Atherosclerosis decreased prostacyclin formation in rabbit lungs and kidneys.

Metabolism of arachidonic acid (AA) was studied in perfused lungs and kidneys of normal and atherosclerotic rabbits by determination of PGE2, PGF2 alpha and the stable metabolites of PGI2 (6-keto-PGF1 alpha) and TXA2 (TXB2). PGI2 was the main AA metabolite formed by normal lungs and kidneys. Atherosclerosis reduced the formation of PGI2 by about 50 % in both organs. TXA2 formation was similarily decreased in lungs. In kidneys, the decrease in PGI2 formation was accompanied by an increase in PGE2 formation.     

Plasma prostaglandin levels and circulating fuel levels in rats with diabetic ketoacidosis: effects of cyclooxygenase inhibitors and of alpha and beta adrenergic blockade

We studied the effects of two structurally unrelated inhibitors of the fatty acid cyclooxygenase and of alpha and beta adrenergic blockade on the elevated plasma levels of 13,14-dihydro-15-keto-prostaglandin (PG)E2, 6-keto-PGF1 alpha and thromboxane (TX)B2, the stable derivatives of PGE2, PGI2 (prostacyclin) and TXA2, respectively, in rats with streptozotocin-induced diabetic ketoacidosis (DKA). Meclofenamic acid and indomethacin each produced a significant decrease in the elevated plasma levels of 13,14-dihydro-15-keto-PGE2, 6-keto-PGF1 alpha and TXB2. Phentolamine significantly reduced the plasma level of TXB2 but had no effect on the elevated circulating levels of glucose, free fatty acids, total ketones, 13,14-dihydro-15-keto-PGE2 or 6-keto-PGF1 alpha. Propranolol significantly reduced the elevated circulating levels of glucose, free fatty acids and total ketones but had no effect on the levels of the three prostaglandin derivatives. The ability of meclofenamic acid and indomethacin to reduce the plasma levels of 13,14-dihydro-15-keto-PGE2, 6-keto-PGF1 alpha and TXB2 confirms that the plasma levels of these three derivatives are elevated in rats with DKA. Since abnormalities in the production of PGI2 and perhaps other cyclooxygenase derivatives may contribute to the pathogenesis of certain important hemodynamic and gastrointestinal features of DKA, cyclooxygenase inhibitors may play a role in the management of selected patients with this disorder. Alpha adrenergic activity is essential for the maintenance of the elevated plasma TXB2 level in rats with DKA. The fall in the plasma TXB2 level during alpha adrenergic blockade appears to reflect inhibition of platelet aggregation and platelet TXA2 production, but other sources of the elevated plasma TXB2 level in DKA are not excluded. Beta adrenergic activity contributes to the maintenance of elevated circulating levels of glucose, free fatty acids and total ketones in experimental DKA but not to the elevated plasma levels of the prostaglandin derivatives.     

Altered myocardial prostaglandin synthesis in spontaneously diabetic rats

Patients with diabetes mellitus have an increased susceptibility to heart disease. The exact mechanism for this phenomenon is unclear. Abnormalities in prostaglandin (PG) production have been suggested as a possible cause. In this connection, we examined the PG synthetic capacity of cardiac microsomes from spontaneously diabetic rats. Cardiac microsomes from diabetic and control rats produced varying amounts of 6-keto-PGF1 alpha (stable degradation product of PGI2), PGE2, PGD2, PGF2 alpha, and TXB2 (stable breakdown product of TXA2). In both instances the production of 6-keto-PGF1 alpha predominated, however, microsomes from diabetic rats showed markedly greater conversion of arachidonic acid to all the PG products, especially 6-keto-PGF1 alpha. When PGF2 alpha metabolism was detected between diabetic and control heart preparations. These results show an enhanced cyclooxygenase activity in diabetic rat hearts without any change in prostaglandin dehydrogenase activity. Such a change may promote some of the cardiac alterations seen in diabetic mellitus.     

