High-resolution magic angle spinning1H NMR spectroscopic studies on intact rat renal cortex and medulla

High-resolution magic angle spinning 1H NMR (MAS-NMR) spectroscopy was used to investigate the biochemical composition of normal renal cortex and renal papilla samples from rats, and results were compared with those from conventional 1H NMR analysis of protein-free tissue extracts. 1H MAS NMR spectra of samples obtained from inner and outer cortex were found to be broadly similar in terms of metabolite profile, and intra- and inter-animal variability was small. However, the MAS NMR spectra from renal papilla samples were qualitatively and quantitatively different from those obtained from cortex. High levels of free amino acids and several organic acids were detected in the cortex, together with choline, glucose, and trimethylamine-N-oxide. The dominant metabolite resonances observed in papillary tissue were from glycerophosphocholine (GPC), betaine, myo-inositol, and sorbitol. On increasing the magic angle spinning rate from 4,200 to 12,000 Hz, the lipid MAS 1H NMR signal profile remained largely unchanged in papillary tissue, whereas "new" resonances from triglycerides appeared in the spectra of cortical tissue, this effect being reversible on returning the spinning rate to 4,200 Hz. Further investigation into the behavior of the lipid components under different spinning rates suggested that the lipids in the cortex were present in more motionally constrained environments than those in the papilla. 1H MAS NMR spectra of tissues are of value both in interrogation of the biochemical composition of whole tissue, and in obtaining information on the mobility and compartmentalization of certain metabolites.