Decreased availability of metabolic fuels suppresses estrous behavior in Syrian hamsters

The availability of oxidizable metabolic fuels affects reproductive physiology and behaviors in female mammals. In Syrian hamsters, 48 h of food deprivation is sufficient to suppress secretion of gonadotropins and ovarian steroids and to prevent the occurrence of ovulation and estrous behavior. These experiments attempted to determine whether the deprivation-induced suppression of lordosis is entirely due to the disruption of ovarian steroid secretion or whether there are also changes in behavioral responsiveness to estradiol and/or progesterone (P). Estrous behavior was induced in ovariectomized hamsters with sequential injections of 5 micrograms of estradiol benzoate (EB) and 200 micrograms P. Food deprivation for 48 h, either before or just after EB treatment, significantly suppressed the amount of time females spent in lordosis during a 5-min test with a sexually experienced male. Treatment with an inhibitor of glycolysis (2-deoxy-D-glucose) in combination with an inhibitor of fatty acid oxidation (methyl palmoxirate) for 48 h mimicked the effects of food deprivation and suppressed the amount of time spent in lordosis after treatment with EB+P. Given alone, neither metabolic inhibitor had an effect on lordosis. These findings indicate that suppression of hamster estrous behavior by metabolic fuel deprivation is at least in part due to a reduced responsiveness to estradiol and/or progesterone. Furthermore, estrous behavior is responsive to metabolic fuels in general. This is unlike hamster ovulatory cycles, which are primarily responsive to glucose availability.