Leukotrienes C4 and D4 induce prostaglandin and thromboxane release from rat peritoneal macrophages

Synthesis of prostanoids and cyclic nucleotides by phagocytosing rat Kupffer cells

Rat Kupffer cells in monolayer culture were allowed to phagocytose unopsonized zymosan granules. They responded with a strongly stimulated synthesis and release of prostanoids, mainly the immunologically determined prostaglandins PGE2 and PGF2 alpha. The same response could be obtained by treatment with the calcium ionophore A23187. The effects of the ionophore and the zymosan particles were of the same magnitude but not additive. The rapid uptake of Ca2+ after contact with phagocytosable material recently described by us [(1983) Eur. J. Biochem. 131, 539-543] appears to mediate the enhanced prostaglandin synthesis. That response was suppressed not only by indomethacin but also by trifluoperazine which does not inhibit Ca2+ entry in the Kupffer cells. Similar effects by R24571 and 4-bromophenacyl bromide support the participation of calcium-calmodulin and of phospholipase A2. The calcium channel blocker Verapamil did not influence the zymosan-provoked production of prostaglandin PGE2 nor were any indications obtained for a feedback inhibition by PGE1 or PGE2. Contact with zymosan resulted in a rapid but transient rise of the intracellular levels of cAMP and cGMP: 10 nM indomethacin completely blocked the increase of both cyclic nucleotides while trifluoperazine elicited different responses in the cAMP and cGMP levels. The stimulated release of prostaglandin E2 was inhibited in a dose-dependent manner by nordihydroguaiaretic acid, an inhibitor of 5-lipoxygenase and by FPL 55712, known as a receptor antagonist for some leukotrienes. This suggests a regulatory role for its metabolites on prostaglandin synthesis.

Renal and systemic hemodynamic responses to intravenous infusion of leukotriene C4 in the rat

We studied the systemic and renal hemodynamic effects of leukotriene C4 (2 micrograms/kg per min for 5 minutes, iv) in the rat. During the period of its infusion, leukotriene C4 produced a significant elevation of mean arterial pressure and reductions in cardiac output and renal blood flow, as measured by electromagnetic flow probes. These effects were abolished by FPL55712 , a putative antagonist of sulfidopeptide leukotrienes, but not by saralasin or indomethacin. Leukotriene C4 also resulted in an average loss of 20% in plasma volume which, during the postinfusion period, perpetuated the low cardiac output state and thus provoked the release of angiotensin II. This vasoactive peptide sustained the elevation in systemic vascular resistance and the reduction in renal blood flow over a 70-minute postinfusion observation period. Consequently, glomerular filtration rate fell by approximately 50%. These angiotensin II-mediated effects were abolished by saralasin. Indomethacin prevented the leukotriene C4-induced loss of plasma volume and, thus, allowed for the significant recovery of cardiac output and renal blood flow during the post-infusion period, thereby preserving glomerular filtration rate. We conclude that leukotriene C4 exerts direct systemic and renal vasoconstrictor, as well as cardiodepressant effects, during the period of its infusion. By virtue of its vasopermeability enhancing effect, leukotriene C4 also results in an immediate loss of plasma volume, an effect which requires the presence of secondarily generated cyclooxygenase products and which perpetuates the hemodynamic abnormalities observed beyond the period of leukotriene C4 infusion.

Thromboxane formation in human polymorphonuclear leukocytes is inhibited by prednisolone and stimulated by leukotrienes B4, C4, D4 and histamine

