The uptake and release of radioactive noradrenaline by the splenic nerves of cats.

1. DL-[(3)H]noradrenaline was infused close-arterially into the spleens of chloralosed cats at rates of 0.625 or 1.25 mug/min for 10 or 20 min and the recovery of noradrenaline and its metabolites in the venous blood measured during the infusion and after nerve stimulation at various times after the infusion.2. During the infusion 41% of the noradrenaline was recovered in the blood as such and 11% as metabolites. The remaining 48% was retained within the spleen.3. The noradrenaline retained in the spleen was slowly released to appear as metabolites in the blood stream. In normal animals the rate of loss from the spleen was 0.22% per minute. In animals given phenoxybenzamine after the end of the infusion this rate was several times greater.4. Splenic nerve stimulation in normal animals or in animals treated with phenoxybenzamine resulted in an increase in the radioactivity of the blood leaving the spleen. Paper chromatography showed this to be radioactive noradrenaline.5. In normal animals the specific activity of the transmitter liberated by nerve stimulation was less than that of the stores of noradrenaline within the spleen. In animals treated with phenoxybenzamine these two values were similar.6. It is suggested that the infused noradrenaline retained in the spleen is largely taken up into nerve fibres and is available for subsequent release by nervous activity.