PURPOSE: Recently, rabbit vagina has been used as an experimental model to elucidate the pathophysiology of female sexual dysfuntion. However, there is few information on the regional differences on the contraction and relaxation mechanisms of the vaginal smooth muscle in the rabbit. MATERIALS AND METHODS: Histological and in vitro strip studies were performed using vaginal walls from 10-week-old New Zealand White rabbits discriminately according to the region (upper, middle or lower) and muscle orientation(longitudinal or circular). The contraction and relaxation responses of the vaginal smooth muscle to various neuromodulators and intrinsic intramural nerve stimulation were assessed. RESULTS: Upper and middle thirds of vagina were histologically characterized by abundant smooth muscle content. while lower third portion was composed of numerous sinusoids scattered among smooth muscle bundles. The peak amplitude of high KCl (60 mM)-induced contraction per tissue strip weight was regionally different (upper >mid > lower). Strong concentration-dependent contractile responses to adrenergic agents(epinephrine, norepinephrine, phenylephrine and isopreterenol) were observed. Contractile responses induced by adrenergic agonists showed regional difference: mainly tonic nature in lower part and strong phasic in middle and upper vagina. Lower third portion was characterized by its prominent relaxation response, which was inhibited by N-omega-nitro-L-arginine methyl ester (NAME, 63.3+/-3.2%) and D-vasoactive intestinal peptide(VIP) (5.6+/-3.4%), a VIP antagonist. The presence of D-VIP amplified the NAME-induced inhibitory effect on the nerve-mediated relaxation(97.1+/-2.1%). The muscle orientation did not affect the results. CONCLUSIONS: Although the contractile response was identified in all regions, relaxation was prominent in the lower third portion of rabbit vagina, Therefore, the use of lower third portion would be recommended for further study on the relaxation response of rabbit vagina. The contractile function of vagina awaits future investigation.
Adrenergic Agonists ; Female ; Humans ; Models, Theoretical ; Muscle, Smooth ; Neurotransmitter Agents ; Nitric Oxide ; Norepinephrine ; Phenylephrine ; Rabbits* ; Relaxation ; Vagina*