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/KATP 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/KATP 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), Nω-Propyl-l-arginine (L-NPA); guanylyl cyclase inhibitor, 1H-[1,2,4]oxidiazolo[4,3-a]quinoxalin-1-one (ODQ); and KATP 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 KATP 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/KATP pathway participates in antinociception induced by exercise.