The Efficacy of L-Arginine for Benign Prostatic Hyperplasia

[Objective] : Recent studies have demonstrated the effectiveness of phosphodiesterase type 5 (PDE5) inhibitor, a known drug for erectile dysfunction, for treating lower urinary tract symptoms (LUTS) of benign prostatic hyperplasia (BPH). Smooth muscle relaxation mediated by the nitric oxide (NO) pathway has been considered to improve urinary symptoms. Hence, we examined whether the administration of L-arginine as a precursor of NO could improve urinary conditions via the NO pathway. We also studied whether the combination of tamsulosin hydrochloride (tamsulosin), a known therapeutic drug for prostatic hyperplasia, and L-arginine administered as therapeutic agents can provide synergistic effects on BPH. [Materials and Methods] : The study subjects comprised 21 patients who visited our hospital with the complaint of LUTS diagnosed as BPH, for which the patients received L-arginine at 1,200 mg/day. First, the changes in urinary symptoms associated with the L-arginine administration were evaluated. After a washout period, 0.1-mg/day tamsulosin was administered. Next, a combination of 0.1-mg/day tamsulosin and 1,200-mg/day L-arginine was administered to determine whether the combination therapy has a synergistic effect against LUTS. International Prostate Symptom Score (IPSS), quality of life (QOL) score, maximum urinary flow rate (Qmax), and residual urine volume were measured before and after the administration of each dose of L-arginine. Furthermore, to determine the role of L-arginine in LUTS, we examined the changes in serum cyclic guanosine monophosphate (cGMP) levels associated with the administration of L-arginine. [Results] : The mean values at baseline versus those after the administration of L-arginine alone were as follows : IPSS, 17.8+-5.5 vs. 15.8+-7.0 ; QOL score, 4.9+-1.2 vs. 4.2+-1.7 ; Qmax, 13.9+-6.9 ml/s vs. 15.6+-6.6 ml/s ; and residual urine volume, 74.5 +-78.6 ml vs. 37.1+-61.2 ml, respectively. Those of tamsulosin versus the combination therapy were as follows : IPSS score, 10.9+-6.1 vs. 11.3+-6.4 ; QOL score, 4.1+-2.0 vs. 3.6+-1.9 ; Qmax, 17.5+-7.7 ml/s vs. 17.8+-10.0 ml/s ; and residual urine volume, 43.8+-51.6 ml vs. 35.5+-60.9 ml, respectively. L-Arginine alone significantly improved the IPSS for "weak stream" (p=0.027), QOL score (p=0.047), and residual urine volume (p=0.003). No significant difference was observed between tamsulosin therapy and the combination therapy. However, the differences between the serum cGMP levels before an