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  • Title: Luteinizing hormone responses to repeated injections of luteinizing hormone releasing hormone in the rat during the oestrous cycle and after ovariectomy with or without oestrogen treatment.
    Author: Higuchi T, Kawakami M.
    Journal: J Endocrinol; 1982 May; 93(2):161-8. PubMed ID: 7045268.
    Abstract:
    In order to characterize the nature of the LH response to exogenous LH releasing hormone (LH-RH) in female rats during the oestrous cycle and after ovariectomy with or without oestrogen treatment, serum LH levels were determined after repeated LH-RH injections (300 ng/kg body wt, six times with 30-min intervals). The LH response to the first LH-RH stimulation was greatest on the days of pro-oestrus and oestrus followed by dioestrus 2 and dioestrus 1. Second and subsequent LH-RH challenges enhanced the LH response only on pro-oestrus and dioestrus 2. Larger doses of LH-RH (3 microgram/kg body wt) induced a small self-priming effect on dioestrus 1 and oestrus. The LH response to the first LH-RH administration increased with time up to 30 days after ovariectomy and then reached a plateau. A small self-priming effect was present in rats ovariectomized for 30 and 60 days, but absent in rats ovariectomized for 5, 10 and 120 days. Oestrogen treatment increased the self-priming effect in rats ovariectomized for 5 days, with little sensitization of the pituitary gland to the first LH-RH injection on the next day. In rats ovariectomized for 120 days, oestrogen treatment enhanced responsiveness to the first and successive LH-RH stimulations on the next day, and further enhancement to the first response only was induced 3 days after oestrogen treatment.
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