Prostaglandin Synthetase Activity Research Articles

C31. Closure of patent ductus arteriosus using intravenous paracetamol : a case series

Abstract Background Although patency of ductal arteriosus is essential for fetal circulation, postnatal ductal closure is critical for postnatal circulation adaptation in order to avoid pulmonary overcirculation with diminished circulation blood flow. Standard medical treatment for patent ductal arteriosus (PDA) consists of pharmacotheraphy and or surgical intervention. Case Summary We present 17 cases of PDA confirmed by echocardiography and was observed for ductal closure after 3 days of intravenous paracetamol intervention (10-15 mg/kg) given every 8 hours. The echocardiography evaluation of PDA status was conducted after those pharmacological intervention and divided based on the gestational age group. In the preterm groups (<36 weeks), 3 cases remained open, 3 cases were closed, and 1 case with reduced flow. In the aterm groups (36-42 weeks), 5 out of 8 cases were closed, while the other 3 showed reduced flow. In the postterm groups (>42 weeks), 1 case was closed and 1 case with reduced flow. Successful rate for PDA closure of each groups were 43%, 62,5% and 50%. Discussion Indomethacin and ibuprofen are standard treaments for PDA closure. However, they have some side effects such as acute renal failure and gastrointestinal complications. From this case series, paracetamol has a promising effect similar to indomethacin and ibuprofen in conducting PDA closure with less side effects. Paracetamol inhibits prostaglandin synthetase activity eventhough its precise mechanism of action remains controversial.

C31. Closure of patent ductus arteriosus using intravenous paracetamol : a case series

Abstract Background Although patency of ductal arteriosus is essential for fetal circulation, postnatal ductal closure is critical for postnatal circulation adaptation in order to avoid pulmonary overcirculation with diminished circulation blood flow. Standard medical treatment for patent ductal arteriosus (PDA) consists of pharmacotheraphy and or surgical intervention. Case Summary We present 17 cases of PDA confirmed by echocardiography and was observed for ductal closure after 3 days of intravenous paracetamol intervention (10-15 mg/kg) given every 8 hours. The echocardiography evaluation of PDA status was conducted after those pharmacological intervention and divided based on the gestational age group. In the preterm groups (<36 weeks), 3 cases remained open, 3 cases were closed, and 1 case with reduced flow. In the aterm groups (36-42 weeks), 5 out of 8 cases were closed, while the other 3 showed reduced flow. In the postterm groups (>42 weeks), 1 case was closed and 1 case with reduced flow. Successful rate for PDA closure of each groups were 43%, 62,5% and 50%. Discussion Indomethacin and ibuprofen are standard treaments for PDA closure. However, they have some side effects such as acute renal failure and gastrointestinal complications. From this case series, paracetamol has a promising effect similar to indomethacin and ibuprofen in conducting PDA closure with less side effects. Paracetamol inhibits prostaglandin synthetase activity eventhough its precise mechanism of action remains controversial.

Investigation of the chemical composition and biological activity of Xylopia aethiopica Dunal (Annonacae)

The phytochemical composition and physicochemical properties of oil extractable from the fruits of Xylopia aethiopica were determined. Extracts’ effects on cell membrane stability and prostaglandin synthetase activity were also evaluated. X. aethiopica oil extracted with chloroform: methanol (2:1, v/v) mixture contained carbohydrates, glycosides, flavonoids, saponins, tannins and phytosterols. The characteristic volatile and sweet smelling nature of X. aethiopica was predominantly inherent in this fraction. The sterol content was 64.30 mg/100 ml; with a high degree of unsaturatedness as evident in its high iodine value (85.76). High pressure liquid chromatographic analysis of the lipid extract revealed a fatty acid profile of palmitic acid (19.21%), palmitoleic acid (0.81%), stearic acid (4.54%), oleic acid (39.12%), linoleic acid (25.98%) and linolenic acid (1.10%). Investigation of the effect of the extract on hypotonicity- induced haemolysis of human red blood cells produced by water showed that the methanol extract of X. aethiopica (XAME) stabilized the red blood cells against the haemolytic action of distilled water. The lipid extract, on the other hand did not show any protective action against the osmotic shock. Xylopia aethiopica fruits may therefore be helpful in the maintenance of the integrity of the cellular membranes. The lipid extract also, in vitro, exhibited a prostaglandin synthetase substrate activity, whereas the methanol extract enhanced the synthesis of prostaglandins using X. aethiopica oil as substrate. The presence of appreciable quantity of unsaturated fatty acids, stabilization of the cellular membrane integrity, promotion of the biosynthesis of the hormone-like substances, prostaglandins, may be responsible for the usefulness of X. aethiopica fruits in the healing of wounds, inflammatory disorders and treatment of post-natal pains. Key words: Xylopia, linoleic acid, membranes, haemolysis, pains.

