NMR studies of renal phosphate metabolites in vivo: effects of hydration and dehydration.

The present study characterizes the 31P-nuclear magnetic resonance (NMR) spectrum of rabbit kidneys in vivo and evaluates the effect of hydration on phosphorous metabolites including the organic solute glycerophosphorylcholine (GPC). Cortical phosphorylethanolamine is the predominant component of the phosphomonoester region of the 31P spectrum. The contribution of blood to the spectrum is mainly from 2,3 diphosphoglycerate, which comprises approximately 30% of the inorganic phosphate region. Acute infusion of 0.9% saline decreases the sodium content of the inner medulla by greater than 50% in 15 min as shown by 23Na imaging. Despite this medullary Na dilution, no change in renal GPC content was observed for greater than 1 h even with the addition of furosemide (2.5 mg/kg) or furosemide and antidiuretic hormone (0.125 U/kg). However, 20 h of chronic hydration with 0.45% saline did result in a 30% decrease in renal GPC content when compared with dehydrated animals. These findings are consistent with GPC not playing a role in the short-term regulation of the medullary intracellular milieu in response to acute reductions in medullary Na content.