American journal of physiology. Endocrinology and metabolismMar 5, 2009

Estradiol increases oxytocin receptor levels in the rat colon

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Updated Mar 21, 2026

Abstract

Estradiol (4-100 microg/kg) increased the excitatory effect of oxytocin on colon motility in ovariectomized rats.

In ovariectomized rats, estradiol treatment enhanced oxytocin's stimulatory impact on colon motility both in live and isolated muscle tests.
Estradiol elevated the expression of oxytocin receptors in the colon.
Oxytocin activated colon motility in vivo during proestrus and estrus phases but not during diestrus, when estradiol levels were lowest.
Blocking oxytocin receptors or sodium channels reduced the excitatory effects of oxytocin on colon motility.
Oxytocin receptors were identified in the myenteric plexus of the colon.

Simplified

The study was designed to investigate the effect of estradiol on the excitatory effect of oxytocin (OT) on colon motility. Female Wistar rats were used, and some of them were ovariectomized (OVX) and treated with vehicle or estradiol (E(2)). A plastic balloon made of condom was inserted into colon to monitor the change of colonic pressure in vivo. Longitudinal muscle strips of distal colon were prepared to monitor the spontaneous contraction of colon in vitro. Expression of OT receptor (OTR) was investigated by Western blot analysis. Expression of OTR mRNA was detected by RT-PCR. Immunohistochemistry was used to locate OTR. In OVX rats, pretreatment of E(2) (4-100 microg/kg sc) dose-dependently increased the excitatory effect of OT on colon motility both in vivo and in vitro and increased the expression of OTR and OTR mRNA in colon. Systemic administration of OT excited the colon motility in vivo in rats at perioda of proestrus and estrus but did not influence it at diestrus period, when the concentration of plasma E(2) was lowest in the estrous cycle. Pretreatment of atosiban, the specific OTR antagonist, and TTX, the blocker of voltage-dependent sodium channel on nerve fiber, attenuated the excitatory effect of OT on colon motility. OTR was located in myenteric plexus of colon. These results suggested that E(2) increased the excitatory effect of OT on colon motility by upregulating the expression of OTR in myenteric plexus.

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Estradiol increases oxytocin receptor levels in the rat colon

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