Antinociceptive effects of (O-methyl)-N-benzoyl tyramine (riparin I) from Aniba riparia (Nees) Mez (Lauraceae) in mice.

The present study examined the antinociceptive effects of (O-methyl) N-benzoyl-tyramine (riparin I, ripI) isolated from the unripe fruit of Aniba riparia in chemical and thermal behavioral models of pain, such as acetic acid-induced abdominal writhing, formalin, and hot-plate tests in mice. Moreover, the involvement of the nitric oxide pathway as well as the opioid system in the antinociceptive action of ripI in the formalin test was investigated. RipI was administered both orally and intraperitoneally to male mice at single doses of 25 and 50 mg/kg. In the acetic acid-induced abdominal writhing, ripI decreased the number of writhings at both doses. In addition, in the formalin test, ripI reduced the paw licking time at both phases of the test. The effect of the highest dose of ripI in mice formalin test on the early phase was not reversed by naloxone (opioid receptor antagonist) but it was reversed by l-arginine (a nitric oxide precursor) in the late phase, suggesting that ripI may not act through opioid system and possibly acts through inhibition of nitric oxide pathway. In the hot-plate test, ripI increased the reaction time in the hot-plate test at the dose of 25 mg/kg, i.p., confirming the result found in the formalin test. Based on the obtained results, it is suggested that ripI presents antinociceptive activity that may be due to peripheral mechanisms (nitric oxide pathway) and central mechanisms, discarding the involvement of opioid system.