Arachidonic acid metabolism by bovine placental tissue during the last month of pregnancy

Progesterone receptors, oestrogen receptor alpha and glucocorticoid receptors in the bovine intercaruncular uterine wall around parturition

The bovine intercaruncular uterine wall expresses steroid hormone receptors throughout pregnancy. Concentrations of specific hormones undergo massive changes during the peripartal period and modulate the synthesis of their own receptors. This is well documented for the placentome, but respective data concerning the intercaruncular uterine wall are completely lacking. Thus, intercaruncular uterine wall segments from cows (I) being 8 and 9 months pregnant (slaughtered cows) and (II) cows undergoing a premature caesarean section 269-282 days after artificial insemination (AI) with (IIa, b) or without (IIc) induction of birth with PGF(2alpha) agonist or (III) receiving a caesarean section during severe dystocia (n=6, 5, 5, 5, 6 and 4 animals, respectively) were studied. In four naturally calving cows (IV) endometrial biopsies were obtained within 30 min after the expulsion of the calf. All tissue probes were fixed for 24h in 4% formaldehyde, routinely embedded in paraffin, and cut at 4 microm. Progesterone receptors (PR), estrogen receptor alpha (ERalpha) and glucocorticoid receptors (GR) were assessed using specific antibodies and staining intensities were documented employing an immunoreactive score (IRS). PR, ERalpha and GR exhibited cell type- and location-specific distribution patterns. IRS for PR and ERalpha did not differ between groups. GR-IRS of endometrial stromal cells, however, were higher in animals undergoing premature caesarean section after induction of birth compared to animals slaughtered during month 8 or 9 of pregnancy or animals receiving caesarean section following dystocia. Results of the present study indicate that steroid hormone receptor amounts within the intercaruncular uterine wall do not (PR, ERalpha) - or in a tissue-specific manner (GR) only - change during the peripartal period, although respective hormones undergo massive changes during this period. This is in strict contrast to the placentome. Comparatively lower local tissue estrogen concentrations around term may be one cause for this difference.

Bovine retained placenta: hormonal concentrations in fetal and maternal placenta

The aim of this study was to evaluate the relationship between the occurrence of retention of the fetal membranes (RFM) and the hormonal concentrations of progesterone, estradiol-17beta, prostaglandin E(2) (PGE(2)), prostaglandin F(2alpha) (PGF(2alpha)), oxytocin (OT), oxytocin receptor (OT-R), endothelin-1 and angiotensin II (Ang II) in the placental tissues of cattle. Parturition was induced in nine Holstein cows by a single injection of PGF(2alpha) on Day 274 of gestation. Six out of nine cows in the induced group did not release the fetal membranes within 12 h after parturition and served as the RFM group, and the remaining three cows in that group, which released their fetal membranes within 12 h, served as the non-RFM group. Five other cows calved spontaneously and served as controls. The placental tissues were collected immediately (0 h) and at 6 h after parturition. The hormonal concentrations were measured by enzyme immunoassay in maternal and fetal placental tissues from RFM, non-RFM and control cows. There were no differences in P4 and E2 concentrations among the RFM, non-RFM and control groups. The mean PGF(2alpha) concentration of the RFM group was lower than those of the non-RFM and control groups in the maternal part of the placenta. In maternal tissues, the OT and OT-R concentrations in the RFM group were lower than those at 0 and 6 h after parturition in the non-RFM group. Additionally, the Ang II concentration of the RFM group in both the maternal and fetal parts of placental tissues tended to be higher than those of the other groups. In conclusion, the present results suggest that ET-1 and Ang II may play differential tissue-specific roles in the placental unit that may amplify the local endocrinological cascade involving OT, OT-R and PGF(2alpha) interactions which are necessary for normal placental separation in the cow.

Prostaglandin E(2) 9-keto reductase activity in bovine retained and not retained placenta

Prostaglandin E(2) 9-keto reductase (9-KPR) activity shifts reversibly PGE(2) into PGF(2 alpha) and may be responsible for the control of prostaglandins (PGs) levels in, among others, placental tissues. The retention of fetal membranes in cows is the postpartum disorder where the disturbances in PGs metabolism have been reported. It has been argued whether these disturbances are due to alterations in 9-KPR activity. In this study, the activity of the enzyme was determined in maternal and fetal bovine placental tissues which were divided into 6 groups as follows: (A) caesarian section before term without retained fetal membranes (n=10), (B) caesarian section before term with retained fetal membranes (n=10), (C) caesarian section at term without retained fetal membranes (n=12), (D) caesarian section at term with retained fetal membranes (n=12), (E) spontaneous delivery at term without retained fetal membranes (n=12), (F) spontaneous delivery at term with retained fetal membranes (n=12). The enzyme activity was measured spectrophotometrically and expressed in nanokatals (nkat) per protein content. The activity increased towards parturition and was significantly higher in maternal than in fetal part of placenta in all groups examined. The significantly higher values in retained than in not retained placental tissues were observed in the samples examined. The present results indicate that the disturbances in 9-KPR activity in bovine retained placenta exist but their reasons still require further experiments.

