Profiles of the response to noradrenaline in the whole and bisected rat vas deferens

1 The present study was carried out to look at the differences between the whole and bisected rat vas deferens in response to cumulative and non-cumulative administration of noradrenaline in terms of sensitivity and maximum response. An effort was made to quantify the parameters characterizing the various components of the mechanical response to single concentrations of the agonist. 2 The sensitivity, as measured by the -log EC50 value for noradrenaline, was significantly lower in the prostatic portion than in the whole vas deferens and epididymal portion. The maximum contractions reached by the epididymal and the prostatic half were 65.03 ± 10.43% and 13.84 ± 5.28% of the maximal contraction evoked by noradrenaline in the whole rat vas deferens. 3 Various concentrations of noradrenaline were tested as single concentrations in the three preparations. Three components of the response to noradrenaline were individualized, i.e. an early rapid phasic component followed by a second slower tonic component with spikes superimposed. The time-course of these components, as well as their ratios, were different depending on the concentration of agonist tested and on which half of the vas deferens was considered. 4 The importance of oxidation of exogenous noradrenaline as well of the neuronal and extraneuronal uptake mechanisms was considered. EDTA was devoid of any action. Cocaine enhanced the potency and the maximum contraction of noradrenaline and all the parameters related to the different phases of the contraction were increased. Hydrocortisone at the highest concentration employed (2 × 10−5M) was able to reduce significantly the -log EC50 value of the cumulative concentration–response curve to noradrenaline and both the phasic and tonic components of the contraction to noradrenaline (3 × 10−6M). 5 In conclusion, our evaluation of the parameters of the mechanical response of the whole and bisected vas deferens to noradrenaline rationalize the, often contradictory, findings of the current litterature. Chiefly, the attainment of a careful description of the features of the response to noradrenaline can offer a dependable approach to the study of the underlying mechanisms of the three components.