Mark Wefers Bettink

Chapter 5 86 causes macrohemodynamic and microcirculatory changes and inhibits mitochondrial complex I (Choumar et al., 2011). Until now, we did not directly compare an ex vivo muscle biopsy with our in vivo technique. This study therefore aims to perform this direct comparison of in vivo and ex vivo data in a clinically relevant model of sepsis. Monitoring changes in ODR with the PpIX-TSLT during endotoxemia, as a model for sepsis, is promising. Showing changes in in vivo mitochondrial function due to an intervention would strengthen the PpIX-TSLT as a monitor. In classic respirometry the substrate succinate is used to study mitochondrial oxygen consumption linked to electron flow through complex II (Silva and Oliveira, 2011). In isolated mitochondria from endotoxemic rats the addition of succinate resulted in a normalization of mitochondrial oxygen consumption (Protti et al., 2007). We therefore measured with PpIX-TSLT whether succinate had similar effects on the mitochondrial respiratory chain in vivo in a rat model of endotoxemia with succinate pre-treatment. Until now, two important questions remained unanswered. The first question is how our PpIX-TSLT measurements in skin relate to in vi vo and ex vivo measurements in muscle, as the standard tissue for mitochondrial biopsies and measurements (experiment A). The second question is whether measurements performed with PpIX-TSLT besides detection of gross changes in mitochondrial respiration, are also sensitive enough to monitor therapeutic effects (experiment B). Successful in vivo measurement of mitochondrial parameters could help unravel the pathophysiology involved in critical illness. Additionally, it would provide a new technique for guiding therapies aimed at improving mitochondrial function. Material and Methods Subjects and preparation The experimental protocols (A; DEC 129-14-03 and B; DEC 129-12-11) were approved by the Animal Research Committee of the Erasmus University Medical Center Rotterdam. Animal care and handling were performed in accordance with the guidelines for Institutional and Animal Care and Use Committees. For this study, 54 male Wister rats (Charles River, the Netherlands; body weight 280-350 g) were used, 14 rats in protocol A (age 77-111 days) and 40 rats in protocol B (age 59-73 days). Anesthesia was induced by an intraperitoneal injectionof amixture of ketamine 90mg kg -1 (Alfasan, Woerden, theNetherlands),