Universidad de Buenos Aires Facultad de Ciencias...
During pregnancy in most mammals, the hypothalamic-hypophyseal-ovarian axis (HHO) is inhibited by the negative feedback of ovarian hormones (E2, Pg, inhibins) on the hypothalamus and pituitary gland. However, the plains vizcacha (Lagostomus maximus) presents continuous recruitment and development of...
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| Formato: | Tesis doctoral acceptedVersion |
| Lenguaje: | Español |
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Universidad de Buenos Aires. Facultad de Ciencias Veterinarias
2023
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| Acceso en línea: | http://repositoriouba.sisbi.uba.ar/gsdl/cgi-bin/library.cgi?a=d&c=avaposgra&cl=CL1&d=HWA_7158 https://repositoriouba.sisbi.uba.ar/gsdl/collect/avaposgra/index/assoc/HWA_7158.dir/7158.PDF |
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| Sumario: | During pregnancy in most mammals, the hypothalamic-hypophyseal-ovarian axis (HHO) is inhibited by the negative feedback of ovarian hormones (E2, Pg, inhibins) on the hypothalamus and pituitary gland. However, the plains vizcacha (Lagostomus maximus) presents continuous recruitment and development of preovulatory follicles throughout gestation, resetting of the steroidogenic activity of the primary corpus luteum (pCL) and development of accessory corpus luteum (aCL) at mid gestation, all these leading to an increase of luteal Pg that enables to carry the pregnancy to term. The decrease of Pg from 70-gestation days allows for the reactivation of the reproductive axis. This decrease in serum Pg results in the surge of GnRH, followed by the release of pituitary FSH which promotes follicular development. Then, an increase in serum E2 and synthesis and surge\nof LH result in the formation of new aCL and reactivation of the luteal steroidogenic\nactivity between days 100 and 120 of pregnancy. Given the key action of GnRH and\novarian hormones over the activity of the reproductive axis, the present study aimed to elucidate the role of the pituitary gland in the reactivation of the HHO during gestation in the plains vizcacha. To prove this hypothesis, the pituitary dynamic throughout gestation,\nthe effect of ovarian hormones on pituitary activity and its relationship with pseudo-\novulation and active corpus luteum formation during pregnancy were investigated. To achieve this, pregnant and non-pregnant adult females were used, and ex vivo and in\nvivo physiological experiments, such as pituitary explant cultures and bilateral\novariectomy with hormonal replacement were carried out. During gestation, before the\nHHO reactivation, low levels of ovarian inhibin allowed pituitary FSH release, which\nwould also induce formation of E2 producing mature follicles. After the luteinization of\nmature follicles induced by LH, increased E2 and Pg levels would exert positive feedback\nover LH release, but not over pituitary GnRHR expression. After this LH surge, FSHR\nexpressed in corpora lutea of P3 females would stimulate aromatase activity and\nconsequently, an increment of E2. Meanwhile, IGF1R would also favor ovarian E2 and\nPg synthesis during mid-gestation. The high levels of ovarian inhibin expression\nobserved in P3 would pinpoint this factor as a possible regulator of pituitary GnRHR\nexpression at this stage. On the other hand, differential effect of pituitary estrogen\nreceptors was determined for non-pregnant females, being RE? the receptor involved in\nGnRHR expression increment and RE? in LH synthesis and release. Nevertheless, both\nE2 and Pg would induce negative feedback on the synthesis and release of LH through the GnRHR activated- signaling pathway mediated by Egr-1 and Sf-1. Altogether, this work shows the differential effect of ovarian hormones over the GnRHR expression and its pathway for LH synthesis in pregnant and non-pregnant females of this species of a wild rodent with HHO reactivation during gestation |
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