Regression of the corpus luteum (CL) is characterized by a decay in progesterone
(P4) production (functional luteolysis) and disappearance of luteal tissues
(structural luteolysis). In mares, structural luteolysis is thought to be caused by
apoptosis of luteal cells, but functional luteolysis is poorly understood.
20α-hydroxysteroid dehydrogenase (20α-HSD) catabolizes P4 into its biologically
inactive form, 20α-hydroxyprogesterone (20α-OHP). In mares, aldo-keto reductase (AKR)
1C23, which is a member of the AKR superfamily, has 20α-HSD activity. To clarify whether
AKR1C23 is associated with functional luteolysis in mares, we investigated the expression
of AKR1C23 in the CL in different luteal phases. The luteal P4 concentration
and levels of 3β-hydroxysteroid dehydrogenase (3β-HSD) mRNA were higher in the mid luteal
phase than in the late and regressed luteal phases (P<0.05), but the level of 3β-HSD
protein was higher in the late luteal phase than in the regressed luteal phase
(P<0.05). The luteal 20α-OHP concentration and the level of AKR1C23
mRNA were higher in the late luteal phase than in the early and mid luteal phases
(P<0.05), and the level of AKR1C23 protein was also highest in the late luteal phase.
Taken together, these findings suggest that metabolism of P4 by AKR1C23 is one
of the processes contributing to functional luteolysis in mares.
In mares, prostaglandin F 2α (PGF 2α ) secreted from the endometrium is a major luteolysin. some domestic animals have an autoamplification system in which PGF 2α can stimulate its own production. here, we investigated whether this is also the case in mares. In an in vivo study, mares at the mid-luteal phase (days 6-8 of estrous cycle) were injected i.m. with cloprostenol (250 µg) and blood samples were collected at fixed intervals until 72 h after treatment. Progesterone (P 4 ) concentrations started decreasing 45 min after the injection and continued to decrease up to 24 h (P < 0.05). In turn, 13,14-dihydro-15-keto-PGF 2α (PGFM) metabolite started to increase 4h after an injection and continued to increase up to 72 h (P < 0.05). PGF receptor (PTGFR) mRNa expression in the endometrium was significantly higher in the late luteal phase than in the early and regressed luteal phases (P < 0.05). In vitro, PGF 2α significantly stimulated (P < 0.05) PGF 2α production by endometrial tissues and endometrial epithelial and stromal cells and significantly increased (P < 0.05) the mRNa expression of prostaglandin-endoperoxide synthase-2 (PTGS2), an enzyme involved in PGF 2α synthesis in endometrial cell. These findings strongly suggest the existence of an endometrial PGF 2α auto-amplification system in mares.
Evaluation of a new chemiluminescent enzyme immunoassay, the PATHFAST assay system
(PATHFAST), for measurement of circulating progesterone in mares was performed. Five mares
at the mid-luteal stage were administrated a single i.m. injection of prostaglandin F2α
analog (PGF2α; cloprostenol 250 μg/ml), and then blood samples were collected from the
jugular vein at 0, 15, 30 and 45 min, at one-hour intervals until 24 and at 48 hr via a
catheter in the jugular vein. To monitor the physiological changes in circulating
progesterone in mares after induced luteolysis, concentrations of progesterone in whole
blood and serum samples were measured by PATHFAST. In addition, concentrations of
progesterone in serum samples measured by PATHFAST were compared with those measured by
radioimmunoassay (RIA) and enzyme immunoassay (EIA). Using PATHFAST, the serum
concentrations of progesterone in mares correlated highly with those of whole blood
samples (r=0.9672, n=88). The serum concentrations of progesterone as measured by PATHFAST
correlated well with RIA (r=0.9654, n=88) and EIA (r=0.9323, n=112). An abrupt decline in
circulating progesterone in whole blood samples was observed within 2 hr (50%), followed
by a gradual decline until 48 hr later. The results for progesterone in whole blood
samples correlated highly with those in serum samples, and the declining pattern
paralleled that of the serum samples. These results demonstrated that PATHFAST is useful
in the equine clinic as an accurate diagnostic tool for rapid assay of progesterone within
26 min, using unextracted whole blood.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.