The role of alpha1D-adrenoceptors in prostatic contraction examined using protection studies

1 The aim of the study was to investigate the role of the alpha1D-adrenoceptor in alpha1-adrenoceptor-induced contraction of human prostate by means of protection experiments. 2 Responses of human prostate strips to noradrenaline were recorded, along with responses of rat aorta and vas deferens, tissues possessing predominantly alpha1D- and alpha1A-adrenoceptors respectively, for comparison. alpha1-adrenoceptors were then inactivated by incubation with the irreversible antagonist phenoxybenzamine. In some tissues alpha1A- or alpha1D-adrenoceptors were 'protected' from inactivation by incubation in the presence of the selective alpha1A- or 1D-adrenoceptor antagonists 5-methylurapidil and BMY 7378 before recording further responses to noradrenaline. 3 Phenoxybenzamine reduced the maximum noradrenaline-induced response and the potency of noradrenaline in all tissues. In rat vas deferens and human prostate, 5-methylurapidil protected alpha1A-adrenoceptors in a concentration-dependent manner. In rat aorta, 10 nM BMY 7378 almost fully protected alpha1D-adrenoceptors. However, concentrations of BMY 7378 up to 30-fold higher failed to protect receptors in the human prostate. 4 These results suggest that in human prostate functional alpha1D-adrenoceptors do not contribute to noradrenaline-induced contractile responses.