Myocardial prostacyclin and thromboxane A2 synthetase activities during ischemia and reperfusion in isolated rabbit heart

The aim of the study was to determine the prostacyclin (PGI2) and thromboxane A2 (TXA2) synthetase activities of myocardial tissue and their variation during ischemia and reperfusion. Regional ischemia was induced by 10 min occlusion of the left anterior descending coronary artery in isolated Langendorff rabbit hearts. Biosynthesis of PGI2 and TXA2 were carried out by using arachidonic acid as substrate and left ventricle microsomes (LVM) from ischemic and non-ischemic areas as sources of PGI2 and TXA2 synthetase. 6-keto-PGF1 alpha and TXB2, stable metabolites of PGI2 and TXA2 respectively, were determined by radioimmunoassay. Experiments carried out under the adopted conditions showed that LVM were able to synthetise PGI2 as well as TXA2 from arachidonic acid. On the other hand, ischemia depressed both PGI2 and TXA2 synthetase activities of cardiac tissue: the depression was more pronounced on TXA2 synthetase than on PGI2 synthetase with no significant difference between ischemic and non-ischemic regions. Moreover, ischemia increased the ratio 6-keto-PGF1 alpha/TXB2 indicating therefore that it can facilitate the formation of PGI2. The post ischemic reperfusion of the heart counteracted the decrease in PGI2 synthetase induced by ischemia which returned to the normal level: reperfusion also slightly reversed the decrease in TXA2 the decrease in TXA2 synthetase. However, the diminution in TXA2 synthetase of non-ischemic myocardium was attenuated but it remained lower than the normal level. These results suggested that the whole left ventricle is affected by regional ischemia. Furthermore it appears that myocardial TXA2 synthetase is more vulnerable than PGI2 synthetase to a lack of oxygen and nutrients.     

Evidence for a bidirectional prostaglandin endoperoxide shunt between platelets and the bovine coronary artery

While platelets have been shown to be capable of supplying prostaglandin (PG) H2 to endothelial cells in culture for PGI2 synthesis, endothelial cells have been shown unable to supply PGH2 to platelets for thromboxane (TX) A2 synthesis. We incubated rings of the bovine coronary artery (BCAR) with human platelets treated with aspirin (to inhibit cyclooxygenase) or CGS 13080 (to inhibit TXA2 synthase) in the presence of 20 microM arachidonic acid. BCAR, with damaged endothelium, produced significantly less PGI2 than that with intact endothelium. However, co-incubation with CGS 13080-treated platelets resulted in an increase in PGI2 independent of endothelium, demonstrating a shunt of PGH2 from platelets to BCAR. Co-incubation of BCAR with aspirin-treated platelets resulted in a net increase in TXA2 demonstrating a shunt of PGH2 from BCAR to platelets. Employing [14C]PGH2 as substrate, BCAR with and without intact endothelium produced similar amounts of 6-keto-[14C]PGF1 alpha. Likewise, homogenates (50 micrograms protein) of intimal and subintimal regions of BCAR and BCAR converted similar amounts of PGH2 to 6-keto-PGF1 alpha. These data suggest that vascular production of PGH2 is more dependent on an intact endothelium than is the conversion of PGH2 to PGI2. These data also suggest a potential for a bidirectional exchange of PGH2 between platelets and vascular wall during platelet-vascular wall interactions.     

Comparison of umbilical vein models for measurement of relative prostacyclin and thromboxane production

There is growing evidence that blood vessels generate TXA2 in addition to PGI2. We examined effluents from continuously perfused human umbilical vein and supernatants from umbilical vein rings for TXB2 and 6-keto-PGF1 alpha measurements (stable metabolites of TXA2 and PGI2, respectively). TXB2 and 6-keto-PGF1 alpha were identified in all samples. 6-keto-PGF1 alpha to TXB2 ratio was higher in intact vein effluents than in the venous ring supernatants (112:1 and 28:1, respectively, P less than 0.01). Arachidonate stimulation increased 6-keto-PGF1 alpha and TXB2 levels similarly in the intact vein effluent. In contrast, stimulation of the venous rings resulted in a relatively larger increase in TXB2 than in 6-keto-PGF1 alpha. This caused 6-keto-PGF1 alpha to TXB2 ratio to decline (p less than 0.01). The identity of TXB2 was confirmed in several different ways. These data suggest that 1) human umbilical veins produce TXA2 in addition to PGI2, 2) TXA2 release is more by venous rings than by the intact vein probably reflecting contribution from non-endothelial layers, and 3) arachidonate stimulation causes relatively greater release of TXA2 than of PGI2 from the venous rings, whereas release of PGI2 and TXA2 is similar from the intact vein.     