Dexamethasone makes the gastric mucosa susceptible to ulceration by inhibiting prostaglandin synthetase and peroxidase--two important gastroprotective enzymes.

The plausible mechanism by which dexamethasone makes the gastric mucosa susceptible to ulceration has been studied. As acid aggravates ulcer, the role of dexamethasone on acid secretion was first investigated. Dexamethasone stimulates both basal and drug (mercaptomethylimidazole)-induced gastric acid secretion by 100 and 50% respectively in male Wister rats 24 h after intramuscular administration at the dose of 1 mg/kg body wt. This stimulated acid secretion is 93% blocked by cimetidine indicating increased liberation of histamine in the process. Pretreatment of dexamethasone before 24 h produces ulcer in 30% of the pylorus- ligated rats and aggravates the ulcer index by 82% in both pylorus and esophagus ligated rats. The incidence of ulceration in the latter cases is also increased by 25%. As mucosal prostaglandin synthetase and peroxidase play an important role in gastroprotection through biosynthesis of prostaglandin and by scavenging endogenous H2O2 respectively, the effect of dexamethasone on the activities of these gastroprotective enzymes were studied. Prostaglandin synthetase and peroxidase activities of the mucosa are significantly inhibited by 87 and 83% respectively by 24-h pretreatment with dexamethasone. The results indicate that dexamethasone makes the mucosa prone to ulceration by inhibiting the activity of prostaglandin synthetase to block the gastroprotective action of prostaglandin and also by inhibiting the peroxidase, thereby elevating the endogenous H2O2 level to generate more reactive hydroxyl radical responsible for the mucosal damage.

Inhibition of gastric mucosal prostaglandin synthetase activity by mercaptomethylimidazole, an inducer of gastric acid secretion—plausible involvement of endogenous H 2O 2

We have reported earlier that mercaptomethylimidazole (MMI), an antithyroid drug of thionamide group, induces gastric acid secretion at least partially through the liberation of histamine, sensitive to cimetidine. Now, we show that the drug has a significant inhibitory effect on the cyclooxygenase and peroxidase activity of the prostaglandin (PG) synthetase of the gastric mucosal microsomal preparation. The effect can also be mimicked by low concentrations of H 2O 2. While studying the possible intracellular effect of MMI on acid secretion, a cell fraction (F 3) enriched in parietal cell was isolated by controlled digestion of the mucosa with protease. This cell fraction is activated by MMI as measured by increased O 2 consumption. The activation is sensitive to omeprazole, a proton-pump inhibitor, indicating that the activation is due to increased acid secretion by MMI. MMI was also found to directly inhibit the peroxidase activity of the F 3 cell fraction and may thus increase the intracellular level of H 2O 2. The cyclooxygenase activity of the PG synthetase of the F 3 cell fraction is also inhibited by MMI and the effect can be reproduced by low concentrations of H 2O 2. Both MMI and H 2O 2 can also inhibit the peroxidase activity of the PG synthetase. We suggest that in addition to the activation of the parietal cell by MMI possibly through endogenous H 2O 2, MMI induces acid secretion in vivo by inactivating the PG synthetase thereby inhibiting the biosynthesis of PG and removing its inhibitory influence on acid secretion so that the histamine released by MMI can stimulate acid secretion with maximum efficiency.

