Acclimatization of the systemic microcirculation to alveolar hypoxia is mediated by an iNOS-dependent increase in nitric oxide availability.

Rats breathing 10% O2 show a rapid and widespread systemic microvascular inflammation that results from nitric oxide (NO) depletion secondary to increased reactive O2 species (ROS) generation. The inflammation eventually resolves, and the microcirculation becomes resistant to more severe hypoxia. These experiments were directed to determine the mechanisms underlying this microvascular acclimatization process. Intravital microscopy of the mesentery showed that after 3 wk of hypoxia (barometric pressure ~380 Torr; partial pressure of inspired O2 ~68-70 Torr), rats showed no evidence of inflammation; however, treatment with the inducible NO synthase (iNOS) inhibitor L-N6-(1-iminoethyl) lysine dihydrochloride led to ROS generation, leukocyte-endothelial adherence and emigration, and increased vascular permeability. Mast cells harvested from normoxic rats underwent degranulation when exposed in vitro to monocyte chemoattractant protein-1 (MCP-1), the proximate mediator of mast cell degranulation in acute hypoxia. Mast cell degranulation by MCP-1 was prevented by the NO donor spermine-NONOate. MCP-1 did not induce degranulation of mast cells harvested from 6-day hypoxic rats; however, pretreatment with either the general NOS inhibitor L-NG-monomethyl arginine citrate or the selective iNOS inhibitor N-[3-(aminomethyl) benzyl] acetamidine restored the effect of MCP-1. iNOS was demonstrated in mast cells and alveolar macrophages of acclimatized rats. Nitrate + nitrite plasma levels decreased significantly in acute hypoxia and were restored after 6 days of acclimatization. The results support the hypothesis that the microvascular acclimatization to hypoxia results from the restoration of the ROS/NO balance mediated by iNOS expression at key sites in the inflammatory cascade.NEW & NOTEWORTHY The study shows that the systemic inflammation of acute hypoxia resolves via an inducible nitric oxide (NO) synthase-induced restoration of the reactive O2 species/NO balance in the systemic microcirculation. It is proposed that the acute systemic inflammation may represent the first step of the microvascular acclimatization process.

Burns: Pathophysiology of Systemic Complications and Current Management.

As a result of many years of research, the intricate cellular mechanisms of burn injury are slowly becoming clear. Yet, knowledge of these cellular mechanisms and a multitude of resulting studies have often failed to translate into improved clinical treatment for burn injuries. Perhaps the most valuable information to date is the years of clinical experience and observations in the management and treatment of patients, which has contributed to a gradual improvement in reported outcomes of mortality. This review provides a discussion of the cellular mechanisms and pathways involved in burn injury, resultant systemic effects on organ systems, current management and treatment, and potential therapies that we may see implemented in the future.

Mast Cell: A Multi-Functional Master Cell.

Mast cells are immune cells of the myeloid lineage and are present in connective tissues throughout the body. The activation and degranulation of mast cells significantly modulates many aspects of physiological and pathological conditions in various settings. With respect to normal physiological functions, mast cells are known to regulate vasodilation, vascular homeostasis, innate and adaptive immune responses, angiogenesis, and venom detoxification. On the other hand, mast cells have also been implicated in the pathophysiology of many diseases, including allergy, asthma, anaphylaxis, gastrointestinal disorders, many types of malignancies, and cardiovascular diseases. This review summarizes the current understanding of the role of mast cells in many pathophysiological conditions.

Ubiquinol decreases hemorrhagic shock/resuscitation-induced microvascular inflammation in rat mesenteric microcirculation.

