Circadian rhythms in renal excretion and hemodynamics in sprague
-dawley normotensive and transgenic tgr(mren-2)27 hypertensive
rats.
M., Pons, Schnecko A., Witte K., Lemmer B., Waterhouse J. M. and
Cambar J.
Groupe d'Etude de Physiologie et Physiopathologie R[acute]enales,
UFR des Sciences Pharmaceutiques - 146 rue L[acute]eo Saignat -
Bordeaux - FRANCE, Institute for Pharmacology and Toxicology-
Heidelberg, Mannheim - GERMANY, School of Human Sciences, Liverpool
John Moores University and School of Biological Sciences, University
of Manchester - UNITED KINGDOM
APStracts 3:0152R, 1996.
Patients with secondary hypertension frequently display abnormal
circadian blood pressure profiles, characterized by a failure to
decrease blood pressure at night. The transgenic TGR (mRen-2)27 rat
strain, developing fulminant hypertension after the mouse salivary
Ren-2 renin gene has been integrated into its genome, provides a
fundamental model of genetic hypertension. Because of an inverse
circadian blood pressure profile and an unchanged rhythmic pattern of
heart rate compared to the normotensive Sprague-Dawley (SPRD) strain,
it was proposed to serve as an animal model of genetic hypertension.
It was the aim of the present study to investigate the circadian
rhythmicity in renal function of the transgenic rat in order to
determine whether hypertension and disturbed circadian blood pressure
profile would affect kidney function. Urinary water, electrolyte and
protein excretion, as well as glomerular filtration rate (GFR) and
renal plasma flow (RPF), were determined in unrestrained freely
moving transgenic hypertensive (TGR) and Sprague-Dawley (SPRD)
normotensive control rats, collecting urine and arterial blood every
4h. Significant and similar circadian rhythms were found in renal
excretion and hemodynamics in both normotensive and hypertensive
strains. Peaks occurred in the active dark period while troughs were
found in daytime for all parameters. However, it has to be pointed
out that, though the circadian profiles were not grossly perturbed in
hypertensive animals, some small differences between SPRD and TGR
strains did exist in renal function. These discrepancies were
precisely related to acrophase, showing a slight phase-delay and also
to relative amplitude in TGR. This study demonstrates that the
inverted circadian blood pressure profile affected only slightly the
circadian rhythms in kidney function in TGR compared to the SPRD.
These findings support the notion that time-dependent changes in
systemic blood flow may be of greater importance for circadian
regulation of kidney function than systemic blood pressure.
Received 5 February 1996; accepted in final form 27 March 1996.
APS Manuscript Number R72-6.
Article publication pending Am. J. Physiol. (Regulatory Integrative
Comp. Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 1 May 96