Background: α1-Adrenoceptors are highly concentrated in the urethral smooth muscles and may play an important role in the contraction of this area. However, detailed examinations of age-related changes of the properties of urethral smooth muscle have rarely been undertaken.
Methods: The contractile properties of urethras from young non-parous and old parous female beagles were determined with a urethral function study, macroscopic autoradiography for urethras using [3H]-labeled tamsulosin and morphometry of the urethral muscles.
Results: The antagonistic effect (pA2) of prazosin for norepinephrine was 7.76 ± 0.13 in young dogs and 7.62 ± 0.06 in aged dogs. The specific binding of [3H]-tamsulosin (a relatively selective α1A-adrenoceptor antagonist) was recognized diffusely in proximal urethras with in vitro autoradiography. The density of binding in smooth muscles was approximately 60 and 40% in circular longitudinal layers, respectively, for both dogs.
Conclusions: The female canine urethra had α1A- and α1L-adrenoceptors. No age-related changes were seen in the function of the proximal urethra, distribution of α1-adrenoceptor binding sites and smooth muscle densities.