Experimental criteria for evaluating prostaglandin biosynthesis and intrinsic function

Characterization and physiological variation in prostaglandin, prostacyclin and thromboxane synthesis by corpora lutea, non-luteal and uterine tissues during pseudopregnancy in the rabbit

To determine if luteal as well as uterine prostaglandin production is associated with luteal regression, the conversion of (14C) arachidonic acid into prostaglandin (PG) F2 alpha, PGE2, PGD2, prostacyclin (measured as its stable metabolite 6-keto-PGF1 alpha) and thromboxane (measured as its stable metabolite TXB2) was characterized and measured in microsomes from the uterus, corpora lutea and nonluteal tissue of the rabbit on days 8, 12 and 15 of pseudopregnancy. PGF2 alpha production was increased on day 15 compared to days 8 or 12 of pseudopregnancy in corpora lutea and in the uterus. In uterine microsomes, 6-keto-PGF1 alpha production was also elevated on day 15. No significant changes in the production of PGF2 alpha, TXB2 or PGD2 were observed with uterine or luteal microsomes. Arachidonic acid metabolism by microsomes from nonluteal tissue was not significantly different on any day examined. These results suggest that intraluteal, as well as uterine PGF2 alpha production may contribute physiologically to the final phase of luteal regression.

Leukotriene B4 level in neutrophils from allergic and healthy subjects stimulated by low concentration of calcium ionophore A23187. Effect of exogenous arachidonic acid and possible endogenous source

Peripheral blood neutrophils from patients with allergic rhinitis and from normal subjects were incubated for 5 min at 37 degrees C with 0.15 microM calcium ionophore A23187 in the absence or presence of exogenous arachidonic acid (2.5 to 10 microM). In neutrophils from allergic patients, the leukotriene B4 (LTB4) level was significantly increased by exogenous arachidonic acid in a concentration-dependent manner (16.2 +/- 4.2 and 38.1 +/- 6.8 pmol/5 min per 2 X 10(6) cells in the absence and presence of 10 microM arachidonic acid, respectively; P less than 0.005; n = 8). The LTB4 level in neutrophils from healthy subjects was only 0.97 +/- 0.17 pmol/5 min per 2 x 10(6) cells (n = 5) and was not enhanced by exogenous arachidonate. When cells from allergic patients were challenged in the presence of exogenous [1-14C]arachidonic acid, released LTB4 was radiolabeled and the incorporated radioactivity increased with the labeled arachidonate concentration. Labeled LTB4 was never detectable after incubating neutrophils from normal donors with exogenous labeled arachidonate. When neutrophils were incubated with [1-14C]arachidonate for 1 h, the different lipid pools of the two cell populations were labeled but both types of neutrophils produced unlabeled LTB4 in response to ionophore stimulation. The hydrolysis of choline and ethanolamine phospholipids into diacyl-, alkenylacyl- and alkylacyl-species revealed that solely the alkylacyl-subclass of phosphatidylcholine was unlabeled. We conclude (i) that neutrophils from allergic patients stimulated by low ionophore concentration produce more LTB4 than neutrophils from healthy subjects and incorporate exogenous arachidonate, (ii) that endogenous arachidonate converted to LTB4 by the 5-lipoxygenase pathway may provide only from 1-O-alkyl-2-arachidonoyl-glycero-3-phosphocholine.

