Leptin is a 16 kDa protein that exerts important effects on the regulation of 
food intake and energy expenditure by interacting with the leptin receptor in 
the brain and in many other tissues. Although leptin is produced mainly by white 
adipose tissue, several laboratories have shown low levels of leptin production 
by a growing number of tissues including the anterior pituitary gland. Many 
studies have implicated leptin in anterior pituitary function including the 
observation that homozygous mutations of the leptin receptor gene led to morbid 
obesity, lack of pubertal development and decreased GH and TSH secretion. In 
addition, leptin functions as a neuroendocrine hormone and regulates many 
metabolic activities. Leptin also interacts with and regulates the 
hypothalamic-pituitary-adrenal, the hypothalamic-pituitary-thyroid and the 
hypothalamic-pituitary-gonadal axes. All of the anterior pituitary cell types 
express the leptin receptor. However, leptin has been localized in specific 
subtypes of anterior pituitary cells indicating cell type-specific production of 
leptin in the anterior pituitary. Subcellular localization of leptin indicates 
co-storage with secretory granules and implicates hypothalamic releasing 
hormones in leptin secretion from anterior pituitary hormone cells. Leptin 
signal transduction in the anterior pituitary has been shown to involve the 
janus protein-tyrosine kinase (JAK)/signal transducer and activation of 
transcription (STAT) as well as suppressor of cytokine signalling (SOCS). These 
proteins are activated by tyrosine-phosphorylation in anterior pituitary cells. 
The various steps in pituitary leptin signal transduction remain to be 
elucidated.