Variable tissue expression of transferrin receptors: relevance to acute respiratory distress syndrome.

Acute respiratory distress syndrome (ARDS) is associated with altered plasma and lung iron chemistry. Iron can promote microbial virulence and catalyse pro-oxidant reactions, thereby contributing to the oxidative stress that characterises the syndrome. Therefore, the expression of ferritin and transferrin receptors (TfR) were sought in the lungs and hearts of rodents treated with lipopolysaccharide (LPS), and measurements of TfR and ferritin protein expression were taken from lung biopsy specimens from patients with ARDS and appropriate controls. TfR messenger ribonucleic acid (mRNA) was significantly upregulated in the lungs and significantly downregulated in the hearts of rats 4 h after LPS. Ferritin mRNA levels (light and heavy chains) remained unaltered. Protein TfR levels were significantly upregulated in lungs and downregulated in hearts 4 h post-LPS. Ferritin protein levels were significantly downregulated in lungs compared to baseline values but were unaltered in hearts. Nonhaem iron levels were increased in lungs and decreased in hearts, and iron-regulatory-protein activity increased in hearts but not lungs. TfR protein levels were significantly increased in lung biopsies from patients with ARDS compared to controls. Transferrin receptors are upregulated in rodent lungs during inflammation but are downregulated in the heart. Transferrin receptor protein levels were significantly increased in the lungs in clinical acute respiratory distress syndrome. These findings have implications for the pathogenesis of acute respiratory distress syndrome, especially in relation to the role of iron as a mediator of oxidative stress.

Regional transcapillary albumin exchange in rodent endotoxaemia: effects of fluid resuscitation and inhibition of nitric oxide synthase.

Sepsis is characterized by increased microvascular permeability and regional variations in capillary perfusion, which may be modulated by nitric oxide (NO) and reversed by fluid resuscitation (FR). The effects of saline FR and NO synthase blockade [by N(G)-nitro-L-arginine methyl ester (L-NAME)] on microvascular albumin transport and perfused capillary density were assessed in anaesthetized Wistar rats with acute normodynamic endotoxaemia. Separate dual-isotope techniques were employed to measure the permeability index (PI(A)) and the permeabilityxsurface area product index (PI(B)), which provide different and complementary information regarding blood-tissue albumin exchange. PI(A) represents the tissue/blood distribution volume ratio of albumin. PI(B) is a composite measure of endothelial permeability and the vascular surface area available for albumin exchange, and therefore takes into account the effect of altered blood volume. Capillary density was quantified by fluorescence microscopy following circulation of Evans Blue-labelled albumin. Compared with controls, PI(A) was reduced significantly in lipopolysaccharide (LPS)-treated animals in skeletal muscle and skin, probably due to blood volume redistribution rather than to changes in permeability. PI(B) was increased significantly in LPS-treated animals in the kidney, mesentery, skeletal muscle, skin and lung, and in the small bowel following FR. FR also improved the LPS-induced metabolic base deficit, but did not alter capillary density. L-NAME significantly attenuated the LPS-induced rise in PI(B) in the lung. In conclusion, acute endotoxaemia induces tissue-dependent variations in microvascular albumin exchange. FR improves acid-base disturbance in endotoxaemia, through mechanisms other than microvascular recruitment. NO appears to increase microvascular permeability in endotoxaemia, an effect that may be attenuated by L-NAME, particularly in the lung.

Lung injury following pulmonary resection in the isolated, blood-perfused rat lung.

Lung resection may be complicated by postpneumonectomy pulmonary oedema. Oxidant generation following surgery-induced ischaemia-reperfusion may be responsible. This hypothesis was tested utilizing isolated, in situ, blood perfused rodent lungs subjected to continuous perfusion (control subjects); one lung ventilation followed by pneumonectomy (group 1); or one lung ventilation followed by reinflation of the collapsed lung (group 2). In control subjects, no significant changes in markers of oxidant damage, oxygenation, pulmonary artery pressure or extravascular albumin extravasation were detected. In group 1 lungs, hydroxyl radical-like damage was detected in association with impaired oxygenation (p<0.05), and increased pulmonary artery pressure and extravascular albumin accumulation in both lungs. In group 2, there was evidence of hydroxyl radical-like damage, and a fall in oxygenation (p<0.05) occurred during one lung ventilation. There was a transient rise in pulmonary artery pressure following lung reinflation and extra vascular albumin accumulation was significantly increased in both lungs (right>left, p<0.05). Both changes were attenuated (p<0.05) following treatment with the reactive oxygen species (ROS) scavenger superoxide dismutase (group 2a) and the nitric oxide synthase inhibitor N(G)-nitro-L-arginine methyl ester (group 2b). Hydroxyl radical-like damage was undetectable following nitric oxide synthase inhibition. Oxidant stress may contribute to the pathologies seen in this model of lung injury.

