PT - JOURNAL ARTICLE AU - Willias Masocha AU - Gyongyi Horvath AU - Ahmad Agil AU - María Ocaña AU - Esperanza Del Pozo AU - Margit Szikszay AU - José M. Baeyens TI - Role of Na<sup>+</sup>,K<sup>+</sup>-ATPase in Morphine-Induced Antinociception AID - 10.1124/jpet.103.052977 DP - 2003 Sep 01 TA - Journal of Pharmacology and Experimental Therapeutics PG - 1122--1128 VI - 306 IP - 3 4099 - http://jpet.aspetjournals.org/content/306/3/1122.short 4100 - http://jpet.aspetjournals.org/content/306/3/1122.full SO - J Pharmacol Exp Ther2003 Sep 01; 306 AB - We evaluated the modulation by Na+,K+-ATPase inhibitors of morphine-induced antinociception in the tail-flick test and [3H]naloxone binding to forebrain membranes. The antinociception induced by morphine (1-32 mg/kg, s.c.) in mice was dose-dependently antagonized by ouabain (1-10 ng/mouse, i.c.v.), which produced a significant shift to the right of the morphine dose-response curve. The i.c.v. administration of three Na+,K+-ATPase inhibitors (ouabain at 0.1-100, digoxin at 1-1,000, and digitoxin at 10-10,000 ng/mouse) dose-dependently antagonized the antinociceptive effect of morphine (4 mg/kg, s.c.) in mice, with the following order of potency: ouabain &gt; digoxin &gt; digitoxin. This effect cannot be explained by any interaction at opioid receptors, since none of these Na+,K+-ATPase inhibitors displaced [3H]naloxone from its binding sites, whereas naloxone did so in a concentration-dependent manner. The antinociception induced by morphine (5 mg/kg, s.c.) in rats was antagonized by the i.c.v. administration of ouabain at 10 ng/rat, whereas it was not significantly modified by intrathecally administered ouabain (10 and 100 ng/rat). These results suggest that the activation of Na+,K+-ATPase plays a role in the supraspinal, but not spinal, antinociceptive effect of morphine. The American Society for Pharmacology and Experimental Therapeutics