Serotonin binding sites during proestrus and following estradiol treatment

The binding of 3H-5-HT to hypothalamic, hippocampal and striatal membranes from female rats was examined. During the day of proestrus, there was a significant increase in binding from morning to evening. The increase reflected changes in both Kc and Bmax. Effects of estradiol were examined in ovariectomized rats, and changes in 3H-5-HT binding resulted from an increase in the Kd after estradiol treatment. These in vivo effects of estradiol were not seen when tissue was incubated in vitro with estradiol. However, the compound, polyvinylpyrrolidone, used in the in vitro incubation significantly increased the Kd for binding to 3H-5-HT and estradiol attenuated the increase. The potential significance of these changes to serotonin's modulation of reproductive function is discussed.