Leptin is a hormone that is produced in fat cells and functions to regulate body weight and eating. It was the first hormone discovered within fat cells and is part of the class of hormones now known as adipokines (hormones produced in the fat). Other hormones made in fat cells include adiponectin and resistin. In the mid-1950s, a mouse was discovered at Jackson Laboratories that ate a large amount of food and performed very little physical activity and became very obese. The gene required for the mouse to become obese was known as the ob gene. Mice that had two ob genes were the only mice to become obese and subsequently these animals were named the ob/ob mice. Leptin was discovered in the mid-1990s as the hormone that was responsible for the obesity observed in the ob/ob mouse. The word leptin comes from the Greek word lepthos, which means thin.

Leptin was originally hypothesized to regulate how much food a person eats and how much physical activity he or she performs. The ob/ob mouse was very obese and had no leptin in its body. Once these leptindeicient mice were given an infusion of leptin, they stopped eating and lost their extra body weight. It was later determined that when a normal mouse (not the ob/ob mouse) had a large amount of adipose tissue (fat cells), then it would have high levels of leptin. When leptin levels are high, the animals' appetite would decrease (they would eat less food), and the amount of physical activity they use would increase (they would move more in their cages). Alternatively, when leptin levels are low (in a thin animal), the animals' appetite would increase (they would eat more food) and the amount of physical activity they use would decrease (they would move less in their cages).

Leptin is believed to travel from fat cells to the brain. A leptin receptor is located on the brain which helps move leptin across the blood-brain barrier. Once in the brain, leptin is able to regulate if a person is hungry or if he or she satiated. Leptin works in the hypothalamus region of the brain and affects neuropeptide Y pathway, agouti related protein (AGRP) pathway, and the pro-opiomelanocortin (POMC) pathway as well as other pathways. Originally, leptin was believed to only be produced in fat cells, but small amounts of leptin are produced in other tissues as well such as the stomach, intestines, and the brain.

Once leptin was discovered in 1994, it was hypothesized that people who were overweight or obese must have had very low levels of this hormone and that is why people who are overweight or obese eat so much. Many biotechnology and pharmaceutical companies were interested in making a synthetic leptin as a treatment to control body weight. However, the opposite hypothesis was observed. People who were obese or overweight had more leptin than people who were thin. It was then proposed that overweight and obese people might be leptin resistant, that is their tissues were no longer responsive to the actions of leptin. Another proposed hypothesis was that leptin primarily works when people do not eat. When a person does not eat a sufficient amount of food, they may enter a starvation-like state. During these starvation conditions, the leptin begins to work and tells the body that it needs to eat.

Leptin deficiencies in humans, like the ones observed in the ob/ob mice, are very rare. There have been a few documented medical cases of members from the same family displaying similar symptoms that the ob/ob mice displayed. The children with the deficiency would eat large portions of food and do very little exercise. They were extremely obese. Treating these leptin-deficient patients with synthetic leptin alleviated all of their symptoms. These patients would have a reduction in body weight and normalization in the amount of food they ate and the amount of physical activity in which they engaged.

Additional studies were performed on the relatives of the children who were leptin deficient. These relatives were heterozygous for the leptin gene (i.e., missing some of the genetic information to make leptin). They had a lower amount of leptin levels compared to individuals with similar amount of body weight and body fat. When these individuals were given synthetic leptin as a treatment, they also had a reduction in the amount of food they ate, increase in physical activity, a decrease in body weight and decrease in body fat percentage. Overweight and obese subjects who were given very large doses of leptin had very little to modest effect in regard to changes in eating, physical activity, body weight, and body fat.

In addition to eating and physical activity, leptin has the ability to affect and/or regulate many other systems in the body. Leptin-deficient mice are often sterile. This is because leptin deficiencies may affect the synthesis of the sex hormones (i.e., testosterone and estrogen). When the leptin-deficient mice were given the synthetic leptin, the infertility disappeared. Leptin plays an essential role in the growth of neurons in the brain.

AMP-activated protein kinase (AMPK) is an essential molecule that is often said to be a master switch of metabolism. When it is turned on, the use of fatty acids in the body is increased and when it is shut of fatty acid utilization decreases. Leptin plays a role in turning of AMPK. Leptin also plays a role in regulating glucose (sugar) and insulin metabolism in the body. Animals that were insulin resistant (prediabetic) and given leptin infusions had a normalization of their blood glucose and became more insulin sensitive. It is believed to affect glucose and insulin metabolism through its effects on the liver.

Since its initial discovery in the mid-1990s, leptin has proven to be a very interesting hormone to study. It is clear that it plays a role in regulating how much food a person may eat and how much energy they will use. Additionally, leptin can influence many other systems in the body and its function continues to be elucidated.

Free term papers are not written to satisfy your specific instructions. You can use our professional writing services to buy a custom written research paper, term paper, or essay on Obesity at affordable price. CustomTermPapers is the best solution for those who seek help in writing term papers, essays, and research papers related to Obesity and other relevant topics.