T. Viganò

Bronchoconstriction by histamine and bradykinin in guinea pigs: Relationship to thromboxane A2 generation and the effect of aspirin

Histamine 2.5, 5, 10 or 20 microgram/kg i.v. induce a pronounced bronchospasm in guinea-pigs, accompanied by a dose-related increase of TXA2 in arterial blood, as revealed by contraction of rabbit isolated aorta and by radioimmunoassay. Aspirin 10 mg/kg prevented formation of TXA2-like material without significantly modifying the severity of the bronchospasm. Bradykinin 0.5, 1 or 2 microgram/kg i.v. acted similarly, except that pretreatment with aspirin blocked both the increased airway resistance and release of TXA2. Aspirin also blocked the increase in blood pressure and heart rate caused by histamine or bradykinin.

PGI2-generation and antithrombotic activity of orally administered defibrotide.

Abstract Defibrotide, a polydeoxyribonucleotide extracted from mammalian organs (laboratory code Fraction P), displays antithrombotic activity after oral administration on different animal species. This activity is also demonstrated in a typical local thrombonecrotic hemorrhagic lesion caused by endotoxin in rabbit (Shwartzman reaction). Defibrotide prevents and antagonizes this kind of lesion in a dose dependent and in a long lasting way. The ability of Defibrotide to increase generation of PGI2 from vascular tissue following oral administration, is demonstrated and the mechanism of this phenomenon discussed.

ATROPINE INHIBITS THROMBOXANE A2 GENERATION IN ISOLATED LUNGS OF THE GUINEA‐PIG

1 Histamine (0.5 to 5 μg) and slow reacting substance of anaphylaxis (SRS‐A, 0.05 to 0.3 u), injected in the isolated, perfused lungs of normal and ovalbumin‐sensitized guinea‐pigs, promote formation and release of thromboxane A2(TXA2) and other arachidonate metabolites, the effect being more pronounced in sensitized lungs. 2 Carbachol injected (1 to 10 μg) or perfused (1 μg ml−1 min−1) through normal or sensitized lungs does not elicit formation of TXA2 and prostaglandins. Furthermore the increased generation of arachidonate metabolites due to histamine is not altered by carbachol. 3 Atropine and ipratropium bromide (1 μg ml−1 min−1) reduce significantly the increased rate of production of TXA2 caused by histamine and SRS‐A both in normal and sensitized lungs, whereas hexamethonium (10 to 25 μg ml−1 min−1) is ineffective. 4 The mechanism of action of atropine in inhibiting the increased generation of TXA2 is clearly not related to its antimuscarinic or antihistaminic properties. The drug might act at the early events, involved in the activation of arachidonic acid metabolism. The results suggest new sites of action for atropine which, besides the control of the vagal bronchomotor tone, interferes directly with the primary mediators of anaphylaxis.

Defibrotide, an antithrombotic substance which prevents myocardial contracture in ischemic rabbit heart

Defibrotide, a polydeoxyribonucleotide obtained from mammalian lungs, reduced in a dose-dependent fashion the ischemic contracture due to low perfusion (0.2 ml/min) of isovolumic left heart of rabbit and abolished the irregular rhythm of the heart, thereby restoring the cardiomechanical activity upon reperfusion (20 ml/min). Defibrotide stimulated the release of PG-like material from the heart in a dose-dependent manner without modifying the basal contractility. Both PGE2 and PGI2 (10 ng/ml) have an antiischemic activity on this preparation as shown by the partial reduction of the ischemic contracture and by the improvement of heart contractility upon reperfusion. Indomethacin infusion (1 microgram/ml) completely removed both the antiischemic activity of Defibrotide (400 micrograms/ml) and its ability to increase the generation of prostaglandins in the rabbit heart. These results suggest that Defibrotide has a beneficial influence on ischemic rabbit heart through an increase in prostaglandin synthesis. However other mechanisms not necessarily related to prostaglandin generation, such as a direct effect on membrane function deactivation and mitochondrial Ca2+ overload, should be considered in explaining the antiischemic activity of Defibrotide in the rabbit heart.

Cisternal and Lumbar CSF Levels of Arachidonate Metabolites After Subarachnoid Haemorrhage: An Assessment of the Biochemical Hypothesis of Vasospasm*

SummarySeveral naturally occurring compounds have been identified in human cerebrospinal fluid (CSF) after subarachnoid haemorrhage (SAH) as possible vasoactive agents involved in the biochemical mechanism of vasospasm. The authors have measured, in 30 patients admitted for SAH, CSF concentrations of two arachidonic acid metabolites, Prostacyclin and Prostaglandin D2, as representative of vasodilator and vasoconstrictor compounds. CSF samples were made available by lumbar punctures and intraoperative cisternal punctures. Nine patients presented with symptomatic vasospasm: lumbar CSF Prostaglandin D2 levels are significantly higher than in patients without vasospasm. The Cisternal Prostaglandin D2 level is significantly higher than the lumbar CSF concentration; CSF Prostacyclin levels do not significantly differ in the two groups of patients. These data suggest the presence of an imbalanced biochemical situation responsible for promoting vasospasm. The evaluation of cisternal levels of arachidonate metabolites support the hypothesis of the clotting phenomenon around the ruptured aneurysm wall as an important predictive pattern of vasospasm onset after SAH, as shown in computed tomography.

