[Contraction of various zones of the rat testicular capsule in vitro induced by noradrenaline].

The contractions induced by Noradrenaline (NA) on several preparations of the testicular capsule of the rat have been studied. Increasing concentrations of NA were added both in a single and cumulative way to the whole capsule and to some portions: the mediastinal and non mediastinal portions and to the anterior and posterior portions. All the preparations show concentration-dependent responses to NA except the non mediastinal portion. The maximal amplitude of the contraction was induced in the mediastinal portion, where the greatest amount of contractile cells exists. The NA dose that induces the maximal effect (Emax) is different in each preparation. A lower pD2 is obtained in the cumulative curves when they are compared with the non cumulative curves. In both concentration-response curves a desensitizing effect appears, when 3 X 10(-6)M of NA is reached in the cumulative ones and with higher NA doses in the non cumulative ones. Repeated single doses of NA (10(-5)M) also show desensitization. This effect is independent of the resting time between consecutive doses and it is not modified by propranolol (10(-6)M), normetanephrine (10(-5)M) or TMB-8 (10(-5)M), but it is decreased by imipramine (3 X 10(-8)M) and indomethacin (3 X 10(-6)M). This suggests that neural uptake and release of prostaglandins might be involved in this desensitization.