Cortical and medullary betaine-GPC modulated by osmolality independently of oxygen in the intact kidney

Renal osmolyte concentrations are reduced during reflow following ischemia, Osmolyte decreases may follow oxygen depletion or loss of extracellular os molality in the medulla. Image-guided volume-localized magnetic resonance ( MR) microspectroscopy was used to monitor regional osmolytes during hyposmo tic shock and hypoxia in the intact rat kidney. Alternate spectra were acqu ired from 24-mu l voxels in cortex and medulla of the isolated perfused kid ney. There was a progressive decrease in the combined betaine-glycerophosph olylcholine (GPC) peak intensity of 21% in cortex and 35% in medulla of nor moxic kidneys between 60 and 160 min after commencing perfusion. Hypoxia ha d no significant effect on the betaine-GPC peak intensity in cortex or medu lla, despite a dramatic reduction in tubular sodium, potassium, and water r eabsorption. The results suggest that cortical and medullary intracellular osmolyte concentrations depend on osmotically regulated channels that are i nsensitive to oxygen and dissociated from the oxygen-dependent parameters o f renal function, the fractional excretion of sodium, the fractional excret ion of potassium, and urine-to-plasma inulin concentration ratio.