Evidence that somatostatin releases endogenous substance(s) responsible for its presynaptic inhibitory effect on rat vas deferens and guinea pig ileum.

The ability of somatostatin to inhibit the muscular twitches elicited by field stimulation of rat vas deferens and guinea pig ileum was studied. Evidence should be summarized which would suggest that the presynaptic inhibitory effect of somatostatin on chemical neurotransmission is indirect. Its effect on vas deferens is partly mediated via alpha 2-adrenoceptors and due to the released noradrenaline, in guinea pig ileum, however, it seems likely that it releases an unidentified inhibitory substance which, in fact, inhibits the release of acetylcholine, and thereby twitches of the ileum. The fast tachyphylaxis seen following repeated administration of the peptide is likely due to its indirect action.