Effect of nitric oxide on skin blood flow of intact and morphine- dependent rats

Introduction: The relation between morphine and nitric oxide release has been shown. Due to important role of nitric oxide in regulation of skin blood flow, the aim of this study was to investigate the effect of nitric oxide synthase inhibitor (L-NAME) and nitric oxide synthesis precursor (L-arginine) on skin blood flow of intact and morphine-dependent rats. Methods: Skin blood flow of hind paw was measured using Laser Doppler Flowmetry (LDF) technique. Animals became morphine dependent by a well established protocol. Results: Subcutaneous injection of L-arginine (10 or 20 mg/kg) respectively increased skin blood flow by 39% and 64% in intact rats and by 37% and 65% in morphine-dependent rats. There was no significant difference between blood flow in intact and morphine-dependent rats. L-NAME (1 or 5 mg/kg) diminished skin blood flow of intact rats by 35% and 58.7% and skin blood flow of morphine-dependent rats by 29.1% and 60.5%, respectively. There was no significant difference between these two groups. The effect of L-arginine was abolished by pretreatment with L-NAME in morphine-dependent as well as intact groups. Conclusion: Our results suggest that changes in the level of nitric oxide, cause the same skin blood flow alterations in both morphine-dependent and intact rats. More experiments are needed to elucidate the level of nitric oxide release in skin vascular system following dependency.