[Activity of presynaptic alpha-adrenoreceptors during prolonged perfusion with adrenaline]

The release of 3H-noradrenaline and contractile response to transmural stimulation of the rat vas deferens decreased according to the concentration of the perfused noradrenaline. In the course of continuing perfusion with noradrenaline and clonidine no increase in the release of the transmitter in response to the stimulation occurred which would suggest a desensitization, i. e. a lowered sensitivity of presynaptic alpha-adrenoreceptors. Possible reasons of the absence of desensitization of presynaptic alpha-adrenoreceptors under a prolonged action of adrenomimetics, are discussed.