Loss of hypothalamic nuclear-bound XXXX receptors: factors involved and the relationship to heat termination in female @entity840 .

@entity1420 @entity840 @entity53 @entity1871 @entity1515
The hypothesis that the termination of sexual receptivity (heat) in female @entity840 results from loss of @entity1871 receptors from hypothalamic cell nuclei was tested. First, we attempted to find an optimal dose of @entity1420 that would result in a prolonged period of sexual receptivity. Ovariectomized @entity840 were implanted with 10% @entity53 capsules. Forty hours later, each received one of several sized @entity1420 capsules before being tested hourly for @entity1515 . Surprisingly, none of the @entity1420 doses resulted in delayed heat termination. In order to determine whether elevated levels of @entity53 and @entity1420 maintain elevated levels of nuclear @entity1871 receptors despite the lack of effect on heat duration, animals were treated as described above except that only one size @entity1420 capsule (3.0 cm) or an empty capsule was implanted. Despite elevated serum @entity1420 concentrations, nuclear @entity1871 receptor levels decreased gradually and approached control levels at about the same time as heat termination had occurred in similarly-treated animals. Cytosol @entity1871 receptor levels decreased following @entity1420 treatment and remained lowered at all times measured. In order to further investigate the relationship between blood @entity1420 concentrations and retention of nuclear @entity1871 receptors we decreased blood @entity1420 concentrations by removing @entity1420 capsules 2 h following insertion. Nuclear @entity1871 receptor levels declined gradually concurrent with a decline in serum @entity1420 levels in animals exposed to @entity1420 capsules for only 2 h. In animals exposed to capsules continuously, nuclear @entity1871 receptor levels again decreased but at a slightly slower rate. In order to test the effect of @entity1420 capsule removal on female sexual behavior, ovariectomized @entity840 were treated as described and tested hourly for @entity1515 . Fewer animals in the group exposed to @entity1420 capsules for 2 h became sexually receptive as compared to animals continuously-exposed to @entity1420 capsules. Of those animals that did respond, heat termination had occurred by the same time that nuclear @entity1871 receptor levels had returned to control levels in similarly-treated animals. These experiments support the hypothesis that heat termination results from the loss of @entity1871 receptors from hypothalamic cell nuclei. In addition, they demonstrate that circulating @entity1420 levels play a role in regulating nuclear @entity1871 receptor retention.
