Kinetic parameters of a new narcotic agonist, azidomorphine.

The kinetic parameters of azidomor phine (6-deoxy-6-dihydro-azido-isomorphine), a new highly potent semisynthetic derivative of morphine was studied on the longitudinal muscle strip of guinea-pig ileum and with the hot-plate method. Azidomorphine reduced the neuro-effector transmission in the longitudinal muscle strip and this effect was antagonized by naloxone in a competitive manner. In contrast to morphine, the agonist concentration (ID50) of azidomorphine failed to exert an antagonistic effect in this test. The analgetic effect of azidomorphine was much more easily antagonized by naloxone than that of morphine. However, the opposite was observed in the hot-plate test with azidomorphine and morphine when nalorphine was used as antagonist. The significant differences in the kinetics between morphine and azidomorphine indicate that some important differences in their interaction with the receptor might exist between the two structurally related substances.