The cause of a depressed glomerular filtration rate after an ischaemic insult: whole kidney and superficial nephron study in the dog

Abstract

Twenty-four hours after 90 min clamping of the left renal artery in dogs, the glomerular filtration rate (GFR) was decreased in the whole kidney (0.34 ml.min-1g KW-1 [KW = Kidney weight] vs 0.64 in contralateral unclamped kidney) just as in the single nephron (SNGFR, 19.7 vs 51.8 nl.min-1). Renal blood flow (RBF) did not change; single nephron glomerular blood flow (SNGBF) was decreased by 9% only. After injection of Lissamine green into the renal artery, brief diffuse tinting of the whole kidney surface was observed. Thereafter, patchy coloration - corresponding to passage of the dye through patient tubuli - took place in approximately one-quarter to one-third of the kidney surface. Micropuncture measurements were carried out in these areas. The values of hydraulic pressure in peritubular capillaries and proximal convolutions were not different from those found in controls; directly measured glomerular capillary pressure was decreased (48.7 vs 59.5 mmHg). The ultrafiltration coefficient(Kf) was significantly depressed (2.7 vs 3.8 mmHg.nl-1.min). Total kidney and arteriolar resistances remained unchanged but afferent resistance (RA) was elevated (11%) and efferent resistance (RE) was lowered (23%) compared with those of controls. Ninety-seven percent of proximally microinjected 3H-inulin was recovered from the control kidney but only 85% from the kidney rendered ischaemic. In conclusion, the typical findings at 24 h after 90 min ischaemia are low GFR and SNGFR with normal RBF and almost normal superficial SNGBF values. This phenomenon is mainly due to a decrease in Kf and a decrease in RE with a simultaneous increase in RA; back-leak through damaged tubuli seems to play only a minor role.