The effects of certain drugs on the uptake and release of [3H]noradrenaline in rat whole brain homogenates

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Abstract
Twelve drugs were studied with respect to their effects on inhibition of neuronal uptake of [3H]noradrenaline ([3H]NA) and on release of this amine from presynaptic nerve terminals. An in vitro method, using a crude synaptosomal homogenate prepared from rat whole brain, was employed. All drugs tested were found to produce some release of [3H]NA although tyramine was by far the most potent drug in this respect; tripelennamine and cocaine were observed to produce the least release. Studies of inhibition of NA uptake again demonstrated tyramine to be the most potent of the 12 drugs although in this case it did not differ significantly from cocaine and tripelennamine. The remaining compounds also showed decreased accumulation of [3H]NA and all 12 drugs produced uptake inhibition at a lower dose than that required for release of the amine. A correlation between releasing potency and lipophilicity of the compounds indicated that tyramine seemed to be acting in a different manner from the remaining compounds. A correlation between inhibitory potency and lipophilicity could be demonstrated for only six of the drugs, with tyramine, tripelennamine and cocaine showing the greatest deviation from this relationship.