The effect of age on release of norepinephrine by tyramine from rat heart

The effect of age on the capacity of tyramine to promote the release of norepinephrine (NE) at the cardiac adrenergic neuroeffector junction was investigated in isolated hearts of rats, 6, 12 and 24 months of age. Hearts were perfused by the method of Langendorff and tyramine was administered in increasing doses as a bolus injection. There was no age-related difference in the effect of tyramine on NE release nor on the relationship between the amount of NE released and chronotropic response induced by the released NE. These findings indicate that there is no difference in the effectiveness of tyramine in promoting the release of NE from the tyramine-sensitive pool as a function of age.