Leptin's Actions on the Reproductive Axis: Perspectives and Mechanisms

Abstract

Energy availability influences reproductive fitness. The activity of the reproductive axis is sensitive to the adequacy of nutrition and the stores of metabolic reserves. The adipocyte-derived hormone leptin is postulated to reflect the state of nutrition and energy reserves and serve as a metabolic gate to the reproductive system. Genetically obese ob/ob mice (lacking endogenous leptin) are infertile, and treatment of these animals with exogenous leptin stimulates the activity of the reproductive endocrine system and induces fertility in both sexes. Severely food-restricted animals have reduced circulating levels of leptin, which are associated with markedly reduced secretion of the gonadotropins, LH, and FSH. Treatment of food-restricted mice, rats, sheep, and monkeys with exogenous leptin reverses the diet-induced inhibition of gonadotropin secretion. Leptin has also been suggested to have a role in timing the onset of puberty in several species, although evidence that leptin is the primary metabolic signal for initiating the onset of puberty in any species is controversial. Notwithstanding this debate, it is undisputed for all species studied to date that adequate levels of leptin in the circulation are essential (but not sufficient) for pubertal progression and that leptin treatment can reverse the delay in sexual maturation caused by food restriction. Double-label in situ hybridization studies in the brain of the mouse, rat, and monkey have revealed that hypothalamic neurons expressing proopiomelanocortin and neuropeptide Y coexpress the leptin receptor, whereas no evidence has been adduced that GnRH neurons express this receptor. Together, these observations suggest that leptin is a metabolic signal to the neuroendocrine reproductive system and that under conditions of inadequate energy reserves, low leptin levels act as a metabolic ''gate'' to inhibit the activity of the neuroendocrine reproductive axis in both sexes.

Caloric restriction: Impact upon pituitary function and reproduction

“…The primary locus of leptin action upon reproduction is generally considered to be at the level of the hypothalamus (Cheung et al, 2000;Cunningham et al, 1999). In animals with a normal energy balance, i.e.…”

Metabolic changes in early lactation and impaired reproductive performance in dairy cows

“…NPY is known as a potent stimulator of feed intake, but NPY may also be the connection between leptin and the GnRH producing neurons. In addition, the connection between leptin and GnRH may also be fulfilled by pro-opiomelanocortin (POMC) and also direct actions of leptin on GnRH containing neurons have been suggested to explain the effect of leptin on GnRH [21].…”

Effect of Central Antileptin Antibody on the Onset of Female Rat Puberty

“…Importantly, their fertility can be reversed by leptin treatment in both sexes [7, 8]. The ob/ob leptin deficient and db/db leptin resistant mouse models have greatly advance our understanding regarding the pivotal role of leptin in reproduction [9, 10]. Moreover, the ability of leptin to accelerate the onset of puberty in normal female mice has been demonstrated [9].…”