EFFECT OF HYPOXIA ON TISSUE METABOLISM. ^1H-NMR STUDY OF LACTATE METABOLISM AND CHANGES IN ^1H-NMR RELAXATION TIMES OF SKELETAL MUSCLE

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1. Relationship between NMR relaxation times and muscle fiber type was investigated. The study concerns different types of ICR mouse muscles, the soleus which is a slow twitch red (type I) muscle and the anterior tibialis muscle, a fast twitch white (type II) muscle. NMR measurements were performed on a 90-MHz Fourier transform NMR spectrometer (Fx90A, JEOL). T_1 was measured by the inversion recovery method. T_2 was measured by the Hahn spin-echo method. Mean T_1 values of type I and type II fiber were 1.03 * 0.03 sec and 1.04 * 0.02 sec, respectively. There was no significant difference between them. T_2 is divided into fast (T_<2f>) and show (T_<2s>) components by fitting the transverse magnetization decay curve. The T_<2f> and T_<2s> values of type II fiber were significantly longer that those of type I fiber (T_<2f>:type I 33.2 * 1.4 msec, type II 34.4 * 0.9 msec,p<0.05, T_<2s>:type I 67.9 * 5.3msec, type II 75.1 * 0.9 msec, p<0.01). Since there was no significant difference in T_ … More 1, which correlates with water content of tissues, between different types of muscle fiber, difference in T_2 may be attributed to conformational changes in macromolecules in muscle fiber.2. To measure a T_2 of muscles in vivo, we developed modified depth-pulse sequence added to spin-echo meth-od. A 2.0-Tesla, 31-cm-bore superconducting magnet (BEM 250/80,Otsuka Electronics Co.) and a 2-cm surface coil was used. Spectral localization was achieved by changing a flip angle (rheta). T_2 values obtained from each layer of five-layered phantom containing albumin solution were the same value as measured with a 90MHz Fourier trans-form NMR spectrometer (Fx90A,JEOL). Compared with spin-echo method, our modified depth-pulse sequences obtained proper T_2 values of albumin solution in 3rd layer (10.5mm-depth) of phantom. T_2 of human forearm muscle was determined with the modified depth-pulse method in vivo. The T_2 values were shorter than that of in vitro measurements, which may cause inhomogeneity of biological tissues.3. We measured ^1H-NMR spectrum of lactate solution. A2.0-Tesla, 31-cm-bore superconducting magnet (BEM250/80, Otsuka Electronics Co.) and a 2cm-surface coil was used. Although 1,3,3,1 pulse sequence was applied to achieve water suppression, complete suppression was not obtained. Lactate spectra was detected more than 0.01M solution. However, signal intensity of lactate did not correlate with their concentrations less than 0.01M. Less