Category: signaling
Detrusor (bladder smooth muscle) contracts via M3 muscarinic activation (parasympathetic, mediates voiding); relaxes via β3-adrenergic (sympathetic, mediates storage). Bladder neck + prostatic urethra contract via α1A-adrenergic (impedes voiding in BPH). Overactive bladder (OAB) Rx blocks the contraction signal: muscarinic antagonists (oxybutynin, tolterodine, solifenacin, darifenacin, fesoterodine) or activates the relaxation signal (β3-agonist mirabegron, vibegron). BPH Rx removes urethral resistance: α1-blockers (tamsulosin α1A-selective uroselective; alfuzosin, silodosin uroselective; doxazosin, terazosin non-selective also useful for BP). Long-term BPH: 5α-reductase inhibitors (finasteride, dutasteride — covered in END-1 HPG axis) shrink prostate over months.