Repeated Administration of the Cannabinoid WIN Alters the Isoflurane-Sparing Effect of Morphine and Dexmedetomidine.

The impacts of morphine and dexmedetomidine on the MAC of isoflurane were studied in rats constantly medicated with the cannabinoid WIN 55,212-2. METHODS: Prior to the administration of morphine, the MAC was measured in both untreated rats (MAC (ISO)) and those treated with a cannabinoid (MAC (ISO + CANN)). The effects of morphine (MAC (ISO + MOR)) and dexmedetomidine (MAC (ISO + DEX)) on untreated rats and rats treated for 21 days with the cannabinoids (MAC (ISO + CANN + MOR)) and (MAC (ISO + CANN + DEX) were also studied. RESULTS: MAC (ISO) was 1.32 ± 0.06, and MAC (ISO + CANN) was 1.69 ± 0.09. MAC (ISO + MOR) was 0.97 ± 0.02 (26% less than MAC (ISO)). MAC (ISO + CANN + MOR) was 1.55 ± 0.08 (8% less than MAC (ISO + CANN)), MAC (ISO + DEX) was 0.68 ± 0.10 (48% less than MAC (ISO)), and MAC (ISO + CANN + DEX) was 0.67 ± 0.08 (60% less than MAC (ISO + CANN)). CONCLUSIONS: Medication with a cannabinoid for 21 days augmented the MAC of isoflurane. The sparing effect of morphine on isoflurane is lower in rats constantly medicated with a cannabinoid. The sparing effect of dexmedetomidine on the minimum alveolar concentration of isoflurane is greater in rats repeatedly medicated with a cannabinoid.

Minimum Alveolar Concentration of Isoflurane in Rats Chronically Treated with the Synthetic Cannabinoid WIN 55,212-2.

The minimum alveolar concentration MAC of isoflurane was measured in rats chronically treated with WIN 55,212-2. METHODS: The MAC of isoflurane was determined in 24 male rats from expiratory samples at time of tail clamping under the following conditions: without treatment MAC(ISO), in rats treated for 21 days with WIN 55,212-2 MAC(ISO + WIN55), and in rats 8 days after stopping treatment with WIN 55,212-2 (MACISO + WIN55 + 8D). RESULTS: The MAC(ISO) was 1.32 ± 0.06. In the MAC(ISO + WIN55) group, the MAC increased to 1.69 ± 0.09 (28%, p-value ≤ (0.0001). Eight days after stopping treatment with WIN55, the MAC did not decrease significantly, 1.67 ± 0.07 (26%, p-value ≤ 0.0001). CONCLUSIONS: The administration of WIN 55,212-2 for 21 days increases the MAC of isoflurane in rats. This effect does not disappear 8 days after discontinuation of treatment with the synthetic cannabinoid.

Evidence for the Participation of ATP-sensitive Potassium Channels in the Antinociceptive Effect of Curcumin.

BACKGROUND: It has been reported that curcumin, the main active compound of Curcuma longa, also known as turmeric, exhibits antinociceptive properties. The aim of this study was to examine the participation of ATP-sensitive potassium channels (K(ATP) channels) and, in particular, that of the L-arginine-nitric oxide-cyclic GMP-K(ATP) channel pathway, in the antinociceptive effect of curcumin. METHODS: Pain was induced by the intraplantar injection of 1% formalin in the right hind paw of Wistar rats. Formalin-induced flinching behavior was interpreted as an expression of nociception. The antinociceptive effect of oral curcumin was explored in the presence and absence of local pretreatment with L-NAME, an inhibitor of nitric oxide synthase, ODQ, an inhibitor of soluble guanylyl cyclase, and glibenclamide, a blocker of K(ATP) channels. RESULTS: Oral curcumin produced a dose-dependent antinociceptive effect in the 1% formalin test. Curcumin-induced antinociception was not altered by local L-NAME or ODQ, but was significantly impaired by glibenclamide. CONCLUSIONS: Our results confirm that curcumin is an effective antinociceptive agent. Curcumin-induced antinociception appears to involve the participation of K(ATP) channels at the peripheral level, as local injection of glibenclamide prevented its effect. Activation of K(ATP) channels, however, does not occur by activation of the L-arginine-nitric oxide-cGMP-K(ATP) channel pathway.