Biosynthesis of salivary prostaglandins in the lone star tick, Amblyomma americanum

Dopamine-induced saliva from ticks fed [ 3H]arachidonic acid contained the radiolabelled prostaglandins E 2, F 2α, D 2, and B 2, the latter probably derived from PGE 2 owing to the alkalinity of tick saliva. Prostaglandin synthetase (PGS) activity in the salivary gland homogenate from the lone star tick, Amblyomma americanum, could not be detected by standard radiometric methodologies successfully employed for tissues from many animal species, including numerous arthropods. Modifications to the assay conditions had no effect. The presence of a PGS-inhibitor in the salivary glands was ruled out. It is postulated that the PGS in A. americanum salivary glands may be considerably different from that found in other animals, including vertebrate hosts.

Role of renal metabolism in risk to toxic chemicals.

The kidneys are capable of carrying out extensive oxidation, reduction, hydrolysis, and conjugation reactions. Renal cortex has high activities of cytochrome P450 and glutathione (GSH) S-transferase. In contrast, renal medulla has high activity of prostaglandin synthetase, which can catalyze co-oxidation of xenobiotics. While these pathways are found in many tissues and at higher activities than in kidney, several key enzymes of the mercapturic acid pathway are found at especially high activities in cells of the renal proximal tubule. Investigations over the last two decades demonstrated that GSH conjugation is not only a mechanism for detoxification of reactive electrophiles. Rather, metabolism of GSH S-conjugates to the corresponding cysteine S-conjugates represents a branch point: cysteine S-conjugates may be metabolized by the cysteine S-conjugate N-acetyl-transferase to mercapturic acids, which are nontoxic and are excreted, or they may be substrates for the pyridoxal phosphate-dependent cysteine conjugate beta-lyase, which catalyzes either a beta-elimination or a transamination reaction to produce unstable thiols. These thiols rearrange to form potent acylating species that can covalently bind to cellular macromolecules, thereby producing cytotoxicity, mutagenicity, and carcinogenicity. In addition to the beta-lyase, two other renal enzymes, L-2-amino (2-hydroxy) acid oxidase and cysteine conjugate S-oxidase, can bioactivate chemicals to produce nephrotoxic species. Several halogenated alkanes and alkenes are bioactivated by these pathways. These findings show that mammalian kidney is highly active in bioactivation of xenobiotics. Although the properties of the corresponding enzymes in humans may differ, it is clear that renal metabolism can be a critical determinant of risk to chemical injury.

Effect of stress on the antioxidant enzymes and gastric ulceration.

The effect of cold-restraint stress on the antioxidant enzymes of the rat gastric mucosa was studied with a view to finding out their role in stress induced gastric ulceration. Histological examination revealed stress induced extensive damage of the surface epithelial cell with lesions extending up to submucosa in some cases. Stress causes time-dependent increase in histamine and pepsin content but decrease in acid content of the gastric fluid with the progress of ulceration (ulcer index) for two hours. The tissue lipid peroxidation was significantly increased as evidenced by accumulation of malondialdehyde. Since lipid peroxidation results from the generation of reactive oxygen species, stress effect was studied on some antioxidant enzymes such as superoxide dismutase, peroxidases and prostaglandin synthetase as a function of time. The time dependent increase in stress ulcer correlates well with the concomitant increase in superoxide dismutase activity and decrease in peroxidase and prostaglandin synthetase activity. This creates a favourable condition for accumulation of endogenous H2O2 and more reactive hydroxyl radical (OH.). Administration of antioxidants such as reduced glutathione or sodium benzoate prior to stress causes significant decrease in ulcer index and lipid peroxidation and protection of gastric peroxidase activity suggesting the involvement of reactive oxygen species in stress induced gastric ulceration. This is supported by the in vitro observation that OH. can also inactivate peroxidase and induce lipid peroxidation. As prostaglandin is known to offer cytoprotection, stress-induced loss of prostaglandin synthetase activity appears to aggravate the oxidative damage caused by reactive oxygen species.

