³¹P NMR Relaxation Does Not Affect the Quantitation of Changes in Phosphocreatine, Inorganic Phosphate, and ATP Measured In Vivo During Complete Ischemia in Swine Brain

Abstract

Ischemia-induced changes in 31P NMR relaxation were examined in 16 piglets. NMR spectra were acquired under control conditions and during complete cerebral ischemia induced via cardiac arrest. Changes in T1 were assessed directly in six animals during control conditions and after 30-45 min of complete ischemia when changes in brain Pi levels had reached a plateau. The T1 for Pi did not change, i.e., 2.3 +/- 0.5 s during control conditions versus 2.4 +/- 1.0 s during ischemia. To evaluate phosphocreatine and ATP, two types of spectra, with a long (25-s) or short (1-s) interpulse delay time, were collected during the first 10 min of ischemia (n = 10). Both types of spectra showed the same time course of changes in phosphocreatine and ATP levels, implying that the T1 relaxation times do not change during ischemia. There were no changes in the linewidths of phosphocreatine, ATP, or Pi during ischemia, implying that the T2* values remain constant. Our results suggest that the 31P T1 and T2* for phosphocreatine, Pi, and ATP do not change during ischemia, and therefore changes in 31P NMR peak intensity accurately reflect changes in metabolite concentrations.

Evaluation of Potential Effectors of Agonal Glycolytic Rate in Developing Brain Measured In Vivo by 31P and 1H Nuclear Magnetic Resonance Spectroscopy

“…This implies that the T, corresponding to these peaks did not change, and therefore changes in the intensity of peaks in spectra collected using a 1-s interpulse delay should accurately reflect changes in concentration . In analogous past experiments we found that the T, of P;, PCr, and NTP did not change during ischemia (Corbett and Laptook, 1993) .…”

“…The [glucose]r,, ;,,, , ;, in individual animals after injecting insulin or infusing glucose ranged from 1 to 64 mM for newborns and from 2 to 44 mM in 1-month-olds . The [glucose],,, ;, was altered so that glucose-dependent changes in AGR could be studied (see Corbett et al ., 1991Corbett et al ., , 1993 . For the 12 animals kept normocarbic, complete ischemia was induced via the intravenous injection of KCI, and changes in levels of cerebral metabolites were recorded with continuous NMR scanning for 30 min.…”

“…Therefore, it was valid to use changes in peak height to quantify hypercarbia-induced changes in phosphorylated metabolite concentrations . Previous experiments have shown that the line width of P;, PCr, NTP, and lactate do not change during ischemia (Corbett et al ., 1991 ;Corbett and Laptook, 1993) . Because a 1-s interpulse delay time was used .…”

“…To test for this, two NMR spectra were obtained in an interleaved fashion using a delay time of 25 and 1 s, respectively, during control and hypercarbia for 13 animals . A 25-s delay time should be adequate for near-complete relaxation, because the T, values of P ;, PCr, and ß-NTP in swine brain range from 1 .2 to 6 s (Corbett and Laptook, 1993) . The percent change in the height of P ; , PCr, and ß-NTP from control to hypercarbia did not differ significantly between data col-J.…”

Intracellular Calcium Dynamics and Cellular Energetics in Ischemic NG108‐15 Cells Studied by Concurrent 31P/19F and 23Na Double‐Quantum Filtered NMR Spectroscopy

“…Spectra were acquired under conditions that did not allow complete relaxation of all 31P and 1912 nuclei [pulse widths of 25 jis for 31P (45°)and 70 jis for '9F (45°)]; however, calculation of [Ca2~I, was assumed to remain unaffected as the spin-lattice relaxation time constant (T 1) values of the free and bound forms of 1 ,2-bis (2-amino-S-phenoxy ) ethane-N,N,N',N'-tetraacetic acid (BAPTA) are similar in tissue (Kirschenlohr et al, 1988). The T1 values for all 31P and 1912 nuclei were assumed to be constant during ischemia [demonstrated for 31P NMR T, values for in vivo brain (Corbett and Laptook, 1993)], allowing comparison of changes in the relative intensity of resonances. Hardware requirements for the pulse sequence included a direct synthesis radiofrequency transmitter and a broadband (or switchable) probe (16 mm id.)…”