Wx. Wu et al., CHARACTERIZATION OF OXYTOCIN RECEPTOR EXPRESSION AND DISTRIBUTION IN THE PREGNANT SHEEP UTERUS, Endocrinology, 137(2), 1996, pp. 722-728
At the end of pregnancy, the myometrium becomes extremely sensitive to
oxytocin (OT) as result of a dramatic increase in the number of OT re
ceptors (OTR), indicating an important role for OTR in the process of
labor. There are no studies in sheep in which the physical properties
and histological distribution of OTR are evaluated in relation to part
urition. Also, no studies have been performed in any species to simult
aneously examine the distribution of OTR at the messenger RNA (mRNA) a
s well as the protein levels in the same tissues and correlate those c
hanges with the patterns of myometrial activity that occur at labor. I
n the present studies, we have used a polyclonal anti-OTR antibody and
Western blot analysis to determine the apparent molecular mass of ovi
ne OTR in late pregnant sheep myometrium and endometrium. We also exam
ined the distribution of OTR mRNA and protein expression in the intact
myometrium and endometrium and in individual cultured cells using in
situ hybridization and immunocytochemistry. The expression of OTR and
its mRNA has been correlated with the patterns of activity observed in
the pregnant sheep myometrium. Western blot analysis of myometrial an
d endometrial extracts revealed a major form of OTR with an approximat
e molecular mass of 66 kDa. Both immunocytochemistry and in situ hybri
dization localized OTR and its mRNA in myometrial cells and glandular
cells of the endometrium. Increased OTR and its mRNA expression in the
myometrium and endometrium were correlated with the occurrence of myo
metrial contractions. OTR was also demonstrated by immunocytochemistry
in the smooth muscle of myometrial bleed vessels. Localization of OTR
and its mRNA in pregnant sheep myometrial cells is consistent with th
e hypothesis that OTR plays an important role in regulating myometrial
contractility, Positive staining of OTR in endometrial glandular cell
s supports the view that OT is involved in PG production by the endome
trium in late pregnancy. Increased expression of OTR and its mRNA in t
he myometrium during labor further indicates that changes in tissue OT
R play a significant role in the mechanism of parturition. Increased e
xpression of OTR and its mRNA in endometrium may relate to the role of
OT in regulating PG production by the endometrium during labor.