Comparison of in vivo 31P-MR spectra of the brain, liver, and kidney of adult and infant animals.

In vivo 31P-magnetic resonance spectroscopy (MRS) was used to determine the phosphorus metabolite levels in the brain and kidney of infant rabbits and adult rats and in the liver of infant rabbits and adult and infant rats. For 31P-MRS of the brain, a surface, radiofrequency coil was placed on the anterosuperior region of the head; for 31P-MRS of the liver and kidney, a radiofrequency coil was chronically implanted either between the hepatic lobes or around the kidney. 31P-MR spectra were found to show large variations in the levels of the phosphorus metabolites depending on the species, the organ, and the age of the animal. The phosphate monoester (MP)/adenosine triphosphate (ATP) ratio was significantly higher and the phosphocreatine (PCr)/ATP ratio was significantly lower in the brains of infant rabbits than in the brains of adult rats. Comparison of these data with data reported for humans and other animals suggests that these differences are due mainly to differences in age and not to differences among species. The phosphodiester (PD)/ATP ratio was found to be significantly higher in the livers of infant rabbits than in the livers of adult and infant rats - a difference more likely related to the species than to age. The kidneys of the infant rabbits showed a higher PCr/ATP radio than the kidneys of the adult rats, but this difference might be due to the influence of PCr in the surrounding muscle.