CIRCADIAN CHANGES IN URINARY GLYCOSAMINOG LYCAN EXCRETION IN NORMAL RAT

Particular chemical structure and original molecular arrangement make the glomerular basement membrane (GEM) to play a key role in the glome rular filtration, by restraining selectively the transglomerular pathw ay of high molecular weight charged macromolecules. The present study gives evidence, for the first time in the literature, of circadian cha nges in physiological urinary glycosaminoglycans (GAGs) excretion, mai n components of the GEM, in normal rats. Urine was collected every 4 h ours during 6 consecutive spans in 45 Sprague-Dawley rats, housed in i ndividual metabolism cages (8.00-12.00, 12.00-16.00, 16.00-20.00, 20.0 0-00.00, 00.00-04.00 and 04.00-08.00). GAGs, water, protein and electr olyte excretion were quantified in each sample. The analysis of these solute temporal changes was done by the cosinor method and shows that a circadian rhythm can be detected. These rhythms exhibit a significan t increase between 20.00 and 8.00, with a peak between 00.00 and 04.00 and a minimum between 12.00 and 20.00. A precise estimation of the rh ythmic characteristics permitted to detect the acrophase of each param eter nearly at the same time, respectively at 23.25 for diuresis, 23.3 3 for GAGs, 23.32 for proteins, 23.32 for sodium and 23.44 for potassi um excretion. Such chronophysiological data suggest a tight correlatio n between urinary GAGs excretion and urinary water and electrolyte exc retion in physiological conditions, in normal rats. Because of the gre at complexity of the factors involved in the kidney the renal excretio n regulation, the different origins of these temporal changes are larg ely discussed.