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. / Graduation date: 1991
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/37547 |
| Date | 14 November 1990 |
| Creators | Prater, Patrice L. |
| Contributors | Stormshak, Fredrick |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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