Characterization and localization of a putative oxytocin receptor in the cervix of the oestrous ewe

Abstract

The purpose of the present study was to investigate the presence of high-affinity oxytocin-binding sites (putative oxytocin receptors) in the cervix of the non-pregnant ewe. [3H]Oxytocin binding to the peripheral layers of cervical tissue (comprising the serosal layer and the least dense collagenous and muscular layers) and the remaining dense collagenous cervical tissue were studied separately. [3H]Oxytocin-binding sites were detected in membrane fractions prepared from both of these regions, but binding to the peripheral cervix was variable and binding site concentrations were low, hence these were not characterized further. A high-affinity oxytocin-binding site, having a dissociation constant of 1.8 nmol/l, was characterized in the dense collagenous regions of the cervix of ewes killed during the oestrous period. Similar dissociation constants were determined for [Arg8]-vasopressin and the oxytocin-specific agonist [Thr4, Gly7]-oxytocin in competition studies. [3H]Oxytocin binding to peripheral cervical tissue and to the dense collagenous cervix was generally low or undetectable during the luteal phase, but increased in both tissues around the time of luteolysis. Although specific binding to both tissues was variable during the oestrous period, it was higher at this time than during the luteal phase. [3H]Oxytocin-binding site concentrations were also found to be higher within the inner dense collagenous cervix of oestrous ewes than of pregnant, ovariectomized or anoestrous animals.(ABSTRACT TRUNCATED AT 250 WORDS)

An in vitro investigation of the actions of reproductive hormones on the cervix of the ewe in the follicular stage: The effects of 17β-estradiol, oxytocin, FSH, and arachidonic acid on the cervical pathway for the synthesis of prostaglandin E2

“…Our previous studies have shown that there were increased levels of estradiol receptor a, OTR, cPLA 2 , and COX-2 in the ovine cervix during the periovulatory period of the estrous cycle [18]. These observations are consistent with those of other groups who have also reported high levels of these proteins during the periovulatory period in the cervix [14,[19][20][21] or uterus [22] and provide evidence to support our hypothesis that the reproductive hormones (17b-estradiol, FSH, and oxytocin) collectively regulate cervical relaxation by stimulating COX-2-mediated synthesis of cervical PGE 2 .…”

“…It has been previously reported that in the bovine [9] and ovine cervix [5,10], during the follicular phase of the estrous cycle, there is an increase in the expression of the FSH receptors suggesting that the gonadotrophic hormone might play a role in the pathway of PGE 2 synthesis and final cervical relaxation. Moreover, in the ewe, high concentrations of estradiol during the periovulatory period [11,12] are associated with increasing the cervical expression of the oxytocin receptor (OTR) [13,14], and oxytocin acting through OTR stimulates cytoplasmic phospholipase A2 (cPLA 2 )-induced release of arachidonic acid (AA) from the phospholipid membranes in ovine and bovine endometrial tissues [15,16]. This pathway linking oxytocin to AA is important because AA is the substrate for cyclooxygenase 2 (COX-2) which converts it into prostaglandin H, the precursor for PGE 2 [17].…”

Uterine peristalsis during the follicular phase of the menstrual cycle: effects of oestrogen, antioestrogen and oxytocin

“…In oestrous ewes, oxytocin binding site concentrations were highest within the inner dense collagenous cervix in comparison with pregnant, ovariectomized or anoestrous animals (Matthews and Ayad, 1994). Since oxytocin was found to stimulate prostaglandin E 2 output in vitro in bovine cervical tissue and since prostaglandin E 2 is capable of softening cervical tissue (Fuchs et al, 1996b), the preovulatory softening of the cervix and widening of the external cervical os in women may be an action of oxytocin mediated by prostaglandin E 2 .…”

Up-Regulation of Oxytocin Receptor Messenger Ribonucleic Acid and Protein by Estradiol in the Cervix of Ovariectomized Rat1

“…Studies in the cervix, however, are limited. Earlier experiments have characterized OTR in homogenized cervix using receptor-binding techniques [20,21]. OTR in the pregnant [22] and nonpregnant [1] bovine cervix, demonstrated by immunohistochemistry, is present in epithelial cells at the luminal surface of the mucosa as well as smooth muscle cells.…”