Effects of long- and short-term gonadectomy on the hypothalamo-hypophysial (LH-releasing hormone-LH) system in oestrogen-treated male and female rats.
Considerable differences have previously been found in the hypothalamo-hypophysial responsiveness to oestrogen, depending upon the time between gonad removal and exposure to oestrogen. In the present study a detailed analysis was made of some of the differences which may exist in pituitary LH-releasing hormone (LHRH) receptors and the amount of LH released in response to electrochemical depolarization of the medial preoptic area after 2 or 7 days of oestradiol treatment of long- and short-term gonadectomized male and female rats. The pituitary glands of long-term gonadectomized males and females secreted more LH in response to two pulse injections of LHRH than did short-term gonadectomized rats. The amount of LH released on day 2, however, was equivalent to that secreted after 7 days of oestradiol treatment. Moreover, long-term gonadectomized males and females had equivalent LHRH receptor concentrations, which were greater than those of short-term gonadectomized animals. Peak serum LH concentrations observed after preoptic stimulation were equivalent in short- and long-term castrated rats after 2 days of oestrogen exposure. Serum LH concentrations following preoptic stimulation in short-term gonadectomized males and females were significantly greater on day 7 than on day 2 of oestradiol treatment, whereas in long-term gonadectomized animals the stimulated release of LH was equivalent both in magnitude and time of peak release on both days.(ABSTRACT TRUNCATED AT 250 WORDS)
D000818:Animals; D004558:Electric Stimulation; D004958:Estradiol / Q000494:pharmacology*; D005260:Female; D007987:Gonadotropin-Releasing Hormone / Q000494:pharmacology; D007030:Hypothalamo-Hypophyseal System / Q000502:physiology*; D007986:Luteinizing Hormone / Q000378:metabolism; D008297:Male; D009919:Orchiectomy; D010052:Ovariectomy; D010902:Pituitary Gland / Q000187:drug effects / Q000378:metabolism; D011301:Preoptic Area / Q000502:physiology; D051381:Rats; D011919:Rats, Inbred Strains; D013997:Time Factors
D007987:Gonadotropin-Releasing Hormone; D004958:Estradiol; D007986:Luteinizing Hormone