Isolated rat heart perfusion and high-resolution phosphate-31 nuclear magnetic resonance (31P-NMR) spectroscopy were used to elucidate the effects of Mg during reperfusion of the ischemic myocardium. After an ischemic period of 9 min, the hearts were reperfused with 0, 0.6, or 2.4 mM Mg during the entire 24-min reperfusion period or with 15 mM Mg during the first 12 min before returning to the physiological concentration of 0.6 mM during the last 12 min. Free intracellular Mg calculated by 31P-NMR rose during ischemia and fell gradually during reperfusion. The two groups reperfused with 15 mM Mg exhibited a significantly enhanced rate of recovery of adenosine triphosphate, creatine phosphate, intracellular pH, and coronary flow rate than the three other groups. Myocardial potassium was significantly higher, and inorganic phosphate was significantly lower at the end of the reperfusion period in these groups. The hearts reperfused with 0 mM Mg presented a significantly higher frequency of ventricular fibrillation (VF) than the other groups. It is concluded that reperfusion with high Mg improves the postischemic recovery of metabolism and function in the rat heart, whereas a Mg-free reperfusion solution increases the frequency of VF.
Magnetic resonance spectroscopy of fluorine (19F) has been used to noninvasively study the in vivo pharmacokinetics of a model drug, fleroxacin (a fluoroquinolone antibiotic agent), in healthy human subjects. After oral administration, fleroxacin was detected in 19F magnetic resonance spectra from both liver and calf muscle and four magnetic resonance examinations were undertaken during a 24-hour period. By combining plasma analysis by high performance liquid chromatography with the magnetic resonance data, the following pharmacokinetic parameters (mean values) were obtained: tmax, 1.4, 4.6, and 5.6 hours in liver, plasma, and muscle, respectively; Cmax, 53, about 250, and about 60 mumol/L in plasma, liver, and muscle, respectively; t1/2, 4.4 hours (fast phase) and 10.8 hours (slow phase) in liver and 14.2 hours in plasma. The study documents for the first time the potential use of 19F magnetic resonance spectroscopy to noninvasively observe the time-related changes of a fluorine-containing drug in human tissues after oral administration.
31P NMR spectroscopy was used to investigate whether improved functional recovery in ischaemic preconditioning was due to improved metabolic recovery in isolated rat hearts. The preconditioning stimulus was global ischaemia of 1 or 4 min followed by 12 min of reperfusion (Langendorff mode). The hearts were then subjected to a main ischaemic period of 16 min and 40 min of reperfusion. Functional and metabolic recoveries of hearts were compared to a control group subjected only to the main ischaemia. Preconditioning improved recovery of contractile function during the final reperfusion. Thus left ventricular developed pressure (LVDP) and heart rate (HR) product after 40 min of reperfusion recovered to 56, 67 and 68% in the control group, 1 min group and 4 min group, respectively. However, the metabolic recovery was comparable in all groups. CrP and ATP recovered to levels of 67-78% (CrP) and 35-41% (ATP), and pH to a level of 7.13-7.15 (not different from baseline values) at the end of the final reperfusion. We conclude that the improved functional recovery in preconditioning is not due to a higher level of high energy phosphates or less acidosis during the final reperfusion.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.