Nutrition, immune function, and inflammation: an overview

The collective evidence suggests that nutritional insult to both cell-mediated and humoral immunity in the presence of protein-energy malnutrition contributes to abnormalities of inflammation. The primary goal of nutritional support in inflammatory disease is to provide adequate energy and protein to meet endogenous requirements for tissue repair, IL-1 production, and restored cellular function, thus preventing secondary infection. Substrate provision should aim at improving the acute phase of injury while avoiding immune dysfunction. This goal may be achieved by altering the eicosanoid pathway toward a more regulated inflammatory state. In the context of allograft response, macrophages are central to the initiation of allosensitization by virtue of their ability to present antigen to T-cells. Activated T-cells may further modulate macrophage function by the secretion of lymphokines. Manipulation of macrophage eicosanoid production by dietary omega-3 PUFA may reduce cellular immune response. (table; see text) Nutritional support should also focus on providing essential micronutrients, with their potentially immunomodulating role, as adjunctive therapy in order to protect the host from toxic effects of free-radicals and chemicals released during inflammatory events. (Feeding regimens currently under investigation and development are presented in Table 4.) By integrating dietary immunotherapy with the use of recombinant hormones, monoclonal antibodies, and various available monokines, an optimal outcome for each patient may be achieved. However, effective application of immunotherapy to nutritional supplementation will require accurate monitoring of immune function in individual patients in order to avoid inappropriate treatment.

Involvement of thromboxane and leukotriene in arachidonate induced coronary constriction in diabetic rats

Vascular responsiveness to sodium arachidonate was examined in isolated perfused hearts from rats with streptozotocin-induced diabetes. In diabetic rats arachidonate induced a biphasic coronary vascular response characterized by initial vasoconstriction followed by prolonged vasodilation. Non-diabetic rats showed only a vasodilator response. The vasoconstrictor phase found in diabetic rats was abolished by ONO-3708, a selective thromboxane A2 antagonist. Indomethacin partly inhibited the vasoconstrictor response, the residual response being abolished by a leukotriene antagonist, ONO-1078. The vasodilator response, however, was completely abolished by indomethacin in both diabetic and nondiabetic rats. Furthermore, the coronary constrictor response to leukotriene D4 was enhanced in diabetic compared to nondiabetic rats. These results suggest an involvement of leukotriene in the vasoconstrictor response to arachidonate in diabetic rats, especially when cyclooxygenase is inhibited.

The significance of prostacyclin produced by pregnant rat myometrium: the relationship between myometrial prostacyclin producing activity and passive stretch of myometrium by growing conceptus

The present experiment was performed to elucidate the significance of prostacyclin (PGI2) produced by pregnant rat myometrium. PGI2-like substance producing activity of various portions of the uterus was measured at selected gestational stages by platelet bioassay; surface area per 1 gm of uterine wall enveloping one conceptus was calculated; and spontaneous contractility of myometrium of both conceptus and non-conceptus regions and the effects of authentic PGI2 on it were examined. PGI2-like substance producing activity increased with advancing pregnancy, but the activity varied according to area of the myometrium, being highest in the area where it was most greatly stretched by the growing conceptus and lowest where no conceptus was contained. Spontaneous contractility was reduced in regions with high PGI2 producing activity. Though authentic PGI2 generally exhibited a stimulatory effect, it had an inhibitory effect on Day 10 pregnant myometrium. From these results, it may be concluded that the producing activity of PGI2, which remarkably increases in the conceptus region with the advance of pregnancy, keeps the uterine wall relaxed, making the uterus adapt to the growth of the fetus. Passive myometrial stretch by the growing conceptus is thought to be one of factors which enhance myometrial PGI2 producing activity.

Examination of mouse and rat tissues for evidence of dual forms of the fatty acid cyclooxygenase

The possibility that the enzymatic generation of prostaglandin E2 (PGE2) and PGF2 alpha results from the catalytic activity of two distinct forms of the fatty acid cyclooxygenase was studied in microsomes prepared from kidney, lung, and brain of the mouse and rat. Three criteria established previously to detect the dual cyclooxygenase forms in the rabbit brain were used in the present study: (1) different time course profiles of microsomal PGE2 and PGF2 alpha biosynthesis from exogenous arachidonic acid; (2) elimination of the synthesis of one PG in vitro by non-steroidal anti-inflammatory drug concentrations that did not affect the synthesis of the other PG and; (3) selective autocatalytic inactivation of one cyclooxygenase by preincubation with arachidonic acid. Incubations with PGH2 endoperoxide as substrate tested whether the altered PG biosynthesis resulted from an effect on the endoperoxide utilizing enzymes and not on the cyclooxygenase. Of the six tissues examined, only the mouse brain microsomes satisfied all the criteria. The microsomes prepared from the mouse kidney produced mixed results. We conclude that the mouse brain but not the rat brain gives evidence for two distinct forms of the fatty acid cyclooxygenase. Additional distinguishing features of the different cyclooxygenases are required to determine if the cyclooxygenase forms are found in mouse kidney.