Effects of indomethacin, NS-398 (a selective prostaglandin H synthase-2 inhibitor) and protein synthesis inhibitors on prostaglandin production by the guinea-pig placenta

The outputs of PGF(2 alpha), PGE2 and 6-keto-PGF(1 alpha)were similar from the day 22 guinea-pig placenta and sub-placenta in culture, except for PGE2 output from the sub-placenta which was lower. Between days 22 and 29 of pregnancy, the outputs of PGF(2 alpha), PGE2 and 6-keto-PGF(1 alpha)during the initial 2 h culture period increased 6.9-, 1.1- and 3.2-fold, respectively, from the placenta, and 2.1-, 1.4- and 2.2-fold, respectively, from the sub-placenta. Therefore, there was a relatively specific increase in PGF(2 alpha)production by the guinea-pig placenta between days 22 and 29 of pregnancy. The output of PGFM from the cultured placenta also increased between days 22 and 29, indicating that the increase in PGF(2 alpha)output was due to increased synthesis rather than to decreased metabolism. By comparing the amounts of prostaglandins produced by tissue homogenates during a 1 h incubation period, it appears that there is approximately a 2-fold increase in the amount of prostaglandin H synthase (PGHS) present in the guinea-pig placenta between days 22 and 29. NS-398 (a specific inhibitor of PGHS-2) and indomethacin (an inhibitor of both PGHS-1 and PGHS-2) both inhibited prostaglandin production by homogenates of day 22 and day 29 placenta. Indomethacin was more effective than NS-398, except for their actions on PGF(2 alpha)production by the day 29 placenta where indomethacin and NS-398 were equiactive. Indomethacin and NS-398 were both very effective at inhibiting the outputs of PGF(2 alpha), PGE2 and 6-keto-PGF(1 alpha)from the day 22 and day 29 placenta and sub-placenta in culture, indicating that prostaglandin production by the guinea-pig placenta and sub-placenta in culture is largely dependent upon the activity of PGHS-2. The high production of PGF(2 alpha)by the day 29 placenta is not dependent on the continual synthesis of fresh protein(s), as inhibitors of protein synthesis did not reduce PGF(2 alpha)output from the day 29 guinea-pig placenta in culture.

The enzymes responsible for the metabolism of prostaglandins in bovine placenta

The following review presents some data on the enzymes of synthesis and catabolism of prostaglandins in bovine placenta. The available literature confirms the anabolic and catabolic ability of bovine placenta to metabolise prostaglandins, but there is little direct information about the pathways involved. The aim of the review is to describe what is known about the physico-chemical properties and activity of enzymes involved in prostaglandin metabolism in bovine placenta.

The analysis of fatty acid content and phospholipase A2 activity in placenta of cows with and without retained fetal membranes

The aim of the following study was the comparison of phospholipase A2 (PLA2) activity and fatty acids content in cows with and without retained fetal membranes. The activity of the enzyme and levels of fatty acids were measured in maternal and fetal placental tissues obtained from cows immediately after spontaneous parturition without (group A) and with (group B) retained fetal membranes. PLA2 activity was statistically significantly (P < 0.05) higher in group A than in group B, and was significantly lower in the fetal part than in the maternal part of placenta in both groups. The content of the examined fatty acids-myristic (14:0), palmitic (16:0), palmitoleic (16:1), stearic (18:0), oleic (18:1), linolenic (18:3), arachidic (20:0), arachidonic (20:4, AA)-was higher in group A than in B. Concentration of linoleic acid (18:2) showed the opposite relationship. There was a positive correlation between enzyme activity and content of det2ermined fatty acids. The results seem to confirm the bypothesis that the arachidonic acid pathway is altered in cases of retained placenta in cows.

Effects of fenprostalene and estradiol-17 beta benzoate on parturition and retained placenta in dairy cows and heifers

It was hypothesized that a high dose of estrogen in conjunction with a long-acting PGF2 alpha analog would synchronize parturition within a narrow time frame and reduce the incidence of retained placenta. On d 276 of gestation, 14 animals (9 cows and 5 heifers) per group received a placebo (group A), 1 mg of fenprostalene (group B), 50 mg of estradiol-17 beta benzoate (group C), or both (group D). Treatment with estradiol-17 beta benzoate increased serum concentrations of estradiol-17 beta from 228 pg/ml at treatment to 642 and 683 pg/ml at 24 h posttreatment for groups C and D, respectively. Concentration of estradiol-17 beta in group A increased gradually to 526 pg/ml at 24 h prepartum. Progesterone concentrations were reduced by fenprostalene but not by estradiol-17 beta benzoate. Estradiol-17 beta benzoate did not reduce incidence of retained placenta in animals treated with fenprostalene (group B vs. group D) but tended to reduce incidence in uninduced animals (group A vs. group C). Thus, short-term elevation of estradiol-17 beta to normal prepartum concentrations did not regress the corpus luteum, induce parturition, or reduce incidence of retained placenta. However, elevation of estradiol-17 beta for longer periods might enhance placental separation. Conversely, fenprostalene induced calving approximately 2 d after treatment. In this study, 90% of animals treated with fenprostalene calved within a 20-h period, but with a high incidence of retained placenta.

