Modulation of bladder alpha1-adrenergic receptor subtype expression by bladder outlet obstruction.

Purpose: alpha1-Adrenergic receptor (alpha1AR) antagonists are effective for relieving obstructive and irritative symptoms in patients with bladder outlet obstruction. While the alpha1aAR is responsible for prostate smooth muscle relaxation and outlet obstruction relief, to our knowledge the mechanisms underlying the relief of irritative symptoms remain to be determined. Therefore, we investigated mechanisms by which bladder alpha1AR subtypes may be involved in this process.

Materials And Methods: We studied 42 rats, including 6 unoperated controls, 17 sham operated controls and 19 obstructed animals. Animals were characterized for baseline voiding pattern, followed by surgical intervention or sham surgery to establish obstruction (1.09 mm. restricted opening). After 6 weeks to enable the development of detrusor hypertrophy, voiding behavior was reexamined, the animals were sacrificed and bladder tissue was immediately placed in liquid nitrogen. alpha1AR subtype messenger (m)RNA was quantitated using quantitative competitive reverse transcriptase-polymerase chain reaction and protein expression was determined using radioligand binding with the alpha1AR antagonist [125iodine]2-(-[4-hydroxyphenyl]-ethyl-aminomethyl)tetralone (saturation analysis for total alpha1AR density and competition analysis with BMY7378 and 5-methylurapidel to determine alpha1AR subtypes).

Results: In this model 6-week surgical obstruction produced a 6.3-fold increase in bladder weight versus sham operation (p <0.001), concurrent with increased voiding frequency versus before obstruction (p <0.004). Although bladder alpha1AR density did not increase overall with obstruction, striking changes in alpha1AR subtype expression occurred. In control animals 70% of alpha1AR mRNA was the alpha1a subtype, 5% were alpha1b and 25% were alpha1d, whereas in obstructed animals bladder alpha1AR expression changed to 23% alpha1a, 2% alpha1b and 75% alpha1d. Changes in alpha1AR mRNA expression were of similar magnitude throughout the bladder dome, mid body and base. Parallel changes were also evident at the protein level with 100% alpha1aAR expression in control animals changing to new onset alpha1dAR expression (mean plus or minus standard error of mean 36% +/- 7%) in animals with a 5-fold or greater increase in bladder weight.

Conclusions: Our findings indicate a remarkable increase in bladder alpha1dAR mRNA and protein expression after 6 weeks of obstruction and resultant detrusor hypertrophy. This finding is potentially important since alpha1dARs have 10 to 100-fold higher affinity for the endogenous neurotransmitter norepinephrine than the alpha1a or alpha1bAR subtypes. These findings imply that targeting alpha1d may provide a new therapeutic approach for controlling bladder irritative symptoms and possibly detrusor overactivity associated with bladder outlet obstruction.