Effect of (1-24)adrenocorticotrophin on the uptake of 3H-norepinephrine by the rat atria.

Spontaneously beating rat atria were incubated with 3H-norepinephrine both in the presence and absence of (1-24)ACTH. A significant reduction in the uptake and retention of radioactivity was found in atria pretreated with (1-24)ACTH. A kinetic study of the uptake process showed similar Km values for both the control (24.1 x 10(-8) M) and (1-24)ACTH pretreated (22.2 x 10(-8) M) groups, but a significantly different Vmax. The Km values were similar to that reported for the neuronal reuptake process (Uptake 1). It was concluded that the ACTH-induced enhanced myocardial sensitivity to catecholamines previously reported, could be explained in part on the basis of an inhibition of neuronal uptake by (1-24)ACTH. The inhibition of neuronal uptake by (1-24)ACTH was dose-dependent.