Amiloride Relaxes Rat Corpus Cavernosum Relaxation In Vitro and Increases Intracavernous Pressure In Vivo.

INTRODUCTION: The antihypertensive effects of thiazide diuretics such as hydrochlorothiazide are commonly associated with erectile dysfunction. The association of hydrochlorothiazide/amiloride is not associated with erectile dysfunction. The hypothesis is that amiloride has beneficial effect in penile erection and, therefore, counterbalances the hydrochlorothiazide-induced disruptive effect. AIM: To investigate the effects of amiloride and its analogues hexamethylamiloride and benzamil on rat isolated corpus cavernosa (CC) and intracavernous pressure (ICP) in anaesthetized rats. METHODS: Rat isolated CC were incubated with amiloride, hexamethylamiloride, and benzamil (10 and 100 µmol/L each), followed by phenylephrine, potassium chloride, and electrical field stimulation (EFS). Their effect on the relaxant responses to EFS and sodium nitroprusside were also determined. Oral (30 mg/kg) and intraperitoneal (3 mg/kg) treatments with amiloride were also investigated on nerve-evoked ICP. MAIN OUTCOME MEASURES: In vitro functional studies and in vivo ICP measurement on rat CC were performed. Additionally, phosphodiesterase type V isoform A1 activity and the mRNA expressions of Na+/H+ pump, epithelial sodium channel exchangers (ENaC) channels (α-, ß- and γ subunits) and Na+/Ca2+ exchangers were evaluated in CC tissues. RESULTS: Amiloride and its analogues significantly reduced the phenylephrine-, potassium chloride-, and EFS-induced CC contractions, which were not changed by nitro-L-arginine methyl ester (100 µmol/L) or indomethacin (6 µmol/L). In phenylephrine-precontracted CC tissues, amiloride itself caused concentration-dependent relaxation and significantly increased the EFS-induced relaxation. Oral and intraperitoneal treatment with amiloride significantly increased the ICP. Phosphodiesterase type V isoform A1 activity was not affected by amiloride. Na+/H+ pump, ENaC, and Na+/Ca2+ exchanger mRNA expressions were all detected in rat CC tissues. CLINICAL IMPLICATION: Amiloride analogues may have therapeutic potential for erectile dysfunction. STRENGTH & LIMITATIONS: The interesting effect of amiloride in penile erection was observed in both in vitro and in vivo methods. The evidence at the moment is restricted to rat CC. CONCLUSION: Amiloride reduces in vitro CC contractility and enhances erectile function after oral and intraperitoneal administration, possibly via inhibition of ENaC. Campos R, Claudino MA, de Oliveira MG, et al. Amiloride Relaxes Rat Corpus Cavernosum Relaxation In Vitro and Increases Intracavernous Pressure In Vivo. J Sex Med 2019;16:500-511.

Hydrochlorothiazide Potentiates Contractile Activity of Mouse Cavernosal Smooth Muscle.

INTRODUCTION: Hydrochlorothiazide has a negative influence on penile erection but little is known about the mechanism(s) involved. AIMS: To characterize the effects of this diuretic on mouse corpus cavernosum (CC) smooth muscle in vitro and ex vivo. METHODS: CC strips of C57BL/6 mice (12-16 weeks old) were mounted in organ baths containing Krebs-Henseleit solution and tissue reactivity was evaluated. Expression of genes encoding diuretic targets and enzymes involved in penile erection were evaluated by polymerase chain reaction. MAIN OUTCOME MEASURES: Stimulation-response curves to phenylephrine (10 nmol/L-100 µmol/L) or to electrical field stimulation (1-32 Hz) were constructed, with or without hydrochlorothiazide. Strips of CC from mice after long-term hydrochlorothiazide treatment (6 mg/kg/day for 4 weeks) with or without amiloride (0.6 mg/kg/day for 4 weeks) in vivo also were studied. Nitric oxide and Rho-kinase pathways were evaluated. RESULTS: Hydrochlorothiazide (100 µmol/L) increased the maximum response to phenylephrine by 64% in vitro. This effect was unaffected by the addition of indomethacin (5 µmol/L) but was abolished by N((ω))-nitro-L-arginine methyl ester (100 µmol/L). Hydrochlorothiazide (100 µmol/L) potentiated electrical field stimulation-induced contraction in vitro, but not ex vivo. Long-term treatment with hydrochlorothiazide increased the maximum response to phenylephrine by 60% and resulted in a plasma concentration of 500 ± 180 nmol/L. Amiloride (100µmol/L) caused rightward shifts in concentration-response curves to phenylephrine in vitro. Long-term treatment with hydrochlorothiazide plus amiloride did not significantly increase the maximum response to phenylephrine (+13%). Reverse transcriptase polymerase chain reaction did not detect the NaCl cotransporter in mouse CC. Hydrochlorothiazide did not change Rho-kinase activity, whereas amiloride decreased it in vitro and ex vivo (approximately 18% and 24% respectively). A 40% decrease in Rock1 expression also was observed after long-term treatment with hydrochlorothiazide plus amiloride. CONCLUSION: Hydrochlorothiazide potentiates contraction of smooth muscle from mouse CC. These findings could explain why diuretics such as hydrochlorothiazide are associated with erectile dysfunction.