UPTAKE OF NORMETANEPHRINE AND NOREPINEPHRINE BY COCAINE-TREATED RAT HEART

¹ Department of Pharmacology, Yale University School of Medicine, New Haven, Connecticut

Isolated rat hearts, in which both catechol-O-methyl transferase and monoamine oxidase had been inhibited, were perfused with either H³-norepinephrine or H³-normetanephrine, 4 x 10^-8 M, in the presence of 10^-6 or 10^-4 M cocaine. The uptake of norepinephrine could be resolved into two components with widely different rates of equilibration. Amine taken up by the rapidly equilibrating component was easily washed out by 10 min of perfusion with aminefree medium, whereas that accumulated by the slowly equilibrating component was more resistant to washout. Normetanephrine, in contrast, was taken up by a single component which was very similar to the rapidly equilibrating component of norepinephrine uptake. The affinity of normetanephrine for this component was 9.8 times that of norepinephrine. An increase in the concentration of cocaine failed to affect the uptake of either amine by the rapidly equilibrating component, but markedly reduced the uptake of norepinephrine by the slowly equilibrating component. It is proposed that the slowly equilibrating component represents neuronal uptake of norepinephrine, whereas the rapidly equilibrating component may represent extraneuronal uptake of amine.