Characterisation of non-adrenergic, non-cholinergic responses in the vaginal wall

This thesis describes experiments to characterise non-adrenergic, non-cholinergic (NANC) relaxation responses in the rabbit vaginal wall. Specifically the roles of nitric oxide (NO), neuropeptides, purines and pyrimidines as mediators of these responses were investigated. The results of this investigation suggest that after inhibition of adrenergic and cholinergic responses, electrical field stimulation (EFS) of pre-contracted vaginal wall strips results in NANC relaxations. These relaxations are partially mediated by NO acting via soluble guanylate cyclase to increase levels of the second messenger cyclic guanosine-3', 5'-monophosphate (cGMP). However the major proportion of these responses is not mediated by NO and is not accompanied by increased cGMP or cyclic adenosine-3', 5'-monophosphate (cAMP). Vasoactive intestinal peptide (VlP)-related neuropeptides are able to concentration-dependently induce relaxation responses in the vaginal wall. However, my results suggest that these neuropeptides are not involved in NANC relaxations, since they are associated with increased cAMP and are inhibited by a-chymotrypsin, whilst NANC relaxations are unaffected. Other neuropeptides investigated did not induce relaxations, and so are unlikely to be involved in mediating NANC responses in the vaginal wall. Purines and pyrimidines were also found to induce relaxation responses in the vaginal wall. Furthermore adenosine- and ATP-induced responses are associated with increased cAMP levels. However the fact that inhibitors of these responses have no effect on NANC relaxations and the fact that NANC relaxations are not associated with increased cAMP levels suggest that purines and pyrimidines are also not mediators of NANC responses in this tissue. NANC relaxations of vaginal wall strips from ovariectomized rabbits were also investigated, but were not found to differ greatly from those from control animals. In conclusion, NANC relaxation responses in the rabbit vaginal wall from both normal and ovariectomized animals are in part mediated by NO, whilst the mediator of the major component of these responses remains unidentified