556-562. 1974.-The mechanisms responsible for the adaptive tive increase in glomerular filtration rate of residual ne-increase in glomerular filtration rate (GFR) following unilateral phrons following reduction in total renal mass by unilateral nephrectomy were studied in mutant Wistar rats having accessible nephrectomy. surface glomeruli. Pressures and flows were measured in single glomeruli of the left kidney 2-4 wk after right nephrectomy and in GLOSSARY OF SYMBOLS a normal hydropenic control group. Following uninephrectomy, whole-kidney GFR and kidney weight increased in proportion(by about 40%); these increases were accompanied by uniform increases in superficial cortical single-nephron(SN) GFR and glomerular plasma flow (GPF). As in control rats, filtration pressure equilibrium was observed after uninephrectomy. Mean transcapillary hydraulic pressure difference((AP)) increased from 34 to 40 mmHg. The ultrafiltration coefficient (Kf), the product of effective hydraulic permeability and capillary surface area, was determined in uninephrectomized rats under conditions designed to prevent the achievement of filtration pressure equilibrium(2y0 plasma loading). KE was found to be identical, on the average, to the value recently reported for rats with intact kidneys (0.078 nl/(s l mmHg). The findings suggest that the adaptive increase in SNGFR following uninephrectomy results primarily from increases in GPF and (AP), with the increase in GPF accounting for approximately three-fourths of the increase in SNGFR. compensatory hypertrophy; intrarenal pressures; chronic renal disease; colloid osmotic pressure; hemodynamics

REDUCTION IN FUNCTIONAL RENAL MASS, whether the result of disease or surgical excision, generally leads to an adaptive increase in the rate of glomerular ultrafiltration in surviving nephrons(1, 3, 4, 18-20, 23, 26, 29). The mechanisms responsible for this adjustment in ultrafiltration have yet to be defined, owing, at least in large part, to the fact that glomeruli are rarely encountered as surface structures in the mammalian kidney and are, therefore, inaccessible to direct study in vivo. This restriction has been overcome, however, in that a unique strain of Wistar rats endowed with surface glomeruli has recently been discovered in the laboratory of Dr. Klaus Thurau, Physiological Institute, Munich, Germany. Using these rats, and appropriate techniques for determining the glomerular transcapillary driving forces for ultrafiltration, we have found it possible to gain appreciable insight into the mechanisms governing ultrafiltration under a variety of physiological and pathophysiological conditions