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    Melatonin and ghrelin differentially modulate plasma oxytocin level and noradrenalin release in hypothalamic paraventricular nucleus in female rats
    (2010) Özcan, Mete; Alçin, Ergül; Aydın, Mehmet; Kutlu, Selim; Bakoş, Jan; Jezova, Daniela; Yılmaz, Bayram
    Oxytocin secretion, playing key role in parturition and lactation process, is regulated by neuroendocrine mechanisms. Cholecystokinin (CCK)-induced noradrenalin release in hypothalamus stimulates oxytocin secretion to the circulation. The effect of melatonin and ghrelin hormones on noradrenalin concentration in hypothalamic paraventricular nucleus (PVN) and oxytocin level in plasma were assessed in this study. Anaesthetized virgin female Wistar rats were set at a sterotaxic frame after carotid artery cannulation. Melatonin vehicle to the vehicle group, intra-arterial CCK to the CCK group and CCK plus melatonin intracerebroventricularly injected to the melatonin group. In the other procedures, artificial cerebrospinal fluid (control group) and ghrelin were intracerebroventricularly injected. Microdialysis was performed into PVN in all animals and noradrenalin concentrations were analyzed by high performance liquid chromatography obtained from dialyzed in 20 min periods for four time. Blood samples were obtained via intra-arterial cannula for same intervals with microdialysis samples and plasma oxytocin levels were analyzed with radioimmunoassay. One-Way ANOVA was used for statistical evaluations. Noradrenalin concentration in PVN and oxytocin level in plasma increased in the second period in CCK group compared to vehicle group (p<0.001 and p<0.05, respectively). Noradrenalin and oxytocin values decreased compared to CCK group in the second period. Plasma oxytocin level was significantly high in the 4th period in ghrelin group compared to control (p<0.05) while noradrenalin concentrations in PVN did not change. The results of present study were brought into light that melatonin have inhibitory effect on CCK-induced oxytocin secretion to the circulation in virgin female rats. Melatonin also inhibits noradrenalin release in PVN. As for ghrelin, this hormone stimulates plasma oxytocin secretion without affecting noradrenalin release in PVN. These results reveal that melatonin and ghrelin have different modulatory effects on oxytocin secretion.