Antinociceptive profile of dynorphin in the rat.

Morphine, bremazocine, dynorphin(1-17) and two of its fragments (1-13) and (1-8) all increased nociceptive pressure thresholds in the rat after intracerebroventricular administration. Morphine also increased nociceptive heat thresholds in the hotplate test at similar dose-levels. In contrast, bremazocine and the dynorphins were totally inactive against the noxious heat stimulus. This profile of antinociceptive activity is typical of kappa receptor agonists.