Adenosine receptor antagonism affects regional resting vascular resistance during rat peritoneal sepsis

Regional haemodynamic responses to adenosine receptor activation vary across time following lipopolysaccharide treatment in conscious rats

BACKGROUND AND PURPOSE

Studies using adenosine receptor antagonists have shown that adenosine-mediated vasodilatations play an important role in the maintenance of regional perfusion during sepsis, but it is unclear whether vascular sensitivity to adenosine is affected. Here, we assessed regional haemodynamic responses to adenosine agonists and antagonists in normal and lipopolysaccharide (LPS)-treated rats to investigate a possible role for adenosine in the haemodynamic sequelae.

EXPERIMENTAL APPROACH

Male Sprague-Dawley rats were chronically instrumented with pulsed Doppler flow probes to measure regional haemodynamic responses to adenosine-receptor agonists (adenosine, 2-choloro-N6-cyclopentyladenosine (CCPA)) and antagonists (8-phenyltheophylline (8-PT), 8-cyclopentyl-1,3-dipropylxanthine (DPCPX)), at selected time points in control and LPS-treated rats.

KEY RESULTS

The responses to 8-PT were consistent with endogenous adenosine causing bradycardia, and renal and hindquarters vasodilatation in control rats, whereas in LPS-treated rats, there was evidence for endogenous adenosine causing renal (at 1.5 h) and hindquarters (at 6 h) vasoconstriction. In control animals, exogenous adenosine caused hypotension, tachycardia and widespread vasodilatation, whereas in LPS-treated rats, the adenosine-induced renal (at 1.5 h) and hindquarters (at 6 h) vasodilatations were abolished. As enhanced A1 receptor-mediated vasoconstriction could explain the results in LPS-treated rats, vascular responsiveness to a selective A1-receptor agonist (CCPA) or antagonist (DPCPX) was assessed. There was no evidence for enhanced vasoconstrictor responsiveness to CCPA in LPS-treated rats, but DPCPX caused renal vasodilatation, consistent with endogenous adenosine mediating renal vasoconstriction under these conditions.

CONCLUSIONS AND IMPLICATIONS

The results show changes in adenosine receptor-mediated cardiovascular effects in endotoxaemia that may have implications for the use of adenosine-based therapies in sepsis.

THE EXTRACELLULAR CARDIAC PURINE METABOLOME IN SEPSIS

The total cardiac purine metabolome includes all of the adenine and guanine nucleoside and nucleosides and related molecules involved throughout the intracellular and extracellular compartments and various cell types in the heart. In considering purines as molecules involved in autocrine and paracrine communication, effective interstitial concentrations of the nucleoside adenosine, or purine metabolites, are of greatest interest. These molecules arise from the complex interactions between cardiac-specific cell types, including fibroblasts and myocytes, and noncardiac cells, such as tissue-resident macrophages and other immune cells that have vascular access. In the interstitial environment, adenosine can regulate vascular resistance, contractile function, and immunochemical interactions. The breakdown of purines can produce reactive oxygen species that also influence autocrine and paracrine interactions. A central enzyme in this paradigm, adenosine deaminase, is a pivotal molecule in regulating the balance between pro-inflammatory and anti-inflammatory signaling cascades. A new role for adenosine deaminase as an allosteric regulator of relevant membrane proteins has yet to be explored in the heart.

Bigendothelin-1 (1-21) fragment during early sepsis modulates tau, p38-MAPK phosphorylation and nitric oxide synthase activation

Earlier we have demonstrated that inhibition of endothelin biosynthesis ameliorates endotoxemia-induced inducible nitric oxide synthase (iNOS) activation and phosphorylation of p38-mitogen activated protein kinase (pp38-MAPK). Therefore, in the present study, we tested the hypothesis that activation of endothelin (ET)-1 biosynthesis using bigET-1 during early sepsis would upregulate iNOS and affect myocardial function in the rat. Male Sprague-Dawley rats (350-400 g) were anesthetised using Nembutal (50 mg/kg, i.p.) and jugular vein, tail artery (Mean arterial pressure, MAP) and right carotid arteries (advanced to left ventricle, LV) were cannulated. The rats were randomly divided into saline-, bigET-1- and C-terminal fragment of bigET-1 (bigET-1(22-38))-treated groups. Sepsis was induced using i.p. injection of cecal inoculum obtained from a donor rat (200 mg/kg in 5 ml 5% sterile dextrose water, D5W). Sham animals received an i.p. injection of D5W (5 ml/kg). MAP and LVP were recorded and cardiodynamic parameters were calculated at 0, 2, 6, 12 and 24 h post sham or sepsis-induction. A significant elevation in LV isovolumic relaxation rate constant (tau), LV end diastolic pressure (LVEDP) and rate pressure product (RPP) was observed in vehicle-treated septic group at 24 h. BigET-1 significantly increased concentration of LV ET-1 both in sham and septic groups. BigET-1 elevated tau and LVEDP both in sham and septic animals as early as 12 h which persisted through 24 h. However, bigET-1(22-38) elevated LVEDP in septic group at 24 h but not in sham group. BigET-1 accentuated the levels of plasma nitric oxide byproduct (NOx) levels in both sham and septic animals at 6, 12 and 24 h. Sepsis increased myocardial iNOS at 24 h. BigET-1 significantly upregulated expression of myocardial iNOS and pp38-MAPK. The data suggest that increased substrate availability for ET-1 at the time of sepsis-induction contributes in diastolic dysfunction, iNOS activation and p38-MAPK phosphorylation.

