Differential inhibition of fetal vascular prostacyclin and platelet thromboxane synthesis by monsteroidal anti-inflammatory drugs in humans

To study the synthesis of proaggregatory, vasoconstricting thrombone A₂ (TxA₂) by human fetal platelets we evaluated the formation of its stable metabolite thromboxane B₂ (TxB₂) during thrombin-induced spontaneous clotting of blood from the umbilical vein of 13 healthy infants. We further compared the effects of acetylsalicyclic acid, indomethacin, naproxen sodium and diclofenac sodium on platelet TxA₂ production in response to thrombin-induced aggregation during spontaneous clotting, and on prostacyclic (PGI₂) production by umbilical arteries in a superfusion system by measuring the 6-keto-prostaglandin F_1α (6-keto-PGF_1α) concentration in the superfusate. For every drug four concentrations covering the clinically significant range were studied. The basal production of TxB₂ by fetal platelets (181.5±22.5 ng/ml, mean±SEM) was comparable with that of adults (216.1±11.5 ng/ml). The concentrations of the drugs needed for 50 % inhibition of TxB₂ generation were 19.0 umol/1 for acetylsalicylic acid, 0.09 umol/1 for indomethacin, 0.06 umol/1 for diclofenac sodium and 4.2 umol/1 for naproxen sodium. The basal production of 6-keto-PGF_1α by umbilical arteries was 24.5±3.2 ng/min/g. The concentrations of the drugs needed for 50 % inhibition of 6-keto-PGF_1α production were 360.0 umol/1 for acetylsalicylic acid, 4.0 umol/1 for indomethacin, 2.3 umol/1 for diclofenac sodium and 15.0 umol/1 for naproxen sodium. Thus fetal platelet cyclo-oxygenase was 4–44 times more sensitive to these prostaglandin synthesis inhibitors than umbilical artery cyclo-oxygenase.     

Effect of inhibition of thromboxane production on the leukotriene D4-mediated bronchoconstriction in the guinea pig

Leukotriene D₄ (LTD₄) administered intravenously to anesthetized, spontaneously breathing guinea pigs elicited decreases in dynamic lung compliance (C_dyn) and airway conductance (G_AW) with a maximal response achieved at 0.5 min. Simultaneously, plasma levels of thromboxane metabolite, TxB₂, and the prostacyclin metabolite, 6-keto-PGF_1α, increased 10-fold over pre-LTD₄ levels. Pretreatment of the guinea pigs with meclofenamic acid delayed the onset of the LTD₄-induced bronchoconstriction, antagonized the magnitude of the decreases in C_dyn and G_AW, and blocked the increase in plasma TxB₂ and 6-keto-PGF_1α levels. The thromboxane synthetase inhibitor, UK 37,248, suppressed the LTD₄-induced bronchoconstriction, while it completely blocked TxB₂ production without significantly affecting 6-keto-PGF_1α. The SRS-A end organ antagonist, FPL 55712, blocked both the LTD₄-induced bronchoconstriction and the production of the arachidonic acid metabolites. These results suggest that thromboxane A₂ plays an important role in mediating part of the bronchoconstriction elicited by intravenously administered LTD₄ in the guinea pig.     

Identification of the major urinary metabolite of thromboxane B2 in the monkey

Thromboxane B₂ (TxB₂) was biosynthesized from prostaglandin endoperoxides (PGG₂, PGH₂) using guinea pig lung microsomes and infused into an unanesthetized monkey. Urine was collected and TxB₂ metabolites were isolated by reversed phase partition chromatography and high performance liquid chromatography. A major metabolite (TxB₂-M) was found to be excreted in greater than two-fold abundance relative to other metabolites. Its structure was determined by gas chromatography-mass spectrometry to be dinorthromboxane B₂. $\text{In vitro}$ incubation of TxB₂ with rat liver mitochondria yielded a C₁₈ derivative with a mass spectrum identical to that of TxB₂-M, substantiating that the major urinary metabolite of TxB₂ in the monkey is a product of a single step of β-oxidation.     

