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J F Seccombe

Publications and source records attributed to J F Seccombe.

8 recordsLinked to original sources
PubMed1998

Hypomagnesemia inhibits nitric oxide release from coronary endothelium: protective role of magnesium infusion after cardiac operations.

BACKGROUND: Postoperative hypomagnesemia is common in patients who have undergone cardiac operations and is associated with clinically significant morbidity resulting from atrial and ventricular dysrhythmias. Magnesium supplementation may increase the cardiac index in the early postoperative period. METHODS: The action of the magnesium cation on coronary vascular reactivity was studied. Segments of canine epicardial coronary artery were suspended in organ chambers to measure isometric force (95% O2/5% CO2, 37 degrees C). RESULTS: In coronary segments constricted with prostaglandin F2alpha (2 x 10[-6] mol/L), acetylcholine and adenosine diphosphate (10[-9] to 10[-4] mol/L) induced vasodilation in arteries with endothelium (n=10, each group; p < 0.05). Acetylcholine-mediated vasodilation was blocked by NG-monomethyl-L-arginine (10[-4] mol/L) and NG-nitro-L-arginine (10[-4] mol/L), two inhibitors of nitric oxide synthesis from L-arginine (n=10, p < 0.05). The removal of magnesium from the organ chamber solution impaired vasodilation in response to acetylcholine and adenosine diphosphate. However, normal endothelium-dependent vasodilation could be restored by return of magnesium to the bathing solution. Vascular relaxation in response to bradykinin (10[-9] to 10[-6] mol/L), which was found to induce endothelium-dependent vasodilation independent of nitric oxide production, was unaffected by magnesium removal (n=10). CONCLUSIONS: Hypomagnesemia selectively impaired the release of nitric oxide from the coronary endothelium. Because nitric oxide is a potent endogenous nitro-vasodilator and inhibitor of platelet aggregation and adhesion, hypomagnesemia could promote vasoconstriction and coronary thrombosis in the early postoperative period.

Acetylcholine↗
PubMed1995

Novel technique to bioassay endocardium-derived nitric oxide from the beating heart.

Nitric oxide is a potent vasodilator and antiplatelet substance released by the vascular endothelium. In the current study, isolated rabbit hearts were perfused retrograde in the aortic root with a balanced salt solution using a Langendorff technique. To perfuse the right cardiac chambers, an inflow cannula was placed in the superior vena cava and an outflow cannula in the right ventricular apex via the pulmonary artery. To detect endocardial vasodilator production, right heart perfusate was used to bathe a "bioassay" segment of canine coronary artery denuded of endothelium. Perfusate from unstimulated hearts did not alter smooth muscle tone in the bioassay tissue. Calcium inophore, a potent stimulus for endothelial nitric oxide production, produced relaxation of the bioassay smooth muscle when added to the cardiac perfusate but not when applied directly to the bioassay segment. Cardiac effluent vasodilator activity was abolished by removal of the endocardium or addition of nitric oxide synthesis inhibitors, but not by prostanoid inhibitors. These experiments describe a practical method to bioassay endocardial nitric oxide production in the beating heart.

Animals↗
PubMed1995

Coronary artery endothelial function after myocardial ischemia and reperfusion.

BACKGROUND: The consequences of ischemia-reperfusion injury on myocytes has been studied intensely, and previous investigations of methods of myocardial protection during global and regional ischemia have focused on resultant alterations in myocardial function. However, the coronary artery endothelium is also vulnerable to damage, and only recently have investigators been able to assess coronary endothelial function. METHODS: This review examines some aspects of coronary flow abnormalities that occur after ischemia and reperfusion. In addition, we summarize recent data that address the hypothesis that injury to the coronary artery endothelium may contribute to the pathophysiology of global (and regional) cardiac ischemia and reperfusion. RESULTS: It appears that ischemia and reperfusion selectively injure a component in the receptor/G-protein complex linking receptor-stimulus coupling to the activation of nitric oxide synthase. Further, oxygen radicals may contribute to this injury. Recent investigations demonstrate that oxygen radicals impair the receptor/G-protein complex specific to the nitric oxide signal transduction pathway rather than causing global receptor/G-protein dysfunction. CONCLUSIONS: The understanding of endothelial cell function and the elucidation of the nitric oxide pathway should further clarify our understanding of the pathogenesis of endothelial reperfusion injury and coronary vasospasm and contribute to the development of effective therapeutic interventions.

Amino Acid Oxidoreductases↗
PubMed1994

Oxygen radical-mediated vascular injury selectively inhibits receptor-dependent release of nitric oxide from canine coronary arteries.

