Protective Effect of L-Arginine against Oxidative Damage as a Possible Mechanism of its Beneficial Properties on Spatial Learning in Ovariectomized Rats

Introduction: The role of ovarian hormones and nitric oxide (NO) on oxidative damage in brain tissues as well as learning and memory has been widely investigated. The present study was carried out to evaluate the effect of the precursor of NO, L-Arginine on learning and brain damage due to oxidative stress in ovariectomized (OVX) rats. Methods: Thirty-two rats were divided into four groups: 1) Sham, 2) OVX, 3) Sham-L-Arginine (Sham-LA) and 4) OVX-L-Arginine(OVX-LA). The animals of sham-LA and OVX-LA were treated with 500 mg/kg of L-Arginine. The animals in Sham and OVX groups received 1 ml/kg saline. The animals were tested in Morris water maze and finally, the brains were removed and MDA and total thiol concentrations were measured. Results: The escape latency and swimming path in OVX group were significantly higher than in Sham group (p < 0.01). The animals in OVX-LA group had significantly lower swimming path length and escape latency compared to OVX group (p < 0.01) while, there was no significant difference between Sham-LA and Sham groups. In OVX-LA group, the brain tissues total thiol concentration was significantly higher, and MDA concentration was lower than of OVX group (p < 0.001). There was no significant difference between Sham-LA and Sham groups. Discussion: It seems that the beneficial properties of L-Arginine on spatial learning of ovariectomized rats are in part due to its protective capacity against oxidative damage.