Melatonin restores diminished neurogenic reactivity of the juvenile rat tail artery

The effect of melatonin on neurogenic reactivity of the juvenile rat tail artery segment was studied. The electrical field stimulation-evoked contraction of the segment decreased in the course of the experiment. Melatonin (0.1 microM) applied at different time points of the experiment produced an increase in the contraction, which directly correlated with a spontaneous decrease in the electrical field stimulation-evoked response. The increase in the potentiating effect of melatonin in the course of the experiment was not due to sensitization of the segment to this substance. Noradrenaline-evoked contraction of the vessel segment was not changed by melatonin. The data indicate that melatonin restores the diminished neurogenic reactivity of the juvenile rat tail artery probably by potentiation of the contractile response of the vessel, but this effect is hardly due to a change in sensitivity of the postjunctional membrane to noradrenaline.