P-31 nuclear magnetic resonance spectral changes in obstructed or dehydrated kidney

Abstract

Rat kidneys subjected to urinary obstruction or dehydration in vivo both develop marked increases in the area under a peak resonating in the phosphodiester region on their P-31 nuclear magnetic resonance spectra. The chemical species responsible for these changes was assessed using physiologic manipulations which altered the concentration of phosphate in the urine or increased the urine pH. Obstructed kidneys of rats fed a normal diet had a 140 ± 50% increase in a peak resonating at 3.31 ± 0.05 ppm after 3 hours of obstruction (P < 0.01). Low phosphate diet which decreased urine phosphate concentration by 98% virtually eliminated this increase in peak area, where saline diuresis which decreased urine phosphate concentration by 50% markedly at attenuated it. Acute phosphate loading which doubled urine phosphate concentration markedly accentuated the increase in peak area. Alkalinizing the urine with acetazolamide (changing urine pH from 6.2 ± 0.2 to 8.0 ± 0.1) shifted the resonance frequency of this increasing peak from 3.31 ± 0.06 to 5.45 ± 0.11 ppm (P < 0.01). Rats fed a normal diet developed increases (57 ± 15%, P < 0.05) in a peak resonating at 2.84 ± 0.03 ppm following 48 hours of dehydration. Rats fed a low phosphate diet had a comparable increase in the relative area of this peak (46 ± 16%, P < 0.05). Alkalinization of the urine did not affect the position or intensity of this peak under conditions of dehydration. We conclude from these data that the chemical species responsible for the P-31 NMR spectral changes following urinary obstruction is urinary inorganic phosphate chemically shifted because of the low urine pH, but that changes in urine phosphate do not cause the spectral changes occurring with dehydration where renal phosphodiesters appear to accumulate.