Prostacyclin and thromboxane formation in human umbilical arteries following stimulation with vasoactive autacoids

The formation of prostacyclin (PGI2) and thromboxane A2 (TXA2) (measured as the stable metabolites 6-keto-PGF1 alpha and TXB2) during stimulation with vasoactive autacoids was registered in human umbilical arteries perfused in vitro. Responses were registered within 3-4 minutes after addition of the substances. Both angiotensin I and II were found to increase the formation of PGI2 while depressing that of TXA2. Serotonin increased the formation of TXA2 but not that of PGI2. Both PGE2 and PGF2 alpha stimulated the PGI2 formation. The TXA2 mimetic U46619, increased PGI2 production, whereas PGI2 slightly increased the formation of TXA2. All responses were found to be completely inhibited by indomethacin.     

Testing the "redirection hypothesis" of prostaglandin metabolism in the kidney

Furosemide increases the synthesis of two major renal eicosanoids, prostacyclin (PGI2) and thromboxane A2 (TXA2), by stimulating the release of arachidonic acid which in turn is metabolized to PGG2/PGH2, then to PGI2 and TXA2. PGI2 may mediate, in part, the early increment in plasma renin activity (PRA) after furosemide. We hypothesized that thromboxane synthetase inhibition should direct prostaglandin endoperoxide metabolism toward PGI2, thereby enhancing the effects of furosemide on renin release. Furosemide (2.0 mg . kg-1 i.v.) was injected into Sprague-Dawley rats pretreated either with vehicle or with U-63,557A (a thromboxane synthetase inhibitor, 2 mg/kg-1 followed by 2 mg/kg-1 X hr-1). Urinary 6ketoPGF1 alpha and thromboxane B2 (TXB2), reflecting renal synthesis of PGI2 and TXA2, as well as PRA and serum TXB2, were measured. Serum TXB2 was reduced by 96% after U-63,557A. U-63,557A did not affect the basal PRA. Furosemide increased PRA in both vehicle and U63,557A treated rats. However, the PRA-increment at 10, 20 and 40 min following furosemide administration was greater in U-63,557A-treated rats than in vehicle-treated rats and urine 6ketoPGF1 alpha excretion rates were increased. These effects of thromboxane synthesis inhibition are consistent with a redirection of renal PG synthesis toward PGI2 and further suggest that such redirection can be physiologically relevant.     

High glucose levels modulate eicosanoid production in uterine and placental tissue from non-insulin-dependent diabetic rats during late pregnancy

Severe uterine and placental disturbances have been described in diabetes pathology. The relative severity of these changes appears to correlate with high glucose levels in the plasma and incubating environment. In order to characterize changes in eicosanoid production we compared uterine and placental arachidonic acid conversion from control and non-insulin-dependent diabetes mellitus (NIDDM) rats on day 21 of pregnancy, into different prostanoids, namely PGE2, PGF22alpha, TXB2 (indicating the production of TXA2) and 6-keto-PGF1 (indicating the generation of PGI2). PGE2, PGF2alpha and TXB2 production was higher and 6-keto-PGF1alpha was similar in diabetic compared to control uteri. PLA2 activity was found diminished in the NIDDM uteri in comparison to control. A role for PLA2 diminution as a protective mechanism to avoid prostaglandin overproduction in uterine tissue from NIDDM rats is discussed. Placental tissues showed an increment in TXB2 generation and a decrease in 6-keto PGF1alpha level in diabetic rats when compared to control animals. Moreover, when control uterine tissue was incubated in the presence of elevated glucose concentrations (22 mM), similar generation of 6-keto PGF1alpha and elevated production of PGE2, PGF2alpha and TXB2 were found when compared to those incubated with glucose 11 mM. Placental TXB2 production was higher and 6-keto PGF1alpha was lower when control tissues were incubated in the presence of high glucose concentrations. However, high glucose was unable to modify uterine or placental prostanoid production in diabetic rats. We conclude that elevated glucose levels induced an abnormal prostanoid profile in control uteri and placenta, similar to those observed in non-insulin-dependent diabetic tissues.     

Does gentamicin induce acute renal failure by increasing renal TXA2 synthesis in rats?

