The role of nitric oxide on the analgesic effect of tramadol

Abstract Aims: The involvement of NO modulation in tramadol's mechanism of action is demonstrated indirectly by the alteration of the effect with the use of nitric oxide synthase inhibitor nitroG-L-arginine methyl ester (L-NAME). We aimed to investigate the alterations in serum and spinal cord NO levels following tramadol used alone or in combination with L-NAME or specific neuronal nitric oxide synthase (NOS) inhibitor 7-nitroindazole (7-NI), beside the changes in tail immersion reponses. Methods: Seventy-seven rats were randomly allocated into 7 groups. Group 1: sham group; Group 2: no drug; Group 3: tramadol 10 mg kg−1; Group 4: L-NAME 5 mg kg−1 + tramadol 10 mg kg−1; Group 5: L-NAME 10 mg kg−1 + tramadol 10 mg kg−1; Group 6: 7-NI 50 mg kg−1 + tramadol 10 mg kg−1; Group 7: 7-NI 100 mg kg−1 + tramadol 10 mg kg−1. Apart from Group 1, all the animals were exposed to a tail immersion test before medications (baseline) and 15 min after the tramadol injection. Following the tail-immersion test, a blood sampl...