Effects of exercise on energy-regulating hormones and appetite in men and women.

When previously sedentary men and women follow exercise training programs with ad libitum feeding, men lose body fat, but women do not. The purpose of this study was to evaluate whether this observation could be related to sex differences in the way energy-regulating hormones and appetite perception respond to exercise. Eighteen (9 men, 9 women) overweight/obese individuals completed four bouts of exercise with energy added to the baseline diet to maintain energy balance (BAL), and four bouts without energy added to induce energy deficit (DEF).

Animal models in the study of nutritional infertility.

Purpose Of Review: To summarize the physiological bases of infertility during undernutrition.

Recent Findings: When energy expenditure consistently exceeds intake, survival receives temporary priority over fertility, and reproduction is deferred until conditions are more favorable. This nutritional infertility is due to inhibition of both gonadotropin-releasing hormone secretion and copulatory behaviors.

Corticotropin-releasing factor receptor subtypes mediating nutritional suppression of estrous behavior in Syrian hamsters.

Caloric deprivation inhibits reproduction, including copulatory behaviors, in female mammals. Decreases in metabolic fuel availability are detected in the hindbrain, and this information is relayed to the forebrain circuits controlling estrous behavior by neuropeptide Y (NPY) projections. In the forebrain, the nutritional inhibition of estrous behavior appears to be mediated by corticotropin-releasing factor (CRF) or urocortin-signaling systems.

Neuroendocrinology of nutritional infertility.

Natural selection has linked the physiological controls of energy balance and fertility such that reproduction is deferred during lean times, particularly in female mammals. In this way, an energetically costly process is confined to periods when sufficient food is available to support pregnancy and lactation. Even in the face of abundance, nutritional infertility ensues if energy intake fails to keep pace with expenditure.

Metabolic fuels, neuropeptide Y, and estrous behavior in Syrian hamsters.

Of the various environmental factors influencing reproduction, food availability plays a particularly significant role, and an insufficient supply of oxidizable metabolic fuels inhibits reproduction in female mammals. When ovariectomized, steroid-primed hamsters are food deprived for 48 h, estrous behavior is suppressed. However, the specific neuroendocrine alterations that mediate the suppression of estrous behavior are unknown.

Lessons from experimental disruption of estrous cycles and behaviors.

In female mammals reproduction is highly sensitive to the food supply. During lean times, females suspend reproductive attempts in favor of maintaining processes necessary for survival; fertility is restored once the food supply is again abundant. Nearly all aspects of reproduction are affected, including puberty, adult ovulatory cycles, and reproductive behaviors.

Forebrain sites of NPY action on estrous behavior in Syrian hamsters.

Food deprivation and similar metabolic challenges inhibit estrous behavior in female Syrian hamsters. The relevant metabolic cues appear to be detected in the hindbrain, and this information is then relayed synaptically to the forebrain circuits controlling estrous behavior. Neuropeptide Y (NPY) may be one of the neuropeptides/neurotransmitters serving this function.

Acute fasting decreases sexual receptivity and neural estrogen receptor-alpha in female rats.

Acute food deprivation or chronic food restriction suppresses reproduction in female mammals. Although a link between undernutrition and ovarian function is well established in rats, a similar link with reproductive behavior in this species is yet to be described. Therefore, we compared the display of estrous behaviors induced by exogenous steroid hormone treatment in ovariectomized fed and fasted rats.

Disinhibition of female sexual behavior by a CRH receptor antagonist in Syrian hamsters.

Several conditions that inhibit female sexual behavior are thought to be associated with altered corticotropin-releasing hormone (CRH) activity in the brain. The present experiments examined the hypothesis that endogenous CRH receptor signaling mediates the inhibition of estrous behavior by undernutrition and in other instances of sexual dysfunction. Intracerebroventricular (ICV) infusion of CRH or urocortin inhibited estrous behavior in ovariectomized steroid-primed hamsters.

Food deprivation inhibits estrous behavior in hormone-treated Syrian hamsters despite elevated estradiol levels.

Estradiol and progesterone (P) induce female mammalian reproductive behaviors, which are, in turn, sensitive to food availability. When ovariectomized, steroid-primed hamsters are food deprived for 48 h, estrous behavior is suppressed. While this suppression of estrous behavior may be due to alterations in neural steroid receptor levels, it is also possible that decreased levels of circulating estradiol could be involved in mediating this suppression.