Dembińska-Kieć A

Formation of leukotriene C4-like material by rat brain tissue

Pieces of rat brain incubated in oxygenated Tyrode solution were stimulated with the divalent cation ionophore A 23187. Incubation media were assayed for leukotriene (LT) C4-like immunoreactivity as well as for prostaglandin (PG) D2, 6-keto-PGF1 alpha and thromboxane (TX) B2 using specific and sensitive radioimmunoassays. Spontaneous release of the cyclooxygenase products but only of trace amounts of LTC4-like immunoreactivity was detected. Stimulation with ionophore A 23187 increased the level of cyclooxygenase products and to a smaller extent the level of LTC4-like immunoreactivity. Inhibition of cyclooxygenase by indomethacin was paralleled by a significantly increased release of LTC4-like material under basal conditions as well as in the presence of ionophore A 23187. On the other hand, the synthesis of LTC4-like material was significantly decreased by the lipoxygenase inhibitors quercetin and nordihydroguaiaretic acid. The presence of LT-like material in rat brain incubates was confirmed by bioassay. The capacity of brain tissue to synthesize LT-like material may be important for cerebral blood flow as well as cellular functions in the central nervous system.

Effect of carbenoxolone on the biological activity of nitric oxide: relation to gastroprotection

1 The interactions between carbenoxolone and nitric oxide (NO) were examined by investigating their effects on human platelet aggregation, on rat aortic strips precontracted by phenylephrine and on protection of rat gastric mucosa against ethanol‐induced injury. 2 Carbenoxolone (100–300 μm) caused a significant and concentration‐dependent potentiation of rat peritoneal neutrophil (RPN)‐, 3‐morpholino‐sydnonimine (SIN‐1)‐ or iloprost‐induced inhibition of platelet aggregation. Higher concentrations (500 μm) of carbenoxolone alone markedly inhibited platelet aggregation. Pretreatment with carbenoxolone (100–300 μm) antagonized the reversal of the RPN‐ or SIN‐1‐induced antiaggregatory effect by oxyhaemoglobin (10 μm). 3 Rat aortic strips with intact endothelium precontracted by phenylephrine (0.1–0.3 μm) were relaxed by carbenoxolone (100–300 μm) in a concentration‐dependent manner. Relaxations were abolished by mechanical removal of the endothelium or by incubation with methylene blue (10 μm) or NG‐nitro‐l‐arginine (l‐NNA, 100 μm). Sodium nitroprusside (10 nm)‐induced relaxations of endothelium‐denuded rat aortic strips were potentiated by carbenoxolone (100 μm). 4 The carbenoxolone (200 mg kg−1, p.o.)‐induced gastroprotection against ethanol was antagonized by l‐NNA (5–40 mg kg−1) in a dose‐dependent manner. Pretreatment of rats with indomethacin (10 mg kg−1, s.c.) increased the effect of l‐NNA. 5 The results suggest that the activity of carbenoxolone in the experimental systems tested is due to phosphodiesterase inhibition, although radical scavenging properties of the drug could contribute to some of the effects observed. In the rat gastric mucosa both increased prostaglandin levels and effects on the NO system could contribute to the protective action of carbenoxolone.

The effects of platelet-activating factor on flow rate and eicosanoid release in the isolated perfused rat gastric vascular bed

In the isolated rat stomach perfused via the vasculature in situ under constant pressure bolus injections of platelet-activating factor (PAF, 3, 16, or 50 ng) induced dose-dependent, long-lasting reductions of flow rates and simultaneously significant increases in the release of cysteinyl-leukotrienes (cys-LT), thromboxane (TX) B2 and 6-keto-prostaglandin (PG) F1 alpha. Reversed phase high pressure liquid chromatography demonstrated the release of a mixture of comparable amounts of LTC4, LTD4 and LTE4 by PAF. Inhibition of cys-LT synthesis by the lipoxygenase inhibitors nordihydroguaiaretic acid (NDGA) and L-651,896 did not significantly affect PAF-induced flow reduction indicating that endogenous cys-LT are of minor importance for the PAF effect on gastric vascular flow. This conclusion is supported by the fact that the cys-LT receptor antagonist FPL 55712 in a concentration (1 x 10(-6) M) that completely antagonized gastric flow reduction by exogenous LTC4 (1 x 10(-7) M) had no effect on the PAF-induced reduction of flow. The cyclooxygenase inhibitor indomethacin aggravated the PAF-induced flow reduction suggesting that the endogenous vasodilator PGI2 might act as a functional PAF antagonist in the rat gastric vascular bed. In contrast to FPL 55712 the PAF antagonist BN 52021 significantly and concentration-dependently antagonized the PAF effect on gastric vascular flow. The results demonstrate that PAF and LTC4 induce flow reductions in the rat gastric vascular bed by activating different receptors and that endogenous eicosanoids released by PAF do not contribute significantly to the PAF effect on gastric vascular flow.