Closure of Abdominal Wall Defects Using Acellular Dermal Matrix

BACKGROUND

After some abdominal surgical procedures, the abdominal wall defect may be too large for closure by tension-free approximation of the wound margins because of tissue loss or swelling of the abdominal viscera. A variety of absorbable and nonabsorbable prosthetic materials have been used for emergency abdominal wall reconstruction. Of these materials, polytetrafluoroethylene (PTFE) sheets have proved to be the most efficacious.

METHODS

This study compared the efficacy of allogenic acellular dermal matrix (ADM) and PTFE as prosthetic materials for wound closure in rats with surgical, full-thickness, 2 x 3-cm abdominal wounds. Healing was studied among animals with and those without experimentally induced peritonitis for 21 days after surgery.

RESULTS

Acellular dermal matrix became vascularized and incorporated into the wound bed and was partially or fully epithelialized without the need for skin grafting. As a result, little superficial bleeding was seen, and ADM effectively closed the wounds even in the presence of peritonitis. Wounds treated with ADM also showed a significant reduction in wound area (sterile:p < 0.001; contaminated:p < 0.05). In contrast, PTFE temporarily closed the wounds, but was not incorporated into them. It consequently evoked the formation of extensive underlying granulation tissue that showed significant superficial bleeding when the PTFE was removed. Very limited wound contraction occurred in PTFE-treated wounds, and some instances of evisceration and fistula formation were observed. Wounds treated with both types of material showed significant amounts of adhesion to visceral organs underlying the wound site.

CONCLUSIONS

Acellular dermal matrix exhibits a number of favorable features relative to PTFE for closing sterile or contaminated full-thickness abdominal wall defects.

Therapeutic potential for transient inhibition of adenosine deaminase in systemic inflammatory response syndrome

OBJECTIVE

We sought to determine the potential usefulness of 2'-deoxycoformycin (pentostatin), an inhibitor of adenosine deaminase, as a postinsult, or prophylactic treatment for systemic inflammatory response syndrome resulting from fecal peritonitis.

DESIGN

Prospective, randomized, controlled experiment.

SETTING

Small animal basic science laboratory.

SUBJECTS

Male Spague-Dawley rats, weighing 300 to 350 g.

INTERVENTIONS

Rats with fecal peritonitis (intraperitoneal cecal slurry) were treated with 1 mg/kg pentostatin intraperitoneally 24 hrs before, or intravenously when signs of illness presented (2 hrs after induction of peritonitis). Signs of illness included tachycardia, tachypnea, and leukopenia. All rats received 50 mL/kg 0.9% saline resuscitative fluid at 2 hrs.

MEASUREMENTS AND MAIN RESULTS

Survival to day 6 was 100% in nonseptic sham rats, but 33% in untreated septic rats. In rats given pentostatin either 2 hrs after the insult, or 24 hrs before the insult, 6-day survival improved to 81% and 78%, respectively. Histology revealed diffuse peritonitis, and evidence of systemic inflammatory response syndrome, including local and distant site vascular damage and leukocyte activation. These responses to the septic challenge were abrogated by pentostatin treatment. Return of significant amount of tissue adenosine deaminase activity by 24 hrs and later recovery of white blood cell counts argue against any potential for inappropriate immunosuppression by pentostatin.

CONCLUSIONS

These data indicate that the novel use of pentostatin to prevent systemic inflammatory response syndrome secondary to fecal peritonitis shows uncommon promise as a therapeutic tool. All indices of systemic inflammatory response syndrome were abrogated and survival improved when pentostatin was not given until after signs of the illness became manifest. Because protection was afforded with treatment 24 hrs in advance of the inciting insult, pentostatin also has the unique potential for use as a true prophylactic agent.

