saralasin and Proteinuria

A partial renal vein constriction (RVC) was induced acutely in Munich-Wistar rats. RVC caused a marked reduction in glomerular plasma flow rate, and rises in glomerular transcapillary hydraulic pressure difference and efferent arteriolar resistance. These changes were associated with a marked increase in urinary protein excretion, on average from a baseline level of 8 to approximately 120 mg/24 hrs per kidney. Infusion of saralasin, an angiotensin II (AII) antagonist, largely normalized these indices, including urinary protein excretion (to approximately 35 mg/24 hrs per kidney), despite continued RVC. In separate rats, fractional clearances of neutral [125I]dextrans (molecular radii = 18-60 A) (CDEX/CIN) were measured. RVC caused a significant increase in CDEX/CIN for large dextrans (greater than or equal to 44A), but not small dextrans (less than or equal to 42A). Saralasin infusion led to a partial return toward baseline values of CDEX/CIN for the large dextrans. On the basis of the heteroporous membrane theory for glomerular filtration, the glomerular sieving defect during RVC was attributed to an increase in the relative fluid flux through a group of large non-selective pores. A marked alteration in glomerular microcirculatory pattern induced by enhanced action of endogenous AII in turn seemed to account largely, although not entirely, for the impairment of glomerular size-selectivity during RVC.

Topics: Angiotensin II; Animals; Capillaries; Constriction; Dextrans; Glomerular Filtration Rate; Kidney Glomerulus; Molecular Weight; Pressure; Proteinuria; Rats; Rats, Inbred Strains; Renal Veins; Saralasin

Moderate autologous nephrotoxic serum nephritis (NSN) in rats causes no reduction in GFR despite a reduction in ultrafiltration coefficient (Kf) to less than one-half of normal. An increase in intraglomerular hydraulic pressure maintains GFR, but the signal and efferent mechanisms for this adaptation remain unknown. Indomethacin and saralasin were used to study the possible roles of prostaglandins and angiotensin II (A-II) in the adaptation to NSN. Indomethacin decreased renal blood flow (RBF) in NSN (-8.6%, P less than 0.001), but not in controls. Renal vascular resistance (RVR) increased in NSN (+ 9.6%, P less than 0.01), but decreased in controls (-5.6%, P less than 0.01). GFR decreased in NSN (-22.3%, P less than 0.01), but increased in controls (+ 10.3%, P less than 0.001). Urinary PGE2 excretion decreased markedly both in NSN and controls. With combined treatment using indomethacin and saralasin, RBF increased in NSN (+ 22.4%, P less than 0.001), but did not change in controls. RVR decreased in NSN (-21.5%, P less than 0.001), but was unchanged in controls. GFR remained unchanged both in NSN and controls. With saralasin alone, RBF increased both in NSN (+ 21.4%, P less than 0.001) and in controls (+ 14.4%, P less than 0.001). RVR decreased both in NSN (-21.8%, P less than 0.001) and controls (-18.7% P less than 0.001). GFR increased (+ 12.3%, P less than 0.05) in NSN, but did not change in controls. Urinary PGE2 excretion was increased in NSN compared to controls, decreased markedly in NSN after either indomethacin or saralasin infusion.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Angiotensin II; Animals; Antibodies; Basement Membrane; Blood Pressure; Dinoprostone; Glomerulonephritis; Indomethacin; Kidney; Kidney Glomerulus; Prostaglandins; Prostaglandins E; Proteinuria; Rats; Saralasin; Vascular Resistance

Clinical and experimental studies suggest that accumulation of phlogogenic macromolecules in the glomerular mesangium may lead to mesangial expansion and eventual glomerulosclerosis. In focal glomerulosclerosis and nephrotic syndrome entrapment of macromolecules is observed in areas of glomerulosclerosis. To determine whether mesangial uptake of radiolabeled, heat-aggregated IgG (AG125I), a biologically active macromolecular protein, is influenced by increased glomerular filtration barrier permeability, we evaluated the glomerular uptake of AG125I in three models of proteinuria: aminonucleoside of puromycin nephropathy (PAN), adriamycin nephropathy, and Heyman's nephropathy. Rats were studied approximately 1 week after onset of proteinuria. AG125I was measured in preparations of isolated glomeruli and compared to simultaneous blood, liver, and spleen levels. Only rats with PAN had a marked increase in glomerular AG125I compared to control rats, 7.8 versus 2.6 micrograms/mg of glomeruli, respectively. We then evaluated whether a continuous infusion of a competitive inhibitor of angiotensin II, saralasin (300 micrograms/kg of body weight/minute), influenced mesangial uptake of AG125I in PAN rats. Strikingly, glomerular AG125I in rats with PAN was reduced to levels comparable to that observed in control rats infused with only saralasin, 2.8 versus 3.0 micrograms/mg of glomeruli, respectively. This effect on glomerular AG125I content was independent of any significant effect of saralasin on blood, hepatic, or splenic levels of AG125I. Moreover, these changes in glomerular AG125I in saralasin-infused rats with PAN did not appear to directly correlate with changes in whole kidney function. These studies also demonstrated that proteinuria per se did not influence mesangial uptake of macromolecules. Thus, these data indicated that angiotensin II had an important effect on intraglomerular factors that modulate mesangial localization of phlogogenic macromolecules.

Topics: Angiotensin II; Animals; Glomerular Filtration Rate; Glomerular Mesangium; Immunoglobulin G; Infusions, Parenteral; Iodine Radioisotopes; Kidney Glomerulus; Liver; Male; Permeability; Proteinuria; Rats; Rats, Inbred Strains; Renal Circulation; Saralasin; Spleen

To test whether angiotensin (AII) induces proteinuria via its effect on renal hemodynamics, or by another mechanism, two experimental approaches were used. In the first, it was found that AII was as effective in inducing proteinuria in nephrotic as in intact rats. In all AII augmented proteinurias, filtration fraction was increased. These effects plus electrophoretic profiles of AII proteinuria in intact rats suggested that hemodynamic changes underly the increased glomerular permeability to protein. In the second approach, the AII inhibitor, sar-ala-angiotensin, does not itself induce proteinuria or changes in GFR and RPF, but prevented the hemodynamic responses to AII and the proteinuric response as well.

Topics: Angiotensin II; Animals; Electrophoresis, Polyacrylamide Gel; Female; Hemodynamics; Kidney; Nephrosis; Proteinuria; Puromycin Aminonucleoside; Rats; Saralasin