INFLUENCE OF AGE ON CONTROL OF NOREPINEPHRINE RELEASE - CA2-2 RECEPTORS( CHANNELS AND DOPAMINE D)

Possible age-related changes in the roles of L- and N-type Ca2+ channe ls and dopamine D-2 receptors in control of norepinephrine release wer e investigated in tail arteries of F-344 rats. Nifedipine had no effec t on stimulation-evoked tritium efflux at 6 or 24 months of age; howev er, omega-conotoxin GVIA reduced efflux by 70 to 80% at both ages even when frequency of stimulation was altered. Activation of prejunctiona l dopamine D-2 receptors by the selective agonist N-0923 N-propyl-N-2- thienylethylamino)-5-hydroxytetralin] inhibited contractile responses to transmural nerve stimulation in a frequency and concentration-depen dent manner. Effects were similar from 6 to 26 months. Furthermore inh ibition by N-0923 of stimulation-evoked [H-3] norepinephrine efflux wa s not different at 12 and 24 months. Thus, N-type Ca2+ channels predom inate in control of norepinephrine release, and this is unchanged with advancing age or stimulation intensity. Furthermore, D-2 receptor-med iated inhibition of norepinephrine release is not altered with advanci ng age.