α1-adrenergic receptor subtypes in human detrusor

Purpose: To identify and quantitate alpha(1)-adrenergic receptor (alpha(1)AR) subtype expression in human detrusor. Materials and Methods: Initial studies to determine alpha(1)AR expression in human detrusor were performed using saturation binding with [I-125]HEAT. Once the presence of alpha(1)ARs was documented, subtype (alpha(1a), alpha(1b), alpha(1d)) expression at the mRNA level (and comparison with rat) was determined with RNase protection assays (human detrusor) and RT-PCR (human detrusor, rat whole bladder). Competition binding analysis with the alpha(1d)AR-selective ligand BMY7378 was used to measure alpha(1)AR subtype expression at a protein level in human detrusor. Results: alpha(1)AR expression in human detrusor was low but reproducible (6.3 +/- 1.0 fmol./mg. total protein). RNase protection assays performed on total RNA extracted from human detrusor revealed the following alpha(1)AR subtype expression: alpha(1d) (66%) > alpha(1a) (34%), and no alpha(1b). RT-PCR confirmed alpha(1)AR subtype mRNA distribution in human detrusor with alpha(1d) (approximate to 60-70%) > alpha(1a) (approximate to 30-40%), and a lack of alpha(1b) mRNA. Rat whole bladder expressed different alpha(1)AR subtype mRNA than human detrusor, with alpha(1a) approximate to alpha(1b) approximate to alpha(1d). The presence of alpha(1d) > alpha(1a) expression in human detrusor was confirmed at a protein level by competition analysis utilizing BMY7378 which revealed a two-site fit, with K-i and high affinity binding (66%) consistent with the alpha(1d)AR subtype. Conclusions: Human detrusor contained two alpha(1)AR subtypes (alpha(1d) > alpha(1a)), a finding that is different from rat, another commonly used animal model. Since non-subtype selective alpha(1)AR antagonists ameliorate irritative bladder symptoms (in men and women with/without outlet obstruction), and Rec 15/2739 (alpha(1a) selective antagonist) does not improve symptom scores in BPH, our findings suggest bladder alpha(1d)ARs may provide a potentially novel mechanism underlying these therapeutic benefits.