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We have used (13C)-1H NMR spectroscopy at 360.13 MHz to resolve the 13C coupled proton resonance of glutamate and lactate in the rat brain in vivo. The time required for the 13C fractional enrichment of the 4-CH2 position of brain glutamate to reach isotopic steady state was determined during a continuous infusion of D-[1-13C]glucose. Under conditions of ischemia, measurements made of the 3-CH3 of lactate in (13C)-1H NMR spectra revealed the relative contribution of brain glucose and glycogen to lactate formation. (13C)-1H NMR was 11 times more sensitive than 13C NMR for the detection of 13C in the 3-CH3 position of lactate and 6 times more sensitive for the detection of 13C in the 4-CH2 of glutamate under similar in vivo conditions.

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The DEPT pulse sequence (1T/2)(H,y) -(2J)-1 -1T(H), (1T/2)(C,x) -(2J)-1 -8(H ,x)1T(C) -(2J)-1 -(acquire 13C) is analyzed theoretically for a variable 8 pulse for three spin systems: CH, CH 2 , and CH,. It is shown that the pulse train produces an enhanced distortion-free 13C signal which has the following characteristics: (a) there is phase coherency within and between the components of the 13C multiplets; (b) the enhancements vary with 8 as (rH/rdsin 8 for CH, (rH/rdsin 28 for CH 2 , and (3rH/4rd (sin 8 + sin 38) for CH,. Experimental evidence is provided for these predictions. An important application of the DEPT pulse train is for the generation of both individual proton-coupled and proton-decoupled 13C methine (CH), methylene (CH 2 ), and methyl (CH,) subspectra. This can be readily achieved by forming suitable combinations of DEPT spectra determined at 8 = (17'/4), (17'/2), and (317'/4). Such spectral editing is less sensitive to variations in J values than the INEPT pulse sequence. Signal enhancement for 195Pt and 2'Si NMR signals are also demonstrated using the DEPT sequence. The only disadvantage of this pulse train compared with the INEPT sequence appears to be its greater sensitivity to spin relaxation, a consequence of its time span.