Influence of age and dietary restriction on norepinephrine uptake into cardiac synaptosomes

The purpose of this study was to determine whether aging alters neuronal uptake of norepinephrine (NE) in the rat heart and if dietary restriction influenced the effect of age on this system. Cardiac synaptosomes were prepared from 6-, 12- and 24-month-old male F344 rats fed ad libitum (AL) or a diet restricted (DR) to 60% of AL intake. Cardiac synaptosomes were incubated with 50, 100, 200, or 400 nM [3H]NE for 10 min at 37 degrees C with and without desmethylimipramine (DMI), a selective neuronal-uptake blocker. DMI-sensitive [3H]NE uptake was calculated as the difference between samples with and without DMI. NE uptake was adjusted for the number of cardiac synaptosomes in each sample by dividing by the endogenous NE content in each sample. The Vmax for uptake ([3H]NE/min/ng NE) declined significantly between 6 and 12 months in AL rats and between 12 and 24 months in DR rats. Km was not significantly different between age or diet groups. The change in Vmax with age suggests that the number of NE transporters per synaptosome may decline with age and that DR delays this effect of age. There were no differences in the sensitivity to DMI between age or diet groups.