Human polymorphonuclear leukocytes (PMNL) were incubated for 60 min at 37 degrees C with 20 microM or 100 microM prednisolone, and stimulated thereafter for 1 min with 10 nM LTB4, 10 nM LTC4, 10 nM LTD4 or 10 microM histamine. The amount of thromboxane B2 (TXB2) formed by PMNLs was measured by radioimmunoassay. PMNLs spontaneously released TXB2 during 60 min incubation, and the rate of formation was significantly reduced in the presence of 20 microM or 100 microM prednisolone. LTB4, LTC4, LTD4, and histamine stimulated the rate of TXB2 production during 1 min incubation to 93-, 49-, 60-, and 55-fold, respectively. Preincubation with prednisolone for 60 min had a slight inhibitory effect on the stimulated TXB2 formation but TXB2 production still remained many fold as compared to its spontaneous rate of formation. The present study indicates that human PMNLs are capable of synthetizing TXB2, and its spontaneous rate of formation is inhibited by a synthetic glucocorticoid, prednisolone. The great stimulatory effect of LTB4, LTC4, LTD4, and histamine suggests that these agents may activate phospholipases or other acylhydrolases which liberate arachidonate for eicosanoid biosynthesis.

Leukotrienes: clinical significance

The leukotrienes, so named because of their initial identification in leukocyte preparations and the presence of three conjugated double bonds (a conjugated triene), are metabolites of the same polyunsaturated fatty acids (e.g., arachidonic acid) that give rise to the prostaglandins, thromboxanes, and several other families of biologically active lipids. Their potential clinical importance derives from their effects on vascular and other smooth muscle reactivity and on leukocyte function. Several leukotrienes may markedly influence the cellular and vascular responses that constitute an integral part of hypersensitivity and inflammatory reactions of the skin. Preliminary data from several laboratories have been presented that implicate a specific leukotriene in the evolution of the lesions of psoriasis.

Intracerebroventricular and preoptic injections of leukotrienes C4, D4, and E4 in the rat: lack of febrile effect

Experiments were performed to ascertain the effect on core temperature in the rat of central administration of 3 products of the lipoxygenase pathway of arachidonate metabolism. The agents tested were leukotrienes C4, D4, and E4 (LTC4, LTD4, LTE4). In one series of rats, the leukotrienes were injected into the ventral aspect of the third cerebral ventricle (5 microliter injection volume). Each rat received, in separate experimental sessions, an injection of a control solution, of 1 microgram of prostaglandin E1 (PGE1) and of 1 microgram of LTC4, LTD4, or LTE4. In another series of rats, bilateral 1 microliter injections into the tissue of the preoptic region were made. Each animal received a control solution, 40 ng PGE1 (20 ng/side) and 400 ng LTC4, LTD4, or LTE4 (200 ng/side). Neither the intraventricular nor the preoptic injections of any of the leukotrienes produced a significant increase in colonic temperature. However, PGE1 injected intraventricularly or into the preoptic region produced a large, rapidly developing core temperature rise. The strong febrile response to PGE1 and the results of dye distribution studies indicate that the lack of effect of the leukotrienes was not due to incorrect injection cannula placement. The ineffectiveness of the leukotrienes also cannot be attributed to loss of biological activity of these agents during storage. Near the end of the study, samples of each leukotriene were assayed using the guinea pig tracheal strip method and were found to be highly active. The results suggest that, at least in the rat, these 3 arachidonate metabolites are not likely to be important mediators of fever.

A routine source of human peritoneal macrophages

The routine availability of nucleated human cells for experimental use in limited in the absence of venipuncture. In this paper we have demonstrated that macrophages may be harvested routinely from the waste dialysis bags of patients undergoing continuous ambulatory peritoneal dialysis. These cells were identified as macrophages by morphology, adherence, phagocytosis, chemotaxis, non-specific esterase staining and peroxidase staining. Macrophages from patients with end-stage renal disease produced arachidonate cyclo-oxygenase products in a pattern similar to that of ascites macrophages obtained from patients with normal kidney function. Arachidonate metabolism was shown to be manipulatable. Thus, indomethacin blocked synthesis of cyclooxygenase products, and OKY-1581, a specific thromboxane synthase inhibitor, increased the release of prostaglandin E2 and prostacyclin, measured as its stable breakdown product 6-keto-prostaglandin F1, whereas the thromboxane B2 synthesis was effectively inhibited.

