Pituitary Luteinizing Hormone-releasing Hormone Receptors in Ovariectomized Cows after Challenge with Ovarian Steroids
1

Schoenemann, Herman M.; Humphrey, W.D.; Crowder, M. E.; Nett, Terry M.; Reeves, J.J.

doi:10.1095/biolreprod32.3.574

Cited by 61 publications

(52 citation statements)

References 46 publications

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“…In mammals, the hormone that has been examined in the greatest detail with respect to regulation of pituitary sensitivity to GnRH is estradiol, and this steroid was found to increase pituitary responsiveness to GnRH [50]. Moreover, it has been shown to increase mRNA levels of GnRH receptors and their numbers in many species, including sheep [51], cows [52], and several species of laboratory animals [53,54]. However, although this action occurs directly on gonadotrophs, its mechanism of action has yet to be defined [55].…”

Section: Discussionmentioning

confidence: 99%

Sex Steroids Are Involved in the Regulation of Gonadotropin-Releasing Hormone and Dopamine D2 Receptors in Female Tilapia Pituitary1

Levavi‐Sivan¹,

Biran²,

Fireman³

2006

Biology of Reproduction

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Although molecular mechanisms underlying steroid effects on GnRH and dopamine receptors are well documented in mammals, little is known in fish. Herein, we describe the expression of pituitary GnRH and dopamine receptors relative to gonadotropin expression and release. We exposed female tilapia to graded doses of estradiol or 17alpha,20beta-dihydroxy-4-pregnen-3-one (DHP) in vitro, and of estradiol in vivo, and determined mRNA levels of gnrhr1, gnrhr3, drd2, lhb, and fshb by real-time PCR. We also determined gonadotropin levels using specific ELISAs. Exposure to low doses of estradiol caused increased gnrhr3 mRNA levels in vivo and in vitro, probably related to positive feedback on FSH release. Increasing concentrations of estradiol resulted in increased drd2 mRNA levels in vivo and in vitro, inhibition of LH and FSH release, and inhibition of lhb mRNA levels in vivo, possibly related to negative feedback. At high doses of estradiol, FSH release increased in preparation for a new generation of follicles. Exposure to nanomolar doses of DHP resulted in increased drd2 mRNA levels, probably related to negative feedback on LH release. A decrease in drd2 levels at the micromolar range of DHP (concomitant with increased gnrhr3 and fshb mRNA levels) may be related to the recruitment of a new generation of oocytes. Exposure to DHP also resulted in increased lhb mRNA levels toward final oocyte maturation. Salmon GnRH analog (sGnRHa) increased mRNA levels of gnrh1and gnrh3; when combined with DHP, sGnRHa synergistically increased expression of gnrh3 only. These results emphasize the role of sex steroids on positive and negative feedbacks controlling the reproductive cycle.

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Section: Discussionmentioning

confidence: 99%

Sex Steroids Are Involved in the Regulation of Gonadotropin-Releasing Hormone and Dopamine D2 Receptors in Female Tilapia Pituitary1

Levavi‐Sivan¹,

Biran²,

Fireman³

2006

Biology of Reproduction

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“…Along similar lines, a loss of respon siveness to GnRH contributes to termination of the LH surge, since the surge came to a normal end despite the con tinuation of the GnRH signal which had initiated it. The latter finding may be explained, in part, by findings that the number of GnRH receptors in the pituitary declines during the descending phase of the LH surge [9,44,46]. We would submit, therefore, that changes in the pattern of GnRH re lease lead to intracellular changes in the pituitary which alter its responsiveness to the decapeptide [7,37], and so create a demand for a sudden increment in GnRH for development of the preovulatory LH surge.…”

Section: Discussionmentioning

confidence: 99%

Importance of Pituitary and Neural Actions of Estradiol in Induction of the Luteinizing Hormone Surge in the Ewe