Hemorrhagic shock (HS) is a leading cause of death in traumatic injury. Ischemia and hypoxia in HS and fluid resuscitation (FR) creates a condition that facilitates excessive generation of reactive oxygen species (ROS). This is a major factor causing increased leukocyte-endothelial cell adhesive interactions and inflammation in the microcirculation resulting in reperfusion tissue injury. The aim of this study was to determine if ubiquinol (coenzyme Q10) decreases microvascular inflammation following HS and FR. Intravital microscopy was used to measure leukocyte-endothelial cell adhesive interactions in the rat mesentery following 1-h of HS and 2-h post FR with or without ubiquinol. Hemorrhagic shock was induced by removing ~ 40% of anesthetized Sprague Dawley rats' blood volume to maintain a mean arterial blood pressure <50 mmHg for 1 h. Ubiquinol (1 mg/100 g body weight) was infused intravascularly in the ubiquinol group immediately after 1-h HS. The FR protocol included replacement of the shed blood and Lactate Ringer's in both the control and ubiquinol groups. We found that leukocyte adherence (2.3 ± 2.0), mast cell degranulation (1.02 ± 0.01), and ROS levels (159 ± 35%) in the ubiquinol group were significantly reduced compared to the control group (10.8 ± 2.3, 1.36 ± 0.03, and 343 ± 47%, respectively). In addition, vascular permeability in the control group (0.54 ± 0.11) was significantly greater than the ubiquinol group (0.34 ± 0.04). In conclusion, ubiquinol attenuates HS and FR-induced microvascular inflammation. These results suggest that ubiquinol provides protection to mesenteric microcirculation through its antioxidant properties.

Induced hypothermia during resuscitation from hemorrhagic shock attenuates microvascular inflammation in the rat mesenteric microcirculation.

Microvascular inflammation occurs during resuscitation following hemorrhagic shock, causing multiple organ dysfunction and mortality. Preclinical evidence suggests that hypothermia may have some benefit in selected patients by decreasing this inflammation, but this effect has not been extensively studied. Intravital microscopy was used to visualize mesenteric venules of anesthetized rats in real time to evaluate leukocyte adherence and mast cell degranulation. Animals were randomly allocated to normotensive or hypotensive groups and further subdivided into hypothermic and normothermic resuscitation (n = 6 per group). Animals in the shock groups underwent mean arterial blood pressure reduction to 40 to 45 mmHg for 1 h via blood withdrawal. During the first 2 h following resuscitation by infusion of shed blood plus double that volume of normal saline, rectal temperature of the hypothermic groups was maintained at 32°C to 34°C, whereas the normothermic groups were maintained between 36°C to 38°C. The hypothermic group was then rewarmed for the final 2 h of resuscitation. Leukocyte adherence was significantly lower after 2 h of hypothermic resuscitation compared with normothermic resuscitation: (2.8 ± 0.8 vs. 8.3 ± 1.3 adherent leukocytes, P = 0.004). Following rewarming, leukocyte adherence remained significantly different between hypothermic and normothermic shock groups: (4.7 ± 1.2 vs. 9.5 ± 1.6 adherent leukocytes, P = 0.038). Mast cell degranulation index (MDI) was significantly decreased in the hypothermic (1.02 ± 0.04 MDI) versus normothermic (1.22 ± 0.07 MDI) shock groups (P = 0.038) after the experiment. Induced hypothermia during resuscitation following hemorrhagic shock attenuates microvascular inflammation in rat mesentery. Furthermore, this decrease in inflammation is carried over after rewarming takes place.

Rapid vascular responses to anthrax lethal toxin in mice containing a segment of chromosome 11 from the CAST/Ei strain on a C57BL/6 genetic background.

