Expression of leptin and its receptors in various tissues of ruminants.

The energy metabolism of domestic animals is under the control of hormonal factors, which include thyroid hormones and leptin. Leptin signals from the periphery to the centre. It is mostly produced in the white adipose tissue and informs the central nervous system (CNS) about the total fat depot of the body. Low and high levels of leptin induce anabolic and catabolic processes, respectively. Besides controlling the food uptake and energy expenditure leptin is also involved in regulation of the reproduction and the immune system. Leptin is produced in several tissues other than fat. In the present paper the leptin expression of ruminant (Egyptian water buffalo, cow, and one-humped camel) tissues are examined. The mammary gland produces leptin in each species investigated. The local hormone production contributes to milk leptin and most probably helps to maintain lactation. Considerable leptin receptor expression was observed in the milk-producing epithelial cells, which is the same cell type that produces most of the udder leptin. Based on the results tissues participating in production have an autoregulative mechanism through which tissues can be relatively independent of the plasma leptin levels in order to maintain the desired function.