Dehydration reverses vasopressin-v2-receptor antagonist induced
diuresis and aquaporin-2 downregulation in rats.
Marples, David, Birgitte M_nster Christensen, J_rgen Fr_kiaer, Mark A.
Knepper and S_ren Nielsen.
Physiology Department, University of Leeds, Leeds LS2 9NQ, UK, 1
Department of Cell Biology, Institute of Anatomy, University of
Aarhus, DK-8000, Aarhus, Denmark, 2Department of Clinical Physiology,
University of Aarhus, DK-8000 Aarhus C, Denmark, 3National Heart Lung
and Blood Institute, National Institutes of Health, Bethesda, MD,
USA
APStracts 5:0108F, 1998.
To examine the involvement of vasopressin and dehydration in the
regulation of AQP2 expression in rat kidney, we investigated the
effects of treatment for 60 hours with the specific V2-receptor
antagonist OPC31260 (OPC), alone and in conjunction with dehydration
for the last 12 hours. Changes in AQP2 protein and mRNA expression in
kidney inner medulla were determined by Western and Northern
blotting, and AQP2 distribution was analysed by immunocytochemistry
and immunoelectron microscopy. Treatment with OPC31260 increased
urine output four fold, with a reciprocal decrease in urine
osmolality. AQP2 expression decreased to 52 [angstrom]a 11% of
control levels (n=12, p<0.05), and AQP2 was found predominantly in
intracellular vesicles in collecting duct principal cells. This is
consistent with efficient blockade of the vasopressin-induced AQP2
delivery to the plasma membrane, and with the observed increased
diuresis. Consistent with this AQP2 mRNA levels were also reduced in
response to prolonged OPC treatment (30 [angstrom]a 10 % of control
levels, n=9). Five days treatment with furosemide, despite producing
even greater polyuria than OPC31260, was not associated with
downregulation of AQP2 levels, demonstrating that AQP2 downregulation
is not secondary to increased urine flow rate or loss of medullary
hypertonicity. During 12 hour thirsting in the continued presence of
OPC31260 urine output dropped dramatically, to levels not
significantly different from that seen in (non-thirsted) control
animals. In parallel with this, AQP2 levels rose to control levels.
Control experiments confirmed continued effective receptor blockade.
These results indicate that the V2-receptor antagonist causes a
modest decrease in AQP2 expression that is not a consequence of
increased urine flow rate or washout of medullary hypertonicity.
However, this decrease is much less marked than that seen in some
forms of acquired nephrogenic diabetes insipidus. In conjunction with
the effects of thirsting, this suggests that modulation of AQP2
expression is mediated partly, but not exclusively, via V2-receptors.
Received 9 December 1997; accepted in final form 8 June 1998.
APS Manuscript Number F389-7.
Article publication pending Am. J. Physiol. (Renal Physiology).
ISSN 1080-4757 Copyright 1998 The American Physiological Society.
Published in APStracts on 30 July 1998