Influence of Naftopidil on Plasma Monoamine Levels and Lower Urinary Tract Symptoms Associated with Benign Prostatic Hyperplasia

Objectives To clarify the influence of naftopidil, an α1D/A‐adrenergic receptor antagonist, on the autonomic nervous system, we examined the relation between lower urinary tract symptoms (LUTS) and the plasma monoamine levels before and after naftopidil treatment in benign prostatic hyperplasia (BPH) patients. Methods A total of 43 patients with BPH were studied. The frequency of urination, international prostate symptom score (IPSS), quality of life (QOL) index, overactive bladder symptom score (OABSS), and plasma monoamine levels (adrenaline, noradrenaline, dopamine, and serotonin) were evaluated before and after naftopidil treatment. Results Naftopidil significantly improved urinary frequency in daytime and nighttime, IPSS, QOL index and OABSS in all patients, and decreased the plasma adrenaline level at 8 weeks. When the patients were divided into two groups based on the median adrenaline level (40.5 pg/mL) before treatment, urinary frequency in daytime and/or nighttime, incomplete emptying and poor flow in the IPSS, and the QOL index were significantly improved in the high adrenaline (HA) group, but not in the low adrenaline (LA) group. The pretreatment plasma serotonin level was significantly lower in the HA group than in the LA group, but it increased gradually after the start of treatment until there was no difference between the groups. Conclusions The modulation of plasma adrenaline and serotonin levels by naftopidil in patients with increased sympathetic activity contributed to improvement of LUTS associated with BPH, in addition to its antagonistic effects of α1D/A‐adrenergic receptor on the detrusor and prostatic urethral smooth muscle, the urothelium, and the central nervous system.