Immunoreactive Forms of Luteinizing Hormone-Releasing Hormone in the Brains of Aging Rats Exhibiting Persistent Vaginal Estrus

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Abstract
The luteinizing hormone-releasing hormone (LHRH) system in middle-aged female rats exhibiting persistent vaginal estrus (PVE) was examined using immunocytochemical (ICC) techniques. Three LHRH antisera (A-R419, A-R744, A-R422; generously supplied by Dr. A. Arimura) directed toward different portions of the LHRH molecule were utilized to compare the immunoreactive molecular moieties of this hypothalamic peptide present in neurons of aging and young female rats. The immunoreactive forms of the decapeptide detected within neurons of young cycling animals were present within the same regions of the LHRH neurons of PVE females. Immunoreactive LHRH perikarya and fibers in the middle-aged anovulatory females did not differ in their distribution in the basal forebrain from those of young cycling females. Furthermore, no gross morphological differences were apparent at the light microscopic level in LHRH neurons from young and aging females. Of particular importance was the apparent presence of the physiologically active form of the mature decapeptide in terminal regions of the median eminence. These data lead us to propose that failure to release adequate amounts of LHRH from neurovascular terminals and not the lack of availability of this hypothalamic decapeptide contributes to reproductive decline in aging female rats.