Vaginal physiological changes in a model of sexual arousal in anesthetized rats

The understanding of the pathophysiology of female sexual dysfunction suffers from the lack of a convenient model for the study of female genital sexual response. In this study, systemic arterial blood pressure (BP) as well as partial oxygen tension, temperature, and blood engorgement of the vagina [using laser-Doppler flowmetry in arbitrary units (AU)] were measured in anesthetized, ovariectomized (1 wk before the start of the experiment) female rats. Vaginal sexual arousal was replicated by electrical stimulation of the pelvic nerve (PNS). PNS induced reproducible increases in the different vaginal parameters (from baseline value, respectively: 16 +/- 10 to 30 +/- 12 mmHg; 34.9 +/- 0.6 to 36 +/- 0.6 degrees C; 450 +/- 196 to 1,500 +/- 360 AU; P < 0.05, paired t-test) and BP (90 +/- 7 to 123 +/- 13 mmHg, P < 0.05, paired t-test). Vaginal vascular resistance was significantly decreased during PNS (from 0.23 +/- 0.15 to 0.08 +/- 0.02 mmHg/AU). Vaginal wall tension was also measured with a force transducer. PNS induced an increase in vaginal wall tension (1.0 +/- 0.2 g), followed by a decrease under the prestimulation value. Intravenous atropine sulfate (1 mg/kg) injection abolished the increase in vaginal wall tension without significantly affecting vaginal vascular resistance. Intravenous vercuronium bromide (2 mg/kg) injection abolished the decrease in vaginal wall tension. Concomitant electrical stimulation of the paravertebral sympathetic chain inhibited vaginal response induced by PNS. Electrical stimulation of the medial preoptic area of the hypothalamus induced a response qualitatively equivalent to PNS with a significant decrease of vaginal vascular resistance. These data support that vaginal contractions involve both smooth and striated muscles and indicate that neural control of vaginal sexual arousal have great similarities in male and female rats.