Effect of bacterial cell wall and lipopolysaccharide on arachidonic acid metabolism by caruncular and allantochorionic tissues from cows that calved normally and those that retained fetal membranes

Immunoactive eicosanoids may have a role in both placental separation and uterine involution in cattle. In the present study, we examined the effects of bacterial cell wall preparation and endotoxins on in vitro prostaglandin synthesis and arachidonic acid (AA) metabolism by caruncular and allantochorionic tissues. Placentomes were obtained about 6 h post partum from cows that delivered normally (n = 10) or those with retained fetal membranes (n = 4); the tissue explants were incubated for 6 h in the presence of labeled or nonlabeled AA. Prostaglandin F(2alpha) (PGF(2alpha)) and E(2) (PGE(2)) were measured by radioimmunoassay, and labeled AA metabolites were separated by reverse phase-high pressure-liquid chromatography. There was no effect of bacterial cell wall preparations or endotoxins on in vitro caruncular PGF(2alpha) secretion. However, bacterial products increased caruncular PGE(2) secretion in both cows that delivered normally and those with retained fetal membranes. For normal delivery cows caruncular tissue, bacterial product also increased leukotriene B(4) (LTB(4)) and decreased both thromboxane B(2) (TXB(2)) and hydroxy-eicosatetranoic acids (HETE) in vitro secretion. For the allantochorion, bacterial products increased in vitro PGF(2alpha) secretion only in cows that delivered normally and increased PGE(2) secretion essentially in cows with retained fetal membranes. In general, 6 keto PGF(1alpha) was the main metabolite secreted by both allantochorionic and carucular tissues. However, in cows with retained fetal membranes, PGE(2) became the most important metabolite secreted by allantochorion, especially in the presence of endotoxin. In conclusion, these results suggest that bacteria found in the early postpartum uterus or their endotoxin affect primarily caruncular and allantochorionic PGE(2) synthesis.

Metabolism of arachidonic acid by caruncular and allantochorionic tissues in cows with retained fetal membranes (RFM)

The metabolism of arachidonic acid (AA) by caruncular and allantochorionic tissues and its regulation was studied in normal cows (n = 13) and those with retained fetal membranes (RFM; n = 9). Tissues were taken via the vagina about 6 hours postpartum and incubated for 6 hours in minimum essential medium containing tritiated AA alone or in the presence of oxytocin, platelet activating factor (PAF), epidermal growth factor (EGF) or ionophore calcium (A23187). The metabolites of AA were separated by reverse phase-high pressure-liquid chromatography. Tissue concentrations of prostaglandin F2 alpha (PGF2 alpha) and prostaglandin E2 (PGE2) and plasma 13,14-dihydro-15-keto-PGF2 alpha (PGFM) concentration were also measured by radioimmunoassay. For caruncular tissue, less thromboxane B2 (TXB2) and more 6-keto prostaglandin F1 alpha (PGIM) was synthesized in tissue from the animals with RFM than in the controls. Oxytocin, PAF, EGF and A23187 increased only PGIM production in the control animals; A23187 also decreased TBX2 synthesis. For the allantochorion, more PGE2, leukotriene B4 (LTB4) and PGIM and less TXB2, PGF2 alpha and hydroxyecosatetranoic acids (HETE) was synthesized in tissue from cows with RFM than from animals that delivered normally. All of the substances used in this study increased PGIM, PGF2 alpha and LTB4 and decreased TXB2 production by the allantochorionic tissue in control animals. The metabolism of AA by the allantochorionic tissue seems quantitatively under hormonal control. The metabolism of AA at the level of both maternal and fetal components of the placenta in cows with RFM differed from that seen in animals that expelled the membranes normally.

Arachidonic acid and cell signalling in the ovary and placenta

Arachidonic acid (AA) and its metabolites make up a diverse group of signalling molecules important to mediation of metabolic and endocrine function of ovarian and placental cell membranes. This paper reviews recent literature examining AA and eicosanoid involvement in the functional dynamics of follicular development, ovulation and corpus luteum function. The putative roles of AA metabolites in establishment and maintenance of pregnancy are reviewed with reference to decidualization, trophoblast invasion and implantation, maintenance of perfusion of the feto-placental unit and lipid transfer. Finally, recent evidence implicating AA metabolism in mediation of enzyme activity following hormone-receptor coupling within various cells types comprising the placental membranes is reviewed.