Pulmonary vascular response to high-frequency oscillatory ventilation in dogs: lack of effect of indomethacin

The role of prostaglandins (PG) in the pulmonary hypertension associated with high-frequency oscillatory ventilation (HFOV) was investigated in 7 pentobarbital-anesthetized dogs. The magnitude and time course of the mean pulmonary artery pressure (PAP) changes induced by HFOV (20 Hz) was quantified before and after PG-production blockade with 15 mg/kg indomethacin (INDO) i.v. It was found that HFOV before INDO induced a 27.2 +/- 5.6% increase in PAP above baseline and a 30.0 +/- 7.2% one hour after INDO administration. This difference was not statistically significant. The time course of the PAP changes induced by HFOV before and after blocking PG-production by INDO were also similar. Mean airway pressure, PaO2 and PaCO2 during HFOV, before and after INDO were not statistically different. It is concluded that the acute increase in PAP induced by HFOV is not due to PG release.

Incorporation of 5,8,11,14-eicosatetraynoic acid (ETYA) into cell lipids: competition with arachidonic acid for esterification

5,8,11,14-eicosatetraynoic acid (ETYA), a widely used inhibitor of cyclooxygenase and lipoxygenase, inhibited the incorporation of 14C-arachidonic acid into cell lipids of the murine thymoma EL4 whereas oleic acid had no effect. Inhibition appeared to result from the ability of ETYA to compete with arachidonic acid for esterification enzymes and to be itself incorporated into cell lipids. The positional specificity for ETYA incorporation was similar to that of arachidonic acid. ETYA, but not oleic acid competed with arachidonate for activation by a selective arachidonoyl CoA synthetase in lymphocytes. This may explain in part the apparent specificity of effects seen on incorporation into whole cells. In addition ETYA, unlike other arachidonate analogs tested previously, caused significant inhibition of the nonselective acyl CoA synthetase in lymphocytes. These results are discussed with respect to the use of ETYA to examine the role of intrinsic arachidonic acid metabolism in cellular processes.

Epidermal growth factor stimulates release of arachidonic acid in pig epidermis

Epidermal growth factor (EGF) at physiologic concentrations (0.001-0.1 microgram/ml) stimulated the release of [14C] arachidonic acid [14C-AA] from pig epidermis. Although EGF stimulated the release of AA in the absence of exogenously added calcium to some extent, the addition of calcium (0.3-1.2 mM) significantly potentiated the release of AA stimulated by EGF. Ionophore A23187, which is known to stimulate phospholipase A2 activity by opening the calcium gates, potentiated the EGF-stimulated release of AA. The stimulatory effect of EGF was partially inhibited by the addition of mepacrine (70% inhibition at 10 microM) and by the pretreatment of hydrocortisone (60% inhibition at 1.0 microM). The loss of 14C-labeled phospholipids in pig epidermis was mainly due to the degradation of 14C-labeled phosphatidylcholine. Present results and recent reports by other workers suggest that EGF stimulates phospholipase A2 activity and result in the increased release of AA.

Relationship of gastric mucosal damage induced in pigs by antiinflammatory drugs to their effects on prostaglandin production

