The distribution of arachidonic acid in plasma and tissues of patients near term undergoing elective or emergency Caesarean section

The 4-vessel Sampling Approach to Integrative Studies of Human Placental Physiology In Vivo

The human placenta is highly inaccessible for research while still in utero. The current understanding of human placental physiology in vivo is therefore largely based on animal studies, despite the high diversity among species in placental anatomy, hemodynamics and duration of the pregnancy. The vast majority of human placenta studies are ex vivo perfusion studies or in vitro trophoblast studies. Although in vitro studies and animal models are essential, extrapolation of the results from such studies to the human placenta in vivo is uncertain. We aimed to study human placenta physiology in vivo at term, and present a detailed protocol of the method. Exploiting the intraabdominal access to the uterine vein just before the uterine incision during planned cesarean section, we collect blood samples from the incoming and outgoing vessels on the maternal and fetal sides of the placenta. When combining concentration measurements from blood samples with volume blood flow measurements, we are able to quantify placental and fetal uptake and release of any compound. Furthermore, placental tissue samples from the same mother-fetus pairs can provide measurements of transporter density and activity and other aspects of placental functions in vivo. Through this integrative use of the 4-vessel sampling method we are able to test some of the current concepts of placental nutrient transfer and metabolism in vivo, both in normal and pathological pregnancies. Furthermore, this method enables the identification of substances secreted by the placenta to the maternal circulation, which could be an important contribution to the search for biomarkers of placenta dysfunction.

Maternal and umbilical venous plasma lipid concentrations at delivery in the mare

The concentrations and fatty acid composition of the plasma free fatty acid, triacylglycerol and phospholipid fractions were determined in maternal and umbilical cord vein blood samples taken at delivery from 17 mares. Maternal and umbilical vein plasma free fatty acid concentrations were of a similar order and a positive correlation was found between the two levels suggesting that the equine placenta is permeable to fatty acid. Substantial amounts of the essential fatty acids and their longer chain derivatives were seen in both umbilical vein plasma free fatty acid and phospholipid fractions supporting this view. Certain long chain polyunsaturated derivatives of the essential fatty acids found in the umbilical venous plasma phospholipid fraction were not seen in the maternal circulating lipids. The precursor fatty acids were readily available to both foetal and placental tissues and therefore must have been elongated and incorporated into phospholipid by either or both. Very small amounts of the essential fatty acids were found in adipose stores in the newborn foal and virtually no fat stores at all in the newborn foal liver.

Role of prostaglandins in pregnancy-induced hypertension

Enzymes involved in prostaglandin I2 (PGI2) and thromboxane A2 (TXA2) synthesis were studied in maternal and fetal platelets and venous endothelium from normotensive pregnant controls (n = 70), women with mild preeclampsia (MP, n = 45), and severe preeclampsia (SP, n = 34). Activities of phospholipase A2 (PHA2), cyclooxygenase (PGHS), and PGI2 synthetase (PGIS) or TXA2 synthetase (TXAS) were determined in platelets and in endothelial cells. The PGHS enzyme was studied further by immunoblot methodology. In maternal platelets: Vmax (per 10(-10) mol/mg protein) and Michaelis-Menten constant (Km) (10(-7) mol, mean +/- SEM) of PHA2 were 3.0 +/- 0.8, 3.0 +/- 0.7, and 31.7 +/- 10.9* maximum velocity (Vmax) and 1.8 +/- 0.3, 2.0 +/- 0.8, and 0.8 +/- 0.2 (Km) in normal control (NC), mild preeclampsia (MP), and severe preeclampsia (SP), respectively (*P less than 0.05 against NC). The apparent overall PGHS plus TXAS activity was 10.2 +/- 1.8, 23.8 +/- 7.1, and 68.8 +/- 18.8* (Vmax) and 3.2 +/- 1.3, 5.4 +/- 1.4, and 6.9 +/- 1.2* (Km, *P less than 0.05 against NC). TXA synthesis in fetal platelets demonstrated PHA2 activity of 6.4 +/- 1.4, 12.0 +/- 1.3, and 17.2 +/- 3.2* (Vmax) and 3.5 +/- 0.9, 2.2 +/- 1.5, and 0.7 +/- 0.3* (Km, *P less than 0.05 against NC), respectively, whereas an apparent overall PGHS plus TXAS activity was 18.5 +/- 2.8, 87.5 +/- 12.5*, and 3.6 +/- 0.1* (Vmax) and 4.8 +/- 1.0, 8.8 +/- 1.2, and 0.8 +/- 0.3* (Km, *P less than 0.05 against NC).(ABSTRACT TRUNCATED AT 250 WORDS)

