Activation of β-adrenergic receptors during sexual arousal facilitates vaginal lubrication by regulating vaginal epithelial Cl(-) secretion.

INTRODUCTION: Vaginal lubrication, an indicator of sexual arousal and tissue health, increases significantly during genital sexual arousal. Adrenergic alpha-receptors (AR) are an important regulator of genital physiological responses involved in mediating vascular and nonvascular smooth muscle contractility; the role of β-AR in sexual arousal, however, has not yet been investigated.

AIM: The goal of this study was to reveal the functional role of β-AR in modulating vaginal lubrication during sexual arousal and the mechanisms underlying the process.

METHODS: The effects of adrenaline on vaginal epithelial ion transport, intracellular cyclic adenosine monophosphate (cAMP) content ([cAMP]i ), and vaginal lubrication were investigated using short-circuit current (ISC ) of rat vaginas incubated in vitro, enzyme-linked immunosorbent assay (ELISA), and measurement of vaginal lubrication in vivo, respectively. The expressions of β-AR in vaginal epithelium were analyzed by reverse transcription-polymerase chain reaction, western blot, and immunofluorescence.

MAIN OUTCOME MEASURES: Changes of ISC responses; mRNA, protein expressions and localization of β-AR; [cAMP]i ; vaginal lubrication.

RESULTS: Serosal application of adrenaline induced an increase of ISC across rat vaginal epithelium that blocked by propranolol, a β-AR antagonist, rather than phentolamine, an α-AR antagonist. β1/2-AR were both present in rat and human vaginal epithelial cells. Removing Cl(-) or application of CFTR(inh) -172, an inhibitor of cystic fibrosis transmembrane conductance regulator (CFTR), abolished adrenaline-induced ISC responses. The elevated levels of [cAMP]i induced by adrenaline were prevented by the pretreatment with propranolol. Vaginal lubrication measured in vivo showed that adrenaline or pelvic nerve stimulation caused a marked increase in vaginal lubrication, whereas pretreatment with propranolol or CFTR(inh) -172 reduced the effect.

CONCLUSIONS: Activation of epithelial β-AR facilitates vaginal lubrication during sexual arousal by stimulating vaginal epithelial Cl(-) secretion in a cAMP-dependent pathway. Thus, vaginal epithelial β-AR might be another regulator of vaginal sexual arousal responses.