Imbalance of prostacyclin and thromboxane synthesis in Crohn's disease

Synthesis of prostanoids in Crohn's disease was investigated using rectal biopsy specimens maintained in organ culture. As with ulcerative colitis increased synthesis of prostaglandin (PG)E2 was observed when the mucosa was inflamed, compared with uninflamed mucosa in Crohn's disease, and with control biopsy specimens. In contrast with ulcerative colitis differences from control specimens were observed even in the absence of inflammation. There was a raised synthesis of thromboxane (Tx)B2 (stable breakdown product of TxA2); concentrations of 6-keto PGF1 alpha (stable breakdown product of prostacyclin) were unchanged and hence the ratio of 6-keto PGF1 alpha/TxB2 was reduced. These changes might lead to an altered cytoprotective capacity or reduced suppressor cell activity, such as has previously been reported in intestinal lymphocytes in Crohn's disease.

Activation of macrophages by substance P: induction of oxidative burst and thromboxane release

Substance P (SP), a putative neuropeptide transmitter, was examined for its effects on macrophages. Guinea-pig peritoneal macrophages were purified by adherence, challenged with SP and incubated for up to 18 h. Culture supernatants were collected to determine the release of O-2, H2O2 and TXB2. SP dose-dependently evoked O-2 and H2O2 production by C. parvum-activated macrophages and liberation of TXB2 from albumin-elicited macrophages. Generation of these proinflammatory macrophage products by SP may be relevant in the context of neuroinflammatory disease.

Effects of a pyridine derivative thromboxane synthetase inhibitor and its inactive isomer in endotoxic shock in the rat

1 We investigated the effects of a pyridine derivative thromboxane synthetase inhibitor and its inactive ortho isomer on arachidonic acid metabolism and pathophysiological sequelae of endotoxic shock. In vehicle-treated rats, 30 min after intravenous S. enteritidis endotoxin (15 mg/kg), plasma iTxB2 (the stable metabolite of thromboxane A2) increased from non-detectable levels (less than 100 pg/ml) to 763 +/- 250 pg/ml (n = 10). Plasma i6-keto-PGF1 alpha (the stable metabolite of prostacyclin, PGI2) increased to 1850 +/- 426 pg/ml, (n = 9) and plasma iPGE increased to 2350 = 560 (n = 5). Pretreatment with the pyridine active (PA) meta isomer (30 mg/kg i.p.) significantly (P less than 0.05) suppressed iTxB2 to 390 +/- 31 pg/ml (n = 10) although 6-keto-PGF1 alpha levels (1294 +/- 358 pg/ml, n = 5) and plasma iPGE (2847 +/- 1103 pg/ml, n = 5) were not significantly different from the shocked control values. In contrast, pretreatment with, the pyridine inactive (PI) ortho isomer did not significantly affect endotoxin-induced iTxB2 (1431 +/- 194 pg/ml, n = 5) or i6-keto-PGF1 alpha synthesis (628 +/- 266 pg/ml, n = 5). 2 Pretreatment of rats with the Tx synthetase inhibitor, PA, significantly enhanced (P less than 0.05) survival and prevented splanchnic infarction relative to both endotoxin shocked control rats and those pretreated with the PI isomer. 3 Significantly reduced lysosomal labilization, hepatocellular dysfunction and elevations in serum fibrin/fibrinogen degradation products were seen only in groups pretreated with the PA isomer. 4 The beneficial effects of the latter compound in endotoxic shock thus appear to be due to inhibition of Tx synthesis, since its ortho isomer did not inhibit TxA2 synthesis nor did it protect against endotoxic shock.