High arachidonic acid levels in the cord blood of infants of mothers on vegetarian diets

1. Maternal and umbilical cord plasma samples were collected from forty-seven Asian women, twenty-eight life-long vegetarians and seventeen non-vegetarians, during delivery of their babies. The concentrations and fatty acid profiles of the plasma free fatty acid and triacylglycerol fractions were determined. 2. There were no significant differences between the levels of free fatty acid and triacylglycerol in either maternal or cord plasma from vegetarian compared with non-vegetarian Asian women. The fatty acid profiles of the lipid fractions in the two groups were similar. Total plasma free fatty acid levels in the maternal circulation correlated with umbilical cord levels. 3. The levels of linoleic acid in the maternal plasma free fatty acid fraction of the Asian women were much higher than previous reports on mixed populations of European women. In the Asian women arachidonic acid concentrations in both maternal and umbilical circulations were over four times higher than those reported for women unselected for race and diet.

Lipid and glucose metabolism in human placental culture

Placental culture models have been used to increase the understanding of endocrinology and pathophysiology in pregnancy. This article describes glucose and lipid metabolism in several of these models. Of special interest is the availability of arachidonic acid for the production of prostanoids. Ten placentas were collected at the time of cesarean section in term pregnancies without labor. Minced villous tissue was incubated for 48 hours in media with a glucose concentration of 100, 200, or 500 mg/dl. Tissue was dispersed in the media or was left as a single clump during the incubation. Glucose levels in the culture media were measured at 8, 20, 32, and 48 hours. Tissue lipid levels were measured before and after incubation in seven placentas. At 8 hours, glucose utilization ranged from 2.38 +/- 0.40 to 9.44 +/- 1.22 mumol/gm tissue/hr (mean +/- SEM). By 48 hours the cumulative glucose utilization ranged from 1.56 +/- 0.09 to 6.87 +/- 0.38 mumol/gm tissue/hr. Tissue lipid analysis showed most of the fatty acids to be in the phospholipids initially (4477 +/- 179 micrograms/gm tissue). Subsequent to incubation for 48 hours, phospholipid levels fell to a range of 2686 +/- 90 to 3466 +/- 157 micrograms/gm tissue in various culture conditions (p less than 0.005 compared with initial values). Whereas phospholipid levels decreased during incubation, levels of triglycerides and nonesterified fatty acids increased significantly in placental tissue. Arachidonic acid, the precursor of prostaglandins, thromboxane, and prostacyclin, makes up about one quarter of the fatty acid in the initial placental phospholipid. Arachidonic acid follows the pattern of total fatty acids during incubation; it is released from phospholipid and is converted to nonesterified fatty acid and triglyceride. We may conclude from this study that each placenta has a unique glucose utilization rate and a unique capacity to produce triglyceride. In tissue culture, arachidonic acid is released to its nonesterified state much more quickly than it can be converted to prostanoids by cyclooxygenase. The choice of initial glucose concentration, tissue preparation (dispersed in media or left as single clump), and time of incubation all may determine the rate of glucose metabolism, the rate of phospholipid breakdown, the rate of triglyceride production, and the quantity of nonesterified arachidonic acid in placental tissue culture.

The prostaglandin synthase inhibiting ability of maternal plasma and the onset of human labor

Using an enzyme incubation-radioimmunoassay technique we have cross-sectionally studied the prostaglandin synthase inhibiting ability of plasma in relation to human pregnancy. The inhibitory potency of human plasma did not change with the onset of pregnancy, at parturition or during the puerperium. A significant decrease in potency did occur however in the third trimester of pregnancy. This preparturient decrease raises the possibility of a role in the onset of human labor for the factor(s) causing the inhibition.