Effects of protein synthesis inhibition on PGE 2 production in rabbit colonic explants cultured in vitro

Colonic mucosal biopsies cultured for 6 h in the presence of cycloheximide (CH) showed a dose-dependent inhibition of protein synthesis but a biphasic PGE 2 production pattern with an increase in both basal and A23187 stimulated PGE 2 release at 0.2 μM. At 10 μM CH both protein synthesis as well as basal and PMA induced PGE 2 production was inhibited by 90% whereas A23187 stimulated release showed a 50% decrease. At a dose of 100 μM, CH totally blocked also A23187 stimulated PGE 2 release without much further decrease in protein synthesis. The effects of 10 μM CH were time-dependently reversible. In biopsies loaded with 3H-arachidonic acid (AA), 10 μM CH had no apparent effect on phospholipase A 2 activity, nor could exogenous AA overcome the CH inhibition of basal PGE 2 release. No inhibition of prostaglandin synthetase (PS) activity was found in homogenates of biopsies treated with 10 μM CH for 6 h. No direct effect of CH (up to 1 mM) was seen in control homogenates. It is concluded that at least one step in the PGE 2 production is protein synthesis dependent. The effect is however not due to a limitation in the enzymes of the major PS system but more likely to one of its co-factors. This factor only plays a role in the intact cell and its importance seems to be reduced during A23187 conditions possibly due to altered cell status and/or other sources of PS. Commonly used high doses (100 μM) of CH give unspecific effects unrelated to inhibition of protein synthesis.

Major reproduction hormones as regulators of cell-to-cell interactions in humoral immune responses

The effects of chorionic gonadotropin (CG), estradiol, and progesterone on the cell mechanisms that determine the rate of the humoral immune response have been investigated in experiments on ovariectomized and noncastrated mice. CG (40 IU) injected into noncastrated animals increased the antibody response to sheep erythrocytes (SRBC), whereas a higher dose of the hormone (200 IU) had no effect. In contrast, both hormone doses inhibited the immune response in ovariectomized animals. Injection of estradiol (2.5 μg/day), but not progesterone (0.2 mg/day), into ovariectomized mice stimulated the immune response, indicating a possible role of estrogens as mediators of CG immuno-stimulating effect in noncastrated animals. Both CG doses inhibited suppressor cell generation in noncastrated mice, whereas in ovariectomized animals, the hormonal effect was directly opposite. Sex steroid hormones did not influence the formation of suppressor cells. In a syngeneic transfer system, the hormones under study did not change the activity of helper T cell precursors. However, CG administration to noncastrated recipients stimulated an adoptive immune response in a dose-dependent manner. Estradiol, but not progesterone, has the same effect in ovariectomized mice. CG administration (200 IU) to ovariectomized recipients inhibited the plaque-forming cell response. This CG effect depended upon prostaglandin synthetase activity.

The effect of dietary vitamin E and ß-carotene on oxidation processes in the rat testis

The effects of dietary vitamin E and ß-carotene were studied on enzymes involved in arachidonic acid metabolism and other related enzymes in the rat testis. Groups of rats were fed various soybean oil-based semi purified diets. Group 1 was fed a vitamin E-supplemented diet (+ E− ß); Group 2 was fed a ß-carotene-supplemented diet (− E+ ß); Group 3, the control group (−E− ß) was fed a vitamin E-deficient diet; and Group 4, the standard diet group (S), was fed vitamin E plus ß-carotene-standard diet. Soybean oxidized oil was added to the three diet groups — (+ E− ß), (− E+ ß) and (−E− ß), whereas the diet of S group contained non-oxidized oil. After 8 weeks rats were killed, blood and testis samples were collected for biochemical determinations. Vitamin E deficiency caused significant increase in testis thiobarbituric acid value and activities of testis NADPH oxidase, testis 15-lipoxygenase and in plasma pyruvate kinase. In contrast, significant decreases were observed in activity of testis prostaglandin synthetase, compared with antioxidant-supplemented diet groups. We also found a significant increase in 15-lipoxygenase activity in (− E+ ß) diet group, compared with (−E− ß) diet group. Fatty acid analysis of testis parenchyma indicated decrease in palmitate (16:0) and arachidonate (20:4( n−6)), and increase in oleate (18:1( n−6)) linoleate (18:2( n−6)) and linolenate (18:3( n−3)), when compared (−E− ß) diet group with vitamin E-supplemented diet groups. The results suggest that dietary vitamin E has a role in both enzymatic and non-enzymatic peroxidation of polyunsaturated fatty acids in the testis.

