Time course of growth factor expression in mercuric chloride acute renal failure

BACKGROUND: Renal EGF expression decreases in varying models of acute renal failure (ARF). We found previously that the loss of distal tubular EGF during gentamicin ARF is strongest in the cortex, where proximal tubular injury was most severe. To gain more insight into the mechanism underlying this apparent anatomical association, renal growth factor expression was investigated during mercuric chloride ARF, in which proximal tubular injury is most severe in the outer stripe of the outer medulla (OSOM). METHODS: Endogenous renal growth factor expression was investigated by RNA hybridization and by immunohistochemistry in a rat model of mercuric chloride ARF. In addition we determined temporal and spatial profiles of tubular injury, cell proliferation, and mononuclear cell infiltration during the 3-week observation period. RESULTS: Serum creatinine values were maximal 2 days after treatment and were again normalized at day 6. Tubular injury was most severe in the PST and maximal at day 2. Cell proliferation was also higher in the PST and maximal at day 4. Three weeks after treatment, normal renal morphology was restored. Increased numbers of mononuclear cells appeared transiently in the renal interstitium from day 1 on. Most of these cells were macrophages and T lymphocytes; macrophages surrounded preferentially the severely injured PST in the OSOM. In analogy to gentamicin ARF, renal EGF and IGF-I gene expression were decreased early in the setting of mercuric chloride ARF. The decrease in distal tubular EGF staining was most pronounced in the OSOM, i.e. the anatomical area where mercuric-chloride-induced proximal tubular injury was most severe. CONCLUSIONS: Renal EGF and IGF-I gene expression decreases strongly during mercuric chloride ARF. The spatial association between the initial decrease of distal tubular EGF expression and the zone of major proximal tubular injury could originate from metabolic alterations secondary to oxygen starvation. A possible role of mononuclear cells remains to be determined.