Effect of acute ethanol intake on thromboxane and prostacyclin in human

To investigate the effects of acute ethanol administration on the production of proaggregatory thromboxane A₂ (TxA₂) and anti-aggregatory prostacyclin (PGI₂), ethanol (1.5 g/kilogram body weight) was given to eight healthy nonsmoking men, and the stable metabolites thromboxane B₂ (TxB₂) and 6-keto-prostaglandin F_1α (6-keto-PGF_1α), respectively, measured by radioimmunoassay from serial blood samples before drinking and during the ensuing 18 hours. Each subject was studied as his own control on another occasion when only an equivalent volume of water was given. Serum TxB₂ level decreased (p < 0.01) from 206 + 31 ng/ml (mean) ± S.E. to 167² ± 24 and 161 ± 23 ng/ml (two and four hours after beginning of the drinking, respectively) concomitantly with the attainment of maximal blood ethanol concentrations (about 120 mg/100 ml), whereas no changes occurred in plasma 6-keto-PGF_1α concentrations. Our results may provide an explanation for known effects of ethanol on platelet aggregation. They also raise speculation whether TxA₂-inhibition and the antiatherogenic effect of alcohol intake are somehow related.     

Measurement of Prostaglandins in the Cerebrospinal Fluid in Cat, Dog, and Man

Prostaglandins are involved in the modulation of various central functions (neurotransmitters and hypothalamic hormone release, thermoregulation, cerebro-vascular tone) and their levels increase in pathological situations [subarachnoid hemorrhage (SAH), stroke, convulsive disorders, etc.]. This study, using sensitive and specific antibodies, examined levels of four eicosanoids, Prostaglandins E₂ and F_2α(PGE₂, PGF_2α); and the metabolites of PGI₂, 6-keto-prostaglandin F_1α (6-keto-PGF1_α) and of thromboxane A₂, thromboxane B₂ (TxB₂), in the cerebrospinal fluid (CSF) obtained atraumatically from three species (human, canine, and feline). An assessment of the methodologic procedures (extraction and radioimmunoassay) was carried out. Human lumbar cerebrospinal fluid was shown to contain PGF_2α (15–44 pg/ml), 6-keto-PGF_1α (undetectable to 39 pg/ml), and TxB₂ (un-detectable to 28 pg/ml), whereas PGE₂ was undetectable (>18 pg) in all cases. In both animals species the eico-sanoid concentrations were 3-to 30-fold higher than humans for every prostaglandin examined. Although the prostaglandin profile for a given species remained constant (cat, PGE₂:6-keto-PGF_1α:TxB₂:PGF_2α; dog, TxB₂:PGE₂:6-keto-PGF_1α:PGF_2α), the absolute levels were found to be lower in the pentobarbital-anesthetized animals than in conscious cats. The correspondence of the prostaglandin profiles found in cerebrospinal fluid with the profiles reported in the literature in brain homogenates for the same species supports the hypothesis that cerebrospinal fluid levels of prostaglandins reflect the relative rates of synthesis in neural tissue.     

The metabolism of arachidonic acid in isolated perfused fetal and neonatal rabbit lungs

The developmental pattern of fetal and neonatal rabbit lungs to metabolize arachidonic acid (AA) to different cyclo-oxygenase products was studied in isolated rabbit lungs, which were perfused with Krebs bicarbonate buffer. ¹⁴C-AA (66 nmol) was injected into the pulmonary circulation and the nonrecirculating perfusion effluent was collected for four minutes. About ten per cent of the injected radioactivity was found in the 0–4 min perfusion effluent. The metabolites of AA in the effluent were analyzed by thin layer chromatography. The major metabolites of AA were PGE₂ and its 15-keto-derivates, but also PGF_2α and its 15-keto-derivates, TXB₂ and 6-keto-PGF_1α were found in the effluent. The most drastic developmental change was the increase in the amount of 15-keto-metabolites of PGE₂ from late fetal period to the lungs of one day old rabbits (1.8 fold increase between birth and first postnatal day). Smaller changes were detected in the amounts of other cyclo-oxygenase products.     

The metabolism of arachidonic acid to an antiaggregatory compound in isolated lungs of fetal and neonatal rabbits

The developmental pattern of fetal and neonatal rabbit lungs to generate an antiaggregatory compound from arachidonic acid (AA) was studied in isolated rabbit lungs, which were perfused with Krebs bicarbonate buffer. The antiaggregatory effect of the nonrecirculating perfussion effluent was tested by adding a small portion of the effluent to human platelet rich plasma (PRP) in a Born-type aggregometer before the aggregation was induced by ADP. The production of an antiaggregatory compound was minimal, when exogenous AA was not infused into the pulmonary circulation. When arachidonate (40 nmol/min) was infused into the pulmonary circulation of rabbits which were 1 day or 1 week old, the perfusion effluent significantly inhibited the ADP induced aggregation of PRP. Perfused lungs from fetal rabbits (gestation age 28–31 days) formed also an antiaggregatory compound fro AA, but the antiaggregatory effect was not as great as 1 day after birth. It seems that neonatal rabbit lungs metabolize AA more to an antiaggregatory compound than late fetal lungs. The fact that the AA induced production of an antiaggregatory compound is inhibited by simultaneous infusion of indomethacin favours the hypothesis that this antiaggregatory compound could he PGI₂.     

