THE EFFECT OF COCAINE ON THE ³H-NOREPINEPHRINE UPTAKE BY COLD STORED AORTA FROM RABBIT

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The effects of cold storage (2°C) on the uptake of ³H-norepinephrine (³H-NE) by the rabbit aortae were studied. The cold storage progressively decreased the uptake of norepinephrine by strips exposed to low concentration (10^-7 M) of ³H-NE. By the 7th day of storage, the uptake became constant and was not affected by further treatment. Cocaine (10^-5 M) or desipramine (10^-6 M) failed to decrease this residual norepinephrine uptake in the strips stored for more than 5 days. Although cocaine potentiated the norepinephrine response of aortae from young (5 wk.) and old (over 10 months) rabbits equally, the cocaine sensitive norepinephrine uptake of old rabbit aortae was approx. half the value observed in the aortae of young rabbits. Study on ³H-metabolites indicated that the major portion of the radioactivity in the fresh and cold stored tissue was ³H-NE. The content of total ³H-metabolites formed by monoamine oxidase was less in the medium for the cold stored tissue than for the fresh tissue. These results indicate that cocaine sensitive neuronal uptake of norepinephrine by the rabbit aortae disappears after cold storage. These studies, together with previous experiments, strongly support the view that the cocaineinduced potentiation in the aorta involves a postsynaptic component.