• 1 January 1980
    • journal article
    • research article
    • Vol. 212 (2), 232-239
Abstract
The effects of noradrenaline [norepinephrine, NA] and phenoxybenzamine on the stimulation-induced efflux of 3H-transmitter were studied in guinea pig vas deferens to assess how they conform to the expectations of presynaptic receptor theory. The vas were stimulated transmurally with 0.5, 1.0, 3.0 and 10.0 Hz and with 2 different train lengths (10 and 50 pulses), in the presence of the agonist or the antagonist. NA (3 .times. 10-7 M) depressed the stimulation-induced overflow of 3H by .apprx. 60% at each test frequency with 10 pulses and .apprx. 30% with 50 pulses, except at 0.5 Hz. Phenoxybenzamine (3 .times. 10-5 M) increased the efflux of 3H to a diminishing extent with increasing frequency, with both the 10 and 50 pulses, and the effect was not sensitive to train length. The finding that the effect of phenoxybenzamine decreased with frequency and that of NA was essentially independent of frequency suggests that the compounds do not function as agonist and antagonist at a presynaptic adrenoceptor regulating transmitter output. The distinctly different profiles of effect for NA and phenoxybenzamine, with frequency and train length, suggests that they do not have a common mechanism or site of action in achieving their effects.