ATP is involved in myocardial and vascular effects of exogenous bradykinin in ejecting guinea pig heart.

It has recently been reported that bradykinin induces selective left ventricular (LV) relaxation in isolated guinea pig hearts via the release of nitric oxide. Exogenous bradykinin also induces vasodilation, which is only partly due to nitric oxide release. In the present study we investigated the role of adenyl purines on these bradykinin-induced effects. Isolated ejecting guinea pig hearts were studied. LV pressure was monitored by a 2-Fr micromanometer-tipped catheter. ATP concentrations were measured using a luciferin-luciferase assay. Bradykinin (1 and 100 nM) caused a progressive acceleration of LV relaxation together with a transient increase in coronary flow. These effects were inhibited by the nonselective P(2) purinoceptor antagonist suramin (1 microM, n = 6) but were unaffected by the selective P(2x) purinoceptor antagonist pyridoxal phosphate 6-azophenyl-2',4'-disulfonic acid (1 microM, n = 6). These myocardial and vascular effects of bradykinin were associated with increased ATP levels in coronary effluent. These data suggest that the selective enhancement of LV relaxation and rise in coronary flow induced by exogenous bradykinin involve endogenous ATP and the subsequent stimulation of P(2) purinoceptors.

Abnormal tissue oxygenation and cardiovascular changes in endotoxemia.

Experimental sepsis induces disturbances in microcirculatory flow and nutrient exchange that may result in impaired tissue oxygenation. Volume resuscitation is a principal clinical intervention in patients with sepsis. Nitric oxide (NO) has been implicated in the pathophysiology of endotoxemia, but few data exist concerning the effects of either NO synthase inhibition (NOSi) or volume resuscitation on microvascular regulation and tissue oxygenation. Amperometric measurements were made of skeletal muscle (tissue) oxygen tension (PtO2) and its response to changes in fraction of inspired oxygen (FIO2) in rats rendered endotoxemic. Simultaneous measurements were made of systemic hemodynamic indices and arterial blood gas tensions. At normal PaO2, PtO2 in endotoxemic animals was significantly lower than in control animals, with marked attenuation of the response to increasing FIO2. These changes were associated with significant metabolic acidemia. In volume-resuscitated endotoxemic rats, PtO2 and blood pH were unchanged. A significant reduction in the PtO2 response to hyperoxia was observed in animals treated with the NOS inhibitor NG-nitro-L-arginine methyl ester (L-NAME), an effect not reversed by fluid resuscitation. These data suggest that significant tissue hypoxia and abnormal microvascular control occur in endotoxemia. Volume resuscitation can reverse the changes in PtO2, whereas nitric oxide synthase (NOS) inhibition has deleterious effects on muscle PtO2 in both control and endotoxemic animals.

Iron overload upregulates haem oxygenase 1 in the lung more rapidly than in other tissues.

Haem oxygenase-1 is upregulated by numerous insults, including oxidative stress, and under such circumstances it is considered to be a protective stratagem. We have measured the haem oxygenase-1 expression in heart, lung and liver tissues of control and iron-overloaded rats. Lung tissue from iron-overloaded rats displayed a significant increase in the haem oxygenase-1 protein but no changes in haem oxygenase-1 mRNA. Conversely, heart tissue showed a significant increase in haem oxygenase-1 mRNA but no changes in haem oxygenase-1 protein. We conclude that during oxidative stress caused by iron overload, lung tissue responds with a rapid upregulation of haem oxygenase-1 levels.

Regulation of left ventricular relaxation in the isolated guinea-pig heart by endogenous endothelin.