Host allelic variation controls the response to B. anthracis and the disease course of anthrax. Mouse strains with macrophages that are responsive to anthrax lethal toxin (LT) show resistance to infection while mouse strains with LT non-responsive macrophages succumb more readily. B6.CAST.11M mice have a region of chromosome 11 from the CAST/Ei strain (a LT responsive strain) introgressed onto a LT non-responsive C57BL/6J genetic background. Previously, B6.CAST.11M mice were found to exhibit a rapid inflammatory reaction to LT termed the early response phenotype (ERP), and displayed greater resistance to B. anthracis infection compared to C57BL/6J mice. Several ERP features (e.g., bloat, hypothermia, labored breathing, dilated pinnae vessels) suggested vascular involvement. To test this, Evan's blue was used to assess vessel leakage and intravital microscopy was used to monitor microvascular blood flow. Increased vascular leakage was observed in lungs of B6.CAST.11M mice compared to C57BL/6J mice 1 hour after systemic administration of LT. Capillary blood flow was reduced in the small intestine mesentery without concomitant leukocyte emigration following systemic or topical application of LT, the latter suggesting a localized tissue mechanism in this response. Since LT activates the Nlrp1b inflammasome in B6.CAST.11M mice, the roles of inflammasome products, IL-1ß and IL-18, were examined. Topical application to the mesentery of IL-1ß but not IL-18 revealed pronounced slowing of blood flow in B6.CAST.11M mice that was not present in C57BL/6J mice. A neutralizing anti-IL-1ß antibody suppressed the slowing of blood flow induced by LT, indicating a role for IL-1ß in the response. Besides allelic differences controlling Nlrp1b inflammasome activation by LT observed previously, evidence presented here suggests that an additional genetic determinant(s) could regulate the vascular response to IL-1ß. These results demonstrate that vessel leakage and alterations to blood flow are part of the rapid response in mice resistant to B. anthracis infection.

Dexamethasone blocks the systemic inflammation of alveolar hypoxia at several sites in the inflammatory cascade.

Alveolar hypoxia produces a rapid and widespread systemic inflammation in rats. The inflammation is initiated by the release into the circulation of monocyte chemoattractant protein-1 (MCP-1) from alveolar macrophages (AMO) activated by the low alveolar Po(2). Circulating MCP-1 induces mast cell (MC) degranulation with renin release and activation of the local renin-angiotensin system, leading to microvascular leukocyte recruitment and increased vascular permeability. We investigated the effect of dexamethasone, a synthetic anti-inflammatory glucocorticoid, on the development of the systemic inflammation of alveolar hypoxia and its site(s) of action in the inflammatory cascade. The inflammatory steps investigated were the activation of primary cultures of AMO by hypoxia, the degranulation of MCs by MCP-1 in the mesentery microcirculation of rats, and the effect of angiotensin II (ANG II) on the leukocyte/endothelial interface of the mesentery microcirculation. Dexamethasone prevented the mesentery inflammation in conscious rats breathing 10% O(2) for 4 h by acting in all key steps of the inflammatory cascade. Dexamethasone: 1) blocked the hypoxia-induced AMO activation and the release of MCP-1 and abolished the increase in plasma MCP-1 of conscious, hypoxic rats; 2) prevented the MCP-1-induced degranulation of mesentery perivascular MCs and reduced the number of peritoneal MCs, and 3) blocked the leukocyte-endothelial adherence and the extravasation of albumin induced by topical ANG II in the mesentery. The effect at each site was sufficient to prevent the AMO-initiated inflammation of hypoxia. These results may explain the effectiveness of dexamethasone in the treatment of the systemic effects of alveolar hypoxia.

Renin released from mast cells activated by circulating MCP-1 initiates the microvascular phase of the systemic inflammation of alveolar hypoxia.

