| Abstract: | The action of somatostatin (SRIF (somatotrophin release inhibiting factor)) was compared with that of Met-enkephalin (Tyr-Gly-Gly-Phe-Met) in the electrically stimulated guinea pig ileum myenteric plexus longitudinal muscle and with that of an enkephalin analogue (FK 33-824 (Tyr-D-Ala-Gly-MePhe-Met-(O)-ol)) in the rat vas deferens. In both tissues SRIF produced a twitch inhibition which was not antagonized by naloxone and which showed a long-lasting tachyphylaxis. The enkephalins tested produced a naloxone-antagonizable inhibition of twitch in both tissues but no tachyphylaxis. Therefore we conclude that SRIF is not acting at opiate receptors in these tissues. |
