Effect of norepinephrine uptake blockade on contractile responses to adrenergic nerve stimulation of isolated rat blood vessels: influence of age.

It has been shown previously that vascular adrenergic responsiveness is maintained with age in the face of reductions in norepinephrine (NE) content. To test the hypothesis that a concomitant decrease in neuronal NE uptake is responsible for maintenance of contractile responses with age, isolated blood vessel segments from Fischer 344 rats aged 6, 12, 20 and 27 months were studied. Renal artery and vein, femoral artery and vein and tail artery were stimulated with transmural nerve stimulation (TNS) with and without cocaine (3 X 10(-5) M). Similar to previous findings, frequency response curves for 200 pulse trains of TNS did not differ significantly with age, except for the 6 months tail artery at 1, 2 and 4 Hz and the 6 months renal artery at 1 Hz. After addition of cocaine, TNS responses for trains of 200 pulses were increased substantially. Comparison of responses to TNS in the presence of neuronal uptake blockade with cocaine demonstrated no significant differences with age except for the renal vein, where responses at 1 Hz were smaller at 6 months compared to 12 months. Thus, except for the tail artery at 6 Hz, the effect of cocaine on responses to adrenergic nerve stimulation did not vary with age. In the tail artery at 6 months, because control responses were significantly smaller, the effect of cocaine was greater than at other ages. These findings suggest that a decrease in NE uptake with advancing age cannot account for the maintenance of adrenergic responses in the face of a fall in tissue NE content.