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Renal morphometry and proteinuria of the developing MWF/Ztm Rat

: Rittinghausen, S.; Alt, J.; Hackbarth, H.; Messow, C.; Stolte, H.

Zeitschrift für Versuchstierkunde 30 (1987), S.30-31
ISSN: 0044-3697
Gesellschaft für Versuchstierkunde (Wissenschaftliche Tagung) <24, 1986, Heidelberg>
Fraunhofer ITA ( ITEM) ()
morphometry; Proteinuria; rat

A recently selected strain of rats (MWF) demonstrates a greatly increased number of subcapsular glomeruli in direct contact to the renal capsule). Mature, male MWF rats are characterized by a reduced number of nephrons and an increased blood pressure. The albumin (ALB) excretion is high (<4 mg/h) due to an increased glomerular permeability. The morphology and distrubtion of glomeruli within the developing kidney of MWF/Ztm rats aged 2 to 20 d were determinated and related to the urinary excretion of protein in order to find out whether or not glomeruli of MWF rats are leaky from the beginning whether t he leakiness appears later. LEW/Ztm rats were used as reference because of similar body weights.
Morphometry was performed by light microscopy on both kidneys of 60 rats aged 2-20 d. The distribution of the glomeruli the diameter of the nephrogenic zone and the mean distance of superficial glomeruli to the capsule were determined from defined kidney sections. Urine samples were collect e d by massage of the bladder region in 2-16 d old rats. Older animals were put into metabolic cages. Total protein was determined with the Coomassie-Blue method. ALB and high molecular weight proteins (HMWP) were measured by planimetry after micro-disc electrophoresis. After day 10 MWF rats possess a great number of subcapsular glomeruli, which are rare in LEW rats. The mean distance of superficial glomeruli to the renal capsule in MWF rats is smaller. During the first 2 to 3 d p.p. the urinary concentration of ALB and HMWP increases rapidly in both strains and then decreases to a minimum on the day 4-6 staying low until day 16-17. THere is a second phase of high ALB and HMWP excretion on days 18-20. There are no strain differences in protein excretion during days 2 to 20 p.p. However, in contrast to LEW rats MWF rats demonstrate a great increase of ALB excretion between days 40 and 52 from 5 mg/d/kg BW to 104 mg/D/kg BW. The high concentration of ALB and HMWP following birth are poss ible caused by the immature glomerular filtration barrier. The second phase high ALB and HMWP excretion following the maturation of the superficial glomeruli could be due to the rapid increase in glomerular filtration and therefore increased filtered protein load. The time course of the increased ALB excretion as compared to the renal morphology demonstrates that the subcapsular glomeruli per se are not responsible for the increased ALB loss but that some age related changes occur in MWF rats possibly in conjunction with the increased blood pressure or the glomerular hyperfiltration which has been described for this strain.