Potential role of ghrelin on the micturition reflex in rats

INTRODUCTION: The aim of this study was to investigate the effects of intravenous ghrelin administration on the micturition reflex in rats. MATERIAL AND METHODS: Continuous cystometrograms were performed with female Sparague-Dawley rats under urethane anesthesia. Stable micturition cycles were established, and ghrelin was then administered intravenously to evaluate changes in bladder activity. In this experiment investigating the role of opioid systems, ghrelin was administered intravenously at the time of first observed bladder contraction after intravenous administration of naloxone methiodide, an opioid receptor antagonist. RESULTS: Intravenous administration of ghrelin increased intercontraction interval that was dose-dependent. These inhibitory effects returned to pre-controls level within 80 minutes of administration. Similarly, intravenous administration of ghrelin increased threshold pressure in a dose-dependent fashion. These inhibitory effects of ghrelin were antagonized by intravenous naloxone methiodide administration. CONCLUSIONS: These results show that ghrelin inhibits the micturition reflex through an opioid-dependent mechanism in rats under urethane anesthesia.