Roles of adenosine receptor subtypes on the antinociceptive effect of sildenafil in rat spinal cord.
We recently found that the antinociceptive effects produced by intrathecal administration of sildenafil, a phosphodiesterase 5 inhibitor, were reversed by a nonspecific adenosine receptor antagonist, suggesting that adenosine receptors are involved in sildenafil-induced antinociception. Four adenosine receptor subtypes have been identified: A(1), A(2A), A(2B), and A(3). We examined the involvement of spinal adenosine receptor subtypes in the antinociceptive effects of intrathecal sildenafil. Intrathecal catheters were implanted in male SD rats, and nociception was assessed using the formalin test, which consisted of a subcutaneous injection of 50 microl of 5% formalin solution into the hind paw. We examined the effects of an adenosine A(1) receptor antagonist (CPT), an adenosine A(2A) receptor antagonist (CSC), an adenosine A(2B) receptor antagonist (alloxazine), and an adenosine A(3) receptor antagonist (MRS 1220) on sildenafil-induced antinociception. Intrathecal sildenafil suppressed formalin-induced flinching during phases 1 and 2 of the test in a dose-dependent manner. Intrathecal CPT, CSC, alloxazine, and MRS 1220 all suppressed the antinociceptive effects of sildenafil during both phases of the formalin test. These results suggest that sildenafil is an effective treatment for acute pain and the facilitated pain state at the spinal level. Additionally, spinal adenosine A(1), A(2A), A(2B), and A(3) receptors may play a role in sildenafil-induced antinociception.
Lee
Hyung Gon
HG
Department of Anesthesiology and Pain Medicine, Chonnam National University, Medical School, Gwangju, Republic of Korea.
Kim
Woong Mo
WM
Choi
Jeong Il
JI
Yoon
Myung Ha
MH
D000700:Analgesics / Q000494:pharmacology*; D000818:Animals; D007278:Injections, Spinal / Q000379:methods; D008297:Male; D010146:Pain / Q000188:drug therapy* / Q000378:metabolism / Q000503:physiopathology; D010147:Pain Measurement / Q000379:methods; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology; D010879:Piperazines / Q000494:pharmacology*; D011687:Purines / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D018047:Receptors, Purinergic P1 / Q000145:classification* / Q000502:physiology*; D000068677:Sildenafil Citrate; D013116:Spinal Cord / Q000187:drug effects / Q000378:metabolism* / Q000503:physiopathology; D013450:Sulfones / Q000494:pharmacology*; D016896:Treatment Outcome
D000700:Analgesics; D010726:Phosphodiesterase Inhibitors; D010879:Piperazines; D011687:Purines; D018047:Receptors, Purinergic P1; D013450:Sulfones; D000068677:Sildenafil Citrate