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K M Mullane

Publications and source records attributed to K M Mullane.

At least 55 records · Page 3Linked to original sources
PubMed1988

SOD prevents damage and attenuates eicosanoid release in a rabbit model of necrotizing enterocolitis.

Necrotizing enterocolitis (NEC) was produced in anesthetized rabbits by transmural injection of intestinal loops with an acidified solution of casein and calcium gluconate, mimicking the luminal milieu of afflicted neonates. Intravenous infusion of superoxide dismutase (SOD) 15 min after NEC induction prevented intestinal damage. In ex vivo perfused intestinal loops, we determined the sites of eicosanoid release and their contribution to the vascular effects of N-formyl-methionyl-leucyl-phenylalanine (fMLP) and platelet-activating factor (PAF) in damaged and SOD-salvaged intestine. The vascular effluent was the primary site of stimulated eicosanoid release. The vascular responses to fMLP (vasoconstriction) and PAF (vasodilation) were not altered by SOD, although vascular resistance was higher in the SOD group. SOD treatment attenuated 1) transmural fluid shifts in ex vivo perfused intestinal preparations, an index of vascular permeability, 2) fMLP-induced prostaglandin E2, 6-ketoprostaglandin F1 alpha (6-keto-PGF1 alpha), and leukotriene B4 (LTB4) release, and 3) PAF-induced release of 6-keto-PGF1 alpha and LTB4. Stimulated thromboxane B2 release was not altered by SOD. Thus NEC can be established by a luminal insult that causes local generation of free radicals and exaggerated release of prostaglandins and leukotrienes.

6-Ketoprostaglandin F1 alpha↗
PubMed1988

Thromboxane synthetase inhibitors reduce infarct size by a platelet-dependent, aspirin-sensitive mechanism.

Platelets are suggested to exacerbate ischemia-induced myocardial injury, which has led to the study of various antiplatelet therapies including thromboxane synthetase inhibitors (TXSI). Two such agents, benzylimidazole and OKY-046, reduce infarct size commensurate with a diminution in serum thromboxane B2 formation in anesthetized dogs subjected to 90 minutes of coronary artery occlusion followed by 5 hours of reperfusion. In contrast, platelet depletion with specific antiserum does not reduce infarct size but prevents the cardioprotection afforded by the TXSI. Platelet-derived prostaglandin endoperoxides (PGG2 and PGH2), which cannot be converted to thromboxane A2 in the inhibited platelet, can be transformed to PGE2 and PGD2 in plasma and to PGI2 by the blood vessel wall. These prostaglandins are considered "cardioprotective." Consequently, a low dose of aspirin (3-5 mg/kg) given 24 hours before coronary occlusion was used to selectively block the platelet cyclooxygenase enzyme. Aspirin, by itself, does not reduce infarct size, but it suppresses the myocardial salvage induced by OKY-046. Thus, TXSI reduce infarct size by platelet-dependent, aspirin-sensitive mechanism that depends on the redirection of platelet-derived PGG2 and PGH2 to protective metabolites, rather than inhibition of thromboxane A2 per se. Moreover, myocardial salvage induced by the TXSI is accompanied by a reduction in neutrophil accumulation in the myocardium, as indicated by the levels of the neutrophil-specific myeloperoxidase enzyme. Platelet depletion or pretreatment with aspirin prevents the TXSI-induced suppression of neutrophil accumulation. Consequently, it is proposed that the prostaglandin-mediated protective effects of TXSI can be resolved, at least in part, in terms of a braking action on neutrophil activation to prevent leukocyte-dependent tissue injury.

Acrylates↗
PubMed1988

Contribution of oxygen-derived free radicals to experimental necrotizing enterocolitis.

Oxygen-derived free radicals, particularly superoxide anion, are considered important mediators of intestinal injury induced by ischemia/reperfusion based on the protective effects of superoxide dismutase and allopurinol. A role for free radicals was investigated in a model of necrotizing enterocolitis (NEC) which was initiated by a luminal, as opposed to a vascular, insult. Intestinal loops of weanling rabbits received either saline (control loops) or a solution of 10 mg/ml casein and 50 mg/ml calcium gluconate acidified to pH 4 with proprionic acid (treated loops). When the animals were sacrificed 3 hours later, severe damage was noted in the treated loops, which included blunting of villi and edema, with all animals surviving. At 16 hours only 5 of 8 rabbits survived, and 3 had hemorrhagic necrosis. Control loops were normal in each case. Intravenous infusion of superoxide dismutase (4 mg/kg/hr), commencing 15 minutes after NEC induction, totally prevented intestinal injury. On the other hand, pretreatment with allopurinol, an inhibitor of xanthine oxidase, for 2 days (30 and 60 mg/kg by mouth) was not protective against intestinal damage. A cellular infiltration in treated loops was not histologically evident in the majority of animals at 3 hours after treatment, a finding confirmed by the minimal accumulation of 111In-labeled leukocytes in damaged and intact intestinal tissue. These results suggest that superoxide generated locally from sources other than xanthine oxidase play a critical and early role in experimental NEC and that superoxide dismutase may prove to be an effective therapy in this devastating neonatal disease.