Effect of 3-morpholinosydnonimine (SIN-1) and NG-nitro-l-arginine (NNA) on isolated perfused anaphylactic guinea-pig hearts

SummaryThe modulating effects of exogenous and endogenous nitric oxide (NO) on the cardiac anaphylactic reaction and eicosanoid release were investigated in isolated perfused sensitized guinea-pig hearts using 3-morpholinosydnonimine (SIN-1), the active metabolite of molsidomine, as NO-donor and NG-nitro-l-arginine (NNA) as an inhibitor of NO biosynthesis. Infusion of SIN-1 (final concentrations in the perfusates 0.3 or 1.0 mmol/l) elevated coronary flow under basal conditions as well as during cardiac anaphylaxis, while NNA (0.1 mmol/l) decreased basal coronary flow and aggravated the anaphylactic coronary constriction. Both drugs did not modify the characteristic biphasic profile of the coronary constriction after antigen challenge with an initial more severe phase followed by a less pronounced long-lasting flow reduction. Neither SIN-1 nor NNA affected spontaneous heart rate. However, while NNA tended to prolong the duration of antigen-induced arrhythmias, SIN-1 (1 mmol/l) had an inhibitory effect. This protection might be related to the increased coronary flow in the presence of SIN-1. SIN-1 inhibited anaphylactic release of cysteinyl-leukotrienes (LT) and 6-keto-prostaglandin (PG) F1α, but did not influence thromboxane (TX) B2 release. On the other hand, NNA (0.1 mmol/l) inhibited anaphylactic release of TXB2, but had only marginal effects on the release of cysteinyl-LT and 6-keto-PGF1α. The results suggest that exogenous and endogenous NO functionally antagonize the effects of vasoconstrictor mediators released after antigen challenge. Additional effects of high concentrations of SIN-1 and NNA on antigen-induced eicosanoid release could modulate the vascular actions of these drugs during cardiac anaphylaxis.

Effects of exogenous prostaglandins on the release of leukotriene C4-like immunoreactivity and on coronary flow in indomethacin-treated anaphylactic guinea-pig hearts

SummaryIt is known that both vasoconstrictor cyclooxygenase products and sulfidopeptide-containing leukotrienes (LT) contribute to the biphasic coronary constriction observed in isolated perfused anaphylactic guineapig hearts. We have now investigated the effects of the cyclooxygenase inhibitor indomethacin and of several exogenous prostaglandins (PG) on the release of LTC4-like immunoreactivity and on various symptoms of cardiac anaphylaxis. Indomethacin decreased basal coronary flow and delayed the onset of coronary vasoconstriction after antigenic challenge. Furthermore, indomethacin inhibited cardiac release of 6-keto-PGF1α and thromboxane (TX) B2 and simultaneously enhanced the antigen-induced release of LTC4-like immunoreactivity significantly. Neither the vasodilators PGE2 and PGI2 nor the vasoconstrictors PGF2α, PGD2 and 11,9-epoxymethano-PGH2, a compound with biological properties similar to TXA2, affected the anaphylactic release of immunoreactive LTC4 in the presence of indomethacin. These results suggest that the indomethacin-induced increase in LT release is not due to inhibition of synthesis of a cyclooxygenase product, which normally curbs anaphylactic release of immunoreactive LTC4. The indomethacin effect may rather be explained by diversion of arachidonic acid metabolism away from fatty acid cyclooxygenase towards the synthesis of lipoxygenase products.Although the various PG did not significantly affect cardiac release of LTC4-like immunoreactivity, they antagonized the anaphylactic coronary contriction. This antagonism may be due to direct effects of the PG on vascular smooth muscle tone as well as to indirect effects on the release of anaphylactic mediators not related to LT like histamine and platelet-activating factor. Antigen-induced arrhythmias were completely suppressed by PGF2α, while PGE2 and PGI2 tended to decrease the incidence of arrhythmias and the other PG had no consistent effect. It is concluded that the pharmacological effects of the PG used on coronary flow and arrhythmias during cardiac anaphylaxis are not mediated by inhibition of release of LTC4-like immunoreactivity.

Release and vasoconstictor effect of leukotriene C4-like immunoreactive material in the anaphylactic guinea-pig mesenteric vascular bed

Antigen challenge of sensitized isolated guinea-pig mesentery perfused under constant pressure resulted in a significant flow reduction, which was paralleled by the release of leukotriene (LT)C4-like immunoreactivity into the perfusates. The lipoxygenase inhibitor quercetin inhibited the release of immunoreactive LTC4 and simultaneously abolished the antigen-induced mesenteric flow reduction. Mesenteric flow reduction was also observed after injection of exogenous LTC4. The results demonstrate that LTC4 is a constrictor of the mesenteric vascular bed and that endogenous LTC4-like immunoreactive material is a mediator of anaphylactic vasoconstriction in the guinea-pig mesentery.