Sex differences in platelet thromboxane and arterial prostacyclin production in control and n-6 fatty acid supplemented rats

Sex differences in eicosanoid production in platelets and vessel walls have been studied in control and n-6 fatty acid supplemented rats. In platelet rich plasma (PRP) of control female rats, arachidonic acid (AA) levels in phospholipids (PL), thromboxane B₂ (TxB₂) formation following collagen stimulation and aggregatory responses to collagen were higher than in PRP of male rats. 6 keto PGF_1α release from PRP-perfused isolated aortas were the same for both sexes, but the antiaggregatory activity of the wall was higher in males than in females, in association with a greater sensitivity of male platelets to prostacyclin.The administration of n-6 fatty acid supplements increased AA level in PL, TxB₂ production and aggregation only in male platelets. Production of 6 keto PGF_1α and the antiaggregatory activity of aortic walls were reduced after dietary treatment in males, but biochemical and functional parameters were not correlated in females.The results indicate complex sex-related differences in fatty acid metabolism and eicosanoid production, and in responses to n-6 dietary fatty acids in platelets and the vascular system in the rat.     

Differential effects of various vasoactive drugs on basal and stimulated levels of TXB2 and 6-keto-PGF1α in rat brain

Thromboxane B₂ and 6-keto-PGF_1α (6KPGF_1α), the major stable metabolites of thromboxane and prostacyclin, are present in the CNS, where they appear to be mainly produced within and/or acting upon the vascular district. Their concentrations are of few pg/mg protein in rat brain cortex of animals sacrificed by microwave (MW) radiation, procedure which inactivates tissue enzymes and allows the determination of endogenous “basal” levels of eicosanoids. Levels of 6KPGF_1α and especially those of TxB₂ increase several fold over the basal values in brain cortex of animals sacrificed by decapitation followed by a few minute interval before analysis (post-decapitation ischemia, PDI). Pretreatment of animals with the vasoactive drug papaverine, resulted in elevation of brain basal levels of 6KPGF_1α and with the carbochromene derivartive AD₆ in reduction of basal levels of TxB₂, whereas the calcium antagonist nifedipine and dipyridamole did not modify basal levels of the two eicosanoids. Treatments with papaverine and AD₆ reduced the accumulation of TxB₂ and enhanced that of 6KPGF_1α occurring after PDI, to different extents, both resulting, however, in reduction of the TxB₂/6KPGF_1α ratio. Nifedipine instead, decreased the release of both eicosanoids and resulted in elevation of the TxB₂/6KPGF_1α ratio, whereas dipyridamole had no effect. In conclusion, the evaluation of the overall effects of drug treatments on the TxB₂/6KPGF_1α ratio in cerebral tissue, provided useful informations on the pharmacological modulation of vascular eicosanoids in this district.     

RETRACTED ARTICLE: Anti-Inflammatory Effects of Chronic Aspirin on Brain Arachidonic Acid Metabolites

Pro-inflammatory and anti-inflammatory mediators derived from arachidonic acid (AA) modulate peripheral inflammation and its resolution. Aspirin (ASA) is a unique non-steroidal anti-inflammatory drug, which switches AA metabolism from prostaglandin E₂ (PGE₂) and thromboxane B₂ (TXB₂) to lipoxin A₄ (LXA₄) and 15-epi-LXA₄. However, it is unknown whether chronic therapeutic doses of ASA are anti-inflammatory in the brain. We hypothesized that ASA would dampen increases in brain concentrations of AA metabolites in a rat model of neuroinflammation, produced by a 6-day intracerebroventricular infusion of bacterial lipopolysaccharide (LPS). In rats infused with LPS (0.5 ng/h) and given ASA-free water to drink, concentrations in high-energy microwaved brain of PGE₂, TXB₂ and leukotriene B₄ (LTB₄) were elevated. In rats infused with artificial cerebrospinal fluid, 6 weeks of treatment with a low (10 mg/kg/day) or high (100 mg/kg/day) ASA dose in drinking water decreased brain PGE₂, but increased LTB₄, LXA₄ and 15-epi-LXA₄ concentrations. Both doses attenuated the LPS effects on PGE₂, and TXB₂. The increments in LXA₄ and 15-epi-LXA₄ caused by high-dose ASA were significantly greater in LPS-infused rats. The ability of ASA to increase anti-inflammatory LXA₄ and 15-epi-LXA₄ and reduce pro-inflammatory PGE₂ and TXB₂ suggests considering aspirin further for treating clinical neuroinflammation.     