Mesenteric hemodynamic response to circulatory shock

PURPOSE OF REVIEW

The mesenteric hemodynamic response to circulatory shock is substantial and asymmetrical; the vasoconstrictive response disproportionately affects the mesenteric organs. The cardiac output is sustained partially, at no cost in nutrient flow to the mesenteric organs, by vasoconstriction of the mesenteric veins, resulting in the "autotransfusion" of up to 30% of the circulating blood volume into the systemic circulation.

RECENT FINDINGS

Hemorrhagic or cardiogenic shock also results in decreased perfusion pressure, prompting selective vasoconstriction of the mesenteric arterioles to maintain perfusion pressure of the vital organs, here at the selective expense of the mesenteric organs. Septic shock may be associated with increased or decreased mesenteric blood flow but is characterized by increased oxygen consumption, exceeding the capability of mesenteric oxygen delivery.

SUMMARY

The response to any of these conditions can, variably and unpredictably, cause hemorrhagic gastric stress erosions, nonocclusive mesenteric ischemia of the small bowel, ischemic colitis, ischemic hepatitis, acalculous cholecystitis, and/or ischemic pancreatitis. Injury to the mesenteric organs can also initiate the systemic inflammatory response syndrome and, consequently, multiple organ failure.

Inhibiting adenosine deaminase modulates the systemic inflammatory response syndrome in endotoxemia and sepsis

By pharmacological manipulation of endogenous adenosine, using chemically distinct methods, we tested the hypothesis that endogenous adenosine tempers proinflammatory cytokine responses and oxyradical-mediated tissue damage during endotoxemia and sepsis. Rats were pretreated with varying doses of pentostatin (PNT; adenosine deaminase inhibitor) or 8-sulfophenyltheophylline (8-SPT; adenosine receptor antagonist) and then received either E. coli endotoxin (lipopolysaccharide; 0.01 or 2.0 mg/kg) or a slurry of cecal matter in 5% dextrose in water (200 mg/kg). Resultant levels of tumor necrosis factor (TNF)-alpha, interleukin (IL)-1beta, and IL-10 were measured in serum and in liver and spleen. Untreated, 2 mg/kg lipopolysaccharide elevated serum TNF-alpha, IL-1beta, and IL-10. PNT dose dependently attenuated, without ablating, the elevation in serum TNF-alpha and IL-1beta and raised liver and spleen IL-10. PNT also attenuated elevation of TNF-alpha in serum, liver, and spleen at 4 and 24 h after sepsis induction, and 8-SPT resulted in higher proinflammatory cytokines. Modulating endogenous adenosine was also effective in exacerbated (8-SPT) or diminished (PNT) tissue peroxidation. Survival from sepsis was also improved when PNT was used as a posttreatment. These data indicate that endogenous adenosine is an important modulatory component of systemic inflammatory response syndromes. These data also indicate that inhibition of adenosine deaminase may be a novel and viable therapeutic approach to managing the systemic inflammatory response syndrome without ablating important physiological functions.

Interdependence of adenosine and nitric oxide in hepato-splanchnic circulation during sepsis

BACKGROUND

We tested the hypothesis that some of the maintenance of resting, regional hepato-splanchnic perfusion that is mediated by endogenous adenosine (ADO) during sepsis is interdependent with nitric oxide (NO).

MATERIALS AND METHODS

Twenty-four hours after sepsis/sham induction, rats were divided into two groups. Group 1 received a 10-min infusion of the ADO antagonist 8-sulfophenyltheophylline (8-SPT; 0.9 mg/kg x min), followed by 10 min of 8-SPT plus L-NAME (0.5 mg/kg x min). Group 2 received L-NAME first followed by 8-SPT in the presence of L-NAME (all groups: n = 6-10). Hemodynamic and regional hepato-splanchnic blood flow measurements were made prior to infusions, 10 min after initiation of each single agent infusion, and again after double agent infusion.

RESULTS

Twenty-four hours after sepsis hepato-splanchnic blood flow was significantly elevated, compared to nonseptic rats. Both ADO receptor blockade alone and NOS inhibition alone decreased total hepato-splanchnic blood flow to nonseptic values. Decreases in small intestinal and cecal blood flow accounted for the majority of this decrease, but decreased hepatic arterial perfusion contributed as well. No further alterations were seen when 8-SPT was infused in the presence of L-NAME, nor when L-NAME was infused in the presence of 8-SPT.

CONCLUSIONS

These data indicate that there is significant interdependence of endogenous NO and ADO in maintaining resting small bowel, cecal, and hepatic arterial perfusion during sepsis. The lack of responses in other regions of the hepato-splanchnic circulation demonstrate regional specificity of this ADO-NO interdependence.

