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Oxytocin concentrations increased during pregnancy and during medication with low-dose oral contraceptives (o.c.). Postprandial somatostatin concentrations were lower during medication with o.c. Insulin concentrations were elevated during pregnancy with the same tendency during medication with o.c. Gastrin levels were unaffected during the peripartal period and during medication with o.c. Women who were breastfeeders at 3 months after delivery had higher concentrations of oxytocin and lower somatostatin concentrations post-prandially during pregnancy and fasting at 3 months after delivery compared with non-breastfeeders at 3 months after delivery. Metabolic and behavioral implications are discussed.

The aim of the present study was to investigate whether low-dose oral contraceptives affect oxytocin concentrations in plasma. Twenty women participated in an open cross-over study. Six consecutive blood samples were drawn twice, with a 4-week interval, in the luteal phase of the menstrual cycle when the women were/were not taking oral contraceptives. Plasma levels of oxytocin were analysed with a radio-immunoassay specific for oxytocin. A significant increase in oxytocin concentrations was observed following ingestion of oral contraceptives (p less than 0.02). Women with the highest oxytocin levels during a normal menstrual cycle increased their levels the most when on oral contraceptives. Analysis with high performance liquid chromatography demonstrated that immunoreactive oxytocin found in plasma, whether with or without oral contraceptives, co-eluted with synthetic oxytocin standard. An interesting possibility could be that the mental side effects and effects on glucose metabolism occurring after treatment with oral contraceptives might be related to elevated oxytocin levels, since metabolic and CNS effects of oxytocin are known.