SUN-483 High-Fat Diet Suppresses Basal Lh Pulsatile Levels in Female Mice at Estrus

Abstract

Pubertal timing and reproductive maturation in females are known to be susceptible to obesogenic diets. Metabolic energy balance and reproduction are homeostatic processes that are tightly regulated, in part, by hypothalamic neurons in the arcuate nucleus (ARC) and high-fat diet is reported to steadily increase estradiol levels in rodents compared to standard chow. Estradiol regulates the hypothalamic-pituitary-gonadal axis via negative feedback mechanisms in estrogen-sensitive ARC neurons by modulating the pulsatile release of the gonadotropin luteinizing hormone (LH). However, it is unclear how exactly the circulating estradiol milieu of adult females interacts with a state of high caloric fat intake to alter the parameters of LH release, such as pulse frequency, pulse amplitude, and basal set points of pulsatile release. The objective of this study was to use a non-invasive method of measuring pulsatile LH release patterns at different stages of the estrous cycle in mice fed a high-fat diet, using an ultrasensitive mouse LH assay (1). Starting at weaning age (21 days old), female C57BL/6J mice were fed ad libitum with either regular chow diet (RD) or 60% kcal high-fat diet (HFD), and free access to water. After 12 weeks on either RD or HFD, estrous cyclicity was determined via examination of vaginal cytological smears. Blood samples were collected when mice were at diestrus, followed by one full estrous cycle, and then collected again at estrus. To examine LH pulsatile release during both estrous cycle stages, mice had tail tips snipped and whole blood samples were collected and immediately frozen in assay buffer at 10-second intervals for 3 hours (between 0900 and 1200 hours). Pulsatile LH release was analyzed for pulse frequency, basal mean LH levels, and pulse amplitude using the DynPeak algorithm program. Compared to RD controls, mice fed a HFD displayed significantly lower basal LH levels during estrus, but not diestrus. However, there were no differences in pulse amplitude between HFD and RD fed mice. Mice on HFD (at both diestrus and estrus) also showed a trend towards increased pulse frequency. These results suggest that endogenous circulating estradiol influences the impact that HFD has on regular pulsatile release of LH by changing the set point for basal LH levels, thereby modulating when obesogenic diet-induced changes may be most detrimental. This has implications on how diet may put women at risk of failing reproductive health when ovarian estradiol levels drastically change, for example during menopause or with hormone replacement therapy. 1) Steyn FJ et al. Development of a methodology for and assessment of pulsatile luteinizing hormone secretion in juvenile and adult male mice. Endocrinology 2013;154(12):4939-4945. doi:10.1210/en.2013-1502.