The neuronal and extraneuronal uptake and metabolism of 3H-(-)-noradrenaline in the rabbit iris.

The disposition of 3H-(-)-noradrenaline (NA) was studied in the iris isolated from albino and pigmented rabbits. Pigment cells bind some NA, but do not metabolize it. Cocaine-sensitive neuronal uptake leads either to an extensive neuronal deamination of NA (when vesicular uptake is inhibited by pretreatment of the animals with reserpine) or to a pronounced accumulation of NA in the axoplasm (if, additionally, neuronal monoamine oxidase is inhibited). Corticosterone-sensitive extraneuronal uptake leads to O-methylation of NA by extraneuronal catechol-O-methyl-transferase. In the rabbit iris, there is no extra-neuronal deamination of NA. In contrast to findings with other tissues, the extraneuronal O-methylation of NA in the rabbit iris is not saturable.