NMR Monitoring of Phosphate Metabolism of Rat Skeletal Muscle during Hemorrhage and Resuscitation

Phosphorus nuclear magnetic resonance (NMR) spectroscopy allows noninvasive monitoring of intracellular high-energy metabolites. In the present study we used topical NMR to monitor intracellular levels of ATP, creatine phosphate (CrP), inorganic phosphate (Pi), and pH in the biceps femoris muscle of rats during hemorrhagic shock and resuscitation. Twelve rats weighing 300–500 gm were anesthetized and bled to a mean arterial pressure (MAP) of 50–55 mm Hg for 90 minutes. Then they were resuscitated with lactated Ringersʼ until MAP returned to normal or resuscitation fluid equaled four times the shed blood volume. During resuscitation, the rats fell into one of two groupssurvivor group (n = 5) which could be successfully resuscitated for 60 minutes or longer; or nonsurvivor group (n = 7) which died during resuscitation. In both groups, ATP levels were maintained during hemorrhage and resuscitation. Intramuscular pH dropped about 0.2 pH units in both groups at the end of hemorrhage; however, pH was restored back toward baseline in the survivor group. CrP levels were lower in the nonsurvivor group at the end of hemorrhage. After resuscitation, CrP returned to nearly baseline levels in the survivor group; in the nonsurvivor group, CrP was further depleted after resuscitation. Pi levels were increased in both groups at the end of hemorrhage, but in the survivor group Pi decreased during the first 15 minutes of resuscitation; in the nonsurvivor group Pi increased further to four times baseline levels. This study demonstrated that topical NMR can quantitate a metabolic deficit in skeletal muscle during hemorrhage and resuscitation. The results show that improvement of intracellular Pi and CrP levels correlated with survival.