Allopurinol↗
PubMed1987

Leukocyte-derived metabolites of arachidonic acid in ischemia-induced myocardial injury.

Within minutes of occlusion of a major coronary artery the polymorphonuclear leukocytes (PMNs) are activated whereby they adhere to the vascular endothelium and migrate through the endothelial layer. Interactions with the endothelium can promote increased vascular resistance, diminished collateral flow, capillary blockade, and predisposition to vasospasm, as well as enhanced vascular permeability. On subsequent reperfusion entrapped leukocytes contribute to the no-reflow phenomenon, while more leukocytes gain access to the previously ischemic region. The leukocytes infiltrate the myocardium where they exacerbate the process of tissue injury and the development of arrhythmias. The release of leukocyte-derived mediators including arachidonic acid (AA) metabolites and oxygen-derived free radicals probably underlies these activities of the leukocytes. PMNs contain active lipoxygenase enzymes capable of metabolizing AA to products that are not normally found in the myocardium, and can dominate the metabolic profile of that tissue, leading to changes in myocardial integrity and function. Inhibitors of the lipoxygenase enzymes suppress the accumulation of leukocytes into the ischemic myocardium and reduce infarct size. However, because the drugs prevent cell invasion it cannot be inferred that a lipoxygenase metabolite per se is deleterious to the ischemic heart, inasmuch as any leukocyte-dependent mechanism of injury will be attenuated whether it is mediated by eicosanoids or by any other leukocyte-derived product. Additional studies with specific inhibitors/antagonists are required to determine the biochemical mechanisms underlying the different aspects of leukocyte-mediated myocardial injury.

Arachidonic Acid↗
PubMed1987

Impaired endothelium-dependent relaxations in rabbits subjected to aortic coarctation hypertension.

Rabbits were rendered hypertensive by suprarenal coarctation of the abdominal aorta. Seven days later, endothelium-dependent and endothelium-independent vascular relaxations were examined in vascular rings taken from hypertensive (thoracic aorta, carotid artery) and normotensive (abdominal aorta) regions. Relaxation of phenylephrine-contracted rings in response to endothelium-dependent agonists (acetylcholine, A23187) was impaired, compared with that in sham-operated and intact controls, in regions exposed to the elevated blood pressure (i.e., above the coarctation). Responses to acetylcholine and A23187 in the abdominal aorta, below the coarctation, were not altered. The diminished endothelium-dependent responses in the thoracic aorta were not affected by pretreatment with the cyclooxygenase inhibitor indomethacin. In contrast to acetylcholine and A23187, responses to the endothelium-independent agonist nitroprusside were not attenuated in vessels from hypertensive regions, indicating that the defect occurred in the endothelium. The EC50 for acetylcholine-induced relaxations of thoracic aorta correlated significantly with mean arterial pressure above the coarctation, indicating that the extent to which endothelium-dependent relaxation is impaired is in proportion to the degree of blood pressure elevation. This study suggests that the diminished relaxations by endothelium-dependent agonists is a local response to the elevation of blood pressure and is not due to a circulating factor.

Acetylcholine↗
PubMed1987

A neutrophil-derived cytochrome P450-dependent metabolite of arachidonic acid modulates neutrophil behavior.

Recently, the metabolism of arachidonic acid to two unidentified products (Peak 1 and Peak 2) by a cytochrome P-450 dependent mixed function oxidase has been described in canine polymorphonuclear leukocytes (PMNs). This study assessed the biologic activity of one of these metabolites, Peak 2, on PMN function. Peak 2 was formed biologically following addition of exogenous arachidonic acid to canine PMNs pretreated with BW755c to inhibit lipoxygenase and cyclooxygenase enzymes, and purified by high performance liquid chromatography following separation by column chromatography. Peak 2 (20-200 ng/ml) inhibited calcium ionophore A23187-induced aggregation and the second phase of LTB4-induced aggregation. Additionally, Peak 2 inhibited A23187-induced PMN adhesion to columns of Sephadex G-25. BW755c (94 microM), which increased the formation of Peaks 1 and 2 by almost 300%, also inhibited A23187-induced PMN adhesion. In contrast, Peak 2 did not inhibit the release of superoxide anions or immunoreactive LTB4, after stimulation of the PMNs with A23187. Thus, Peak 2 may modulate some activities of canine PMNs. Because the biologic activity of Peak 2 is opposite to that of LTB4, which promotes PMN aggregation and adhesion, and because LTB4 may be metabolized by a cytochrome P-450-dependent mixed function oxidase to less active metabolites, this enzyme system may play a central role in the control of PMN function.

