Feuermann, Y., Institute of Animal Science, Agricultural Research Organization, Volcani Center, P.O. Box 6, Bet Dagan 50250, Israel, Department of Animal Science, Fac. Agric., Food Environ. Qual. S., Hebrew University of Jerusalem, P.O. Box 12, Rehovot 76100, Israel
Mabjeesh, S.J., Department of Animal Science, Fac. Agric., Food Environ. Qual. S., Hebrew University of Jerusalem, P.O. Box 12, Rehovot 76100, Israel
Shamay, A., Institute of Animal Science, Agricultural Research Organization, Volcani Center, P.O. Box 6, Bet Dagan 50250, Israel

Leptin, a protein hormone produced and secreted predominantly by white adipose tissue, has a critical role in the regulation and coordination of energy metabolism. Identification of leptin in the milk of several mammals, including humans, led us to investigate its presence and regulatory effect in the cow mammary gland. The expression of leptin receptor in tissue culture of lactating mammary gland was augmented approximately 25 times by prolactin, but had no effect on virgin calf mammary tissue. Expression of leptin in tissue culture from mammary glands of lactating cows was enhanced 2.2-fold by prolactin. No effect of prolactin on leptin and leptin receptor expression was found in mammary gland tissue culture from calves. Leptin-enhanced fatty acid synthesis in the presence of prolactin, but had no effect without presence of prolactin. A similar pattern was found in the expression of α-casein and β-lactoglobulin in mammary gland explants from a lactating cow. Our findings indicate that leptin plays an important role in mammary gland lactogenesis, and that the expression of leptin requires the presence of prolactin.