Reduced alveolar Po(2) in rats produces a rapid systemic inflammation characterized by reactive O(2) species generation, mast cell (MC) degranulation, leukocyte-endothelial interactions, and increased vascular permeability. The inflammation is not initiated by the low systemic Po(2) but rather by the release of monocyte chemoattractant protein-1 (MCP-1) from alveolar macrophages (AMO) activated by alveolar hypoxia. Circulating AMO-borne MCP-1 induces MC degranulation, which activates the local renin-angiotensin system (RAS) and mediates the microvascular inflammation. This study was directed to determine the mechanism of RAS activation by MCP-1-induced MC degranulation. Experiments in isolated rat peritoneal MCs showed the following: 1) Western blots and immunocytochemistry demonstrated the presence of renin and angiotensin-converting enzyme (ACE) in MCs and their release upon degranulation; 2) MCP-1-induced degranulation of MCs incubated in plasma produced an increase in angiotensin II (ANG II) concentration; and 3) this increase was inhibited completely by the following agents: the MCP-1 receptor antagonist RS-102895, the specific rat renin inhibitor WFML, or the ACE inhibitor captopril administered separately. Captopril also inhibited ANG II generation by MCs incubated in culture medium plus ANG I. The results show that peritoneal MCs contain active renin, which activates the RAS upon degranulation, and that peritoneal MCs are a source of ACE and suggest that conversion of ANG I to ANG II is mediated predominantly by ACE. This study provides novel evidence of the presence of active renin in rat peritoneal MCs and helps explain the mechanism of activation of the RAS during alveolar hypoxia.

Effects of intragastric fructose and dextrose on mesenteric microvascular inflammation and postprandial hyperemia in the rat.

OBJECTIVES: Fructose superfused on the mesenteric venules of rats induces microvascular inflammation via oxidative stress. It is unknown whether intragastric fructose exerts a similar effect and whether fructose impairs postprandial hyperemia (PPH). The goals were to determine whether intragastric fructose administration promotes leukocyte adherence and whether fructose, owing to its oxidative properties, may also impair nitric oxide-dependent PPH in the mesenteric microcirculation of rats. METHODS: Leukocyte adherence to mesenteric venules, arteriolar velocity, and diameter were measured in Sprague-Dawley rats before and 30 minutes after intragastric (1 mL 0.5 M, ~0.3 g/kg) dextrose (n = 5), fructose (n = 6), and fructose after intravenous injection of the antioxidant α-lipoic acid (ALA, n = 6). RESULTS: Only fructose increased leukocyte adherence: control 2.3 ± 0.3 per 100 µm; fructose 9.7 ± 1.4 per 100 µm (P < .001). This effect was independent of changes in venular shear rate: control 269 ± 48 s(-1); fructose 181 ± 27 s(-1) (P > .05, r(2) = 0.083 for shear rate vs leukocyte adherence). Dextrose had no effect on leukocyte adherence: control 1.52 ± 0.13 per 100 µm; dextrose 2.0 ± 0.7 per 100 µm (P > .05). ALA prevented fructose-induced leukocyte adherence: control 1.9 ± 0.2 per 100 µm; fructose + ALA 1.8 ± 0.3 per 100 µm (P > .05). Neither fructose nor dextrose induced PPH: arteriolar velocity: control 3.3 ± 0.49 cm/s, fructose 3.06 ± 0.34 cm/s (P > .05); control 3.3 ± 1.0 cm/s, dextrose 3.15 ± 1.1 cm/s (P > .05); arteriolar diameter: control 19.9 ± 1.10 µm, fructose 19.7 ± 1.0 µm (P > .05); control 21.5 ± 2.6, dextrose 20.0 ± 2.7 µm (P > .05). CONCLUSIONS: Intragastric fructose induced leukocyte adherence via oxidative stress. Neither dextrose nor fructose induced PPH, likely because of the inhibitory effect of anesthesia on splanchnic vasomotor tone.

Alveolar macrophages initiate the systemic microvascular inflammatory response to alveolar hypoxia.

