Serial renal function in an ovine model of unilateral fetal urinary tract obstruction

Renal tubular and glomerular function following ovine fetal urinary tract obstruction has been studied predominantly in anesthetized, exteriorized fetuses immediately after relief of obstruction. Since surgery and anesthesia may alter fetal cardiovascular and renal physiology, we developed a chronically catheterized, ovine model of unilateral fetal urinary tract obstruction to compare function of the unobstructed and obstructed kidneys repeatedly after relief of obstruction. Split renal function of the previously obstructed kidneys and unobstructed kidneys was measured serially in 7 fetal sheep after obstruction at 55 to 85 days per 147 days of gestation for 30 to 49 days. Seventy-five split clearances were determined on days 1, 2, 3 to 4 and 5 to 6 postoperatively. Not every fetus was studied each day. By 2-way ANOVA, renal function was stable on day 1 after surgery and did not change with time. Previously obstructed kidneys had lower creatinine clearance (0.16 versus 0.71 ml. per minute, p equals 0.0001), higher fractional sodium excretion (33.04 versus 6.02 per cent, p equals 0.0001) and higher urine sodium/creatinine ratio (4.80 versus 0.90 mEq. per mg., p equals 0.0001). Urine flow in the unobstructed kidneys did not differ significantly from that of the obstructed kidneys (0.122 versus 0.083 ml. per minute, p equals 0.35). Obstruction reduced kidney weight (4.7 versus 9.7 gm., p equals 0.0006), cortical thickness (-39 per cent) and nephrogenic zone (-59 per cent), and it increased collecting duct dilatation and medullary fibrosis. No cysts or dysplasia was noted. Fetal urinary tract obstruction for 39.7 days alters renal histology, glomerular function and tubular function. Renal function is stable by 1 day after catheterization and does not change from days 1 to 6 following relief of obstruction.