Metabolic control of food intake and estrous cycles in Syrian hamsters. I. Plasma insulin and leptin

Abstract

The "adipostat hypothesis" refers to the idea that circulating hormone concentrations reflect levels of body adiposity and act as signals to control food intake and reproduction. Implicit in the adipostatic hypothesis are the following two assumptions: 1) plasma levels of adipostatic hormones accurately reflect body fat content and 2) decreased plasma concentrations of adipostatic hormones necessarily result in increased food intake and inhibited reproductive processes. The present experiments are designed to test these assumptions. Fat and lean Syrian hamsters were either fasted for 12, 24, 36, or 48 h or allowed ad libitum access to food. Contrary to the first assumption, plasma leptin and insulin levels in fat hamsters dropped dramatically by 12 h after the start of a fast, with no significant change in body fat content and no postfast hyperphagia. Lean hamsters showed anestrus after a 48-h fast but not after a 24-h fast. Contrary to the second assumption of the lipostatic hypothesis, lean hamsters fasted for 24 h and then refed for the next 24 h had leptin levels that were not significantly elevated compared with those of 48-h-fasted hamsters. Thus, in adult female Syrian hamsters, plasma leptin concentrations do not accurately reflect body fat content under all conditions; normal estrous cyclicity does not necessarily require plasma leptin concentrations higher than those of fasted hamsters; and decreased plasma leptin levels do not result in increased food intake.

Suppression of kisspeptin expression and gonadotropic axis sensitivity following exposure to inhibitory day lengths in female Siberian hamsters

“…The Arc monitors current energy state and relays this information to the reproductive axis (Smith and Grove, 2002). In times of reduced energy availability, reproduction is inhibited (Bartness, 1996;Schneider et al, 2000). In addition to mediating the reproductive axis through energetic signaling, estrogen-receptor-positive Arc projections also act on GnRH terminals in the median eminence to modulate their output (Lehman, 1997).…”

Non-invasive measurement of fecal estrogens in the spotted hyena (Crocuta crocuta)

“…Knowledge about a female's reproductive state is essential to understanding aspects of her basic biology, including her fertility, behavior (Altmann et al, 2004;Maestripieri, 1999;Ramirez et al, 2004;Wise, 1974), nutritional requirements (Lambert et al, 2005;Schneider et al, 2000), and immune function (Gu et al, 2005;Hernandez-Gonzalez et al, 2006). Despite the importance of understanding reproductive cycles in females, there are many species for which we know virtually nothing about variation in reproductive status, particularly within free-living populations of large predatory mammals.…”

Pituitary Leptin-A Paracrine Regulator of Gonadotropes: A Review

“…The rise in serum leptin that is seen at midcycle is too slow for it to be a regulator of the LH surge [93]. Furthermore, Schneider et al report that nutrition alone can restore LH pulses lost by fasting [14,15]. The timing of this response did not match that for the restoration of adipocyte leptin [50,94,95].…”

“…This could relate to its role in facilitating the utilization of nutrients, like glucose and free fatty acids [14][15][16][17][18]121]. It may also play a role in maintaining gonadotropes, or it may regulate placental or gonadal functions.…”

“…However, the widespread distribution of leptin receptors throughout the body has suggested that this cytokine performs additional functions [13]. Schneider et al [14][15][16][17][18] have reviewed leptin's effects on fuel utilization, showing that leptin works with insulin to facilitate the use of glucose and free fatty acids.…”