Site-specific regulation of organic osmolytes along the rat
nephron.
Schmolke, Michael, Angela Bornemann, and Walter G. Guder.
Institute for Clinical Chemistry, Bogenhausen Hospital Munich,
Germany
APStracts 3:0091F, 1996.
The regulation of organic osmolytes was investigated in acute
furosemide and chronic lithium diuresis along the nephron and in
urinary bladder of rats. Sorbitol, myo-inositol,
glycerophosphorylcholine and betaine were measured enzymatically or
by liquid chromatography (HPLC) in homogenates and
bioluminometrically in microdissected tubules. In untreated rats all
osmolytes except myo-inositol increased along the corticopapillary
axis. An efflux of all osmolytes (-50%) was observed in homogenates
of outer and inner medulla after acute furosemide diuresis (15 min;
Uosmo = 329 mosmol/kg H2O) and for both polyols in microdissected
tubules (30 min). In urinary bladder only low concentrations of myo
-inositol were found not being affected by furosemide treatment.
Chronic lithium treatment (7 d; Uosmo = 385 mosmol/kg H2O) decreased
inner medullary but not outer medullary osmolyte concentrations. The
results confirm a site-specific organic osmolyte pattern along the
rat nephron which is rapidly changed in a segment-specific way by
different mechanisms of diuresis. The bladder epithelium does not
accumulate organic osmolytes, because no "osmotic gap" exists
across the basolateral membrane. The osmotic difference across the
apical membrane is maintained by the apical tightness of these cells.
Received 2 October 1995; accepted in final form 14 May 1996.
APS Manuscript Number F331-5.
Article publication pending Am. J. Physiol. (Renal Fluid Electrolyte
Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 28 May 96