title: Sildenafil increases diclofenac antinociception in the formalin test.
abstract: The antinociceptive activity of an inhibitor of phosphodiesterase 5, alone or combined with diclofenac, was assessed in the formalin test. Local administration of diclofenac produced a significant antinociception in both phases of the formalin test in female Wistar rats. In contrast, 1-[4-ethoxy-3-(6,7-dihydro-1-methyl-7-oxo-3-propyl-1H-pyrazolo [3,4-d]pyrimidin-5-yl)phenylsulfonyl]-4-methyl piperazine (sildenafil, an inhibitor of phosphodiesterase 5) produced significant antinociception, only during the second phase of the formalin test. Non-effective doses of sildenafil (25-100 microg/paw) significantly increased the antinociceptive effect of an inactive dose of diclofenac (25 microg) in both phases of the test. The antinociception produced by the drugs alone or the combination was due to a local action, as its administration in the contralateral paw was ineffective. Since sildenafil is a potent and selective inhibitor of phosphodiesterase 5, our results suggest that this drug produced its antinociceptive activity, and increased that of diclofenac, probably through the inhibition of cyclic GMP degradation.
authors.affiliation: Departamento de Farmacobiología, Centro de Investigación y de Estudios Avanzados del Instituto Politécnico Nacional, México, D.F., Mexico.
authors.forename: R
authors.initials: R
authors.lastname: Asomoza-Espinosa
authors.forename: R
authors.initials: R
authors.lastname: Alonso-López
authors.forename: T
authors.initials: T
authors.lastname: Mixcoatl-Zecuatl
authors.forename: P
authors.initials: P
authors.lastname: Aguirre-Bañuelos
authors.forename: J E
authors.initials: JE
authors.lastname: Torres-López
authors.forename: V
authors.initials: V
authors.lastname: Granados-Soto
mesh_terms: D000700:Analgesics / Q000494:pharmacology*; D000818:Animals; D016861:Cyclooxygenase Inhibitors / Q000494:pharmacology; D004008:Diclofenac / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D004357:Drug Synergism; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D005260:Female; D005557:Formaldehyde / Q000008:administration & dosage; D010146:Pain / Q000209:etiology / Q000517:prevention & control*; D010147:Pain Measurement; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology; D010879:Piperazines / Q000494:pharmacology*; D011687:Purines; D051381:Rats; D017208:Rats, Wistar; D000068677:Sildenafil Citrate; D013450:Sulfones
chemical_list: D000700:Analgesics; D016861:Cyclooxygenase Inhibitors; D004791:Enzyme Inhibitors; D010726:Phosphodiesterase Inhibitors; D010879:Piperazines; D011687:Purines; D013450:Sulfones; D004008:Diclofenac; D005557:Formaldehyde; D000068677:Sildenafil Citrate