Biochemical changes detected by microdialysis in subcutaneous tissue during experimental endotoxemia in rat

Introduction

Shock is defined currently as tissue oxygen metabolic disorders. It is most important to understand oxygen metabolic disorders in individual tissue. Microdialysis allows the determination of the metabolic condition in regional tissue and it appears ideal to determine the regional metabolic tissue conditions during endotoxemia.

Objective

This study was designed to assess the regional metabolic tissue conditions on markers of tissue metabolism (lactate in regional tissue: tissue lactate (TL)) and tissue partial oxygen pressure (PtO₂) during severe endotoxemia and to compare them with variables determined by standard monitoring (hemodynamics, blood gas analysis, blood lactate (BL)).

Materials and methods

Male Wister rats (body weight 270–300 g) were used for this study. The rats in the control group (n = 6) were injected with saline of 2 ml intraperitoneally, and the rats in the experimental group (n = 6) were treated with intraperitoneal injection of lipopolysaccharide (LPS) of 40 mg/kg. The hemodynamic parameters, arterial blood gas analysis, BL and PtO₂ were measured in both groups. TL and pyruvate in subcutaneous tissue were measured using microdialysis. These parameters were measured every 50 minutes until 400 minutes after LPS was administered.

Results

In the control group, all parameters were not changed during the observation period of 400 minutes. In the experimental group, the mean arterial pressure (MAP) remained fairly stable until 300 minutes after injection of LPS, and the MAP gradually decreased subsequently. While the MAP was maintained, the PtO₂ gradually decreased linearly (Figure 1). TL increased with time linearly. Meanwhile, BL did not change from 150 to 250 minutes; after 300 minutes it increased abruptly in the experimental group (Figure 2).

Figure 1

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Figure 2

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Conclusion

In our experimental endotoxemia model it has been shown that partial pressure of oxygen in subcutaneous tissue decreased even if systemic blood pressure was maintained. Boekstegers and colleagues [1] revealed that mean skeletal muscle PO₂ was increased in patients with sepsis compared with patients with limited infection. We obtained conflicting results to those of Boekstegers and colleagues. The reason for this is unknown. BL abruptly increased during 50–150 minutes, probably from abnormal metabolism induced by LPS in whole-body organs. It is considered that BL did not show a rise during 150–250 minutes due to metabolization of lactate in liver and muscle. TL, which is insusceptible of lactate metabolism by other organs, may reflect abnormality of tissue metabolism precisely.