Peripheral and central antinociceptive action of Na+-K+-2Cl- cotransporter blockers on formalin-induced nociception in rats

The possible local peripheral and spinal (intrathecal) antinociceptive effect of Na+-K+-2Cl(-) cotransporter (NKCC) inhibitors was investigated in the rat formalin test. Nociceptive flinching behavior induced by formalin (M) injection in the hind paw was assessed following administration of cotransporter inhibitors. Local peripheral pretreatment in the ipsilateral paw with bumetanide (ED30, 27.1 +/- 12.7 mu g/paw), piretanide (ED30, 109.2 +/- 21.6 mu g/paw) or furosemide (ED30, 34.3 +/- 5.0 mu g/paw), but not vehicle (DMSO 100%), produced dose-dependent antinociception in phase 2 of the test. Local bumetanide had the greatest effect (similar to 70% antinociception). Bumetanide also inhibited formalin-induced flinching behavior during phase 1 (ED30, 105.6 +/- 99.1 mu g/paw). Spinal intrathecal pretreatment with bumetanide (ED30, 194.6 +/- 97.9 mu g), piretanide (ED30, 254.4 +/- 104.9 mu g) or furosemide (ED30, 32.0 +/- 6.9 mu g), but not vehicle (DMSO 100%), also produced antinociception in phase 2. In this case, only intrathecal furosemide reduced flinching behavior during phase 1 (ED30, 99.4 +/- 51.4 mu g) and had the maximal antinociceptive effect in phase 2 (similar to 65% antinociception). The opioid receptor-antagonist naloxone (2 mg/kg, s.c.) did not reverse antinociception induced by either peripheral or spinal administration of NKCC blockers. Our data suggest that the Na+-K+-2Cl(-) cotransporter localized in sensory neurons at intraspinal and peripheral sites is involved in formalin-induced nociception. (c) 2004 International Association for the Study of Pain. Published by Elsevier B.V. All rights reserved.