Endogenous and exogenous effects of PGF2α during luteolysis in mares

Seasonal absence of supplementary corpora lutea in pregnant mares and the relationship with pregnancy loss

Two experiments were conducted in the Northern (UK) and Southern (Brazil) hemispheres to determine the effect of season (month of conception) on the development of supplementary CL (SCL) and the relationship with pregnancy loss. In experiment 1, 199 pregnancies were followed between Day 14 and term, to determine the number of SCL and pregnancy viability (Northern Hemisphere). From the 199 pregnancies, 178 were obtained from inseminations during the breeding season (March-September), while the rest, 21 pregnancies resulted from conceptions in the non-breeding season (October to February). Pregnancies conceived in the breeding season were more likely (P < 0.01) to have at least 1 SCL (75.8 %, 135/178) than pregnancies from the non-breeding season (33 %, 7/21). However, the pregnancy loss between Days 35 and 120 of pregnancy in mares with no SCL was similar (3.5 %, 2/57; P >0.1) than from mares with SCL (1.4 %, 2/142). In Experiment 2 (Southern Hemisphere), three groups of recipients were used based on their ovarian activity at the time of embryo transfer: Anestrus (n = 8), transitional (n = 7) and cyclic (n = 7) recipient mares. While all transitional and cyclic mares developed at least 1 SCL, only 50 % of anestrous recipients (4/8) developed SCL by 120 of gestation. In conclusion, the development of SCL in pregnant mares is influenced by the time of season of conception, therefore it appears to be regulated by the photoperiod and the endogenous seasonal variation in gonadotropin concentrations. Mares with no SCL were not at increased risk of pregnancy loss.

The Timing of the Maternal Recognition of Pregnancy Is Specific to Individual Mares

The present experiment aimed at determining whether the timing of the maternal recognition of pregnancy (MRP) was specific to individual mares by determining when luteostasis, a failure to return to oestrus, reliably occurred in individuals following embryo reduction. Singleton (n = 150) and synchronous twin pregnancies (n = 9) were reduced in 10 individuals (5-29 reductions/mare) at pre-determined time points within days 10 (n = 20), 11 (n = 65), 12 (n = 47), 13 (n = 12) or 14 (n = 15) of pregnancy. Prior to embryo reduction, the vesicle diameter was measured in 71% (106/150) of the singleton pregnancies. The interovulatory interval (IOI) was recorded on 78 occasions in seven of the mares in either non-pregnant cycles (n = 37) or those in which luteolysis followed embryo reduction (n = 41). The earliest time post-ovulation at which the embryo reduction resulted in luteostasis in an individual was 252 h (mid-Day 10). Consistency in luteostasis following embryo reduction showed individual variation between mares (272-344 h). Binary logistic regression analysis showed an individual mare effect (p < 0.001) and an effect of the interval post-ovulation at which embryo reduction was undertaken (p < 0.001). However, there was no significant effect of vesicle diameter at the time of embryo reduction (p = 0.099), nor a singleton or twin pregnancy (p = 0.993), on the dependent of luteolysis or luteostasis. The median IOI between individual mares varied significantly (p < 0.05) but was not correlated to the timing of MRP. The timing of MRP varied between the mares but was repeatable in each individual. The factors and mechanisms underlying the individuality in the timing of MRP were not determined and warrant further study.

Regulatory changes of local produced prostaglandins in corpus luteum after experimentally induced luteolysis in the cow

The objective of the study was to evaluate the expression patterns of prostaglandin F2alpha (PGF), prostaglandin E2 (PGE), PGF receptor (FP), PGE receptors (EP2 and EP4), prostaglandin-endoperoxide synthase 2 (PTGS2) and prostaglandin synthases (PGFS and PGES) in corpora lutea (CL) during experimentally induced luteolysis in cow. The Fleckvieh cows in the mid-luteal phase (days 8-12, control group) were injected with cloprostenol (PGF analogue), and CL were collected by transvaginal ovariectomy before (days 8-12, control group) and at 0.5, 2, 4, 12, 24, 48 and 64 h after PGF application (n = 5 per group). The mRNA expression was determined by RT-qPCR, the hormone concentrations by enzyme immunoassay and localization by immunohistochemistry. PTGS2 gene expression increased significantly 2 h after PGF application, followed by continuous and significant downregulation afterwards. The PGF tissue concentration increased significantly just after PGF injection and again during structural luteolysis (after 12 h), whereas PGE concentration significantly decreased during structural luteolysis. The FP receptor mRNA decreased significantly at 2 h and again at 12 h after PGF. In contrast, EP4 receptor mRNA increased significantly just after the PGF application (0.5 h). The immunostaining of PGES and PTGS2 on day 15-17 shows numerous positive luteal cells, followed by lower activity afterwards on day 18 (luteolysis). In conclusion, the changes of examined prostaglandin family members in CL tissue after PGF application may be key components of the local mechanisms regulating the cascade of actions leading to functional and subsequent structural luteolysis in the bovine ovary.

