Hypothalamic Luteinizing Hormone (LH): Characteristics and Response to Hypophysectomy

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Abstract
This study describes the finding of an immunoassayable and bioassayable luteinizing hormone (LH) in the rat hypothalamus. Validation of the immunoassay for LH in hypothalamic extracts is presented. Chromatographic patterns of hypothalamic LH were found to be identical with those of rat pituitary LH. Radioimmunoassay values of serial dilutions of hypothalamic extract paralleled dilution values of rat pituitary LH. Furthermore, such homogenates promoted release of testosterone from dispersed rat testis cells in vitro. This effect was largely abolished by prior incubation of homogenate with an antiserum to rat LH. Following removal of the anterior pituitary, LH levels in the hypothalamus persist but drop significantly, signifying that this particular brain-based LH is partially dependent on the presence of a functioning pars distalis. Immunoassayable LH measured in other areas of the rodent central nervous system did not change following hypophysectomy.