How important is the α₁-adrenoceptor in primate and rodent proximal urethra? Sex differences in the contribution of α₁-adrenoceptor to urethral contractility

Urethral smooth muscle (USM) contributes to urinary continence by contracting during the urine storage phase, which is mainly mediated by activation of postjunctional α₁-adrenoceptors. Males and females show differences in the functioning of the lower urinary tract and the most common urinary tract symptoms (LUTS). LUTS in men typically occur in association with bladder outlet obstruction, whereas in women urinary urge-incontinence symptoms are more common. Therefore, this study aimed to evaluate sex differences in α₁-adrenoceptor subtype expression and their importance in proximal urethra contraction in the mouse (C57BL6/J) and marmoset (Callithrix jacchus). Contractile responses to phenylephrine, norepinephrine, potassium chloride (KCl), and electrical-field stimulation (EFS) were evaluated. Phenylephrine, norepinephrine, KCl, and EFS produced markedly greater contractions in male mice and marmoset USM compared with females. The sex differences remained unchanged by N^ω-nitro-L-arginine (L-NAME; nitric oxide synthase inhibitor), atropine (muscarinic receptor antagonist), and PPADS (P2X1-purinoceptor antagonist). Additionally, selective α₁A (but not α₁B- and α₁D-)-adrenoceptor antagonists significantly reduced phenylephrine-induced USM contractions. qRT-PCR for α₁A-, B-, and D-adrenoceptor subtypes revealed a marked presence of the α₁A-adrenoceptor subtype in male USM, but not females. Male mouse urethra also exhibited a higher tyrosine hydroxylase mRNA expression. Histomorphometric analysis showed a greater USM area in male than female mice. In conclusion, male mouse and marmoset proximal USM shows strong α₁A-adrenoceptor-induced contractions and abundant α₁A-adrenoceptor expression, whereas α₁A-adrenoceptor-mediated mechanisms are much less important in females. The differential expression of α1-adrenoceptors in the proximal urethra may contribute to the higher incidence of urinary incontinence in women and obstructed voiding in men.