4,5-Dihydro-1-(3-(trifluoromethyl)phenyl)-1H-pyraz↗
PubMed1987

Endothelium, arachidonic acid, and coronary vascular tone.

Vasoactive mediators play an important role in the control of coronary vascular tone. Arachidonic acid (AA) metabolites and endothelium-derived vasoactive factors have been implicated in coronary vasoregulation. AA can be metabolized via three separate routes in blood vessels, mediated by cyclooxygenase, lipoxygenase, and cytochrome P-450-dependent monooxygenase enzymes. AA can evoke endothelium-dependent relaxations that are due in part to the formation of cytochrome P-450-dependent metabolites, inasmuch as drugs that modify cytochrome P-450 activity produce parallel changes in endothelium-dependent relaxations to AA. Moreover, some cytochrome P-450-derived metabolites formed biologically cause relaxations of isolated blood vessels. A cytochrome P-450-dependent pathway does not appear to contribute to endothelium-dependent relaxations induced by acetylcholine, which suggests that there may be a number of endothelium-derived relaxing factors (EDRFs). In addition, two endothelium-derived contractile factors have been described, including an unidentified cyclooxygenase metabolite of AA and a polypeptide isolated from cultured cells. As both prostaglandin I2 and acetylcholine-induced EDRF also inhibit platelet aggregation, endothelial injury and loss of these factors may predispose to vasospasm precipitated by release of platelet-derived mediators such as thromboxane A2 (TXA2) and 5-hydroxytryptamine. Unstable angina may be a clinical syndrome in which these events occur, which can be alleviated by inhibition of platelet activation and TXA2 formation with aspirin. Attenuation of endothelium-dependent relaxations can also occur without loss of endothelial cells. Neutrophil-endothelium interactions, precipitated by an ischemic episode, may initiate endothelial dysfunction and underlie the development of vasospasm in some conditions. Whether increased production of endothelium-derived contractile factors also occurs in vasospastic conditions remains to be determined.

Animals↗
PubMed1987

Arachidonic acid-induced endothelial-dependent relaxations of canine coronary arteries: contribution of a cytochrome P-450-dependent pathway.

Arachidonic acid (AA, 10(-8)-5 X 10(-6) M) induced dose-dependent relaxations of canine coronary arterial rings precontracted with dinoprost that were significantly greater (P less than .001) if the endothelium was intact. Cyclooxygenase inhibition with indomethacin displaced the dose-response curve to AA to the right but did not prevent the relaxant effects of the fatty acid. SKF-525A, an inhibitor of cytochrome P-450-dependent enzymes, also attenuated the response to AA although the combination of SKF-525A and indomethacin prevented any relaxant effect. Induction of cytochrome P-450-dependent enzymes in the coronary artery with 3-methylcholanthrene and beta-naphthoflavone given in vivo (40 mg/kg/day for 3 days) or depletion of these enzymes with cobalt chloride (24 mg/kg/day for 2 days) resulted in an enhancement or diminution, respectively, of AA-induced endothelial-dependent relaxations. These results implicate a cytochrome P-450-dependent mixed function oxidase in the endothelial-dependent relaxations to AA in the canine coronary artery. Precontraction of coronary arteries with U46619 in contrast to dinoprost failed to display endothelial-dependent relaxations to AA, whereas the responses to bradykinin and acetylcholine were also partially attenuated. Pharmacologic manipulations of AA metabolism via cyclooxygenase and cytochrome P-450-dependent monooxygenases indicate that the endothelial-dependent relaxations induced by bradykinin are partially dependent upon metabolites of AA, whereas the relaxations produced by acetylcholine are independent of AA metabolites, suggesting that a number of potential relaxing factors may be released from the endothelium.

Animals↗
PubMed1986

Cytochrome P-450-dependent monooxygenase activity and endothelial-dependent relaxations induced by arachidonic acid.

