Abstract: This paper reviews data on mammary leptin and leptin receptor gene exp
ression as well as on biood and milk leptin levels during the pregnancylactation cycle in humans,rodents and ruminants with the aim of better understanding milk leptin origin and functions.The few published papers report that leptin may be produced by different cell types in the mammary tissue,and may act as a paracrine factor on mammary epithelial cell proliferation.In addition to leptin synthesis,epithelial cells may transfer leptin from the blood,and these two mechanisms may account for the presence of leptin in the milk.If leptin levels in milkare found to be significant,this hormne could be involved in neonate physiology. 

Key words: milk; leptin; function