Effects of Estradiol-Induced Lesions of the Arcuate Nucleus on Gonadotropin Release in Response to Preoptic Stimulation in the Rat

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Abstract
Female Wistar rats treated with a single s.c. injection of 2 mg estradiol valerate (EV) develop gradually progressive, multifocal lesions of the arcuate nucleus. They also exhibit persistent vaginal estrus and endocrine profiles characteristic of animals sustaining anterior hypothalamic deafferentiation. In this study, EV-treated females with the arcuate lesions released significantly less LH [lutropin] 1 h following electrochemical stimulation of the medial preoptic area (MPOA) than did normally cycling controls in proestrus. FSH [follitropin] release in response to MPOA stimulation was the same for both groups. As plasma LH concentrations were not significantly different between EV-treated and control animals 1 h after the injection of a potent LHRH [luliberin] analog, the reduced LH response to MPOA stimulation appears to reflect a primarily hypothalamic defect. However, the EV treatment also affected pituitary responsiveness to long-term stimulation as evidenced by reduced LH responses to the LHRH analog after 2 and 3 h. No such differences were seen in the FSH response.