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 Title: Induction of the oxytocin receptor and its role in luteolysis in sheep Author(s): Zhang, Jiahua Doctoral Committee Chair(s): Hixon, James E. Department / Program: Biology, Veterinary Science Discipline: Biology, Veterinary Science Degree Granting Institution: University of Illinois at Urbana-Champaign Degree: Ph.D. Genre: Dissertation Subject(s): Biology, Veterinary Science Abstract: The objectives in this study were to evaluate the influence of withdrawal of progesterone on induction of the uterine oxytocin receptor in the absence and presence of estradiol and to determine whether or not estradiol of ovarian follicular origin is necessary for induction of the oxytocin receptor and the pulsatile secretion of prostaglandin F$\sb{2\alpha}$ (PGF$\sb{2\alpha}$) during spontaneous luteolysis. Continuous treatment with progesterone for 9 or 12 days reduced the density of oxytocin receptors in endometrium and myometrium when compared to the vehicle-treated groups. In the endometrium, withdrawal of progesterone after day 9 resulted in an increase in the concentration of oxytocin receptor on day 13 (P $<$ 0.01) and estradiol enhanced the effects of progesterone withdrawal (P $<$ 0.01). Otherwise, the effect of estradiol was to reduce oxytocin receptor concentrations (P $<$ 0.01). X-irradiation prolonged the luteal phase of the estrous cycle. Estradiol treatment reversed the effects of X-irradiation and shortened the estrous cycle when compared to the ewes which received sham X-irradiation and placebos. About 50 percent of PGFM peaks overlapped with oxytocin peaks and no difference in the percentage of overlapped PGFM peaks was observed between estradiol-treated ewes and the ewes receiving placebos. Estradiol treatment decreased the interval between PGFM peaks (P $<$ 0.01) and increased the interval between oxytocin peaks (P $<$ 0.01). Lower concentrations of oxytocin receptor in the endometrium (P $<$ 0.01) but higher concentrations of oxytocin receptor in the myometrium (P $<$ 0.01) were observed in estradiol-treated ewes when compared to the ewes treated with placebos. In conclusion, withdrawal of progesterone induces the formation of oxytocin receptor in endometrium and these effects are enhanced by estradiol. The reduced interval between PGFM peaks that was observed in the estradiol-treated ewes was associated with an earlier onset of luteolysis which is consistent with the idea that the frequency of PGF$\sb{2\alpha}$ is an important component of its luteolytic action. About 50% of the oxytocin and PGFM peaks overlapped, suggesting that oxytocin is not the only factor controlling the pulsatile secretion of PGF$\sb{2\alpha}$. The oxytocin-independent PGF$\sb{2\alpha}$ pulses may be sensitive to the effects of estradiol. Issue Date: 1991 Type: Text Language: English URI: http://hdl.handle.net/2142/23613 Rights Information: Copyright 1991 Zhang, Jiahua Date Available in IDEALS: 2011-05-07 Identifier in Online Catalog: AAI9124513 OCLC Identifier: (UMI)AAI9124513
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