SUN-239 Effects of High-Fat Diet-Induced Obesity on Pulsatile LH Secretion and Hypothalamic KISS1 Expression in Female Rats

Female obesity is associated with menstrual dysfunction leading to anovulation and infertility. It has recently been reported obesity-induced infertility is involved in the dysfunction of a kisspeptin neuron, a key player in reproduction via direct stimulation of gonadotropin releasing hormone (GnRH) and subsequent gonadotropin release in mammalian species. Previous studies reported that obesity due to high-fat diet (HFD) for 8 months induced a disruption in estrous cyclicity, caused by a decrease in Kiss1 (coding kisspeptin) expression in the hypothalamic arcuate nucleus (ARC) in female rodents. Here we showed the effects of shorter-term (4 months) HFD on pulsatile LH secretion and hypothalamic Kiss1 expression to show pathogenic mechanism underlying obesity-induced infertility. Female Wistar-Imamichi strain rats (7 weeks old) fed on either a standard diet (10% calories from fat) or a high-fat diet (45% calories from fat) for 4 months. Estrous cyclicity and body weight were monitored regularly. All animals were implanted with a jugular catheter and collected blood samples to analyze pulsatile LH secretion, after a week of the ovariectomy with low-dose replacement estradiol to negate influence of changes in ovarian steroid levels and mimic diestrous levels of plasma estrogen. On the next day of the blood sampling, rats were perfused with 0.05 M PBS followed by 4% paraformaldehyde and their brains were collected for in situ hybridization of Kiss1 and Gnrh1. The HFD-fed rats showed progressive increases in body weight, along with hyperphagia and adipose tissue accumulation, compared with control animals. Fifty-eight percent of the HFD-fed rats exhibited irregular estrous cycles, whereas remaining HFD-fed rats showed regular cycles. Two out of 7 rats showing HFD-induced irregular estrous cycles exhibited profound suppression of the LH pulse frequency and the number of Kiss1-expressing cells in the ARC, whereas remaining HFD-fed rats showed normal LH pulses and ARC Kiss1 expressions. The number of Kiss1-expressing cells in the ARC had close positive correlation with LH pulse frequency (R2=0.6872, P<0.001) in both groups. Additionally, the number of Kiss1- or Gnrh1-expressing cells in the anteroventral periventricular nucleus or the preoptic area, were comparable between groups. Taken together, our finding reveals the possibility that irregular menstruation was also induced by changes in the kisspeptin-GnRH independent pathway during the incipient stage of obese infertility.