The authors have recently identified a cytochrome P-450-dependent monooxygenase in vascular tissue, localized primarily to the endothelium. As this enzyme system can metabolize arachidonic acid (AA) to novel products, some of which produce vasodilation, the pathways involved in the vascular actions of AA (10(-8) to 5 X 10(-6) M) were examined on rings of rabbit pulmonary artery. In pulmonary rings with a low basal tension (1.5 g), AA produces a weak contraction which is prevented by removal of the endothelium or the addition of indomethacin (10(-6) M) but not SKF 525A (10(-5) M), suggesting the formation of an endothelial-dependent vasoconstrictor cyclooxygenase product. In contrast, rings precontracted to 3.5 to 4 g tension with phenylephrine (7 X 10(-7) M) exhibit a dose-related relaxation to AA, which is significantly greater (P less than .001, n = 32) in preparations with an intact endothelium. The endothelium-independent relaxation is suppressed by indomethacin whereas indomethacin fails to attenuate the endothelium-dependent response. In contrast, SKF 525A, an inhibitor of cytochrome P-450-dependent monooxygenase, markedly inhibits (P less than .001) AA-induced relaxations in intact rings in a dose-dependent manner while not affecting the response in rings denuded of endothelium. Intact vessels treated with SKF 525A (10(-6) M) appear to show diversion of the AA to vasodilator cyclooxygenase products, since the subsequent addition of indomethacin produces a further reduction of the AA-induced relaxations, whereas by itself indomethacin has no effect.(ABSTRACT TRUNCATED AT 250 WORDS)

4,5-Dihydro-1-(3-(trifluoromethyl)phenyl)-1H-pyraz↗
PubMed1985

Myeloperoxidase activity as a quantitative assessment of neutrophil infiltration into ischemic myocardium.

The infiltration of neutrophils into ischemic myocardium exacerbates myocardial damage upon reperfusion, whereas drugs that inhibit neutrophil activity or function reduce infarct size. Consequently, it is important to accurately assess the myocardial neutrophil content. Histologic sections and radiolabeled cells have been used, but have major limitations. We have developed a method to measure the neutrophils present in cardiac tissue by utilizing a spectrophotometric assay for the neutrophil-specific myeloperoxidase enzyme (MPO) (Bradley et al., 1982a). Coronary artery occlusion and reperfusion in the anesthetized dog induces neutrophil accumulation into the ischemic heart, which shows a linear relationship with time. An increase in activity from 0.014 +/- 0.001 units (u) MPO/100 mg tissue to 0.091 +/- 0.02 u MPO/100 mg is already apparent at the end of the 90-min occlusion period. This activity increases over 5 hr reperfusion to 0.32 +/- 0.018 u MPO/100 mg tissue. Histologic analyses confirmed the temporal association of neutrophil accumulation. Moreover, there is a correlation between infarct size and tissue MPO activity. Measuring the MPO content in preparations of canine neutrophils, which is directly correlated with cell number, allows units of MPO activity to be converted into a tissue neutrophil content. This assay is simple, sensitive, and provides a quantitative index of myocardial neutrophil accumulation that can be used to study the relationship between leukocyte infiltration and myocardial injury.

Animals↗
PubMed1985

Nafazatrom-induced salvage of ischemic myocardium in anesthetized dogs is mediated through inhibition of neutrophil function.

The effects of nafazatrom on leukocyte function in vitro and in vivo were related to its ability to salvage ischemic myocardium in an occlusion-reperfusion model of myocardial injury in the anesthetized dog. Nafazatrom (0.4-75 microM) produced dose-related inhibition in vitro of neutrophil aggregation, superoxide anion generation, arachidonic acid metabolism, and, to a lesser extent, the release of beta-glucuronidase. In contrast, nafazatrom (0.4-37.5 microM) did not substantially influence platelet aggregation or the platelet metabolism of arachidonic acid. In vivo nafazatrom (10 mg/kg, po) reduced infarct size from 58 +/- 3% of the risk area (mean +/- SEM, n = 9) in control dogs to 23 +/- 2% of the risk area (n = 9, P less than 0.01). Nafazatrom also reduced the incidence of accompanying arrhythmias. Nafazatrom-induced myocardial salvage was not associated with any hemodynamic changes; moreover, it was independent of platelets, since thrombocytopenia did not prevent nafazatrom from exerting a protective effect. Measurements of the neutrophil-specific myeloperoxidase enzyme in ischemic myocardium indicate that the smaller infarct size in dogs treated with nafazatrom is accompanied by diminished leukocyte infiltration. Thus, the ability of nafazatrom to inhibit neutrophil function in vitro and cell infiltration in vivo may underly its myocardial-protective effects.

4,5-Dihydro-1-(3-(trifluoromethyl)phenyl)-1H-pyraz↗
PubMed1984

Conversion of arachidonic acid to two novel products by a cytochrome P450-dependent mixed-function oxidase in polymorphonuclear leukocytes.