Alveolar hypoxia occurs as a result of a decrease in the environmental [Formula: see text] , as in altitude, or in clinical conditions associated with a global or regional decrease in alveolar ventilation. Systemic effects, in most of which an inflammatory component has been identified, frequently accompany both acute and chronic forms of alveolar hypoxia. Experimentally, it has been shown that acute exposure to environmental hypoxia causes a widespread systemic inflammatory response in rats and mice. Recent research has demonstrated that alveolar macrophages, in addition to their well known intrapulmonary functions, have systemic, extrapulmonary effects when activated, and indirect evidence suggest these cells may play a role in the systemic consequences of alveolar hypoxia. This article reviews studies showing that the systemic inflammation of acute alveolar hypoxia observed in rats is not initiated by the low systemic tissue [Formula: see text] , but rather by a chemokine, Monocyte Chemoattractant Protein-1 (MCP-1, or CCL2) released by alveolar macrophages stimulated by hypoxia and transported by the circulation. Circulating MCP-1, in turn, activates perivascular mast cells to initiate the microvascular inflammatory cascade. The research reviewed here highlights the extrapulmonary effects of alveolar macrophages and provides a possible mechanism for some of the systemic effects of alveolar hypoxia.

Monocyte chemoattractant protein-1 released from alveolar macrophages mediates the systemic inflammation of acute alveolar hypoxia.

Alveolar hypoxia produces rapid systemic inflammation in rats. Several lines of evidence suggest that the inflammation is not initiated by low systemic tissue partial pressure of oxygen (Po(2)) but by a mediator released into the circulation by hypoxic alveolar macrophages. The mediator activates tissue mast cells to initiate inflammation. Monocyte chemoattractant protein-1/Chemokine (C-C motif) ligand 2 (MCP-1/CCL2) is rapidly released by hypoxic alveolar macrophages. This study investigated whether MCP-1 is the mediator of the systemic inflammation of alveolar hypoxia. Experiments in rats and in alveolar macrophages and peritoneal mast cells led to several results. (1) Alveolar hypoxia (10% O(2) breathing, 60 minutes) produced a rapid (5-minute) increase in plasma MCP-1 concentrations in conscious intact rats but not in alveolar macrophage-depleted rats. (2) Degranulation occurred when mast cells were immersed in the plasma of hypoxic intact rats but not in the plasma of alveolar macrophage-depleted rats. (3) MCP-1 added to normoxic rat plasma and the supernatant of normoxic alveolar macrophages produced a concentration-dependent degranulation of immersed mast cells. (4) MCP-1 applied to the mesentery of normoxic intact rats replicated the inflammation of alveolar hypoxia. (5) The CCR2b receptor antagonist RS-102895 prevented the mesenteric inflammation of alveolar hypoxia in intact rats. Additional data suggest that a cofactor constitutively generated in alveolar macrophages and present in normoxic body fluids is necessary for MCP-1 to activate mast cells at biologically relevant concentrations. We conclude that alveolar macrophage-borne MCP-1 is a key agent in the initiation of the systemic inflammation of alveolar hypoxia.

Alveolar hypoxia-induced systemic inflammation: what low PO(2) does and does not do.

Reduction of alveolar PO(2) (alveolar hypoxia, AH) may occur in pulmonary diseases such as chronic obstructive pulmonary disease (COPD), or in healthy individuals ascending to altitude. Altitude illnesses may develop in non-acclimatized persons who ascend rapidly. The mechanisms underlying these illnesses are not well understood, and systemic inflammation has been suggested as a possible contributor. Similarly, there is evidence of systemic inflammation in the systemic alterations present in COPD patients, although its role as a causative factor is not clear.We have observed that AH, induced by breathing 10% O(2) produces a rapid (minutes) and widespread micro vascular inflammation in rats and mice. This inflammation has been observed directly in the mesenteric, skeletal muscle, and pial microcirculations. The inflammation is characterized by mast cell degranulation, generation of reactive O(2) species, reduced nitric oxide levels, increased leukocyte-endothelial adherence in post-capillary venules, and extravasation of albumin. Activated mast cells stimulate the renin-angiotensin system (RAS) which leads to the inflammatory response via activation of NADPH oxidase. If the animals remain in hypoxia for several days, the inflammation resolves and exposure to lower PO(2) does not elicit further inflammation, suggesting that the vascular endothelium has "acclimatized" to hypoxia.Recent experiments in cremaster microcirculation suggest that the initial trigger of the inflammation is not the reduced tissue PO(2), but rather an intermediary released by alveolar macrophages into the circulation. The putative intermediary activates mast cells, which, in turn, stimulate the local renin-angiotensin system and induce inflammation.

