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  • Title: Anterior pituitary sensitivity in immature female rats stimulated with gonadotrophin releasing hormone in vivo: effect of priming with oestrogen, pregnant mare serum gonadotrophin or brain lesion.
    Author: De Ziegler D, Wilkinson M, Cassard D, Ruf KB.
    Journal: J Endocrinol; 1977 Jul; 74(1):99-109. PubMed ID: 327011.
    Abstract:
    Anterior pituitary sensitivity, assessed in terms of increments in plasma luteinizing hormone (LH) and follicle stimulating hormone (FSH) concentrations to stimulation with 1 or 2 injections of gonadotrophin releasing hormone (GnRH) was investigated in 26-day-old immature female rats which had received 1 of the following priming treatments: 1) 10 mcg estradiol benzoate (EB) as a single injection on Day 23 or Day 25 or on both days, 2) 10 IU pregnant mare serum gonadotrophin (PMSG) on Day 24, 3) an electrochemical brain lesion placed in the mediobasal hypothalamus on Day 23, or 4) control animals received either vehicle alone or a sham lesion. Pituitary sensitivity assessed at 1000 hours on Day 26 after 1 or 2 injections of GnRH was enhanced to a similar degree in the 3 groups treated with EB in terms of LH (p .01). FSH increased somewhat after EB treatment. In contrast, 48 hours after the injection of PMSG pituitary sensitivity, in terms of both LH and FSH, dropped sharply (p .001). Sensitivity to 1 injection of GnRH was unchanged in lesioned rats. However, a 2nd GnRH injection administered after an hour interval induced a slightly larger LH response in control animals. In another study, rats treated with EB on Day 23 and with 1 mg progesterone at 1200 hours on Day 26, pituitary sensitivity increased at both 1400 and 1700 hours as compared with that in the Day 23 EB-treated group at 1000 hours. PMSG-treated rats maintained their state of decreased responsiveness at 1400 hours, but exhibited increased sensitivity at the time of the gonadotropin surge (1700 hours).
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