fang2, WANG Bao-shui 2，Tang Chao-shu3 ( 1. Dept. Physiology, Medical College, Hebei University; 2. Dept. Physiology, College of Vocational and Technological Sanitation, Hebei University, Baoding 071000, China； 3.Dept. Institute of Cardiovascular Research, Peking University First Hospital, Beijing 100034.) Abstract: Objective To investigate the effect of water-immersion restraint stress (WRS) on the nitric oxide (NO) production and its mechanism in rat platelets. Methods Male SD rats underwent WIR stress for 2, 4 and 8 hours. Ulcer index (UI) of stomach was detected by Guth method, nitrite production was measured by Greiss assay, nitric oxide synthase (NOS) activities and L-arginine transport rate were determined by isotope tracer method. Results After 2h WRS, the NO production, the NOS activity and L-arginine transport rate in rat platelets were obviously increased, but they tended to be gradually decreased as the time went on. After 8h of WRS, these parameters were markedly decreased compared with the control group. The gastric ulcer appeared and got more serious after 4h WIR stress. Conclusion Short-term WRS up-regulated L-arginine /NO pathway and increased nitric oxide production in the platelets while long-term WIR stress caused the reversed results.