Background and purpose:
This study investigated whether deletion of the α1A-adrenoceptor gene influences contractile responses of mouse prostate to noradrenaline. Responses of mouse prostate to noradrenaline are known to be mediated by α1L-adrenoceptors, which are thought to be a functional phenotype of α1A-adrenoceptor.
Prostate tissues from α1A-adrenoceptor knockout mice which were homozygous (α1A−/−) and heterozygous (α1A+/−) for the disrupted α1A-adrenoceptor gene, as well as wild-type (α1A+/+) littermates were mounted in glass-isolated organ baths. Electrical field stimulation of nerves and exogenous application of noradrenaline were used to investigate the effects of α1A-adrenoceptor disruption on prostate contractility.
Frequency–response curves to electrical field stimulation (0.5 ms pulse duration, 60 V, 0.1–20 Hz) yielded frequency-dependent contractions. At frequencies of 10 and 20 Hz, prostates from α1A−/− mice elicited an approximately 30% decreased response compared with prostates from α1A+/+ mice. Prazosin (0.3 μM) attenuated responses to electrical field stimulation in prostates from α1A+/+ and α1A+/− mice but not from α1A−/− mice. Increasing concentrations of exogenously administered noradrenaline (10 nM–1 mM) produced mean concentration–response curves in prostates from α1A+/+ and α1A+/− mice, which were not different. Maximum responses to noradrenaline were decreased by approximately 80% in prostates from α1A−/− mice compared with α1A+/+ mice. Prazosin attenuated responses to noradrenaline in all genotypes.
Conclusions and implications:
α1L-Adrenoceptor-mediated responses in mouse prostate are abolished in α1A−/− mice, demonstrating that the α1A-adrenoceptor gene is essential to the manifestation of the prostatic α1L-adrenoceptor phenotype. This implies that α1L-adrenoceptors are indeed a functional phenotype of α1A-adrenoceptor.
British Journal of Pharmacology (2008) 155, 103–109; doi:fn1; published online 16 June 2008