Endogenous Activation of Prostaglandin Synthesis in Rabbit Colonic Explants Cultured in vitro

Rabbit colonic biopsy specimens cultured in vitro showed an optimal release of prostaglandin E2 (PGE2) after 6-7 h of incubation. The amplitude but not the PGE2 production profile was dependent on stimuli applied--that is, A23187 greater than phorbol 12-myristate 13-acetate greater than control. This study was undertaken to determine the nature of this time-dependent optimum. The following hypotheses were tested: increased substrate availability, de novo synthesis of prostaglandin synthetase (PS), and translocation of PS or increased activity of PS. Arachidonic acid, either continuously present or given as a pulse, increased the overall amplitude equally but did not change the production profile. Cycloheximide, 0.2 microM, which inhibited 50% of the protein synthesis, increased the PGE2 production by 80% at 7 h. The cytoskeletal disrupting agent cytochalasin B had no effect. Homogenates of specimens cultured 6 h showed an increased PGE2 production. This was partly explained by a large increase in the PGE2 production capacity of the particulate matter obtained after 45 min of centrifugation at 100,000 g. It is concluded that the PGE2 production peak is due to an activation of preformed PS and that the PS activity is under the control of a peptide inhibitor, dependent on protein synthesis.

Interleukin‐1 potentiates histamine‐induced release of prostacyclin from human endothelial cells

1. In human cultured umbilical vein endothelial cells, interleukin-1 potentiated histamine-induced release of prostacyclin in a time- and concentration-dependent manner. 2. In cells incubated with interleukin-1 for 24 h, maximal potentiation was observed when cells were pre-incubated with 0.5 u ml-1 interleukin-1 before stimulation with histamine (1 microM-1 mM). 3. In cells incubated with 0.5 u ml-1 interleukin-1, 20 min pre-incubation was sufficient to induce a statistically significant potentiation of prostacyclin release induced by 1 microM histamine (P less than 0.05). 4. Nifedipine but not cycloheximide, significantly (P less than 0.05) inhibited histamine-induced release of prostacyclin and interleukin-1 potentiation of histamine-induced release of prostacyclin (P less than 0.05). 5. Incubation with 1 u ml-1 interleukin-1 induced a two fold increase in cellular prostaglandin synthetase activity within 30 min. The enzyme activity increased up to 6 h and was maintained up to 24 h. In cells co-incubated with cycloheximide and 1 u ml-1 interleukin 1, prostaglandin synthetase activity at 24 h was the same as that in unstimulated cells. Prostacyclin release was not significantly inhibited in cells co-incubated with cycloheximide and interleukin 1. 6. These results suggest that interleukin-1 potentiates histamine-induced release of prostacyclin by rapid up-regulation of prostaglandin synthetase activity as well as by inducing synthesis of enzyme protein. These mechanisms may act to potentiate/regulate vascular endothelial responses in inflammatory reactions.

Decreased prostaglandin production by cholesterol-rich macrophages.