Reperfusion after global cardiac ischemia may injure coronary artery endothelium and lead to vasospasm and thrombosis. Oxygen-derived radicals have been implicated as mediators of this process, but the precise mechanism of injury is unknown. We hypothesized that oxygen-derived radicals impair coronary endothelial production of nitric oxide, a potent endogenous vasodilator and inhibitor of platelet adhesion. To test this theory, we developed an in vitro model of reperfusion injury in which segments of epicardial canine coronary artery were suspended in organ chambers (physiologic salt solution, 37 degrees C, 95% oxygen and 5% carbon dioxide) and exposed to oxygen-derived radicals (generated by adding xanthine [10(-4) mol/L] and xanthine oxidase [100 mU/ml] to the bathing solution for 70 minutes). After exposure to oxygen-derived radicals, epicardial coronary artery smooth muscle exhibited normal contraction to potassium ions (20 mmol/L) and prostaglandin F2 (4 x 10(-6) mol/L); also, the rings relaxed normally on exposure to isoproterenol and sodium nitroprusside (10(-9) to 10(-4) mol/L) (n = 6). In contrast, endothelium-dependent vasodilatation to receptor-dependent agonists acetylcholine and adenosine diphosphate (10(-9) to 10(-4) mol/L) was impaired as compared with the reaction of control vessels not exposed to oxygen-derived radicals (n = 18, P < 0.001, and n = 10, P < 0.002, respectively). Importantly, receptor-independent, endothelium-dependent relaxation to the calcium ionophore A23187 was normal (n = 6). Further, endothelium-dependent vasodilatation to receptor-dependent agonist bradykinin (non-nitric oxide pathway) was normal after exposure to oxygen-derived radicals. This is the first study to demonstrate that oxygen-derived radicals selectively impair receptor-dependent nitric oxide production by the coronary endothelium. Diminished nitric oxide production is a likely mechanism of vasospasm and thrombosis after reperfusion of the ischemic heart.

Animals↗
PubMed1990

The subcellular distribution of platelet-activating factor in stimulated human neutrophils.

Exposure of human peripheral blood neutrophils to a variety of phagocytic and soluble stimuli is known to induce the synthesis and secretion of platelet-activating factor (PAF), a unique ether-linked phospholipid. It has recently been observed in this laboratory, that whereas some PAF is secreted to the exterior of the cell, the majority of the newly synthesized PAF is retained intracellularly. This observation led us to investigate the subcellular distribution of intracellular PAF in stimulated human neutrophils, and to question the possible intracellular role of this molecule. Approximately 2 x 10(8) neutrophils were exposed to either the phagocytic stimulus, opsonized zymosan particles (25 particles/cell), the soluble stimulus, Ca2(+)-ionophore A23187 (5 micrograms/ml), or were left unstimulated for up to 30 min. After disruption, the cells were fractionated into nuclei, phagolysosomes, specific granules, azurophil granules, membranes, and cytosol. Fractions were analyzed for representative organellar markers, as well as for total protein, total phospholipid phosphorous, and PAF. In cells that had been exposed to opsonized zymosan particles, the majority of the PAF was localized to the phagolysosomal fraction, with lesser amounts being detected in the membranous and granular fractions of the cells. In neutrophils that had been exposed to A23187, the major portion of the PAF was detected in the membranous fractions with smaller amounts being seen in fractions corresponding to the specific granules. On the basis of these data, combined with the known physicochemical properties of PAF, it is speculated that the PAF detected at discrete intracellular locations in stimulated human neutrophils may play an important role in the endocytic and/or secretory functions of neutrophils.

Calcimycin↗
PubMed1988

The priming of neutrophils by lipopolysaccharide for production of intracellular platelet-activating factor. Potential role in mediation of enhanced superoxide secretion.

LPS priming of the neutrophil results in enhanced release of superoxide upon subsequent stimulation, but the mechanism of this effect remains obscure. The recent recognition that neutrophils synthesize and retain platelet-activating factor within the cell led us to hypothesize that enhanced synthesis of platelet-activating factor in the LPS-primed cell might account for the observed effects of lipopolysaccharide. Using human neutrophils isolated on plasma-Percoll gradients, we found that incubation with 100 ng/ml LPS for 60 min resulted in a small but significant increase in intracellular platelet-activating factor assessed after lipid extraction, TLC, and bioassay. The further stimulation of primed neutrophils with FMLP resulted in a marked increase in neutrophil platelet-activating factor compared with non-LPS-treated controls. The priming effect of LPS was time dependent (30 to 60 min), dose dependent, and inhibited at 0 degree C and did not require protein synthesis. Platelet-activating factor so generated was not released but rather retained within the neutrophil, and the molecular species of platelet-activating factor produced was predominantly 1-O-hexadecyl-2-acetyl-sn-3-phosphorylcholine. Platelet-activating factor production in LPS-treated neutrophils was also enhanced by PMA, suggesting that receptor-mediated events could not account exclusively for the enhancement. Considering the ability of nanomolar concentrations of exogenously added platelet-activating factor to prime the neutrophil for enhanced release of superoxide, the rapid intracellular accumulation of platelet-activating factor that accompanies stimulation of an LPS-primed cell by FMLP may modulate the secretory events that accompany such stimulation.

Adjuvants, Immunologic↗