The effect of corticosterone on the fluxes of 3H-normetanephrine into and out of the extraneuronal compartments of the perfused rat heart.

1. Hearts were obtained from pargyline-pretreated rats and perfused with 40 nM 3H-normethanephrine for 21 min. 87 muM corticosterone reduced the accumulation of 3H-normethanephrine in the heart. 2. When the initial perfusion with 3H-normetanephrine was followed by perfusion of the hearts with amine-free solution for 90 min, efflux of radioactivity was determined. Analysis of efflux curves showed that, apart from its distribution into extracellular space and fluid content of cardiac cavities, radioactivity distributed mainly into one corticosterone-sensitive, extra-neuronal compartment (compartment III, half time for efflux about 6 min). 3. When corticosterone was added to the wash out solution only, it failed to affect the efflux of radioactivity. 4. Although monoamine oxidase was inhibited, some deaminated metabolites of normetanephrine were detected in the efflux. Efflux of 3H-metabolites was monophasic in about half the hearts (short half time corresponding to that of compartment III) and biphasic in the other half. The early phase of efflux (short half time) seemed to represent efflux of newly formed metabolite(s), while the late phase (if present) appeared to be due to efflux of metabolites formed early in the experiment. 5. While corticosterone is known to inhibit the extraneuronal influx and efflux of catecholamines, it appears to impair the influx of normetanephrine without affecting the efflux.