Kinetics of prostacyclin synthetase in umbilical artery microsomes from normal and pre-eclamptic pregnancies

1 Prostacyclin synthetase in umbilical artery microsomes obeys Michaelis-Menten kinetics. 2 The maximum velocity (Vmax) of prostacyclin synthetase prepared from normal umbilical arteries was significantly higher than the Vmax of prostacyclin synthetase in umbilical arteries taken from pre-eclamptic pregnancies. 3 The Michaelis-Menten constant (Km) of the two prostacyclin synthetase preparations was significantly different with the synthetase from pre-eclamptic arteries have a higher affinity for substrate. 4 The limiting factor for prostacyclin synthesis is Vmax at high substrate concentrations which appears to be the case in umbilical arteries. However, at low substrate concentration there would be no difference in prostacyclin synthesis by the two forms of prostacyclin synthetase.

A comparison of the quantitative analysis of 6-oxo-PGF1 alpha in biological fluids by gas chromatography mass spectrometry and radioimmunoassay

Two sensitive and selective quantitative methods for 6-oxo-PGF1 alpha, the stable hydrolysis product of prostacyclin are described and compared. Prostaglandins were extracted from biological fluids with organic solvents. Samples for gas chromatographic mass spectrometric analysis required additional thin-layer chromatographic separation prior to conversion to the O-methyloxime, methyl ester, tri-trimethylsilyl ether. Ion fragments at m/z 418 and 508 (protium) and m/z 422 and 512 (deuterium) were monitored to prepare 6-oxo-PGF1 alpha standard curves. The gas chromatographic mass spectrometric detection limit was 500 pg injected on column with a method coefficient of variation of 11.6% at this level. At 590 pg ml-1 the coefficient of variation for reproducibility of measurement was 1.77%. Antisera raised against a 6-oxo-PGF1 alpha-bovine serum albumin conjugate in sheep had a higher titre and greater selectivity than those raised in rabbits. Cross-reaction of sheep antisera with all prostaglandins and fatty acids tested was less than 0.5%. The radioimmunoassay limit of detection was 60 pg ml-1 (6 pg per tube) with a coefficient of variation of 10.4% (intra-assay) and 10.75% (inter-assay). The double blind comparison of gas chromatographic mass spectrometric and radioimmunoassay quantitation of the same samples gave a correlation coefficient of 0.97. Both methods offer sensitivity, selectivity and reproducibility. Gas chromatography mass spectrometry is necessary to validate the radioimmunoassay method which offers advantages of time, sample capacity and volume, expenditure and sensitivity.

Prostaglandin F production by tissue explants from term pregnancies

Explants of various tissues obtained from pregnant women at term and from nonpregnant women were maintained in culture and their capacities to synthesize prostaglandin (PGF) were evaluated. Myometrial and decidual tissues from pregnant women produced significantly smaller amounts of PGF than those from nonpregnant women, suggesting that PGF production is inhibited during gestation. Decidual PGF synthesis was also inhibited by the addition of progesterone, estradiol or indomethacin. The PGF synthesis of the chorion of women in labor was lower than that of women not in labor. In the later group, the cohrion, decidua and myometrium produced significant amounts of PGF, but amniotic PGF production was negligible. Our findings show that the decidua and chorion, as well as the myometrium, are potentially important sources of PGF production. PGF synthesis during pregnancy also may be affected by local inhibitory influences.

The passage of fat emulsion across the human placenta

Six patients near term were given an intravenous infusion of a fat emulsion (Intralipid) a few hours before normal delivery or Caesarean section. Six other non-infused patients were studied as controls. Maternal venous and umbilical venous and arterial blood samples were taken at delivery and analyzed for individual fatty acid concentrations in triglyceride, free fatty acid (FFA) and phospholipid fractions. The emulsion, being rich in oleic and linoleic acids, affected the composition of the maternal triglycerides. The fetal lipids were also altered and the infusions resulted in large positive umbilical venous-arterial (v-a) differences in FFA and triglyceride fatty acid concentrations, but this was not the case for phospholipid concentrations. The fatty acids with the largest v-a differences were those prominent in the emulsion.

Evidence for fatty acid transfer across the human placenta

Lipid analysis of blood from umbilical artery and vein, experiments on artificially perfused human placentas, measurements of fetal blood triglyceride concentrations and the relative percentage of essential fatty acids in fetal adipose tissue are all consistent with the view that fatty acids cross the human placenta and that the flow to the fetus is influenced by maternal blood concentrations of free fatty acids and triglycerides.