Fructose, but not dextrose, induces leukocyte adherence to the mesenteric venule of the rat by oxidative stress.

Recent evidence indicates that fructose is a pro-inflammatory molecule. Oral fructose induces serum and kidney inflammatory intercellular adhesion molecule-1 (ICAM-1) in rats. Fructose also induces ICAM-1 expression in human aortic endothelial cells (HAEC) and monocyte chemoattractant protein-1 in proximal tubular renal cells. It is not known whether fructose may directly promote inflammation on the intestinal microcirculation. Accordingly, using intravital microscopy we studied the effect of topical fructose and dextrose on leukocyte adherence to the mesenteric venule of the rat. Leukocyte adherence was determined during a control period and after fructose was added to the mesentery, in the presence or absence of the NO donor spermine NONO-ate (SNO), and after i.v. injection of the antioxidant lipoic acid (LA). In separate experiments, we examined the effect of topical dextrose on leukocyte adherence to the mesenteric venule. Venular shear rate was calculated. Fructose, but not dextrose, induced significant inflammation independent of shear rate. This effect was completely blocked by SNO and LA, suggesting that fructose induces inflammation via reactive oxygen species (ROS) generation. These results suggest that fructose present in formulas may adversely affect the intestinal microcirculation of premature infants and potentially contribute to the pathogenesis of necrotizing enterocolitis (NEC).

Alveolar hypoxia, alveolar macrophages, and systemic inflammation.

Diseases featuring abnormally low alveolar PO2 are frequently accompanied by systemic effects. The common presence of an underlying inflammatory component suggests that inflammation may contribute to the pathogenesis of the systemic effects of alveolar hypoxia. While the role of alveolar macrophages in the immune and defense functions of the lung has been long known, recent evidence indicates that activation of alveolar macrophages causes inflammatory disturbances in the systemic microcirculation. The purpose of this review is to describe observations in experimental animals showing that alveolar macrophages initiate a systemic inflammatory response to alveolar hypoxia. Evidence obtained in intact animals and in primary cell cultures indicate that alveolar macrophages activated by hypoxia release a mediator(s) into the circulation. This mediator activates perivascular mast cells and initiates a widespread systemic inflammation. The inflammatory cascade includes activation of the local renin-angiotensin system and results in increased leukocyte-endothelial interactions in post-capillary venules, increased microvascular levels of reactive O2 species; and extravasation of albumin. Given the known extrapulmonary responses elicited by activation of alveolar macrophages, this novel phenomenon could contribute to some of the systemic effects of conditions featuring low alveolar PO2.

The systemic inflammation of alveolar hypoxia is initiated by alveolar macrophage-borne mediator(s).

Alveolar hypoxia produces widespread systemic inflammation in rats. The inflammation appears to be triggered by activation of mast cells by a mediator released from alveolar macrophages, not by the reduced systemic partial pressure of oxygen (PO2). If this is correct, the following should apply: (1) neither mast cells nor tissue macrophages should be directly activated by hypoxia; and (2) mast cells should be activated when in contact with hypoxic alveolar macrophages, but not with hypoxic tissue macrophages. We sought here to determine whether hypoxia activates isolated alveolar macrophages, peritoneal macrophages, and peritoneal mast cells, and to study the response of the microcirculation to supernatants of these cultures. Rat mesenteric microcirculation intravital microscopy was combined with primary cultures of alveolar macrophages, peritoneal macrophages, and peritoneal mast cells. Supernatant of hypoxic alveolar macrophages, but not of hypoxic peritoneal macrophages, produced inflammation in mesentery. Hypoxia induced a respiratory burst in alveolar, but not peritoneal macrophages. Cultured peritoneal mast cells did not degranulate with hypoxia. Immersion of mast cells in supernatant of hypoxic alveolar macrophages, but not in supernatant of hypoxic peritoneal macrophages, induced mast cell degranulation. Hypoxia induced release of monocyte chemoattractant protein-1, a mast cell secretagogue, from alveolar, but not peritoneal macrophages or mast cells. We conclude that a mediator released by hypoxic alveolar macrophages activates mast cells and triggers systemic inflammation. Reduced systemic PO2 and activation of tissue macrophages do not play a role in this phenomenon. The inflammation could contribute to systemic effects of diseases featuring alveolar hypoxia.

