NORADRENALINE INHIBITION OF TRANSMITTER EFFLUX IN A RENAL-ARTERY PREPARATION AND THE PRESYNAPTIC RECEPTOR THEORY

The effect of noradrenaline on the stimulation-induced efflux of tritium in cattle renal arteries preincubated with [3H]noradrenaline was determined. Preparations were stimulated transmurally, with 300 shocks over a range of frequency (1-15 Hz) in the presence and absence of noradrenaline (3 x 10-6 M). The agonist inhibited the efflux most at 1 Hz but the extent of the inhibition did not vary with frequency between 2, 5 and 15 Hz. It is concluded that a negative feedback system, modulating neurotransmitter release, and increasingly activated by endogenously released noradrenaline as the frequency of stimulation rises, cannot account for the pattern of efflux inhibition induced by exogenous noradrenaline.