SKELETAL MUSCLE HIGH ENERGY PHOSPHATES DURING ACUTE ENDOTOXEMIA AND FOLLOWING TRIGGERING OF MALIGNANT HYPERTHERMIA (MH) IN SUSCEPTIBLE SWINE

Abstract

S120 INTRODUCTION: The presence of Cys for Arg mutation in skeletal muscle ryanodine receptors may or may not alter skeletal muscle energy metabolism during acute endotoxemia. It has been reported that triggering of MH in endotoxemic susceptible swine significantly increases mortality [1]. One may postulate that this may be due to depletion of skeletal muscle ATP or its precursors. Thus, we investigated high-energy phosphate (HEP) content in skeletal muscle during acute endotoxemia in pigs with (MHS) and without (MHN) the MH mutation. Alterations in HEPs after triggering of MH in MHS swine were also evaluated as were the effects of dantrolene therapy. METHODS: After approval from the Animal Care and Use Committee, the MHS pigs were divided into 2 groups - one (n=6) received endotoxin prior to triggering with halothane and succinylcholine. The other (n=5) received saline placebo prior to triggering. The MHN group (n=6) also received endotoxin prior to exposure to triggering agents. All swine (= 24 kg) were anesthetized with Telazol, N2 O, and pancuronium; PaCO2 was set at 35-40 mmHg by controlled ventilation via an endotracheal tube. Invasive and non-invasive monitoring allowed for tracking of hemodynamics and respiratory gases. The dose of endotoxin (LPS; 011:B4, Difco, Detroit, MI) was 50 [micro sign]g/kg bolus followed by 200 [micro sign]g/kg IV over 2.5 hours. At the end of this period all swine were exposed to halothane 1.5% + succinylcholine 4 mg/kg. Dantrolene (2 mg/kg) was administered in 2 doses (D1 and D2, see Figure 1 and Figure 2) as soon as triggering occurred (ETCO2 >or=to 70 mmHg) or 10 min after exposure to triggering agents (MHN group). Skeletal muscle tissue for HEP analysis was immediately frozen in liquid N2 after biopsy from the vastus medialis. Samples were obtained before endotoxin or placebo infusion, every 30 min until triggering and, after dantrolene therapy. The lyophilized tissue specimens were analyzed for HEPs using standard HPLC methodology. Data are reported as mean +/- SEM. Statistical significance (p < 0.05) was determined by performing ANOVA and Student's t test.Figure 1Figure 2RESULTS: Despite shock acute exposure to endotoxin did not produce significant deficits in skeletal muscle HEP levels in MHS and MHN swine (Figure 1 and Figure 2). After triggering. AMP levels increased significantly and Phosphocreatine creatine (PCr) and the energy charge (EC=[ATP]+0.5[ADP]/[ATP]+[ADP] +[AMP]) decreased from control only in the endotoxemic pigs. Dantrolene and discontinuation of triggers reversed these changes. DISCUSSION: Triggering MH during acute endotoxemia was detrimental in the MHS pigs. A reduction of PCr, increase in AMP and a decrease in EC suggests impairment of oxidative metabolism during this dual challenge. This may be responsible for the higher mortality observed in these swine [1]. During triggering in the absence of endotoxemia a trend towards reduction of EC was observed. Further studies will be necessary to see if dantrolene in the presence of triggering agents will reverse changes in HEP metabolism.