OBJECTIVE: TO examine the effects of endogenous endothelin-1 on cardiac contraction in the isolated heart using endothelin receptor antagonists. METHODS: Isolated ejecting guinea-pig hearts were perfused with Krebs buffer (1 microM indomethacin) at 37 degrees C, constant loading and heart rate, and high-fidelity left ventricular pressure was monitored by an apical 2F Millar catheter. The effects of the following interventions on left ventricular performance and coronary flow were determined: (a) no treatment (i.e., time controls) (n = 8); (b) the specific ETA receptor antagonist, BQ123 (1 microM, n = 8); (c) the specific ETB receptor antagonist, IRL 1038 (0.1 microM, n = 4; 1 microM, n = 6); (d) exogenous endothelin-1 (0.01 nM, n = 6; 0.1 nM, n = 6); (e) the specific ETB receptor agonist, BQ3020 (5 nM, n = 8). RESULTS: All parameters were stable in control (untreated) hearts. BQ123 induced progressive acceleration of early left ventricular pressure decline and a fall in left ventricular end-diastolic pressure with no effect on peak left ventricular pressure, dP/dtmax, stroke volume or coronary flow. IRL 1038 had no effect on any of these parameters. In contrast, exogenous endothelin-1 exerted potent vasoconstrictor effects associated with a fall in peak left ventricular pressure, dP/dtmax and stroke volume. Similar changes were observed with BQ3020. Concentrations of endothelin-1 < 0.1 nM, which had no vasoconstrictor effect, produced no change in LV function. CONCLUSIONS: These data indicate that basal intracardiac release of endothelin-1 significantly delays LV relaxation in the isolated guinea-pig heart, but has no effect on coronary flow. The contrasting effects of endogenous endothelin-1 (elicited by BQ123) and exogenous endothelin-1 are likely to reflect differences in their site of action and in their effective concentrations at these sites.

Effects of sulphydryl- and non-sulphydryl-containing ACE inhibitors on left ventricular relaxation in the isolated guinea pig heart.

ACE inhibitors exert both acute and chronic beneficial effects on cardiac function (e.g remodelling, diastolic dysfunction). We have previously reported that the ACE inhibitor captopril induces selective left ventricular (LV) relaxant effects in the isolated ejecting guinea pig heart. The aim of the present study was to further investigate the mechanism of the captopril-induced changes in early LV relaxation by comparing the effects of two sulphydryl and two non-sulphydryl containing ACE inhibitors in the same experimental preparation. Isolated ejecting guinea pig hearts were studied under conditions of constant loading and heart rate. LV pressure was monitored by a 2F micromanometer-tipped catheter transducer inserted in the LV cavity. The sulphydryl-containing ACE inhibitors captopril and zofenaprilat enhanced early LV relaxation, whereas the non-sulphydryl-containing ACE inhibitors lisinopril and quinaprilat did not. The effects of captopril and zofenaprilat were attenuated both by the nitric oxide-scavenger haemoglobin and the bradykinin B2-kinin receptor antagonist HOE 140. Neither the oxygen free-radical scavenger superoxide dismutase nor the sulphydryl-containing compound N-acetyl cysteine administered together with lisinopril had any effect on LV relaxation. These data demonstrate that inhibition of intra-cardiac ACE activity may acutely modulate LV relaxation through increased activity of the bradykinin-nitric oxide pathway. The presence of a sulphydryl group on the relevant ACE inhibitor appears to be essential for this LV relaxant effect.

Enhancement of left ventricular relaxation in the isolated heart by an angiotensin-converting enzyme inhibitor.

BACKGROUND: ACE inhibitors exert both acute and chronic beneficial effects on cardiac function (eg, remodeling, diastolic dysfunction) in experimental studies and in patients. They inhibit the formation of angiotensin II as well as the degradation of endogenous bradykinin. We recently reported that bradykinin induces selective left ventricular (LV) relaxant effects in isolated hearts via the release of nitric oxide. The present study examined the direct effects of interaction between the ACE inhibitor captopril and endogenous bradykinin on cardiac contractile function. METHODS AND RESULTS: Isolated ejecting guinea pig hearts were studied under conditions of constant loading and heart rate. LV pressure was monitored by a 2F micromanometer-tipped catheter. Captopril (1 mumol/L, n = 9) caused a progressive acceleration of LV relaxation without significantly affecting early systolic parameters (eg, LV dP/dtmax) or coronary flow. These effects were inhibited by the nitric oxide scavenger hemoglobin (1 mumol/L, n = 5) or by the B2-kinin receptor antagonist HOE140 (10 nmol/L, n = 5). In the presence of captopril, bradykinin (0.1 nmol/L, n = 6) markedly accelerated LV relaxation (significantly more than captopril alone), whereas bradykinin alone (0.1 nmol/L, n = 6) had no effect. CONCLUSIONS: These data indicate that the ACE inhibitor captopril causes an acute and selective enhancement of LV relaxation independent of changes in coronary flow, probably via an endogenous bradykinin/nitric oxide pathway.