Role of kappa opioid receptors during stress responsiveness in rats.

Effects of kappa opioid agonist, ketocyclazocine (KCZ) and its antagonist, M(r) 2266, were evaluated on some stress responses in rats. KCZ (1 or 10 mg/kg, ip) dose-dependently attenuated cold restraint stress (CRS)-induced gastric ulcer formation. Similar gastric cytoprotection was also seen with KCZ (1 or 10 micrograms/rat, icv). Pretreatment of rats with M(r) 2266 (0.3 mg/kg, ip) clearly antagonized the ulceroprotective effects of both ip and icv KCZ. KCZ effects on the gastric mucosa during CRS were also reduced by naltrexone (5 mg/kg, ip) pretreatment. KCZ (1 or 10 mg/kg, ip) also attenuated the plasma corticosterone response to CRS and these effects were blocked by M(r) 2266 (0.3 mg/kg) pretreatment. These results indicate kappa opioid receptor involvement during stress reactions and also suggest possible opioidergic interactions during CRS.