Acute renal failure (ARF) induced with large doses of Gentamicin (GM) (an aminoglycoside) was associated with increased urinary TXB (TXA) excretion which provoked a decrease of the ratios of urinary PGE2/TXB2 and 6-keto-PGF1 alpha (PGI2)/TXB2 excretions. Furthermore, as indicated by light microscopy most of the epithelial cells lining the proximal tubules show obvious lesions varying from swelling of their cytoplasm to complete necrosis. Either the inhibitor, OKY-O46, of TXA-synthetase, or volume expansion (VE) with isotonic saline (IS) of the experimental animals diminished urinary TXB excretion which provoked 1) augmentation of the ratios of urinary PGE/TXB and 6-keto-PGF1 alpha/TXB excretions, 2) elevation of creatinine clearance (Ccr) and 3) diminution of proteinuria (PU). This protection against ARF-by OKY-O46 and VE can a can be seen in microscopic sections where necrosis of proximal tubules is almost absent. Only a few proximal tubules show swelling of their epithelial cells and some focal areas of tubule necrosis. We suggest that the metabolites of arachidonic acid (AA), TXA2 a (potent vasoconstrictor agent) and prostaglandins (PGE2 and PGI2), (potent vasodilator factors), play an important role in the development (TXA2) or in the prevention (PGs) of ARF induced by this antibiotic.     

Activity of prostaglandin biosynthetic pathways in rat pancreatic islets

Isolated pancreatic islets of the rat were either prelabeled with [3H]arachidonic acid, or were incubated over the short term with the concomitant addition of radiolabeled arachidonic acid and a stimulatory concentration of glucose (17mM) for prostaglandin (PG) analysis. In prelabeled islets, radiolabel in 6-keto-PGF1 alpha, PGE2, and 15-keto-13,14-dihydro-PGF2 alpha increased in response to a 5 min glucose (17mM) challenge. In islets not prelabeled with arachidonic acid, label incorporation in 6-keto-PGF1 alpha increased, whereas label in PGE2 decreased during a 5 min glucose stimulation; after 30-45 min of glucose stimulation labeled PGE levels increased compared to control (2.8mM glucose) levels. Enhanced labelling of PGF2 alpha was not detected in glucose-stimulated islets prelabeled or not. Isotope dilution with endogenous arachidonic acid probably occurs early in the stimulus response in islets not prelabeled. D-Galactose (17mM) or 2-deoxyglucose (17mM) did not alter PG production. Indomethacin inhibited islet PG turnover and potentiated glucose-stimulated insulin release. Islets also converted the endoperoxide [3H]PGH2 to 6-keto-PGF1 alpha, PGF2 alpha, PGE2 and PGD2, in a time-dependent manner and in proportions similar to arachidonic acid-derived PGs. In dispersed islet cells, the calcium ionophore ionomycin, but not glucose, enhanced the production of labeled PGs from arachidonic acid. Insulin release paralleled PG production in dispersed cells, however, indomethacin did not inhibit ionomycin-stimulated insulin release, suggesting that PG synthesis was not required for secretion. In confirmation of islet PGI2 turnover indicated by 6-keto-PGF1 alpha production, islet cell PGI2-like products inhibited platelet aggregation induced by ADP. These results suggest that biosynthesis of specific PGs early in the glucose secretion response may play a modulatory role in islet hormone secretion, and that different pools of cellular arachidonic acid may contribute to PG biosynthesis in the microenvironment of the islet.     

Effects of arachidonic acid and prostaglandin F2 alpha in isolated rat lungs

Isolated rat lungs were ventilated and perfused by saline-Ficoll perfusate at a constant flow. The baseline perfusion pressure (PAP) correlated with the concentration of 6-keto-PGF1 alpha the stable metabolite of PGI2 (r = 0.83) and with the 6-keto-PGF1 alpha/TXB2 ratio (r = 0.82). A bolus of 10 micrograms exogenous arachidonic acid (AA) injected into the arterial cannula of the isolated lungs caused significant decrease in pulmonary vascular resistance (PVR) which was followed by a progressive increase of PVR and edema formation. Changes in perfusion pressure induced by AA injection also correlated with concentrations of the stable metabolites (6-keto-PGF1 alpha: r = -0.77, TxB2: -0.76), and their ratio: (6-keto-PGF1 alpha/TXB2: r = -0.73). Injection of 10 and 100 micrograms of PGF2 alpha into the pulmonary artery stimulated the dose-dependent production of TXB2 and 6-keto-PGF1 alpha. No significant correlations were found between the perfusion pressure (PAP) which was increased by the PGF2 alpha and the concentrations of the former stable metabolites. The results show that AA has a biphasic effect on the isolated lung vasculature even in low dose. The most potent vasoactive metabolites of cyclooxygenase, prostacyclin and thromboxane A2 influence substantially not only the basal but also the increased tone of the pulmonary vessels.     

