31P-nuclear magnetic resonance spectroscopy of blood: a species comparison.

31P-nuclear magnetic resonance (NMR) spectroscopy isfrequently used as a tool in the study of organs from various animal species and humans. Because signals arising from the presence of blood are visible in in vivo 31P-NMR spectra of blood-filled organs, such as the heart, it is necessary to correct these spectra for the contribution of blood to the signal. It is unknown whether species differences in 31P signals of blood exist. 31P-containing metabolites of blood from various species were therefore quantified by means of 31P-NMR spectroscopy. Signals of 2,3-bisphosphoglycerate (2,3-DPG); phosphodiesters (PDE); and gamma-, alpha-, and beta-ATP were detected in all 31P-NMR spectra of blood. 2,3-DPG/ATP ratios were significantly higher in dogs, rats, and guinea pigs than in humans but lower in sheep. Pig and rabbit were the only animals with a 2,3-DPG/ATP ratio similar to that of humans. PDE levels varied among species but were significantly lower than in humans only in guinea pigs. The PDE/ATP ratio was relatively similar among all species compared with humans, except dog and guinea pig, where it was significantly higher and lower, respectively. We conclude that because of large species differences, species-specific 31P metabolite ratios should be applied for the correction of in vivo 31P-NMR spectra.