title: Sildenafil induces hyperalgesia via activation of the NO-cGMP pathway in the rat neuropathic pain model.
abstract: Persistent stimulation of nociceptors and C-fibers by tissue injury causes hyperalgesia and allodynia by sensitization of nociceptors and facilitation of synaptic transmission in the spinal cord. The important participant in the inflammatory response of injured peripheral nerve may be nitric oxide (NO). The aim of the present study was to test the sensitivity of PDE5 inhibitor sildenafil in chronic constriction injury (CCI) model a rat model of neuropathic pain. Sciatic nerve injury is associated with development of hyperalgesia 14 days after the nerve ligation. Sildenafil (100 and 200 microg/rat, i.t.) produced a significant decrease in pain threshold, which in lower dose did not alter the nociceptive threshold. The hyperalgesic effect of sildenafil was blocked by L-NAME and methylene blue (MB), which on per se treatment showed antinociceptive effect in nerve ligated rats. The results from the present study indicated that the major activation of NO-cGMP pathway in the chronic constriction injury model of neuropathic pain. The aggravation of hyperalgesic response might be due to the increased cGMP levels resulting in PKG-I activation and its upregulation.
authors.affiliation: Pharmacology R and D, Panacea Biotec Ltd, Lalru, 140501 Punjab, India.
authors.forename: C S
authors.initials: CS
authors.lastname: Patil
authors.forename: S V
authors.initials: SV
authors.lastname: Padi
authors.forename: V P
authors.initials: VP
authors.lastname: Singh
authors.forename: S K
authors.initials: SK
authors.lastname: Kulkarni
mesh_terms: D015106:3',5'-Cyclic-GMP Phosphodiesterases / Q000037:antagonists & inhibitors*; D000818:Animals; D002908:Chronic Disease; D006152:Cyclic GMP / Q000378:metabolism*; D054706:Cyclic Nucleotide Phosphodiesterases, Type 5; D004195:Disease Models, Animal; D004305:Dose-Response Relationship, Drug; D005260:Female; D006930:Hyperalgesia / Q000209:etiology / Q000378:metabolism; D007278:Injections, Spinal; D008297:Male; D008751:Methylene Blue / Q000494:pharmacology; D019331:NG-Nitroarginine Methyl Ester / Q000494:pharmacology; D009569:Nitric Oxide / Q000378:metabolism*; D010146:Pain / Q000150:complications / Q000188:drug therapy / Q000378:metabolism; D017288:Pain Threshold; D010879:Piperazines / Q000008:administration & dosage / Q000009:adverse effects / Q000494:pharmacology; D011687:Purines; D051381:Rats; D017208:Rats, Wistar; D020426:Sciatic Neuropathy / Q000150:complications / Q000188:drug therapy / Q000378:metabolism; D015398:Signal Transduction; D000068677:Sildenafil Citrate; D013450:Sulfones
chemical_list: D010879:Piperazines; D011687:Purines; D013450:Sulfones; D009569:Nitric Oxide; D000068677:Sildenafil Citrate; D015106:3',5'-Cyclic-GMP Phosphodiesterases; D054706:Cyclic Nucleotide Phosphodiesterases, Type 5; C517384:Pde5a protein, rat; D006152:Cyclic GMP; D008751:Methylene Blue; D019331:NG-Nitroarginine Methyl Ester