Experimental analgesic nephropathy: changes in renal structure and urinary concentrating ability in Fischer 344 rats given continuous low doses of aspirin and paracetamol.

Long-term treatment with aspirin and paracetamol produced renal papillary necrosis in female Fischer 344 rats. Aspirin (230 mg/kg body weight/day) and paracetamol (380 mg/kg body weight/day) were dissolved in drinking water and given continuously for up to 65 weeks. Renal morphological changes were examined between 21 weeks and 65 weeks of commencement of analgesic treatment using light and electron microscopy, and were compared with age-matched controls. Structural damage initially occurred in the mid-papillary region, and specifically involved the interstitial cells and interstitial matrix. Necrosis of the epithelium of the thin limbs of the loop of Henle was present only after interstitial changes were well established. Cortical interstitial fibrosis and tubular atrophy occurred after renal papillary changes were observed. There was no evidence of significant vascular damage. Urinary concentrating ability was measured sequentially during the period of analgesic treatment. A decrease in urine concentrating ability was present when early changes to the interstitial cells and matrix were observed, and concentrating ability continued to decrease in parallel with increasing morphological damage. This study describes an animal model of analgesic-induced nephropathy, enabling early morphological changes to be studied and correlated with renal functional changes.