Deferoxamine mimics the pattern of hypoxia-related injury at the microvasculature.

Oxygen is essential for the maintenance of life, and when oxygen levels decline to critical levels, a program of complex mechanisms exists to i) sense hypoxia, ii) respond to minimize acute tissue injury, and iii) result in adaptations that offer protection against further hypoxia challenges. Alternative adaptation-related protection may also be inducible through the increased activity of hypoxia-inducible factors activated by hypoxia mimics such as iron chelation with deferoxamine (DFA). We have characterized a set of hypoxia-related responses at the microvasculature and postulated that microvascular injury in response to hypoxia could be reproduced by the reduction of bioavailable iron through chelation by DFA. We were able to induce a similar degree of leukocyte adherence and emigration and vascular leak with DFA infusion as compared with hypoxia exposure in an intact physiological rodent model. However, in contrast to hypoxia-exposed groups, we were unable to detect reactive oxygen species or alter the injury pattern with reactive oxygen species scavenger in the groups treated with DFA. Thus, we demonstrate that DFA mimics the pattern and intensity of hypoxia-related injury on the microvasculature; however, differences in the time course and mechanism of injury were identified. In addition, DFA saturated with iron did not completely reverse the effects of DFA, suggesting a mechanism(s) beyond a reduction in the bioavailability of iron. These findings may have importance in the targeting of iron for the development of hypoxia mimics that may offer protection against subsequent hypoxia exposure in clinical setting such as myocardial infarction and stroke.

Activated protein C attenuates microvascular injury during systemic hypoxia.

In response to hypoxia, an inflammatory cascade is initiated and microvascular injury ensues. Specifically, within 10 min, leukocyte adherence to the endothelium begins, and leukocyte emigration and vascular leak soon follow. Activated protein C (APC) has been reported to have both anticoagulant and anti-inflammatory properties. Activated protein C is best described in its role as a treatment for sepsis. However, it has been used, with some success, in experimental models of hypoxic injury. We hypothesized that APC would be protective against microvascular injury during systemic hypoxia. Randomized prospective animal study. Adult male Sprague-Dawley rats. To characterize the microvascular response to APC exposure during hypoxia, four rat groups were used: saline control, APC infusion alone (100 mg/kg bolus), hypoxia alone (10% O2), and simultaneous hypoxia + APC infusion. Measurements of leukocyte adherence (no. per 100-microm venule), leukocyte emigration (no. per 4,000 microm(2)), and venular leak by fluorescein isothiacyanate-labeled albumin (Fo/Fi) were performed during intravital microscopy of the intact venular bed. Leukocyte adherence decreased from 14.5 (+/-1.2) cells/100-microm venule in hypoxic rats to 4.4 (+/-1.5) cells/100-microm venule in those treated with both hypoxic gas and APC infusion (P < 0.001). Similarly, leukocyte emigration in hypoxic rats reached 12.3 (+/- 2.2) cells/4,000-microm(2) venule, but was reduced to 3.5 (+/-0.3) cells/4,000-microm(2) venule (P <.001). Venular permeability to protein was also significantly decreased in the APC-treated group from 0.82 (+/-0.14) to 0.25 (+/-0.14) (P < 0.001). The infusion of APC attenuates the inflammatory response during systemic hypoxia at the microvascular level, as evidenced by measurements of leukocyte adherence, emigration, and venular permeability. Further investigation is needed to examine the potential role of APC in the treatment of hypoxic injury.

