CYTOSOLIC ESTROGEN-RECEPTOR CONCENTRATIONS IN THE LUMBOSACRAL SPINAL-CORD FLUCTUATE DURING THE ESTROUS-CYCLE

Estrogen responsive neurons have been anatomically identified with aut oradiographic and immunohistochemical techniques and their distributio n mapped in the lumbosacral spinal cord of female rats. Such neurons c ontain estrogen receptors (ERs). The present study was undertaken to: 1) quantify cytosolic estrogen receptor (ER) concentrations in the lum bosacral spinal cord and 2) determine if there is a relationship betwe en cytosolic ER concentrations and fluctuations in serum estradiol (SE 2) levels during the estrous cycle. Lumbosacral spinal segments were r emoved from intact cycling rats during the morning of proestrus, the a fternoon of proestrus, and the morning of estrus, metestrus and diestr us. Trunk blood was collected at euthanasia and SE2 levels were determ ined using radioimmunoassay. Cytosolic ER concentrations were measured using a dextran-charcoal coated tube method. Concentrations of cytoso lic ERs were low during estrus and metestrus, increased during diestru s with maximum concentrations during the afternoon of proestrus. These changes in ER concentrations paralleled SE2 levels measured in intact cycling animals; i.e., during estrus SE2 levels were low, but began t o rise during metestrus, diestrus, and during the morning of proestrus with a maximum peak increase during the afternoon of proestrus. These data indicate there are fluctuations of cytosolic ER concentrations d uring the estrous cycle and that these changes coincide with changing SE2 concentrations suggesting that ER content is influenced by SE2.