Anticholinergic agents prevent guinea-pig airway constriction induced by histamine, bradykinin and leukotriene C4: Relationship to circulating TXA2

Various doses of histamine, bradykinin and leukotriene C4 caused bronchoconstriction in anaesthetized guinea-pigs which were breathing spontaneously or artificially ventilated; there was a simultaneous, dose-related increase in circulating TXA2. The animals were prepared for continuous recording of extracorporeal circulation in order to detect the appearance in the blood of bioassayable levels of TXA2 -like substance. Furthermore, a TXA2 derivative, the mono-O-Me-TXB2, was radioimmunoassayed. Atropine, oxytropium bromide and ipratropium bromide given in mumol doses prevented both the increased airway resistance and the release of TXA2-like substance in the blood Pirenzepine dihydrochloride was the least active of the drugs tested. The protecting activity of anticholinergics and the relationship with their ability to affect TXA2-like substance generation suggest a new site of action for these drugs besides the blockade of muscarinic receptors.

Mevalonate pathway and isoprenoids regulate human bronchial myocyte proliferation

The role of mevalonate and geranylgeraniol in the control of cellular proliferation of cultured human bronchial myocytes was examined by investigating the effect of simvastatin, an inhibitor of 3-hydroxy-3-methylglutaryl coenzyme A reductase, the rate-limiting enzyme in mevalonate synthesis. Simvastatin inhibited the rate of growth of human bronchial smooth muscle cells in a concentration-dependent manner, with an IC50 value of 0.97 +/- 0.1 microM. Mevalonate (100 microM), as well as geranylgeraniol (5 microM), at their highest non-toxic concentrations, restored cell proliferation to control levels.

Angiotensin II: A releaser for PGI2 from fetal and newborn rabbit lungs

Angiotensin II (AII) induces generation of prostacyclin (PGI2) in rabbit lung in vitro at different ages, i.e., fetus, newborn and adult. Particularly, neonatal rabbit lungs display a pattern of sensitivity to AII in producing PGI2, measured as 6-oxo-PGF1 alpha, which seems to be higher than that observed in fetal lungs. The PGI2 release appears to be specific for AII stimulation since the vasoconstriction induced by noradrenaline and ergotamine was not associated with generation of this lipidic material. The inability of PGI2 to relax the extralobar pulmonary artery in the newborn suggests that the lung microcirculation is the most likely site where the vasodilating and antiaggregatory functions of PGI2 may have a physiological role.

Modulation of arachidonic acid metabolism by orally administered morniflumate in man

Unlike other classic NSAIDs, some fenamates given at therapeutic concentrations, have been shown to inhibit, bothin vitro andin vivo, the 5-lipoxygenase pathway of arachidonic acid cascade as well as the synthesis of cyclooxygenase products. This dual inhibitory property might represent an improvement in anti-inflammatory therapy. The aim of this work was to characterize the effect of morniflumate, admistered at therapeutic dosages to normal human volunteers, on leukotriene B4 (LTB4) and thromboxane (TXB2) synthesis, both in purified PMNs and in whole blood. PMNs, isolated two hours after a single oral administration of morniflumate and at steady-state condition, fully retain their capacity to release LTB4 and TXB2. Since intracellular concentrations of the drug were undetectable, in spite of its elevated concentrations in platelet poor plasma, the results obtained using PMNs suggest a drug loss during the cells purification procedure. In whole blood experiments, morniflumate reduced blood LTB4 synthesis induced by Ca-ionophore A23187 Bx approximately 50%, both after single dose and at steady state; the degree of inhibition showed a pattern similar to the plasma levels of the bioactive metabolite of morniflumate (M1). The inhibition of serum TXB2 levels was higher than 85%. Hence, morniflumate is capable of reducing arachidonic acid metabolism acting both on cyclooxygenase and 5-lipoxygenase. This characteristic might provide a better approach in anti-inflammatory therapy.

Stimulus-related difference in the formation of leukotrienes and PGD2 after immunological and non-immunological challenge of human lung parenchyma "in vitro"

The stimulation of human lung parenchymal fragments with A-23187 induces formation of leukotrienes as well as of PGD2: LTE4 is the compound found in larger amount and independently of the intensity of the stimulus the % of metabolized precursor which is converted to leukotrienes or PGD2 is remarkably similar. However, under conditions of IgE-Anti IgE challenge the predominant conversion of arachidonic acid occurs to PGD2, LTB4 is almost negligible and LTD4 and E4 together represent less than 30% of the oxidative products of arachidonic acid. Whether PGD2 and leukotrienes derive from the same or different subset of cells is unresolved.