Alveolar macrophages are necessary for the systemic inflammation of acute alveolar hypoxia.

Alveolar hypoxia (Fi(O(2)) 0.10) rapidly produces inflammation in the microcirculation of skeletal muscle, brain, and mesentery of rats. Dissociation between tissue Po(2) values and inflammation, plus the observation that plasma from hypoxic rats activates mast cells and elicits inflammation in normoxic tissues, suggest that the response to hypoxia is initiated when mast cells are activated by an agent released from a distant site and carried by the circulation. These experiments tested the hypothesis that this agent originates in alveolar macrophages (AM). Male rats were depleted of AM by tracheal instillation of clodronate-containing liposomes. Four days after treatment, AM recovered by bronchoalveolar lavage were <10% of control. Control rats received buffer-containing liposomes. As expected, alveolar hypoxia (Fi(O(2)) 0.10) in control rats increased leukocyte-endothelial adherence, produced degranulation of perivascular mast cells, and increased fluorescent albumin extravasation in the cremaster microcirculation. None of these effects was seen when AM-depleted rats were exposed to hypoxia. Plasma obtained from control rats after 5 min of breathing 10% O(2) elicited inflammation when applied to normoxic cremasters. In contrast, normoxic cremasters did not develop inflammation after application of plasma from hypoxic AM-depleted rats. Supernatant from AM cultured in 10% O(2) produced increased leukocyte-endothelial adherence, vasoconstriction, and albumin extravasation when applied to normoxic cremasters. Normoxic AM supernatant did not produce any of these responses. The effects of hypoxic supernatant were attenuated by pretreatment of the cremaster with the mast cell stabilizer cromolyn. These data support the hypothesis that AM are the source of the agent that initiates hypoxia-induced systemic inflammation by activating mast cells.

Role of the renin-angiotensin system in the systemic microvascular inflammation of alveolar hypoxia.

Alveolar hypoxia (AH) induces widespread systemic inflammation. Previous studies have shown dissociation between microvascular Po(2) and inflammation. Furthermore, plasma from AH rats (PAHR) induces mast cell (MC) activation, inflammation, and vasoconstriction in normoxic cremasters, while plasma from normoxic rats does not produce these responses. These results suggest that inflammation of AH is triggered by a blood-carried agent. This study investigated the involvement of the renin-angiotensin system (RAS) in the inflammation of AH. Both an angiotensin-converting enzyme (ACE) inhibitor and an angiotensin II (ANG II) receptor blocker (ANG II RB) inhibited the leukocyte-endothelial adherence produced by AH, as well as the inflammation produced by PAHR in normoxic rat cremasters. MC stabilization with cromolyn blocked the effects of PAHR but not those of topical ANG II on normoxic cremasters, suggesting ANG II generation via MC activation by PAHR. This was supported by the observation that ACE inhibition and ANG II RB blocked the leukocyte-endothelial adherence produced by the MC secretagogue compound 48/80. These results suggest that the intermediary agent contained in PAHR activates MC and stimulates the RAS, leading to inflammation, and imply an RAS role in AH-induced inflammation.

Hypobaric hypoxia as a tool to study pregnancy-dependent responses at the maternal-fetal interface.

Establishment of proper oxygen and nutrient supply to the fetus is essential for a successful pregnancy. The maternal-fetal interface is the site of vascular modifications, providing a conduit for the delivery of essential nutrients to the developing fetus. Pregnancy-dependent adaptive vascular responses within the uteroplacental compartment can be exaggerated by exposure to a physiological stressor such as hypoxia. A simple procedure for exposing pregnant rats and mice to hypobaric hypoxia is presented.