Release of Noradrenaline and Dopamine by Nerve Stimulation in the Cat Spleen Perfused with 3 H-dopamine

1. Recovery of (3)H-dopamine and (3)H-L-dopa infused intra-arterially at a constant rate of 20 ng/min into the cat spleen perfused with Krebs bicarbonate solution was 52.6+/-3.8% and 90.5+/-3.1% respectively. Recovery of (3)H-dopamine in spleens treated with alpha-methyl-p-tyrosine was 67.7+/-6.7% and was not significantly different from untreated spleens.2. Release of (3)H-dopamine by nerve stimulation after an infusion of (3)H-dopamine resembled release of endogenous noradrenaline. Release of (3)H-L-dopa and (3)H-L-tyrosine after their infusion did not occur in any consistent manner by nerve stimulation.3. Preferential release of (3)H-noradrenaline formed from (3)H-dopamine was not observed during continuous nerve stimulation. Specific activity of released (3)H-noradrenaline remained constant during any single stimulation period with or without (3)H-dopamine infusion. Treating the cats with alpha-methyl-p-tyrosine did not change the time course of (3)H-noradrenaline release.4. Output of noradrenaline expressed as a percentage of the first minute output in both normal and alpha-methyl-p-tyrosine treated spleens was not significantly different at various times during continuous nerve stimulation.5. Specific activity of released noradrenaline formed from (3)H-dopamine was always greater than the specific activity of the spleen in normal spleens and spleens treated with alpha-methyl-p-tyrosine.6. It is concluded that newly synthesized or infused noradrenaline initially mixes with a more rapidly turning pool and only slowly with the entire tissue store. During continuous nerve stimulation there is no further preferential release of newly synthesized noradrenaline. Released noradrenaline truly represents the state of the releasable pool and will vary with the latter.