The effect of amitriptyline on presynaptic mechanisms in noradrenergic nerves

1 Electrically evoked and resting overflow of tritium was measured from mouse vas deferens previously incubated with [3H]-(--)-noradrenaline. 2 At low concentrations (1.6 X 10(-7) to 4 X 10(-6)M) amitriptyline increased only the evoked tritium overfow while higher concentrations increased both evoked and resting overflow. 3 In the presence of atropine (1 X 10(-6 M) amitriptyline still produced an increase in evoked tritium overflow. 4 In the presence of a concentration of cocaine (1.1 X 10(-5) M) which produced a maximal blockade of the uptake of exogenous noradrenaline the application of amitriptyline still produced an increase in evoked tritium overflow. 5 In the presence of a concentration of phentolamine (1 X 10(-5) M) that produced complete blockade of the presynaptic alpha-adrenoceptors, amitriptyline still produced an increase in evoked tritium overflow. 6 In the presence of cocaine and phentolamine together the effect of amitriptyline on evoked overflow was abolished. 7 It is concluded that amitriptyline may raise synaptic levels of noradrenaline by blocking presynaptic alpha-adrenoceptors controlling noradrenaline release and by blocking its uptake into sympathetic neurones.