Leptin, Serum or Plasma

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Leptin, Serum or Plasma
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Overview

Leptin is produced primarily by white adipose (fat) tissue and blood levels correlated with body fat stores. Increased leptin levels stimulate the central nervous system to reduce appetite and increase energy expenditure.  Leptin is thought to play an important role in the body's response to food deprivation or starvation.

 Leptin is produced primarily by white adipose (fat) tissue and blood levels correlated with body fat stores. Increased leptin levels stimulate the central nervous system to reduce appetite and increase energy expenditure.  Leptin is thought to play an important role in the body's response to food deprivation or starvation.

Ongoing research indicates that leptin is also involved in a diverse array of physiologic functions beyond control of food intake and energy expenditure.  A role for leptin has been implicated in the control of angiogenesis, hematopoiesis, immunity and bone formation, and a number of other functions. Leptin is thought to play a role in normal sexual development and in reproduction. Humans and mice with genetic absence of leptin fail to complete puberty and increased leptin levels in mice lead to early puberty.4 Studies also suggest that leptin levels affect fertility in females and may be involved in the development of normal pregnancy. During pregnancy, the placenta produces leptin, and maternal circulating levels during the second and third trimesters are approximately twice the level of the nonpregnant state.

In humans, many instances are seen where leptin dissociates from the strict role of communicating nutritional status between body and brain and no longer correlates with body fat levels:

  • Leptin plays a critical role in the adaptive response to starvation.
  • Leptin level is decreased after short-term fasting (24–72 hours), even when changes in fat mass are not observed.

  • Serum level of leptin is reduced by sleep deprivation.
  • Leptin levels are paradoxically increased in obesity.
  • Leptin level is increased by emotional stress.
  • Leptin level is chronically reduced by physical exercise training.
  • Leptin level is decreased by increases in testosterone levels and increased by increases in estrogen levels.
  • Leptin level is increased by insulin.
  • Leptin release is increased by dexamethasone.
  • In obese patients with obstructive sleep apnea, leptin level is increased, but decreased after the administration of continuous positive airway pressure. In non-obese individuals, however, restful sleep (i.e., 8–12 hours of unbroken sleep) can increase leptin to normal levels.
  • Leptin levels vary exponentially, not linearly, with fat mass.  Leptin levels in blood are higher between midnight and early morning, perhaps suppressing appetite during the night. The diurnal rhythm of blood leptin levels may be modified by meal-timing.