Submitted September 21, 2006
Returned for revision October 12, 2006
Accepted January 30, 2007
Ovary
Positive Association, in Local Release, of Luteal Oxytocin
with Endothelin 1 and Prostaglandin F2alpha
During Spontaneous Luteolysis in the Cow: A Possible
Intermediatory Role for Luteolytic Cascade Within the
Corpus Luteum
Koumei Shirasuna ,
Takashi Shimizu ,
Ken-Go Hayashi ,
Kaya Nagai ,
Motozumi Matsui ,
and
Akio Miyamoto *
* To whom correspondence should be addressed. E-mail: akiomiya{at}obihiro.ac.jp.
Abstract
Luteolysis is caused by a pulsatile release of
prostaglandin F2alpha (PGF2alpha)
from the uterus in ruminants, and a positive feedback
between endometrial PGF2alpha and luteal
oxytocin (OXT) has a physiological role in the promotion
of luteolysis. The bovine corpus luteum (CL) produces
vasoactive substances such as endothelin 1 (EDN1) and
angiotensin II (Ang II) that mediate and progress
luteolysis. We hypothesized that luteal OXT has an
additive function to ensure the CL regression with EDN1
and Ang II, and has an active role in the luteolytic
cascade in the cow. Thus, the aim of the present study was
to observe real-time changes in the local secretion of
luteal OXT, and to determine its relationship with other
local mediators of luteolysis. Microdialysis system (MDS)
capillary membranes were implanted surgically into each CL
of six cyclic Holstein cows (18 lines/6 cows) on Day 15
(estrus=Day 0) of the estrous cycle. Simultaneously,
catheters were implanted to collect ovarian venous plasma
ipsilateral to the CL. Although the basal secretion of OXT
by luteal tissue was maintained during the experimental
period, the intraluteal PGF2alpha secretion
gradually increased up to 300% from 24 h after the onset
of luteolysis (0 h; time in which progesterone started to
decrease). In each MDS line (microenvironment) within the
CL, the local releasing profiles of OXT were positively
associated with PGF2alpha and EDN1 within the
CL in all 18 MDS lines implanted in the 6 CLs (OXT vs.
PGF2alpha, 50.0%; OXT vs. EDN1, 72.2%; P<0.05).
On the other hand, the intraluteal OXT was weakly related
to Ang II (OXT vs. Ang II, 27.7%). In the ovarian vein,
the peak concentration of PGF2alpha increased
significantly when the peak of PGF2alpha
coincided with the peak of OXT after the onset of
spontaneous luteolysis (P<0.05). In conclusion,
intraluteal OXT may locally modulate secretion of
vasoactive substances, particularly EDN1 and
PGF2alpha within the CL, and thus might be one
of the luteal mediators of spontaneous luteolysis in the cow.
Key words:
Ovary •
Corpus luteum •
Corpus luteum function •
Oxytocin •
Progesterone