The regulation of prostaglandin production by macrophages enriched in cholesterol was examined. Mouse peritoneal macrophages were incubated for 18 h with 25 micrograms/ml of human acetyl-LDL (low density lipoprotein) and trace amounts of labeled arachidonic acid. After cholesterol enrichment, the cells were incubated with phorbol 12-myristate 13-acetate (PMA), calcium ionophore, or zymosan to stimulate endogenous arachidonic acid metabolism. A high performance liquid chromatography profile of the eicosanoids released revealed no qualitative differences between unmodified and modified macrophages. Cholesterol-rich cells, however, released less prostacyclin (PGI2) and prostaglandin E2 (PGE2) compared to unmodified cells, and products from the lipoxygenase pathway became the predominant metabolites. A decrease in the synthesis of PGI2 and PGE2 by cholesterol-rich macrophages was confirmed by radioimmunoassay and radiolabeled experiments. The activity of prostaglandin synthetase was modestly increased in the cholesterol-modified macrophages compared to controls. As an estimation of phospholipase activity, the release of labeled arachidonic acid from membrane phospholipids, however, was significantly decreased in cholesterol-rich macrophages. The phosphatidylinositol fraction was particularly resistant to arachidonate release in response to calcium ionophore and PMA in the modified cells. The measurement of membrane phospholipid fatty acid composition before and after calcium ionophore supported the observation that less arachidonate was released by cholesterol-enriched cells in response to the ionophore. Based on these observations, we propose that prostaglandin synthesis from endogenous arachidonate stores is decreased in the cholesterol-rich macrophage. A decrease in agonist-induced activation of the phospholipase activity is proposed as a mechanism for this effect.

Antibiotic and Anti-inflammatory Analgesic Activities of Harungana madagascariensis Stem Bark

AbstractThis study shows that the aqueous methanol extract of Harungana madagascariensis has a broad spectrum antibiotic activity, decreases greatly the reaction time of mice to heat, inhibits carrageenan induced rat-paw oedema, and inhibits prostaglandin synthetase activity in vitro.

Content and formation of prostaglandins and distribution of prostaglandin-related enzyme activities in the rat ocular system

The steady-state levels of prostaglandin D 2, E 2 and F 2α in the rat eye were 0.5, 0.1 and 1.0 ng/g, respectively, which increased differently among the prostaglandins after a 40-min incubation of the homogenate at 37° C (to 23, 12 and 14 ng/g, respectively). When the eye was dissected into anterior uveal, scleral, and retinal complexes, prostaglandin D 2 was formed in the highest degree in all the complexes, whereas prostaglandin E 2 and F 2α formation was specific to given ocular regions. Three prostaglandin synthetase activities with similar K m values (20–40 μM) were found in the 10000 × g supernatant of these tissues i.e., GSH-independent and soluble D, GSH-dependent and membrane-bound E, and soluble F synthetase activities. These enzyme activities correlated well with the prostaglandin formation in each tissue, D synthetase activity being highest in all the tissues (11–25 nmol/min per g). Three types of prostaglandincatabolizing enzyme activities were detected in the 100000 × g supernatant of the tissues i.e., type II 15-hydroxy dehydrogenase ( K m = 10–30 μM), 9-keto (500 μM) and 11-keto reductase (2.5 mM). The activity of the dehydrogenase was low even in the retina, the tissue with the highest levels (0.51, 0.35 and 0.15 nmol/min per g for prostaglandin E 2, F 2α and D 2, respectively).

Sexual transfer of prostaglandin precursor in the field cricket, Teleogryllus commodus

ABSTRACT. When injected into the haemolymph of newly emerged adult males of the field cricket, Teleogryllus commodus (Walker), [3H]arachidonic acid is incorporated into tissue phospholipids. Two reproductive tissues, testes and accessory glands, incorporate and preserve the labelled arachidonic acid for at least 49 days. With onset of circadian rhythm‐controlled spermatophore production, radioactive arachidonic acid is incorporated into spermatophore phospholipids. After mating with untreated females, radioactivity was detected in spermathecae and in haemolymph from females. Some of the transferred radioactive arachidonic acid is subsequently converted into prostaglandins. Hence, males of T. commodus transfer prostaglandin synthetase activity and substrate by way of spermatophores during mating