Renal arachidonic acid metabolism and cellular changes in the rabbit renal vein constricted kidney: Inflammation as a common process in renal injury models

The process of renal inflammation was examined using the partial renal vein constricted rabbit kidney (RVC) as a model. Forty eight hours of partial renal vein constriction in the rabbit was associated with an increase in prostaglandin (PG) and thromboxane (Tx) production. The perfused RVC kidney showed an enhanced time-dependent increase in PG and Tx production in response to bradykinin stimulation when compared with the unlatered contralateral (CLK) or normal kidney. At 6 hrs of perfusion bradykinin stimulation lateral (CLK) or normal kidney. At 6 hrs of perfusion bradykinin stimulation released 2950±350 ng PGE₂, 61±15 ng TxB₂ from the RVC, and 225±85 ng PGE₂ and undetectable TxB₂ from the CLK. Histological examination of the RVC cortex showed an increase in fibroblast-like cells, a modest increase in the interstitial space and an appearance of macrophages and lymphocytes not seen in the normal of CLK. Endotoxin has been reported to stimulate macrophages in culture to produce PGE₂ and TxB₂. Endotoxin (100 ng)_stimulation of the perfused RVC kidney caused an immediate, followed by a chronically increasing, release of PGs and Tx. Two hours after endotoxin injection 50 ml of effluent fromt the RVC contained 1450±107 ng PGE₂ and 15.0±4.5 ng TxB₂. Other models of renal inflammation (e.g., the hydronephrotic kidney, chronic glomerulonephritis) also show the histological appearance of macrophages. In addition, hydronephrotic kidneys undergo fibroblast proliferation and changes in arachidonic acid metabolism similar to what we observed in the RVC. This work suggests that the inflammatory process (mononuclear cell infiltration), fibroblast-like cell proliferation, and accompanying changes in arachidonate metabolism) is common among different forms of renal injury.     

Prostaglandin removal and metabolism by isolated perfused rat lung

We have investigated the mechanism(s) involved in the removal of prostaglandins (PG) from the pulmonary circulation by the lung. Unidirectional fluxes of PG from the circulation into the lung are measured in an isolated perfused rat lung preparation. Evidence is presented which suggests that a transport system for PG exists in lung tissue. This transport system is responsible for the removal of some PG from the circulation by the lung. PGE₁ and PGF_2α are substrates for this system, whereas PGB₁, PGA₁, and 15-keto-PGF_2α are not. Since PGA₁ is a substrate for the intracellular PG dehydrogenase, the selectivity of the lung's metabolism system for circulating PG is probably due to the selectivity of the transport system for PG. It is shown that the percentage of the pulmonary arterial concentration (C_A) of PGE₁ or PGF_2α that is metabolized on passage through the pulmonary circulation decreases rapidly as C_A increases. When the lungs were perfused with PGE₁ (PGF_2α), the metabolites detected in the venous effluent were 15-keto-PGE₁ (PGF_2α) and 15-keto-13,14-dihydro-PGE₁ (PGF_2α). The time course pattern of the appearance of metabolites in the venous effluent after the initiation of a constant C_A, and the relative concentrations of the metabolites in the venous effluent, were examined as a function of C_A.     

Cholinergic stimulation of vascular prostacyclin synthesis

The production of prostacyclin by rings of rabbit aorta was assessed by the radioimmunoassay of 6-K-PGF_1α. In steady-state conditions, the rings released 11 ng 6-K-PGF_1α per 100 mg tissue in 30 min. Acetylcholine increased this output: a significant effect was detected at 1 μM and at 10 μM the amplitude of stimulation was 10-fold. The production of PGE₂ and PGF_2α was also increased, but to a lesser extent. The stimulatory action of acetylcholine was mimicked by carbamylcholine and inhibited by atropine; it was abolished in a calcium-free medium. Dog and rat aorta also produced more 6-K-PGF_1α in response to cholinergic agonists. A short rubbing of the intimal surface of the aorta removed the layer of endothelial cells and completely abolished the cholinergic effect. It is concluded that in the aorta, cholinergic agonists, acting on a muscarinic receptor, stimulate the production of prostacyclin by endothelial cells.     

