An uptake mechanism for L‐noradrenaline in the cat spleen, associated with the nerves but distinct from uptake₁

1. The characteristics of the uptake of [³H] L‐noradrenaline from 1 μg pulses injected close arterially to the isolated blood perfused cat spleen are described. 2. The spleen took up 355·0±16·0 ng from a first pulse and 321·1±43·6 ng from a second. 3. Uptake from a second pulse was 254·0±30·3 ng in the presence of the Uptake₁ inhibitor desmethylimipramine (DMI) (3·3 × 10⁻⁵ M) and the Uptake₂ inhibitor 17‐β‐oestradiol (17β0) (1·8 × 10⁻⁴ M). 4. Uptake from small 10 ng pulses was also insensitive to DMI and 17β0. 5. Uptake from pulses was abolished by surgical denervation of the spleen, or pre‐treatment with phenoxybenzamine (PBA) (8·8 × 10⁻⁵ M). 6. The pulse uptake process was impaired by omission of red cells from the perfusate. 7. Stimulation of the splenic nerves at 3Hz halved the pulse uptake. 8. Uptake from infusion in the presence of DMI and 17β0 occurred only during the first few minutes of the infusion. 9. It is concluded that an uptake process for L‐noradrenaline distinct from Uptakes₁ and ₂ is present in the spleen and this might be important physiologically.