Suppression of bone marrow stromal cell function by benzene and hydroquinone is ameliorated by indomethacin

Administration of benzene to mice will inhibit bone marrow stromal cell-supported hemopoiesis in cultre. Hydroquinone, a major metabolite of benzene, will cause a similar inhibition of stromal cell function in vitro. Stromal cells produce both an inducer (colonystimulating factor) and an inhibitor (prostaglandin E 2; PGE 2) of hemopoiesis. This research was conducted to determine if prostaglandin synthesis is involved in the suppression of stromal cell function by benzene and hydroquinone. Male B6C3F1 mice were administered benzene (100 mg/kg), indomethacin (1 mg/kg), or benzene plus indomethacin twice a day for 4 consecutive days. On Day 5 bone marrow cells were removed to determine the effect of treatment. In a second series of experiments mouse bone marrow stromal cells in culture were treated with hydroquinone (10 −7 to 10 −4 m), indomethacin (10 −6 m), or a combination of hydroquinone plus indomethacin. Stromal cell function was based on the ability of the treated stromal cells to support granulocyte/monocyte colony development in coculture. The results demonstrated that preadministration of indomethacin in vivo ameliorated benzene-induced inhibition of bone marrow stromal cell function. In vitro, indomethacin ameliorated hydroquinone toxicity to stromal cell function. Benzene administration in vivo induced elevated PGE 2 in bone marrow samples which were prevented by preadministration of indomethacin. However, hydroquinone in vitro did not induce a consistent increase in PGE 2 levels. These results suggested that toxicity to stromal cells was not due solely to increased prostaglandin synthetase activity.

Glucocorticoid and prostaglandin: lack of an inhibitory effect by dexamethasone on the synthesis of 6-ketoprostaglandin F 1α in rat lung

High doses of dexamethasone (1–12 mg/kg twice daily) were administered to pregnant rats for 2 days. The effect of dexamethasone on fetal and maternal lung prostaglandin metabolism was examined on day 21 of gestation. Dexamethasone treatment at all dosages significantly increased conversion of [ 14C]-arachidonic acid to 6-ketoprostaglandin F α in both fetal and maternal lung homogenates. This finding is similar to our earlier finding using lower dosages of dexamethasone and suggests that dexamethasone enhances lung prostaglandin synthetase activity. Because dexamethasone is known to inhibit the activity of phospholipases, we also measured lung immunoreactive 6-ketoprostaglandin F α. The results showed that dexamethasone treatment did not diminish lung 6-keto-prostaglandin F 1α level even at the highest dosage used (12 mg/kg). These results suggest that high dosages of dexamethasone, such as those used in the clinical treatment of septic shock, do not inhibit synthesis of lung prostaglandin.

The inhibitory effect of cytosolic fraction of human decidua on prostaglandin synthesis.

To elucidate the mechanism of suppression of prostaglandin (PG) production in decidua in early pregnancy, the PG synthetase activity of decidua and mid-secretory endometrium was studied. The microsomal fractions and their supernatants were prepared from the tissue by ultracentrifugation at 105,000 g. The standard incubation mixture consisted of the microsomal fraction and 14C arachidonic acid with cofactors, with incubation being carried out for 10 minutes at 37 degrees C. After extraction, the radioactivity of PGE2 was measured and PG synthetase activity was assayed. The apparent Km value for PG synthetase in decidua was 4.6 +/- 0.14 x 10(-6) M (n = 4), whereas that in endometrium was 4.6 +/- 1.18 x 10(-6) M (n = 3). Subsequently, kinetic studies on PG synthetase inhibitor in decidua were carried out. When sheep seminal vesicle was used as an enzyme source, the decidual supernatant showed competitive inhibition. The inhibitory substance in decidua was inactivated after incubation for 15 minutes at 65 degrees C. It seems likely that the suppression of PG biosynthesis in human decidua in early pregnancy is not due to the difference in PG synthetase found in decidua and in endometrium, but due to the existence of PG synthetase inhibitor in decidua.