Thromboxane (TX)A3 and prostaglandin (PG)I3 are formed in man after dietary eicosapentaenoic acid: identification and quantification by capillary gas chromatography-electron impact mass spectrometry

The low incidence of myocardial infarction in Greenland Eskimos has been related to their traditional marine diet rich in eicosapentaenoic acid. However, whether dietary eicosapentaenoic acid is indeed transformed in man to antiaggregatory PGI3 and weakly proaggregatory TXA3 has not been clarified. In our studies we ingested either cod liver oil or mackerel both rich in eicosapentaenoic acid. Formation of TXB3, the hydrolysis product of TXA3, in platelet-rich plasma stimulated ex vivo with collagen was traced by capillary GC/EIMS. Via external standard, TXB3 formation in platelets was estimated to be 5-15% of TXB2 formation. From urine we extracted dinor metabolites of PGI according to a selective method. We utilized delta 17-2,3-dinor-6-keto-PGF1 alpha (PGI3-M) as an index of total body production of PGI3 in analogy to 2,3-dinor-6-keto-PGF1 alpha (PGI2-M), the major urinary metabolite of PGI2. We separated PGI2-M and PGI3-M as the Me, MO, Me3Si derivatives by capillary gas chromatography and identified PGI3-M by EI mass spectrometry. Excretion of PGI3-M, which was not detectable under control conditions, was 83 +/- 25 ng/24 h (SD) after ingestion of cod liver oil and 134 +/- 38 ng/24 h after mackerel ingestion, while excretion of PGI2-M was 162 +/- 52 ng/24 h and 236 +/- 32 ng/24 h, respectively. Our findings with diets rich in EPA show that it is possible in man to change in vivo the spectrum of biologically active prostanoids by nutritional means and alter it in a favourable direction.     

Correlation between dysmenorrheic severity and prostaglandin production in women with endometriosis.

The role of prostaglandins (PGs) in dysmenorrhea of endometriosis is poorly understood. The relationship between dysmenorrheic severity and prostaglandin production was investigated in endometriosis. Slices of normal myometrium, adenomyosis, normal ovary and endometrial cyst were incubated. 6-Keto-PGF1 alpha (a metabolite of PGI2), TXB2 (a metabolite of TXA2), PGF2 alpha, and PGE2 concentrations of the incubation medium were measured by RIA. The results showed that 6-keto-PGF1 alpha production in adenomyosis and endometrial cyst were significantly higher than those in normal myometrium and ovary. A direct relationship between the degree of dysmenorrheic severity and PGs production in tissue in endometriosis was observed.     

Cyclooxygenase inhibition with acetylsalicylic acid unmasks a role for prostacyclin in erythropoietin-induced hypertension in uremic rats

We previously reported that thromboxane (TX)A2 synthesis and receptor blockade prevented recombinant human erythropoietin (rhEPO)-induced hypertension in chronic renal failure rats. The present study was designed to investigate the effect of a cyclooxygenase inhibitor, acetylsalicylic acid (ASA), on blood pressure, renal function, and the concentration of eicosano?ds and endothelin-1 (ET-1) in vascular and renal tissues of rhEPO-treated or rhEPO-untreated uremic rats. Renal failure was induced by a 2-stage 5/6 renal mass ablation. Rats were divided into 4 groups: vehicle, rhEPO (100 U/kg, s.c., 3 times per week), ASA (100 mg x kg(-1) x day(-1), and rhEPO + ASA; all animals were administered drugs for 3 weeks. The TXA2- and prostacyclin (PGI2)-stable metabolites (TXB2 and 6-keto-PGF1alpha, respectively), as well as ET-1, were measured in renal cortex and either the thoracic aorta or mesenteric arterial bed. The uremic rats developed anemia, uremia, and hypertension. They also exhibited a significant increase in vascular and renal TXB2 (p < 0.01) and 6-keto-PGF1alpha (p < 0.01) concentrations. rhEPO therapy corrected the anemia but aggravated hypertension (p < 0.05). TXB2 and ET-1 tissue levels further increased (p < 0.05) whereas 6-keto-PGF1alpha was unchanged in rhEPO-treated rats compared with uremic rats receiving the vehicle. ASA therapy did not prevent the increase in systolic blood pressure nor the progression of renal disease in rhEPO-treated or rhEPO-untreated uremic rats, but suppressed both TXB2 and 6-keto-PGF1alpha tissue concentrations (p < 0.05). ASA had no effect on vascular and renal ET-1 levels. Cyclooxygenase inhibition had no effect on rhEPO-induced hypertension owing, in part, to simultaneous inhibition of both TXA2 and its vasodilatory counterpart PGI2 synthesis, whereas the vascular ET-1 overproduction was maintained. These results stress the importance of preserving PGI2 production when treating rhEPO-induced hypertension under uremic conditions.     