Prostacyclin,thromboxane and prostaglandin F2αin suction blister fluid of human skin: Effect of systemic aspirin and local glucocorticosteroid treatment

Changes in prostaglandin (PG) metabolism are known to be involved in various skin diseases. To elucidate the behavior of hree vasoactive PGs in human skin, namely prostacyclin (PG1₂), thromboxane A₂ (TxA₂) and PGF_2α, their stable metabolites, 6-keto-PGF_1α. TxB₂, and 13, 14 dihydro-15-keto PGF_2α (MPGF_2α), respectively, were measured by radioimmunoassays in suction blister fluids of 29 healthy male subjects. Nine of them were treated with acetylsalicylic acid (0.5 g × 4/day for one day beforehand), eight with local glucocorticoid (clobetasol-17-propionate, Dermovat^R Cream, twice a day for seven days) and 12 served as controls. All three PGs were detected in blister fluid. In controls the mean (±SD) concentration of 6-keto-PGF_1α was 1160 ± 470 pg/ml (n=12) that of TxB₂ 1590 ± 610 pg/ml (n=12) and that of MPGF_2α 1800 ± 710 pg/ml (n=12), levels which are higher than the respective concentrations in human plasma. The preceding aspirin treatment decreased the 6-keto-PGF_1α levels by 40 % (P<0.005), the TxB₂ levels by 80 % (P<0.001) and MPGF_2α levels by 35 % (P<0.05), whereas the preceding local glucocorticoid caused no changes in these PG levels. The results show that 1) PG1₂, TxA₂, and PGF_2α are locally released in the suction blister fluid of healthy human skin, 2) systemic treatment with a PG synthesis inhibiting drug, acetysalicylic acid, reduces this release, and 3) locally applied clobetasol-17-propionate does not affect the levels of prostaglandins and thromboxane as measured by our methods.     

Measurement of thromboxane B2 in human plasma or serum by radioimmunoassay

A radioimmunoassay for thromboxane B₂ (TxB₂), a stable metabolite of thromboxane A₂, is described. The method consists of extraction of TxB₂ into ethyl acetate from acidified plasma or serum samples and saturation analysis using specific antibodies produced in rabbits against TxB₂-BSA conjugate. The 50 % displacement level of the standard curve was 19.1 ± 2.9 pg/tube (mean ± S.D., n = 19). The method blank was 3.4 ± 3.1 pg/ml (n = 15) and the assay sensitivity thus 9.6 pg/ml (mean blank + 2 S.D.). When 100 to 200 pg of TxB₂ were added to plasma, 96.2–103.6 % were recovered. The intra-assay coefficient of variation varied from 6.7 to 9.7 %, and the inter-assay coefficient of variation was 18.6 % (n = 10). The TxB₂ concentration in the plasma of 14 healthy subjects varied from 29.3 to 120.8 pg/ml with a mean ± S.D. of 70.1 ± 26.1 pg/ml, when the blood was collected into tubes containing acetylsalicylic acid (ASA), whereas significantly higher (p < 0.001) TxB₂ concentrations of 68.3 – 285.3 pg/ml with a mean ± S.D. of 151.8 ± 66.6 pg/ml were obtained from the same subjects in the plasma of blood which was collected into tubes containing no ASA. When blood samples from 10 subjects were allowed to clot at 0, +24 or +37°C for 60 min., the TxB₂ concentrations in the sera were 2053 ± 870 pg/ml, 4001 ± 1370 pg/ml and 178557 ± 54000 pg/ml, respectively. The TxB₂ levels in sera which were separated from blood samples incubated at +37°C, correlated significantly (p < 0.001) with the TxB₂ productions in platelet-rich-plasma (PRP) after an induced aggregation. Our results indicate 1) when TxB₂ is measured in plasma, the use of prostaglandin synthesis inhibitor in the collection tubes is necessary and 2) the measurement of TxB₂ in serum of blood which has been kept at +37°C for a strictly standardized period of time could replace the use of PRP in TxB₂ studies.     