Adenosine and nitric oxide regulate regional vascular resistance via interdependent and independent mechanisms during sepsis

OBJECTIVE

Adenosine receptor blockade increases regional resting vascular resistance during sepsis. In healthy subjects, part of adenosine's actions are mediated via stimulation of nitric oxide synthase. Because nitric oxide synthase activity is thought to be a major contributor to altered vascular tone in sepsis, we tested the hypothesis that some of the nitric oxide-mediated resting regional resistance during sepsis is secondary to endogenous adenosine stimulation of nitric oxide synthase.

DESIGN

Prospective, randomized, controlled experiment.

SETTING

Shock-trauma and basic science laboratory.

SUBJECTS

Male Sprague-Dawley rats.

INTERVENTIONS

Twenty-four hours after sepsis or sham induction, rats were separated into two groups (n = 6 to 10 in each group). Group 1 received a 10-min infusion of the adenosine antagonist 8-sulfophenyltheophylline (0.9 mg/kg x min) followed by a 10-min infusion of L-nitro-arginine-methyl ester (0.5 mg/kg x min). Group 2 similarly received L-nitro-arginine-methyl ester followed by 8-sulfophenyltheophylline in the presence of L-nitro-arginine-methyl ester.

MEASUREMENTS AND MAIN RESULTS

Hemodynamic and blood flow measurements (microspheres) were made before infusions, 10 mins after the administration of each single-agent infusion, and 10 mins after combined-agent infusions were administered. No significant resistance alterations were observed in nonseptic rats. In septic rats, adenosine receptor blockade alone increased hepatosplanchnic and skeletal muscle vascular resistance, but no further increases were seen when L-nitro-arginine-methyl ester was added. Nitric oxide synthase inhibition alone increased hepatosplanchnic and skeletal muscle vascular resistances. When 8-sulfophenyltheophylline was added to the infusion, skeletal muscle vascular resistance increased significantly more than with L-nitro-arginine-methyl ester alone, but there were no further increases in hepatosplanchnic resistance. Renal and adipose vascular resistances increased with L-nitro-arginine-methyl ester infusions, and 8-sulfophenyltheophylline produced no effect.

CONCLUSIONS

During sepsis, nitric oxide caused resting vasodilation independent of adenosine in the renal and adipose vasculature. In the hepatosplanchnic circulation, there is reciprocal adenosine-nitric oxide interaction in maintaining resting regional resistance. Skeletal muscle displayed a dual adenosine-mediated (nitric oxide-independent) and nitric oxide-mediated (adenosine receptors required) interaction to regulate resting resistance during sepsis. These data indicate that in the hepatosplanchnic and skeletal muscle vasculature, all of the resting nitric oxide-mediated vasodilation is secondary to endogenous adenosine action, but in adipose and renal vasculature, resting nitric oxide mediated vasodilation is independent of adenosine. Endogenous adenosine also appears to play a significant role in determining resting skeletal muscle resistance that is independent of nitric oxide synthase during sepsis.

Effect of pentaglobin and piperacillin on survival in a rat model of faecal peritonitis: importance of intervention timings

BACKGROUND

Faecal peritonitis is a progressive pathophysiological condition which may lead to multiple organ failure and death. The reason for the associated morbidity and mortality could be attributed to the fact that some of the subtle alterations in cellular function that occur during the early stage of peritonitis are unidentified and consequently missed, leading to inadequate or delayed intervention. Recent studies have shown that early treatment with antibiotic and antisera containing antibodies to lipopolysaccharide (immunoglobulin) improve the survival rate in these patients. The present investigation was undertaken to study the effect of pentaglobin and piperacillin with particular attention to time lag of drug intervention on animal survival following experimental peritonitis.

METHODS

Experimental peritonitis was produced by inoculating 1 ml/kg of faecal suspension (2:1 w/v in saline) into the peritoneal cavity. Two groups of animals were treated with pentaglobin (4 ml/kg) or piperacillin (1000 mg/kg) respectively, whereas rats in another group received both drugs simultaneously. The first dose of each drug was given at 4 h, 6 h, 8 h and 12 h after faecal inoculation followed by 3 additional doses at 8-h intervals. For biochemical studies, separate groups of animals were used in which the treatment was started 4 h after faecal inoculation and the animals were killed at 12 h after the treatment.

RESULTS

Both piperacillin and pentaglobin prolonged survival time of animals which received the treatment within 6 h of faecal insult. The combination of pentaglobin plus piperacillin produced better results as compared to the individual effect. There was a significant decrease in serum superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) and increase in catalase following faeces-induced septicaemia, suggesting a significant increase in oxidative stress. The changes in enzyme levels were significantly attenuated by both the drugs.

CONCLUSION

The findings suggest that intervention with a combination of pentaglobin and antibiotics within 6 h of peritonitis might significantly improve survival rate in rat.