Canine polymorphonuclear leukocytes metabolize [14C] arachidonic acid into 2 unidentified products, separated by thin-layer chromatography and high performance liquid chromatography, and called peak 1 and peak 2. The formation of peak 1 is maximal at 5 minutes and then declines, while the synthesis of peak 2 increases throughout the 30 minute incubation period. The formation of peak 1 and, to a lesser extent, peak 2, was enhanced after dual inhibition of lipoxygenase and cyclo-oxygenase enzymes with BW755C (94 microns) or nafazatrom (37 microns), or after incubation in a calcium-free buffer. In contrast, the formation of these products was inhibited by SKF-525A (50 microns), suggesting a cytochrome P450-dependent mechanism. The presence of cytochrome P450 in neutrophil microsomes was confirmed by measuring aryl hydrocarbon hydroxylase activity and cytochrome P450 content.

Animals↗
PubMed1984

Role of leukocytes in acute myocardial infarction in anesthetized dogs: relationship to myocardial salvage by anti-inflammatory drugs.

The invasion of leukocytes into and around a myocardial infarct was studied in chloralose-anesthetized dogs subjected to 1-hr occlusion of the left anterior descending coronary artery and reperfused for periods up to 5 hr. Polymorphonuclear leukocytes adhering to the endothelium of blood vessels within the ischemic area are evident at the end of the occlusion period. During reperfusion, the leukocytes migrate into the myocardium and large groups of cells can be observed "streaming" toward the irreversibly damaged area after 5 hr reperfusion. Infarcted tissue produces 10 times more 12-hydroxyeicosatetraenoic acid (a metabolite attributed to the invading leukocytes) from arachidonic acid than adjacent "normal" areas of the ventricle. BW755C (10 mg/kg-1 i.v.), which inhibits both the lipoxygenase and cyclooxygenase pathways of arachidonic metabolism, attenuates leukocyte infiltration into the infarcted myocardium, prevents 12-hydroxyeicosatetraenoic acid formation and significantly reduces infarct size (P less than .005). BW755C also significantly diminishes the incidence of cardiac arrhythmias during infarction. In animals where circulating white cells are reduced 60% by treatment with hydroxyurea (20 mg/kg-1 i.v./day for 5 days), there is also a smaller infarct (P less than .01). Indomethacin (5 mg/kg-1 i.v.) and dexamethasone (0.2 mg/kg-1 i.v.), which do not affect leukocyte migration into the ischemic myocardium, do not reduce infarct size. It is proposed that migrating leukocytes contribute to the tissue injury accompanying myocardial ischemia, possibly by the release of proinflammatory mediators such as lipoxygenase products, free radicals (oxygen metabolites) and hydrolytic enzymes. Drugs which reduce the migration and/or activation of leukocytes may be useful in reducing infarct size.

12-Hydroxy-5,8,10,14-eicosatetraenoic Acid↗
PubMed1982

The interactions of platelet-derived mediators on isolated canine coronary arteries.

The interactions of 5-hydroxytryptamine (5-HT) and a thromboxane A2 mimetic, U44069, were investigated on rings of canine coronary arteries. 5-HT (10(-8) - 10(-5) M) and U44069 (10(-9) - 10(-6) M) produce coronary vasoconstriction which is potentiated by indomethacin (3 X 10(-6) M). In the presence of 10(-9) M 5-HT, U44069-induced vasoconstriction is enhanced. Similarly, 10(-9) M U44069 enhances the effects of 5-HT. In both cases this potentiation is greatest in the presence of indomethacin. Synergism between the platelet-derived mediators could contribute to coronary vasospasm and myocardial ischaemia.

Animals↗
PubMed1982

The salvage of ischaemic myocardium by BW755C in anaesthetised dogs.

BW755C, a dual inhibitor of the lipoxygenase and cyclo-oxygenase pathways of arachidonic acid metabolism reduces the size of an infarct produced by 60 min of coronary occlusion followed by 5 hours reperfusion in anaesthetised beagles. This effect of BW755C is observed when the drug is given after the period of occlusion, and is independent of any haemodynamic effect. In contrast, indomethacin, which inhibits only the cyclo-oxygenase pathway, did not influence infarct size. It is suggested that the salvage of acutely ischaemic myocardium by BW755C is due to inhibition of lipoxygenase product formation by migrating cells which invade the damaged myocardium to produce an inflammatory response.

4,5-Dihydro-1-(3-(trifluoromethyl)phenyl)-1H-pyraz↗