The histological localization of noradrenaline in the cat spleen.

1. The histological localization of noradrenaline in the cat spleen has been studied with a fluorescence technique and, after infusing DL-[(3)H] noradrenaline, both by the fluorescence technique and by autoradiography.2. In the normal cat spleen the specific fluorescence of catecholamines is confined to nerve fibres among the smooth muscle of the capsule, trabeculae, arteries and veins. These fluorescent fibres are not present after treating the animal with reserpine or after degeneration of the postganglionic splenic nerves.3. The splenic artery outside the spleen has few visible terminal adrenergic fibres. This is associated with the presence of an external elastic lamina. No terminal fibres were found in the walls of the main splenic vein.4. After infusing DL-[(3)H]noradrenaline 1.25 mug/min for 10 or 20 min fluorescence remained confined to the same sites as in normal cats, i.e. in fibres related to smooth muscle. The red and white pulp and the smooth muscle itself remained free of fluorescence. Autoradiography showed radioactivity in similar sites and with the same pattern as the fluorescent fibres. These results support the conclusion reached in the previous article that noradrenaline infused into the spleen is bound to adrenergic nerves.