Endometrial and luteal responses to a prostaglandin F2alpha pulse: A comparison between heifers and mares

In heifers and mares, multiple pulses of prostaglandin F2alpha (PGF) are generally associated with complete luteal regression. Although PGF pulses occur before and during luteolysis, little is known about the role of minor PGF pulses during preluteolysis on subsequent luteal and endometrial PGF production that may initiate luteolysis. Heifers (n = 7/group) and mares (n = 6/group) were treated with a single minor dose of PGF (3.0 and 0.5 mg, respectively) during mid-luteal phase (12 and 10 days postovulation in heifers and mares, respectively). After treatment, a transient decrease in progesterone (P4) concentrations occurred in heifers between Hours 0–2 but at Hour 4 P4 was not different from pre-treatment. In mares, P4 was unaltered between Hours 0 and 4. Concentrations of P4 decreased in both species by Hour 24 and complete luteolysis occurred in mares by Hour 48. Luteal and endometrial gene expression were evaluated 4 hours post-treatment. In heifers, luteal mRNA abundance of PGF receptor and PGF dehydrogenase were decreased while PTGS2, PGF transporter, and oxytocin receptor were increased. In the heifer endometrium, receptors for oxytocin, P4, and estradiol were upregulated. In mares, luteal expression of PGF receptor was decreased while PGF transporter and oxytocin receptor were increased. The decrease in P4 between Hours 4 and 24 and changes in gene expression were consistent with upregulation of endogenous synthesis of PGF. The hypotheses were supported that a single minor PGF treatment upregulates endogenous machinery for PGF synthesis in heifers and mares stimulating endogenous PGF synthesis through distinct regulatory mechanisms in heifers and mares.

Regression of corpus luteum in cetaceans: A systematic review

Functional and structural change of corpus luteum through the cascade of several genes in the ovary leads to ovulation and pregnancy. In most mammals, the absence of pregnancy leads to the disintegration of the corpus luteum. In the ovary of cetaceans, the regression of the corpus luteum gets delayed and persists on the surface as scars (corpus albicans). The database on luteolysis of mammals was collected and examined to know the mechanisms involved in the corpus luteum regression of cetaceans. Surprisingly, there existed no data on the concerned topic. Some past findings reported the persistence of ovarian scars through the entire life span, while few reported the regression. Also, those investigations were about the physiology and histology of corpus luteum regression. The pathways and the genes involved in the regression of the cetacean corpus luteum remain unexplored. This review is all about the regression of corpus luteum and recommends gene-based evolutionary studies in the future to resolve the existing theories on ovarian scar persistence in cetaceans.

Hormonal regulation and function of an RNA helicase, Ddx5 in corpus luteum of adult Wistar rats

Corpus luteum (CL) is an endocrine tissue involved in regulation of reproductive cycle and early pregnancy establishment. In the present study DEAD-box helicase-5 (Ddx5), a member of the DEAD box family of RNA helicases was investigated for its expression, regulation and function in CL of Wistar rats. Ddx5 was expressed in adult rat CL. Primary cell culture from supra-ovulated ovaries were established for in vitro studies. Addition of luteinizing hormone (LH; 100 ng/ml), a luteotrophic factor in primary cell culture, decreased Ddx5 RNA expression (foldchange:0.6 ± 0.075) while prostaglandin alpha (PGF_2α; 1μM), a luteolytic factor caused an increase (foldchange:2.4 ± 0.4) compared to control group. Under in vivo conditions, the administration of PGF_2α or gonadotropin-releasing hormone antagonist; cetrorelix (CET) caused luteolysis as well as an increase in the protein level of Ddx5 (foldchange:1.9 ± 0.27 and 1.4 ± 0.09 viz.; p < 0.05) in CL of adult rats. LH was administered post CET treatment which suppressed Ddx5 protein expression (foldchange:0.8 ± 0.16; p < 0.05) compared to CET treated group. Further, it was observed that the expression of Ddx5 was upregulated (foldchange:1.5 ± 0.23; p < 0.05) in CL during late pregnancy compared to mid pregnancy concomitant to luteolysis in adult rats. Overall, the results suggest for the first time that Ddx5 is expressed in rat CL and regulated by luteolytic and luteotrophic factors in an inverse fashion. Further, the data significantly correlates ddx5 expression to CL regression suggesting involvement of ddx5 in luteolysis. These results suggest a significant role of Ddx5 in female reproduction biology and warrant in depth examination of the function of Ddx5 in CL.