The cells of the renal medulla adapt osmotically to high extracellular tonicities by high concentrations of organic osmolytes. Intracellular accumulation of these substances is, however, relatively slow. The aim of the present study was to assess the effect of an abrupt rise in extracellular tonicity on intracellular osmotically active substances after prior reduction of medullary contents of organic osmolytes by chronic diuresis. Intra- and extracellular electrolyte concentrations at the papillary tip and the tissue contents of methylamines (glycerophosphorylcholine, betaine), polyols (myo-inositol, sorbitol), and several amino acids were determined in the different kidney zones by electron microprobe analysis and high-performance liquid chromatography in control animals, in rats infused for 6 days with furosemide via osmotic minipumps, and in rats given the vasopressin analogue [deamino-Cys1,D-Arg8]vasopressin (DDAVP) after the chronic furosemide treatment. Chronic diuresis greatly reduced interstitial tonicity and inner medullary contents of methylamines and polyols and moderately reduced inner medullary amino acid contents but did not significantly affect intracellular electrolyte concentrations. When the diuretic rats were infused with DDAVP for 2 h, interstitial tonicity more than doubled and intracellular K and Cl concentrations rose by approximately 60 and 160%, while inner medullary contents of methylamines, polyols, and amino acids were not changed significantly. These data demonstrate that after effective depletion of medullary organic osmolytes by long-term diuresis, the cells of the renal papilla adapt osmotically to an abrupt increase in extracellular tonicities by elevated cell electrolyte concentrations.(ABSTRACT TRUNCATED AT 250 WORDS)
Restoration of urine osmolality (Uosm) and medullary osmolyte contents after chronic diuresis was studied in rats infused for 6 days with furosemide and subsequently given the vasopressin analogue, 1-desamino-8-D-arginine vasopressin (DDAVP). Papillary tip intra- and extracellular electrolyte concentrations were measured by electron microprobe analysis, tissue contents of methylamines (glycerophosphorylcholine, betaine), polyols (myo-inositol, sorbitol), and several amino acids in different kidney zones by high-performance liquid chromatography. Administering DDAVP continuously after diuresis increased Uosm from (means +/- SE) 348 +/- 8 to 1,265 +/- 127 after 1 day and 2,485 +/- 186 mosmol/kgH2O after 3 days. The sum of all osmolytes at the papillary tip rose from 309.2 +/- 28.9 to 690.9 +/- 105.8 and 1,282.8 +/- 21.0 mmol/kg protein after days 1 and 3, respectively. Although interstitial tonicity (sum of Na, Cl, and K concentrations) was increased by 116 and 223% after 1 and 3 days DDAVP, intracellular tonicity was similar in chronic diuresis and following 1 or 3 days DDAVP. Coadministration of DDAVP with betaine, myo-inositol, and choline ("osmolyte treatment") did not accelerate the restoration of Uosm but caused significantly higher contents of osmolytes (except myo-inositol) in inner medulla and/or papilla after 3 days. In a minority of animals, restoration of Uosm and reaccumulation of medullary osmolytes were impeded in both DDAVP- and DDAVP/osmolyte-treated rats. These data indicate that, after chronic diuresis, accumulation of organic osmolytes and restoration of Uosm proceed in parallel. Capacity for transport and/or synthesis of organic osmolytes, rather than their availability, appear to limit reaccumulation on the first day of recovery. By the third day, delivery of some osmolytes or their precursors may limit the restoration of medullary osmolyte content. The failure of some rats to attain sufficient concentrating ability within this time period may be related to deficient reaccumulation of medullary osmolytes.
We compared dynamic computer tomographic CT images of 3 cases of juxtaglomerular (JG) cell tumor with those of 8 cases of renal cell carcinoma (RCC). The JG cell tumor was visualized as a low- to high-density area in case 1, a low-density area in case 2, and a low- to iso-density area in case 3 before contrast enhancement. None of the JG cell tumors were stained during the early phase (1 min), but all were stained moderately during the late phase (5 min) after contrast enhancement. Although all cases of RCC were visualized as a low- to iso-density area before contrast enhancement, they were intensely stained during the early phase with significant washout during the late phase. The present results suggest that the dynamic CT scan is useful in the differential diagnosis of the JG cell tumor and RCC.
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