Effects Of Kappa Opioid Receptor Activation Research Articles

The Antipruritic Effect of Acupuncture on Serotonin-Evoked Itch in Rats

The antipruritic effect of acupuncture was studied using a rat model of hindlimb scratching. After acupuncture or electroacupuncture (EA), which was conducted for 30 min, itch-associated behavior was induced by an intradermal injection of 2% serotonin (20 microl) into the rostral back, and then numbers of scratching bouts were counted for 60 min. During the first experiment, acupuncture stimulations were applied to several different points. However acupuncture significantly reduced numbers of scratchings only when applied to cervical dermatomes. In the second experiment, plain acupuncture, or 2Hz, or 120Hz EA were applied to acupoints LI 11 and LI 4, at which acupuncture stimulation produced the greatest antipruritic effect in the 1st experiment, and as serotonin was administered in the same manner described for the 1st experiment. Results showed that 2Hz EA stimulation tended to increase pruritic bouts by approximately 18% versus the animals treated with plain acupuncture, whereas 120Hz EA stimulation tended to decrease pruritic bouts by approximately 39% compared with animals subjected to plain acupuncture. When nor-binaltorphimine (a kappa-opioid receptor antagonist) was pretreated to elucidate the relation between kappa-opioid receptor and the antipruritic effect of 120Hz EA, it was found to markedly inhibit the antipruritic effect of 120Hz EA. These results suggest that acupuncture and EA stimulation are effective treatments for pruritus if administered to dermatomes corresponding to affected sites or to adjacent dermatomes and that this effect is due to the antipruritic effect of kappa-opioid receptor activation maximally induced by high-frequency EA stimulation.

Activation of k1-opioid receptor as a method for prevention of ischemic and reperfusion arrhythmias: Role of protein kinase C and KATP channels

Intravenous pretreatment with kappa-opioid receptor antagonist (-)-U-50,488 (1 mg/kg) improved heart resistance to the arrhythmogenic effect of coronary occlusion and reperfusion. Selective kappa1-opioid receptor antagonist norbinaltorphimine and nonselective blocker of peripheral opioid receptors methylnaloxone abolished this antiarrhythmic effect. Preliminary blockade of protein kinase C with chelerythrine or inhibition of ATP-dependent K+ channels (K(ATP) channels) with glybenclamide abolished the antiarrhythmic effect of kappa-opioid receptor activation. Selective inhibitor of sarcolemmal K(ATP) channels did not modulate the kappa-opioid receptor-mediated increase in cardiac electrical stability. Our results suggest that protein kinase C and mitochondrial K(ATP) channels play an important role in the antiarrhythmic effect associated with activation of peripheral kappa-opioid receptors.