In an experimental model of reflux nephropathy in the pig. segmental pyelonephritic scarring occurs rapidly in the presence of infected vesicoureteric reflux with intrarenal reflux in the course of 1 - 4 weeks and the process may be modified by early treatment with antimicrobial drugs. These lesions were assessed histologically in terms of their extent and the type of tissue response. Even after this brief period of infection parenchymal damage was often extensive. Early changes were of active chronic inflammation with tubular destruction but little fibrosis. Later features were a variable degree of fibrous scarring with lymphoid follicle formation The histological appearances suggest that direct damage by microorganisms initiates the damage, but other mechanisms such as ischaemia and leakage of urinary constituents may also play a part.Animals treated with antimicrobial drugs after I week of infection showed much less extensive damage. Scarring was focal but both tubular and glomerular changes were found. In controls with scars older than two weeks, an often considerable degree of irreversible damage had occurred which would not be affected by treatment at this stage
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