When did leptin become a reproductive hormone?

Almost 50 years ago the obese mouse model was identified, and parabiosis studies were able to demonstrate that some humoral factor was involved in adiposity, so that the genetics and endocrine nature of this process have been apparent for many years. With the discovery of leptin just a few years ago, early studies validated the role of this protein product of the obese gene. Early studies in the obese mouse model ( ob/ob mouse) demonstrated that the genetic basis was truly a deficiency in leptin. Coincidentally, the relationship to fertility was also associated with leptin. These early studies were also able to demonstrate a relationship to puberty and the time of pubertal development. Very quickly, the recognition that the placenta was a source of leptin and that leptin levels were elevated in pregnancy in a number of species also broadened our appreciation of the relationship to reproductive functions. These many rapidly elucidated relationships to leptin were reported soon after the identification and availability of leptin as a research reagent and have firmly put leptin into the area of reproductive physiology in addition to establishing roles in metabolism, satiety, and energy metabolism. Subsequent studies have expanded all of these situations. Species beyond the rodent model, including the human, have now introduced these physiologic studies into the clinical arena and the role of leptin in fertility, puberty, pregnancy, and genetics. In this issue, all of these topics are reviewed to bring the reader up to date with leptin and its role in reproductive function, many of which overlap with the control of obesity.