Introduction. In our male animal models, hydrogen sulfide (H2S) displayed significant vasodilatory and smooth muscle relaxant effects suggestive of an endogenous physiological role in erectile process.
Aim. In this first exploratory study, we aimed to identify the existence and mechanism of H2S pathway in female sexual physiology.
Methods. Vaginal and clitoral cavernosal smooth muscle strips from New Zealand white rabbits (N = 12) were exposed to stable H2S donor, sodium hydrosulfide hydrate (NaHS.xH2O, 100 µM–1.6 mM), in isometric tension studies. The NaHS responses were repeated after incubations with (i) Nω-nitro-L-arginine (50 µM), 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ) (10 µM) or cis-N-[2-phenylcyclopentyl]-azacyclotridec-1-en-2-amine (MDL 12,330A) (10 µM); and (ii) potassium chloride medium (high K+ 60 mM/low K+ 10 mM), tetraethylammonium (10 mM) or glibenclamide (100 µM). Relaxant effect of NaHS was also compared with those of nitroglycerine (0.18–78.2 µM) and sildenafil (0.084–25.3 µM). Additionally, samples (N = 16) were collected for estimations of plasma and tissue H2S and expression levels of cystathionine γ-lyase (CSE) and cystathionine β-synthase (CBS) proteins.
Main Outcome Measures. In vitro evidences for H2S formation and its physiopharmacological effects.
Results. NaHS produced significant concentration-dependent relaxation of vaginal and cavernosal smooth muscles with inhibitions by combination of ODQ and MDL 12,330A (26.4%), Nω-nitro-L-arginine (22.2%), high K+ (15.1%) or glibenclamide (10.1%). Based on molar potency, NaHS was 18.3 and 6.3 times weaker than nitroglycerine and sildenafil, respectively. Quantitative assays indicated that plasma H2S level was 16.5 ± 2.58 µM, and H2S was synthesized in the clitoral and vaginal smooth muscles (1.8 and 3.9 nmol/mg soluble protein compared with 26.5 nmol/mg in the liver: positive control). Similarly, western blotting identified the protein expression bands of CSE (44.5 kDa) and CBS (63 kDa) in these genital tissue samples.
Conclusion. These pilot studies clearly indicate the smooth muscle relaxant effect of H2S in female genital tract, mediating through cyclic adenosine 3′:5′-monophosphate, nitric oxide-cyclic guanosine monophosphate and K+ATP channels. Taken together with biochemical and molecular evidences for endogenous formation, H2S pathway could be a contributing factor in female sexual responses. Srilatha B, Lingxu H, Adaikan GP, and Moore PK. Initial characterization of hydrogen sulfide effects in female sexual function. J Sex Med 2009;6:1875–1884.