Metabolic and cellular alterations underlying the exaggerated renal prostaglandin and thromboxane synthesis in ureter obstruction in rabbits. Inflammatory response involving fibroblasts and mononuclear cells

Unilateral ureter obstruction in rabbits produced profound changes in endogenous and exogenous renal arachidonic acid metabolism. Isolated perfused hydronephrotic kidneys (removed after 3 or 10 d of ureter obstruction) responded to bradykinin stimulation with a markedly enhanced release of prostaglandin E2 and thromboxane A2. Reversal (3 or 10 d) of the ureter obstruction resulted in a reduction in the vasoactive peptide-induced release of prostaglandin E2 and thromboxane A2 from the perfused hydronephrotic kidney. However, postobstruction reversal of prostaglandin production by the agonist-stimulated perfused kidney was not reflected in the cortical microsomal cyclooxygenase activity, which is greatly enhanced during ureter obstruction and does not decrease after removal of the obstruction. Histological analysis of the renal cortex in rabbits with ureteral obstruction revealed a proliferation of fibroblast-like cells and the presence of mononuclear cells; removal of the obstruction did not result in a disappearance of cortical fibroblasts but did result in a decrease of monocytes. The critical involvement of mononuclear cells in the exaggerated arachidonate metabolism that occurs during hydronephrosis was exhibited by the demonstration that: (a) only the perfused hydronephrotic rabbit kidney responded to administration of endotoxin with a sustained release of prostaglandin E2 and thromboxane A2; (b) the contralateral rabbit kidney, which is devoid of mononuclear cells, did not respond to endotoxin; and (c) the hydronephrotic cat kidney, which exhibits a fibroblast proliferation with a low number of mononuclear cells, did not respond to endotoxin. Thus, proliferation of fibroblast-like cells and the presence of mononuclear cells appear to be involved in the exaggerated prostaglandin and thromboxane production underlying hydronephrosis. The increase in microsomal cyclooxygenase activity is apparently most closely correlated with the increased fibroblastic activation and cellularity, whereas mononuclear cells (possibly via monokines) seem to be critical for the markedly enhanced prostaglandin and thromboxane release induced by endotoxin and bradykinin.

Possible involvement of thromboxane in bronchoconstrictive and hypertensive effects of LTC4 and LTD4 in guinea pigs

The actions of leukotriene (LT) C4 and D4 on the systemic arterial pressure and the insufflation pressure in guinea pigs and rabbits were examined. In guinea pigs, 0.3 - 3 nmole/kg of LTC4 and 0.1 - 1.0 nmole/kg of LTD4 administrated from left jugular vein caused dose-dependent increase of the airway resistance measured by the Konzett-Rössler method and a triphasic blood pressure response; an initial hypotension, a secondary hypertension and a third long-lasting hypotension. All of the hypertensive phase and 100 - 150% of the increase of the airway resistance by LTC4 and LTD4 were inhibited by a selective thromboxane synthetase inhibitor, OKY-1581 (10 mg/kg, i.v.) and only the hypotension was observed. Indomethacin (10 mg/kg, i.p.) also inhibited not only the airway resistance increase, but also the prolonged hypotension by LTC4 and shortened the duration of the hypotension by LTD4. It is suggested that thromboxane might be involved in bronchoconstriction and hypertensive effects by LTC4 and LTD4 and that hypotensive prostaglandin might be involved in the hypotensive phase after LTC4 and LTD4. In rabbits, the increase of the airway resistance by LTC4 and LTD4 (upto 100 nmole/kg, i.v.) was negligible and only the hypotension was observed.

Cardiovascular effects of leukotriene D4 in SHR and WKY rats

Leukotriene D4 (LTD4, 0.8-4 micrograms/kg i.a.) increased blood pressure and heart rate of conscious SHR and WKY rats. LTD4, 20 micrograms/kg (i.a.), caused a short lasting increase in blood pressure and heart rate in WKY. In SHR, LTD4, 20 micrograms/kg (i.a.) caused a triphasic effect: hypotension and bradycardia (0.5-1 min), hypertension and tachycardia (2-5 min) and prolonged hypotension and bradycardia (5-180 min). Leukopenia was observed after LTD4, 20 micrograms/kg in both groups of rats but platelets count was unaffected. These results show that SHR are mor sensitive than WKY to the hypotension-bradycardia effect of LTD4.