The reproductive system of the mammal is exquisitely sensitive to the availability of energy (food) in the external environment. Acute changes in an animal’s energetic status can result in modulation of the hypothalamic-pituitary-gonadal (HPG) axis. Suppression of pulsatile LH secretion has been documented after fasting or food restriction in myriad species, including rats, mice, hamsters, sheep, monkeys, and humans. In addition to its effects on reproductive hormonal profiles in adulthood, food restriction can delay the timing of pubertal onset and directly affect reproductive behavior. proventil inhaler
The caloric challenge resulting from intense exercise has also been shown to inhibit reproductive function in rats and humans, as do pharmacological manipulations that block either glucose mobilization (with insulin) or utilization (with 2-deoxyglucose). Pulsatile LH secretion in fasted animals can be normalized in hours to minutes with refeeding. Fasting-induced LH suppression is believed, ultimately, to be a consequence of reduced release of GnRH from the ventral forebrain, as fasted animals show LH pulses similar in quantity and magnitude to fed animals when given exogenous GnRH.