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Department of Obstetrics and Gynecology (A.-R.F.), Cornell University Medical College, New York, New York 10021; Département dOntogénie et Reproduction, Centre de Reserche du Centre Hospitalier de lUniversité Laval, Centre de Recherche en Biologie de la Reproduction (P.D., M.A.F.), Ste Foy, Quebec, Canada; Institute for Hormone and Fertility Research (M.B.), Hamburg, Germany; Animal Science Department, University of Florida (M.J.F.), Gainesville, Florida 32611
Address all correspondence and requests for reprints to: Dr. A.-R. Fuchs, Department of Obstetrics and Gynecology, Cornell University Medical College, 515 East 71 Street, Room S-412, New York, New York 10021. E-mail: annariitta{at}aol.com
Developmental aspects of oxytocin (OT) receptors (OTR) in uterine
tissues before puberty are not known. Bovine ovaries secrete some
estradiol, but no progesterone, before puberty; the circulating levels
of estradiol are between 1 and 3 pg/ml until puberty. Cross-bred
Angus-Brahman heifers, in which puberty occurs around 12 months of age,
were used to determine the concentrations of OTR from the late fetal
stage to adulthood. PGF2
release in response to OT was
determined in 3-, 6-, and 9-month-old heifers (n = 4 each).
Myometrium, endometrium, and cervical mucosa were obtained from
3-week-old, 3-month-old, 6-month-old, and 9-month-old heifers and from
adult cows at estrus. Whole uterus and cervix were taken from third
trimester fetuses and at birth. [3H]OT binding and
specificity, localization of immunoreactive (ir) OTR, OTR messenger
RNA, and OT-induced release of PGF2
were determined. The
uterus from fetuses and the neonate expressed OTR messenger RNA and
bound [3H]OT. At 3 weeks of age, OTR concentrations per
mg protein were very low, but at 3 months of age they had increased
markedly in all three tissues. At 6 and 9 months of age, levels of OTR
had risen further and were similar to those in adult cows at estrus.
Prepubertal uterus also possessed separate vasopressin VP1 subtype
receptors. The ir-OTR was localized in luminal epithelial cells of
endometrium and cervical mucosa, most of which were ir positive,
whereas in myometrium, clusters of ir-OTR-positive cells were found
among large numbers of ir-OTR-negative cells. The PGF2
response to OT was insignificant in heifers of all age groups, in
contrast to that in cows at estrus. Endometrial cells from 4- to
5-month-old heifers did not respond to OT with PG release in the
absence or presence of added arachidonic acid. Tumor promoters,
lipopolysaccharide, and interleukin-2 also failed to elicit PG release
in vitro, although they induced PG release in similar
cell cultures from cyclic cows. In summary, uterine tissues of
prepubertal heifers have high levels of OTR, which appear to be
developmentally regulated. These receptors are not coupled to PG
synthase, or alternatively, the PG synthase gene is not expressed
before puberty, possibly because the tissues have had no previous
exposure to progesterone.
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