Thromboxane synthase inhibition: implications for prostaglandin endoperoxide metabolism. I. Characterisation of an acute intravenous challenge model to measure prostaglandin endoperoxide metabolism

It has been proposed that thromboxane synthase inhibition (TXSI) may be a useful form of anti-thrombotic therapy and that this is due, in part, to redirection of PGH2 metabolism in favour of PGI2, a potent vasodilator and anti-platelet agent. While redirection has been observed ex vivo there are conflicting reports of its occurrence in vivo. We now describe the characterisation of an acute intravenous challenge model using thrombin, collagen, arachidonic acid (AA) and PGH2 for the study of PGH2 metabolism. Following challenge, plasma concentrations of TXB2, 6-oxo-PGF1 alpha, alleged metabolites of PGI2 (PGI2m) and PGE2 were measured by radioimmunoassay (RIA). Thrombin and collagen challenge resulted in a dose-related increase in plasma TXB2 while AA and PGH2, in addition, elevated 6-oxo-PGF1 alpha and PGI2m. Injection of PGH2 elevated 6-oxo-PGF1 alpha, PGI2m, TXB2 and PGE2 levels. Experimental conditions were defined such that challenge with thrombin (40 NIH units kg-1), collagen (100 micrograms kg-1), AA (1 mg kg-1) and PGH2 (5 micrograms kg-1) and measurement of eicosanoids 0.5 min following challenge were optimal for detection of redirection of PGH2 metabolism in vivo. The identity of immunoreactive TXB2 and 6-oxo-PGF1 alpha was further supported by experiments in which the extracted immunoreactive eicosanoids co-eluted with authentic [3H]standards when subject to reverse phase high performance liquid chromatography (RPHPLC). Evidence is also presented that the levels of plasma eicosanoids measured in this model reflect in vivo biosynthesis.     

Effects of 3,4-dihydroxyacetophenone on the biosynthesis of TXA2 and PGI2 in human placental villus and umbilical artery segments in vitro

In this paper, the effects of 3,4-dihydroxyacetophenone, DHAP (Qingxintong), an active constituent of traditional Chinese medicine, on the biosynthesis of TXA2 and PGI2 in human placental villi and umbilical artery segments of normal term pregnancy in vitro were studied by a perifusion technique. The collected fractions were assayed by radioimmunoassay for TXB2 and 6-keto-PGF1 alpha. The results showed that DHAP inhibited TXA2 and PGI2 production by umbilical artery segments in a dose dependent fashion and in both tissues TXA2 was more sensitive to inhibition than was 6-keto-PGF1 alpha. According to these data it is suggested that DHAP might be useful in treatment of pathologic pregnancies with chronic defective utero-placental circulation such as PIH and IUGR to improve this circulation.     

Formation of prostanoids in human umbilical vessels perfused in vitro

Four major prostanoids (6-keto-PGF1 alpha, PGE2, PGF2 alpha and TXB2) were measured by specific radioimmunoassays in the outputs from human umbilical vessels perfused in vitro. As evaluated by scanning electron microscopy (SEM) only few blood platelets were attached to the vessel wall. After an initial flush with decreasing concentrations of all four prostanoids, a stable stage was reached, lasting for 4-5 hours. During this stage the production could be inhibited by indomethacin and only slightly stimulated with arachidonic acid. The TXA2 synthetase inhibitor UK 38485 depressed the TXB2 production, while only slightly affecting the other three prostanoids at very high concentrations. The arteries produced relatively more 6-keto-PGF1 alpha than did the vein.     

