Functional studies in experimental renal cortical necrosis in the rat

Necrosis of the outer two-thirds of the cortex (CN) was induced with boiling water in the left kidney of rats. Two days afterward, morphological damage was shown to be limited to the superficial cortex; deep nephron population was well-preserved. Glucose reabsorption under basal and glucose loading conditions, and extraction of p-aminohippurate, used as indices of proximal tubule integrity, were normal in control and experimental kidneys 48 h after cortical necrosis. Basal fractional water and electrolyte excretion did not differ between control and experimental kidneys. Calculated mean single-nephron glomerular filtration rate (GFR) and plasma flow for superficial (SupGFR and SupNPF) and juxtamedullary nephrons (JMGFR and JMPF) were similar to those obtained by micropuncture and Hanssen's technique for SupGFR, and for JMGFR by Hanssen's. Volume expansion led to a 27% increase in calculated SupGFR, but no change in JMGFR. The JMPF increased by 81%, whereas SupNPF increased by only 23%, suggesting that, in this model, GFR of deep nephrons may be independent of plasma flow. The results indicate that deep nephrons retain their functional integrity 48 h after cortical necrosis. After volume expansion fractional excretion of sodium was greater, and fractional water reabsorption less, in CN than in control kidneys. Thus handling of sodium and water by superficial and deep nephrons under basal conditions was similar, but reabsorptive capacity for deep nephrons of CN was lower during volume expansion. The present studies suggest that deep nephrons can maintain relatively normal function in cortical necrosis.