In vitro release of [3H]noradrenaline by tyramine from the superior cervical ganglion and in the nictitating membrane of the cat.

1. The release and the metabolism of [3H]noradrenaline ([3H]NA) induced by tyramine was studied in the superior cervical ganglion (cell bodies) and in the nictitating membrane (nerve endings) of the cat. 2. Exposure of the ganglia to 58.0 and 174.0 microM tyramine resulted in the release of 13.7 and 11.8% respectively of the total tissue radioactivity. In the nictitating membrane, the fractional release of radioactivity was directly proportional to the concentration of tyramine (5.8, 58.0 and 174.0 microM). 3. In ganglia [3H]DOPEG accounted for 55.8% of the radioactivity released by 58.0 microM tyramine and only 10.5% of the radioactivity was unmetabolized NA. In presence of 174.0 microM tyramine, [3H]NA increased to 28.0% of the total radioactivity and [3H]DOPEG and [3H]OMDA decreased to 45.3 and 18.9% respectively. 4. In the nerve endings, the contribution of [3H]NA, [3H]DOMA and [3H]NMN increased with the concentration of tyramine while [3H]DOPEG decreased. 5. The deamination is the first step of the metabolic inactivation of [3H]NA induced by tyramine in the cell body of the postganglionic adrenergic neuron while in the nerve endings [3H]NA is preferentially O-methylated.