ABSTRACT: Background: Skeletal muscle wasting and impaired muscle function in response to mechanical ventilation and immobilization in intensive care unit (ICU) patients are clinically challenging partly due to (i) the poorly understood intricate cellular and molecular networks; and (ii) the unavailability of an animal model mimicking this condition. By employing a unique porcine model mimicking the conditions in the ICU with long-term mechanical ventilation and immobilization, we have analyzed the expression profile of skeletal muscle biopsies taken at three time points during a five-day period. Results: We have analyzed the expression profile of skeletal muscle biopsies taken at three time points during a five-day period. Among the differentially regulated transcripts, extracellular matrix, energy metabolism, sarcomeric proteins and LIM protein mRNA levels were down-regulated while ubiquitin proteasome system, cathepsins, oxidative stress responsive genes and heat shock proteins (HSP) mRNAs were up-regulated Conclusions: We conclude that induction of HSPs may play an inherent temporary protective mechanism in skeletal muscle in the early stages of immobilization and mechanical ventilation. The proposed molecular events leading to our final hypothesis are illustrated in the manuscript. Keywords: Treatment, immobilization, muscle function. Sixteen female domestic piglets (Sus scrofa, average body weight 26.5 kg) were used in this study. All piglets were immobilized by anesthesia and mechanically ventilated (Servo 900C, Siemens-Elema, Solna, Sweden). The first m. biceps femoris biopsies (day 1) were obtained from all animals, after administering anesthetics. During the five day study period, four animals were sedated using isoflurane inhalation (Abbott Laboratories, Chicago, Il, USA, 0.8 – 1.3% end-tidal concentration) supplemented by intravenous bolus doses of morphine and ketamine as needed. Biopsies from the m. biceps femoris were obtained on two further separate occasions (days 3 and 5) in these animals. Core body temperature (blood) was maintained in the range of 38.5 – 40°C by a servocontrolled heating pad. The animals received intravenous crystalloid fluid (Ringer’s acetate) to maintain stable blood pressure and urinary output and a glucose infusion (Rehydrex, Fresenius Kabi, Stockholm, Sweden, 25 mg glucose /mL) in the range of 0.5 – 1.5 mg/kg/minute to decrease the effects of catabolism. Each animal received prophylactic streptomycin 750 mg/d and benzylpenicillin 600 mg/d (Streptocillin Vet, Boeringer-Ingelheim, Hellerup, Denmark). Arterial blood gas analysis as well as electrolytes and blood glucose levels were monitored regularly and kept in the normal range throughout the study period.
