ABSTRACT
I. Introduction................................................................................. 221 II The Fasting Rat Model ............................................................... 222
III. A Neural Mechanism Mediating Fasting-Induced Suppression of LH Pulses in Estrogen-Primed OVX Rats ...... 223
IV. Glucoprivic Suppression of LH Pulses in Rats ........................ 224 V. Estrogen Action Sites Mediating Fasting-Induced
Suppression of LH Release ........................................................ 225 VI. Increases in Estrogen Receptor-Containing Cells in the
Brain by Fasting: A Mechanism Explaining the Novel Estrogen Feedback Action .......................................................... 226
VII. A Mechanism by which Fasting or Glucoprivation Induces ER
α
in the Brain ........................................................... 228 VIII. Possible Role of Estrogen Modulating Fasting-or
Glucoprivation-Induced Suppression of LH Secretion ............ 229 IX. Physiological Role of Estrogen Action during Fasting............ 229 X. Acknowledgment ........................................................................ 230
References ............................................................................................. 230
It has been shown that estrogen regulates gonadotropin-releasing hormone (GnRH)/luteinizing hormone (LH) secretion by both positive and negative
feedback action at hypothalamic and pituitary levels. Basal levels of circulating estrogen associated with immature follicles act to suppress GnRH/ LH secretion, whereas the high level of estrogen associated with mature follicles stimulates secretion, eventually leading to the GnRH/LH surge and then ovulation. Thus, the brain receives information regarding follicular development from circulating estrogen levels to maintain GnRH/LH concentrations at an appropriate level and to keep follicular development and the occurrence of ovulation at the right phase of the estrous cycle.
