Morphometry of superficial glomeruli in acute hypertension in the rat

Pressor doses of angiotensin II (AII) were infused intravenously in Munich-Wistar rats to study the effects of acute hypertension on the structural components of the superficial renal corpuscles and urinary protein excretion. All administration raises arterial blood pressure by 38% and increases 13-fold the normal rate of urinary excretion of proteins that contain albumin and IgG. Morphometric analysis of the quantitative characteristics of the glomerular capillaries reveals a 24% increase in the mean cross-sectional area of the capillary profiles and a 33% expansion of the capillary luminal volume. The amount of extracellular material present in the mesangium is also increased by 76%. The surface area of basement membrane available for ultrafiltration remains constant. However, the length density and the total length of the filtration slit diaphragms are reduced by 35 and 24%, respectively. Thus, the major findings of this investigation are as follows: The presence of IgG in the urine suggests a size defect in the glomerular filter with AII-induced hypertension; the dilatation of capillary loops may result in mechanical stretching of the basement membrane, altering the size-selective properties of the glomerular filter in acute hypertension; and the reduced pore area of the filtration slit diaphragms implies a lower hydraulic conductivity of the glomerular filter that may be responsible for the decreased glomerular capillary ultrafiltration coefficient present in this model of hypertension.