Graduate Thesis Or Dissertation
 

Physiological factors affecting ovine uterine estrogen and progesterone receptor concentrations

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  • Two experiments were conducted to determine whether in ewes uterine concentrations of estrogen and progesterone receptors are affected by the presence of a conceptus or by the hormonal milieu associated with extremes in photoperiod to which ewes are exposed. In Exp.1, nine mature ewes were unilaterally ovariectomized by removing an ovary bearing the corpus luteum (CL). The ipsilateral uterine horn was ligated at the external bifurcation and a portion of the anterior ipsilateral uterine horn was removed and assayed for endometrial nuclear and cytosolic concentrations of estrogen receptor (ER) and progesterone receptor (PR) by exchange assays. After a recovery estrous cycle, ewes were bred to a fertile ram. On day 18 of gestation a 10 ml jugular blood sample was collected for measurement of serum concentrations of estradiol -17β (E₂) and progesterone by radioimmunoassay. Ewes were relaparotomized on day 18 and the remaining uterine tissue was removed. Endometrium from both the pregnant and nonpregnant uterine horn was assayed for nuclear and cytosolic ER and PR concentrations. Nuclear and cytosolic ER concentrations on day 10 of the cycle were greater than in endometrium of gravid and nongravid uterine horns on day 18 of gestation (p<.01). Endometrial nuclear PR levels were also greater on day 10 of the cycle than in the pregnant (p<.05) and nonpregnant horn (p<.01) on day 18 of gestation. There were no differences in nuclear and cytosolic ER and PR concentrations between the pregnant and nonpregnant uterine horn on day 18. Serum levels of E₂ and progesterone on day 18 of gestation were 16.56 ± 2.43 pg/ml and 1.74 ± 0.57 ng/ml, respectively. These data suggest that duration of exposure of the uterus to progesterone and(or) the presence of the conceptus causes a reduction in uterine concentrations of ER and PR. Further, an effect of the conceptus, if any, is exerted via a systemic route. In Exp. 2, ten mature ewes were bilaterally ovariectomized in early October. During the onset of the winter solstice (late December), a 10 ml blood sample was collected from five ewes for analysis of serum levels of E₂ and progesterone. Ewes were then laparotomized and approximately one-third to one-half of a uterine horn was removed and assayed for endometrial nuclear and cytosolic ER. The contralateral horn was ligated at the external bifurcation and 10 μg of E₂ in 3 ml of physiological saline was injected into the uterine lumen of the ligated horn. After 48 h, a jugular blood sample was collected for steroid analysis and a section of the E₂ treated horn was removed and assayed for endometrial cytosolic and nuclear ER. This procedure was repeated on the remaining five ewes during the height of the summer solstice (late June). Endometrial nuclear and cytosolic concentrations of ER prior to and after exogenous E₂ stimulation were similar during the winter and summer solstice (p>.05). However, treatment with E₂ increased endometrial nuclear and cytosolic concentrations of ER compared with those of the nonstimulated uterine horn during the winter and summer solstice (p<.05 for each). Serum levels of E₂ prior to luminal treatment of ewes with E₂ during the winter and summer solstice did not differ (16.55 ± 4.05 vs 16.00 ± 3.0 pg/ml, respectively, p>.05). Serum levels of E₂ 48 h after administration of E₂ did not differ among ewes at the winter and summer solstice (18.75 ± 2.4 vs 18.65 ± 1.65 pg/ml, respectively, p>.05). Serum levels of progesterone were basal (<0.10 ng/ml) and did not differ in ewes prior to and after E₂ treatment at the winter and summer solstice (p>.05). These data indicate that physiological factors and(or) hormones such as prolactin and melatonin secreted in response to extremes in photoperiod do not appear to influence uterine concentrations of ER in ovariectomized ewes.
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