Thromboxane and pulmonary hypertension following E. coli endotoxin infusion in sheep: Effect of an imidazole derivative

We assessed the effect of a specific thromboxane synthetase inhibitor (an imidazole derivative) on pulmonary hemodynamics and the concentrations of TxB₂ (TxA₂), 6-keto-PGF_1α (PGI₂), and PGF_2α in pulmonary lymph and transpulmonary blood samples following intravenous administration of E. coli endotoxin (1 μg/kg) in sheep. In control animals the rise in pulmonary artery pressure correlated with increases in plasma and lymph TxB₂ concentrations and large transpulmonary concentration gradients of this metabolite were measured. In imidazle treated animals both pulmonary hypertension as well as increases in plasma and lymph TxB₂ concentrations were substantially reduced. In contrast, peak concentrations of 6-keto-PGF_1α (PGI₂) and PGF_2α were severalfold higher than those measured in control animals. This suggests a shunting of endoperoxide metabolism towards prostacyclin and primary prostaglandins and documents the specificity of the thromboxane synthetase inhibitor. Out study provides evidence that endotoxin-induced pulmonary hypertension is mediated by pulmonary synthesis of TxA₂.     

Infuence of dietary fish on eicosanoid metabolism in man

Two groups of 40 volunteers were given a dietary supplement consisting of 135 g of mackerel or meat (control) paste per day for 6 weeks. Compliance was about 80% in both groups and the daily intake of 20:5(n−3) and 22:6(n−3) from the mackerel supplement was about 1.3 and 2.3 g, respectively. In collagen-activated platelet rich plasma, the potency of blood platelet to produced HHT from arachidonic acid (AA) clearly reduced in the mackerel group, whereas the formation of HHTE from timnodonic acid (TA) increased slightly. Changes in the formation of HHT and HHTE, measured by HPLC, correlated significantly with those of TxB₂ and TxB₃, respectively, measured by GC/MS. Changes in the formation of the lipoxygenase products HETE (ex AA) and HEPE (ex TA) were qualitatively similar to that seen for the cyco-oxygenase products, but quantitatively the responses were smaller. Formation of ir TxB₂ in clotting blood significantly reduced in the mackerel group. In collagen-activated, citrated whole blood, TxB₂ formation tended to be reduced in the mackerel-supplemented volunteers. Mackerel consumption was associated with the formation of considerable amounts of PGl₃, as judged from the appearance of 2,3-dinor-Δ 17-6-keto-PGF_1α in urine. The amount of the major metabolite of PGl₂, 2,3-dinor-6-keto-PGF_1α was not reduced, or even increased. The daily amount of tetranor prostaglandin metabolites in the urine did not change significantly, which indicates that mackerel supplementation did not alter the formation of prostaglandins E and F.     

Increased thromboxane A2 production but normal prostacyclin by the placenta in hypertensive pregnancies

The production of vasodilatory, antiaggregatory prostacyclin (PGI₂) and vasoconstrictory, proaggregatory thromboxane A₂ (TxA₂) by the placenta was studied in the cases of hypertensive pregnancy complications by superfusing pieces from maternal and fetal sides of placentae of 9 pre-eclamptic, 6 hypertensive and 11 healthy women and measuring the release of 6-keto-prostaglandin F_1α (6-keto-PGF_1α) and thromboxane B₂ (TxB₂), the breakdown products of PGI₂ and TxA₂ respectively, from the superfusate. Both sides of the placentae from the controls produced 6-keto-PGF_1α (maternal side 0.5±0.1 ng/g/min dry weight of tissue, mean±SEM; fetal side 0.7±0.2 ng/g/min) and TxB₂ (maternal side 2.5±0.4 ng/g/min; fetal side 2.7±0.5 ng/g/min with no correlation between the two. The 6-keto-PGF_1α production was normal in hypertensive complications whereas the TxB₂ production was increased on the fetal side of the placentae obtained from the pre-eclamptic (3.7±0.3 ng/g/min: p<0.05) and hypertensive women (4.1±0.4 ng/g/min; p<0.025). This may explain the occurrence of microthrombi and infarctions in placentae of hypertensive women.     

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 F_2α (PGF_2α) and prostaglandin E₂ (PGE₂) and plasma 13,14-dihydro-15-keto-PGF_2α (PGFM) concentration were also measured by radioimmunoassay. For caruncular tissue, less thromboxane B₂ (TXB₂) and more 6-keto prostaglandin F_1α (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, PGF_2α 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, PGF_2α 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.