Selective inhibition of arachidonic acid metabolite release from human lung tissue by antiinflammatory steroids

The effects of antiinflammatory steroids on arachidonic acid metabolite release from human lung fragments were analyzed. Incubation of lung fragments for 24 hr with 10(-6) M dexamethasone inhibited the net release of the prostacyclin metabolite 6-keto-PGF1 alpha, PGE2, and PGF2 alpha from lung fragments stimulated with anti-IgE but failed to inhibit the anti-IgE-induced release of PGD2, TXB2, and iLTC4. The IC50 of dexamethasone for inhibition of both spontaneous and anti-IgE-induced 6-keto-PGF1 alpha release was approximately 2 X 10(-8) M, and a 6-hr preincubation with the drug was required for 50% inhibition of prostaglandin release. Other agents were tested for activity in stimulating arachidonic acid metabolite release from human lung fragments. FMLP (fmet-leu-phe) stimulated the release of all metabolites tested (6-keto-PGF1 alpha, PGD2, PGE2, PGF2 alpha, TXB2, iLTC4); platelet-activating factor (PAF), but not lysoPAF, stimulated the release of PGD2, TXB2, and iLTC4. In contrast to the case with anti-IgE, where dexamethasone failed to inhibit net PGD2 and TXB2 release, the steroid inhibited the release of these metabolites stimulated by both FMLP and PAF. The steroid inhibited iLTC4 release induced by the highest concentration of PAF (10(-6)M) but did not inhibit iLTC4 release stimulated by either 10(-7) M PAF, FMLP, or anti-IgE. Because neither FMLP nor PAF caused the release of PGD2 or TXB2 from purified human lung mast cells, and because they also failed to induce histamine release from lung fragments, it is suggested that these stimuli produce PGD2 and TXB2 release in lung fragments through an action on a cell distinct from the mast cell. This suggestion is supported by the selective inhibition of the release of these arachidonic acid metabolites by dexamethasone. We suggest that the inhibitory action of steroids on arachidonic acid metabolite in human lung fragments contributes to their therapeutic efficacy in pulmonary diseases.     

Effects of experimental diabetes on spontaneous contractions, on the output of prostaglandins and on the metabolism of labelled arachidonic acid, in uteri isolated from ovariectomized rats. Influences of estradiol

Spontaneous changes in isometric developed tension (IDT) as a function of time after isolation (contractile constancy) in uteri from control-castrated and castrated chronic streptozotocin-diabetic rats, were explored. The effects of injecting 17-beta estradiol (Eo) were also studied. No differences in the minor changes of contractile constancy, between control and diabetic preparations, during a period of 60 min, were detected, whereas uteri from non-diabetic Eo injected animals (0.5 + 1.0 ug, prior to sacrifice), exhibited a profound reduction of IDT, significantly greater than in tissues obtained from Eo injected-diabetic rats. Moreover, basal generation and outputs into the suspending solution of prostaglandins (PGs) E1, E2 and F2 alpha, were explored in the same groups, at 60 min following tissue isolation. The basal outputs of these three PGs were similar in castrated control rats, but preparations from castrated-diabetics released significantly more PGE1. The administration of Eo to castrated-diabetics, failed to alter the releases of the three PGs explored. In addition, the metabolism of labelled arachidonic acid (AA) into different prostanoids (6-keto-PGF1, PGF2, PGE2 and thromboxane B2-TXB2), was also investigated. The non-diabetic spayed rat uterus converted AA into these four prostanoids, the transformation into 6-keto-PGF1 alpha (as an index of PGI2 formation) being the most prominent. In preparations from diabetic rats the formation) being the most prominent. In preparations from diabetic rats the formation of 6-keto-PGF1 alpha, PGF2 alpha and PGE2, was significantly smaller than in controls, whereas a greater % of TXB2 formation (as an index of TXA2), was detected. On the other hand uterine preparations from non-diabetic spayed rats injected with Eo formed less 6-keto-PGF1 alpha and PGE2 and similar amounts of PGF2 alpha or of TXB2 from AA, than Eo injected controls, whereas uteri from castrated diabetic animals injected with Eo, formed a similar % of 6-keto-PGF1 alpha, PGF2 alpha and PGE2 from AA, than tissue preparations from non-estrogenized controls. However, the enhanced transformation of the labelled fatty acid precursor (AA) into TXB2 in the diabetic group, was significantly reduced by the steroid. The role of the augmented generation and release of PGE1 in uteri from diabetic rats is discussed in terms of precedents indicating the relevance of PGs type E supporting rat uterine motility. In addition the influence of Eo is attractive, because its reducing effect on TX production, in diabetes, a disease known to be accompanied by enhanced synthesis of vasoconstrictor and platelet aggregation TXA2, and by frequent obstructive circulat