The metabolic state of skeletal muscle and brain within intact rats is monitored using high resolution phosphorus nuclear magnetic resonance. Regional disturbances in metabolism (for example, localised ischaemia) are easily observed, indicating the diagnostic possibilities of the method. Measurements are made using 'surface' radiofrequency coils, which we discuss in detail.

When determining high-density lipoprotein cholesterol by use of sodium phosphotungstate-magnesium precipitation method, I found that the pH of the sodium phosphotungstate reagent was a critical factor in the method. Unless the pH of the reagent was less than 7.6, the precipitation of low-density lipoprotein and very-low-density lipoprotein was incomplete. When the specimen pH was between 7.35 and 8.65, the pH of the serum of plasma did not influence the completeness of precipitation. Optimum concentrations of precipitation reagents, determined after the pH of the sodium phosphotungstate reagent was standardized to pH 6. 15, were 40 g/L for sodium phosphotungstate and 2 mol/L for MgCl2. The distribution of high-density lipoprotein cholesterol in a healthy adult population was skewed to the left for women (n = 34; mean = 660 mg/L) and bi-modal for men (n = 44; mean = 460 mg/mL). The central 95% reference interval was 280 to 880 mg/L for women and 250 to 750 mg/L for men.

High-resolution 31P nuclear magnetic resonance spectra at 73.83 MHz are reported for rat heart in vivo. In live rats, it was possible to observe the cardiac content of ATP, phosphocreatine,.and Pi. Only a small amount of wholeblood 2,3-diphosphoglycerate was observed in the spectra, precluding the possibility that blood phosphate compounds were masking the spectra of cardiac phosphate compounds. The 31p nuclear magnetic resonance spectra of in vivo and perfused rat hearts were similar and sup ort the utilization of the perfused rat heart as a model system for studying high-energy phosphate metabolism of the heart in vivo. The dynamic flux of highenergy phosphate compounds was investigated by subjecting the rat to respiratory arrest. In this experiment, the heart followed the classic metabolic pattern known to occur during cardiac arrest; phosphocreatine and then ATP decreased in concentration while Pi increased in concentration. The 31p nuclear magnetic resonance analysis of rat heart in vivo is demonstrated to be a practical and feasible method for studying cardiac high-energy phosphate metabolism.Much information has been gained from the in vitro study of isolated biochemical reactions and physiological functions. However, the ultimate description of these processes must be in terms of their regulation and integration within the living organism. High-resolution 31p nuclear magnetic resonance (NMR) spectroscopy can be used to investigate and monitor molecular events occurring within intact, living cells. This noninvasive, nondestructive method allows the simultaneous and continuous detection of intracellular phosphate compounds such as ATP, phosphocreatine, Pi, and 2,3-diphosphoglycerate and has proved valuable in the study of a variety of cell and organ preparations including bacteria (1, 2), yeast (3), erythrocytes (4, 5), skeletal muscle (6, 7), brain (8), liver (9), kidney (10), and heart (11-13). The application of 31P NMR to the detection of phosphate compounds in intact, living animals was first attempted by Chance et al: (8), who measured the 31p NMR spectrum of the head of a mouse. We report here a different application in which we selectively placed the NMR receiver coil around the organ to be analyzed. Using this technique, we have successfully measured the intracellular level and dynamic flux of ATP and phosphocreatine in the hearts of live rats.MATERIALS AND METHODS Animals. Male Wistar rats (250-350 g) maintained on a standard diet were used throughout.Whole-Animal Procedure. Animals were anesthetized with intraperitoneal Sagatal (60 mg/kg of body weight; sodium pentobarbitone, 60 mg/ml). The trachea was intubated via a tracheostomy and the animal was mechanically ventilated 704-0 breaths per min with 50% nitrous oxide/50% oxygen. The abdomen was entered through an upper midline incision and the diaphragm was incised anterially. Access to the heart was completed by a lower median stenotomy. The animal was then secured in the NMR probe in a vertical position. The NMR receiver coil was intro...

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