The release of 3H-dopamine from the isolated rabbit ileum.

1. Segments of rabbit ileum incubated with (3)H-DOPA or (3)H-dopamine and perfused with McEwen solution spontaneously release (3)H-dopamine; this basal release is doubled when the sympathetic nerves are stimulated. Evidence is presented to show that the release is probably from the sympathetic nerve terminals.2. Both cocaine and bretylium reduce the spontaneous release of (3)H-dopamine as well as the increased release resulting from sympathetic nerve stimulation. Guanethidine depresses the release during nerve stimulation but increases the spontaneous release of the amine. Phenoxybenzamine potentiates both the spontaneous release and that during nerve stimulation.3. Tyramine releases (3)H-dopamine from the preparation but tachyphylaxis to the drug rapidly develops.4. It is concluded that the release of (3)H-dopamine from the sympathetic nerves of the isolated perfused rabbit ileum possesses many of the characteristics of that of noradrenaline from other sympathetically innervated structures.