CHARACTERIZATION OF THE RAT MYOMETRIAL CONTRACTILE RESPONSE TO NEUROPEPTIDE-Y

The in vitro contractile effect of neuropeptide Y (NPY) on rat myometr ial strips was for the first time demonstrated and characterised, and the EC(50) value estimated to be 267 +/- 87 nM. This effect is presuma bly mediated by the NPY1 receptor being responsible for postsynaptic e ffects throughout the peripherial nervous system, thus indicating a di rect uterotonic effect of NPY. Further, the effect was demonstrated to be dependent on extracellular Ca2+. Short-term exposures to NPY marke dly desensitized the tissue affecting subsequent responses to NPY as w ell as to oxytocin (OT). This desensitization was time- and concentrat ion-dependent, but lasted less than three hours. However, long-term in fusions of NPY for 5 days increased the response to both NPY and OT. L ong-term infusions of OT caused a marked decrease of the NPY response, and it is concluded that common pathways for up and down regulation o f the myometrial responsiveness to several peptide hormones may exist.