Involvement of the nitric oxide/CGMP/KATP pathway in antinociception induced by exercise in rats

AimsPhysical exercise is responsible for increasing the nociceptive threshold. The present study aimed to investigate the involvement of the nitric oxide/_CGMP/K_ATP pathway in antinociception induced by acute aerobic exercise (AAc) in rats.Main methodsWistar rats performed exercise in a rodent treadmill, according to an AAc protocol. The nociceptive threshold was measured by mechanical and thermal nociceptive tests (paw-withdrawal, tail-flick and face-flick). To investigate the involvement of the NO/_CGMP/K_ATP pathway the following nitric oxide synthase (NOS) unspecific and specific inhibitors were used: N-nitro-l-arginine (NOArg), Aminoguanidine, N⁵-(1-Iminoethyl)-l-ornithine dihydrocloride (L-NIO), N^ω-Propyl-l-arginine (L-NPA); guanylyl cyclase inhibitor, 1H-[1,2,4]oxidiazolo[4,3-a]quinoxalin-1-one (ODQ); and K_ATP channel blocker, Glybenclamide; all administered subcutaneously at a dose of 2 mg/kg 10 min before exercise started. Plasma and cerebrospinal fluid (CSF) nitrite levels were determined by spectrophotometry.Key findingsIn the paw-withdrawal, tail-flick and face-flick tests, the AAc protocol produced antinociception, which lasted for more than 15 min. This effect was significantly reversed (P < 0.05) by NOS specific and unspecific inhibitors, guanylyl cyclase inhibitor (ODQ) and K_ATP channel blocker (Glybenclamide). Acute exercise was also responsible for increasing nitrite levels in both plasma and cerebrospinal fluid.SignificanceTaken together, these results suggest that the NO/_CGMP/K_ATP pathway participates in antinociception induced by exercise.