Experiments were performed in pigs to examine the relationship between the effects of various nonsteroid antiinflammatory drugs on gastric (fundic) mucosal content of prostaglandin (PG)E2 and 6-keto-PGF1 alpha, and the development of damage to the fundic mucosa under acute and chronic dosage conditions. Oral administration of a single dose of indomethacin (5 mg/kg) caused an almost immediate reduction in mucosal potential difference, followed at 5-15 min by ultrastructurally observed damage to mucosal capillaries, mucous, and parietal cells; efflux of Na+, K+, and Cl- ions into the gastric lumen with an apparent loss of luminal H+ ions; and a statistically significant reduction (from 10-60 min) in fundic prostaglandin content. Thus, under acute dosage conditions, development of mucosal damage by indomethacin was paralleled by the reduction in prostaglandin production. Repeated oral dosage of aspirin, indomethacin, sulindac, or diclofenac to pigs for 10 days significantly reduced gastric mucosal as well as plasma prostaglandin levels, coincident with the development of severe gastric mucosal damage. The relatively less irritant drugs, flufenamic acid, azapropazone, and fenclofenac, failed to significantly decrease gastric mucosal content of prostaglandins, although these drugs have been reported to inhibit prostaglandin synthesis in vitro and also were found to reduce the prostaglandin plasma levels in animals receiving these drugs. Another drug with low irritancy, meseclazone, markedly decreased both mucosal and plasma levels of prostaglandins. The results show that while ulcerogenic drugs reduce the mucosal and plasma prostaglandins levels in parallel with their ulcerogenicity, this relationship does not always hold for drugs with low ulcerogenic activity.

Coronary vasoconstrictor and vasodilator actions of arachidonic acid in the isolated perfused heart of the rat

The administration of arachidonic acid (AA) to the isolated perfused heart of the rat usually produced biphasic coronary responses characterized by initial vasoconstriction followed by prolonged vasodilatation. However, some responses were predominantly vasoconstrictor or vasodilator. The non-steroidal anti-inflammatory agents (NSAA) indomethacin (1-5 mg/l) and naproxen (12.5-25 mg/1) reversibly inhibited both phases of the response induced by AA. Pretreatment of animals with indomethacin (5 mg/kg) or naproxen (25 mg/kg) daily, resulted in unaltered coronary response to AA. Subsequent addition of NSAA to the perfusate produced inhibition of the AA effect. Short infusions of acetylsalicylic acid at low concentrations (2.9 micrograms/ml), dipyridamole (0.6 micrograms/ml) and sulphinpyrazone (28.7 micrograms/ml) selectively inhibited the vasoconstrictor phase of the response to AA. It was confirmed that metabolic coronary dilatation induced by cardiostimulation was inhibited by prolonged AA administration; this effect was prevented by NSAA pretreatment. Reactive hyperaemic responses to short lasting occlusions of coronary inflow were unaffected by NSAA. Linolenic, linoleic, dihomo-gamma-linolenic and oleic acid usually produced decreases in coronary flow which were unaffected by NSAA, dipyridamole or sulphinpyrazone. Intra-aortic injections of AA, prostacyclin (PGI2) and prostaglandin E2 (PGE2) in the intact rat produced a dose-dependent decrease in blood pressure with the AA response inhibited by indomethacin. PGI2 and PGE2 produced long lasting coronary vasodilatation in the isolated heart. The coronary actions of AA appear to be due to its transformation, within the easily accessible vascular wall, into prostaglandin and thromboxane-like substances. We suggest that a vasoconstrictor thromboxane A2-like substance may be responsible for coronary vasospasm. Coronary insufficiency may also result from an inhibition of compensatory metabolic coronary dilatation by increased synthesis of PGE2 within the myocardial cell.

Allergen tachyphylaxis of guinea pigs in vivo; a prostaglandin E mediated phenomenon?

Ovalbumin (OA) sensitized guinea pigs were repeatedly challenged with 1% OA in saline nebulized ultrasonically at the 0, 10, 20, 60 and 70th min. The intensity of bronchial obstruction was measured by body plethysmography. The first three challenges (0. 10, 20 min) caused strong asthmatic reactions in all animals, the last two (60, 70 min) only mild one in 10 out of 15 animals. The development of this "tachyphylaxis" was markedly reduced by pretreatment of the animals with cyclooxygenase inhibitors (indomethacin 10 mg/kg intraperitoneally resp, acetylsalicylic acid 10 mg/kg orally 2 h before tests). The effect of both inhibitors (i.e. inhibition of tachyphylaxis) was abolished by supplementing prostaglandin E2 as aerosol simultaneously to the allergen (100-200 ng per inhalation). The results suggest that allergen tachyphylaxis we have observed in vivo might be due to synthesis of cyclooxygenase products, e.g. prostaglandin E.

