Contractile properties of urethral smooth muscles of young and aged femaledogs: Morphological and pharmacological aspects

Background: alpha(1)-Adrenoceptors are highly concentrated in the urethral smooth muscles and may play an important role in the contraction of this ar ea. 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 o ld parous female beagles were determined with a urethral function study, ma croscopic autoradiography for urethras using [H-3]-labeled tamsulosin and m orphometry of the urethral muscles. Results: The antagonistic effect (pA(2)) of prazosin for norepinephrine was 7.76 +/- 0.13 in young dogs and 7.62 +/- 0.06 in aged dogs. The specific b inding of [H-3]-tamsulosin (a relatively selective alpha(1A)-adrenoceptor a ntagonist) was recognized diffusely in proximal urethras with in vitro auto radiography. 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 alpha(1A)- and alpha(1L)-adrenoc eptors. No age-related changes were seen in the function of the proximal ur ethra, distribution of alpha(1)-adrenoceptor binding sites and smooth muscl e densities.