LH and Estradiol Secretion after HCG and GNRH Treatments in Gilts
Two different mechanisms have been proposed to regulate luteinizing hormone (LH) secretion patterns: a long-loop feedback of estradiol-17 β (E) from the ovaries (Brinkley, 1981) and(or) a short-loop or internal feedback of pituitary hormones themselves (Motta et al., 1969; Docke and Glaser, 1971). In some species the increase in circulating estrogen to a critical level in late follicular phase elicits a surge release of LH by a positive feedback mechanism (Miyake et al., 1977). Results presented by Concannon et al. (1979) suggested that the preovulatory surge of LH in the female dog may be a response to withdrawal of the negative feedback effect of estrogens. Also, this withdrawal might be facilitated by a preovulatory increase in progesterone. Previous work in our laboratory (Ziecik et al., 1987) demonstrated that 1000 and 1500 IU of hCG blocked the post-synchronization preovulatory LH surge in 33% and 50%, respectively, of gilts previously treated with altrenogest and PMSG. The objective of the following study was to investigate the effect of higher doses of hCG in combination with bolus injections of GnRH on the secretion of E and LH.
KeywordsLuteinizing Hormone Luteinizing Hormone Surge Luteinizing Hormone Release Negative Feedback Effect Late Follicular Phase
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