Protection from cerebral ischemia by U-50,488E, a specific kappa opioid analgesic agent.

U-50,488E is a novel analgesic agent with a specific agonist property on the kappa opioid receptor. It is found to protect against the lethal effect of temporary bilateral carotid occlusion (BCO) in Mongolian gerbils and rats of the Fischer strain. Pretreatment with U-50,488E in gerbils before 7 min of BCO reduced the development of behavioral hyperactivity and preserved the hippocampal neurons from ischemic death. This protective effect of U-50,488E resided predominantly in the levo-enantiomer which is also more potent as a kappa analgesic. Two other kappa opioid analgesics, ethylketocyclazocine and bremazocine, shared the effects of U-50,488E in the gerbils. Naloxone and dynorphin 1-13, on the other hand, were without protective effects in the same ischemic model. The ischemic protective effects of U-50,488E may involve the kappa opioid receptor.