et al. 1988

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Two experiments were performed to test the importance of both pituitary and neural sites of action of estradiol in inducing the surge of luteinizing hormone (LH) in the ewe. Both experiments were conducted using an animal model in which pulsatile secretion of gonadotropin-releasing hormone (GnRH) and endogenous secretion of ovarian steroids were eliminated by ovariectomy during seasonal anestrus and treatment with Silastic implants which maintained a luteal-phase level of serum progesterone. The hormonal requirements for the surge were then evaluated by systematic application of GnRH and estradiol signals using pulsatile infusion pumps (for GnRH) and Silastic implants (for estradiol). In experiment 1 the circulating level of estradiol and frequency of GnRH pulses were increased either abruptly or progressively (i.e. mimicking the changes in the estrous cycle between luteolysis and just before the LH surge). Abrupt increments led to an LH surge in all ewes; progressive rises to the same absolute levels did not. However, sudden application of a further large increase in GnRH upon the progressive rise elicited an LH surge in every instance. In experiment 2, a GnRH pulse pattern known to be effective in inducing the LH surge was applied under conditions of differing estradiol concentration: no estradiol, basal estradiol, basal rising to peak estradiol. The GnRH signal elicited high-amplitude surges of LH only in the presence of a peak estradiol concentration. Our findings are consistent with the conclusion that two actions are required for a rise in estradiol to elicit a full-amplitude surge of LH in the ewe: an action on the brain to evoke a sudden increase in GnRH release and an action on the pituitary to maximize its response to GnRH.

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“…In fact, treatment with exogenous progesterone decreased the frequency of LH pulses in ovariectomized ewes (Goodman and Karsch, 1980;Goodman et al, 1982) and postpartum dairy cows (Nation et al, 2000). Nevertheless, data suggest that progesterone does not affect the amount of GnRH receptors in the pituitary gland (Schoenemann et al, 1985) and the negative feedback of progesterone on LH secretion is observed primarily at the level of the hypothalamus (Clarke and Pompolo, 2005), not the pituitary (Lane et al, 2009). Because GnRH neurons do not express progesterone receptors (Herbison et al, 1996;Skinner et al, 2001), the action of progesterone on GnRH secretion is mediated by changes in upstream release of kisspeptin.…”

Section: Low Progesterone Affects Follicle and Embryo Quality And Infmentioning

confidence: 99%

Aspects and mechanisms of low fertility in anovulatory dairy cows

Santos¹,

Wiltbank²,

Ribeiro³

et al. 2016

Anim Reprod

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Postpartum anovulation is a natural process that is observed in most mammals, including women. In lactating dairy cows, the interval from calving to first ovulation typically averages 4 to 5 weeks, but a substantial proportion of cows have not resumed estrous cyclicity by 60 days postpartum. Extended delay in resumption of first postpartum ovulation is known to exert long-lasting detrimental effects on fertility in dairy cows including the lack of spontaneous estrus and subsequent timely insemination postpartum, but when anovular cows have the estrous cycle synchronized for artificial insemination (AI), still pregnancy per AI is reduced and the risk of pregnancy loss increased. Many risk factors exist for extended postpartum anovulatory periods such as negative nutrient balance and diseases, and these risk factors are also known to depress fertility by themselves. A key feature in anovular cows when inseminated is that they develop the ovulatory follicle under subluteal or low concentrations of progesterone. Progesterone from the corpus luteum is pivotal for follicle development, oocyte competence, embryo growth, and endometrial function; however, many of these effects exerted by progesterone are mediated either by secretion of gonadotropins influencing follicular function and oocyte competence or by endometrial histotroph secretion influencing embryo/conceptus growth and developmental biology. Sub-optimal concentrations of progesterone during follicle growth in anovular cows affect morula and early blastocyst quality, alter conceptus gene expression and affect endometrial function increasing the synthesis of prostaglandin F2α . When anovular cows receive sufficient supplemental progesterone during the antral stages of development of the ovulatory follicle, then pregnancy per AI is reestablished and resembled that of estrous cyclic cows that developed the follicle during diestrus. Preliminary data suggest that a minimum concentration of progesterone during follicle growth is needed to optimize fertility in anovular cows, at least 2.0 ng/ml.

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Pituitary Luteinizing Hormone-releasing Hormone Receptors in Ovariectomized Cows after Challenge with Ovarian Steroids 1

Cited by 61 publications

References 46 publications

Sex Steroids Are Involved in the Regulation of Gonadotropin-Releasing Hormone and Dopamine D2 Receptors in Female Tilapia Pituitary1

Sex Steroids Are Involved in the Regulation of Gonadotropin-Releasing Hormone and Dopamine D2 Receptors in Female Tilapia Pituitary1

Importance of Pituitary and Neural Actions of Estradiol in Induction of the Luteinizing Hormone Surge in the Ewe

Aspects and mechanisms of low fertility in anovulatory dairy cows

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