We recently found that continuous intravenous injection of Oxytocin decreases plasma ghrelin concentrations in healthy men (own recent and not yet published data). It is thought that increased circulating Prolactin stimulates appetite in lactating women, but there are no data on the effects of Prolactin on appetite-modulating gut hormones (Grattan). With the proposed study we aim to check the relevance of these findings in normal physiology and to study the breastfeeding-induced changes in circulating ghrelin and PYY concentrations in lactating mothers.