THE OXYTOCIN RECEPTOR ANTAGONIST 1-DEAMINO-2-D-TYR-(OET)-4-THR-8-ORN-OXYTOCIN INHIBITS EFFECTS OF THE 5-HT1A RECEPTOR AGONIST 8-OH-DPAT ON PLASMA-LEVELS OF INSULIN, CHOLECYSTOKININ AND SOMATOSTATIN

0The aim of the present study was to investigate whether the 5-HT1A re ceptor agonist 8-OH-DPAT, which previously has been shown to release o xytocin, also influences plasma levels of gastrointestinal and pancrea tic hormones, and if so, whether such an effect is mediated by an oxyt ocinergic mechanism. For this purpose 8-OH-DPAT (0.5 mg/kg s.c.) was i njected to male rats pretreated with the oxytocin receptor antagonist 1-deamino-2-D-Tyr-(OEt)-4-Thr-8-Om-oxytocin (1 mg/kg s.c.), or vehicle . Thirty min after injection of 8-OH-DPAT, plasma levels of oxytocin w ere significantly increased. 8-OH-DPAT also increased insulin and decr eased CCK and somatostatin levels, effects that were blocked by pretre atment with the oxytocin antagonist. Taken together, these data sugges t that the effect of 8-OH-DPAT on plasma levels of insulin? somatostat in and CCK may be mediated by oxytocin. In previous experiments, we ha ve shown that following i.c.v. application of oxytocin, plasma levels of insulin are increased through a cholinergic mechanism. In this stud y, 2 ng of oxytocin decreased plasma levels of CCK, gastrin and somato statin, effects that were blocked by pretreatment with atropine. Since oxytocinergic fibers which originate in the PVN project to the DMX, w e suggest that the effect on the release of insulin, CCK and somatosta tin induced by the 5 HT1A receptor agonist 8-OH-DPAT may be mediated b y an oxytocinergic activation of a vagal mechanism.