In the kidney, metabolic processes are different among the cortex (COR), outer medulla (OM), and inner medulla (IM). Using matrix-assisted laser desorption/ionization (MALDI) and imaging mass spectrometry (IMS), we examined the change of metabolites in the COR, OM, and IM of the rat kidney after furosemide treatment, compared with vehicle-treated controls. Osmotic minipumps were implanted in male Sprague-Dawley rats to deliver 12 mg/d/rat of furosemide. Vehicle-treated- (n = 14) and furosemide-treated- (furosemide rats, n = 15) rats in metabolic cages received a fixed amount of rat chow (15 g/220 g bw/day/rat) with free access to water intake for 6 days. At day 6, higher urine output (32 ± 4 vs. 9 ± 1 ml/day) and lower urine osmolality (546 ± 44 vs. 1,677 ± 104 mOsm/KgH2O) were observed in furosemide rats. Extracts of COR, OM, and IM were analyzed by UPLC/Q-TOF-MS, where multivariate analysis revealed significant differences between the two groups. Several metabolites, including acetyl carnitine, betaine, carnitine, choline, and glycerophosphorylcholine (GPC), were significantly changed. The changes of metabolites were further identified by MALDI-TOF/TOF and IMS. Their spatial distribution and relative quantitation in the kidneys were analyzed by IMS. Carnitine compounds were increased in COR and IM, whereas carnitine and acetyl carnitine were decreased in OM. Choline compounds were increased in COR and OM, but decreased in IM from furosemide rats. Betaine and GPC were decreased in OM and IM. Taken together, MALDI-TOF/TOF and IMS successfully provide the spatial distribution and relative quantitation of metabolites in the kidney.
- imaging mass spectrometry
- loop diuretics
- urine concentration
- Copyright © 2015, American Journal of Physiology - Renal Physiology