Prostaglandin E production and hypercalcaemia in rats bearing the Walker carcinosarcoma

The hypothesis that there is prostaglandin-mediated hypercalcaemia associated with the Walker carcinosarcoma in the rat was tested by measuring PGE production during the development of the hypercalcaemia, and determining the effects of inhibition of prostaglandin synthesis on serum calcium concentration. Parathyroid hormone (PTH) activity was estimated by the determination of the serum concentration of immunoreactive PTH. There was a 3-fold increase in the urinary excretion of 7α-hydroxy-5,11-diketotetranor-prostane-1,16-dioic acid (PGE-M), a major urinary metabolite of the E prostaglandins from basal levels. Treatment with indomethacin, a potent inhibitor of prostaglandin synthesis, did not lower serum calcium concentrations with two different doses (1·6 mg/kg/day orally and 5 mg/kg/day i.m.); effective inhibition of prostaglandin synthesis was demonstrated by the suppression of PGE-M excretion rates below basal levels. Serum concentrations of immunoreactive PTH were not significantly altered by either tumour growth or indomethacin. Dexamethasone (0·5 mg/kg/day i.m.) attenuated both the increased urinary excretion of PGE-M and the rise in serum calcium concentration, suggesting that one or several lipoxygenase products might be the actual mediators of the hypercalcaemia. We conclude that the hypercalcaemia in the rat with Walker carcinosarcoma is probably not mediated by E-prostaglandins and probably not by any other product of the cyclo-oxygenase pathway. The increased PGE turnover may be considered as a biochemical marker of tumour load, but not as an indicator of a prostaglandin-mediated hypercalcaemia.

Failure of indomethacin to prevent or ameliorate oleic acid pulmonary edema in the dog

The possibility that prostaglandin synthesis inhibition might favorably inhibit the development of animal adult respiratory distress syndrome models was investigated in two groups of dogs; one group was pretreated with indomethacin 3 mg/kg. Both groups received oleic acid 0.15 mg/kg. Measurements of gas exchange and hemodynamics were performed every hour for 5 hours following embolization. Severe pulmonary edema developed in both groups. The indomethacin pretreated group responded similarly to the control group; there was no difference in the 5 hour course of Pa02 (p = .34), P(A-a)02 (p = .21) or QS/QT (p = .99). Prostaglandin synthesis inhibition did not favorably influence the immediate development of acute respiratory failure following oleic acid.

Role of arachidonic acid derivatives in neutrophil aggregation: a hypothesis

Chemotactic substances stimulate neutrophils in suspension to aggregate. Arachidonic acid (but not several structurally related fatty acids) induces a similar neutrophil response. We now report that two blockers of arachidonic acid metabolism, indomethacin and 5,8,11,14-eicosatetraynoic acid, inhibit this arachidonic acid-mediated response. Moreover, both blockers also inhibit aggregation stimulated by a synthetic chemotactic tripeptide, formyl-methionyl-leucyl-phenylalanine, and their potency in doing so parallels their potency in inhibiting the response to arachidonic acid. These results suggest that metabolites of arachidonic acid may stimulate certain neutrophil functions and be involved in cellular responses to at least some chemotactic substances.

Prostaglandin E1 inhibits acute cell dehydration thirst

Intraperitoneally injected PGE1 (100 micrograms/Kg) inhibits specifically the drinking induced by both IP and IV 2 M NaCl (6 ml/Kg) and compound 48/80 (100 micrograms/Kg, IP). Probenecid (150 mg/Kg, IP) which is not a dipsogen, has no effect on the PGE1 induced inhibition of acute cell dehydration thirst. It is concluded the PGE1 acts upon the peripheral mast cells, inhibiting their secretion and thus affecting the water intake associated with the activation of these cells either by hypertonicity or specific stimulants of amine release. These results raise the possibility that endogenous prostaglandins might be involved in the modulation of some of the signals which convey to the brain information on the tonicity of the body fluids.