Potential role of fluctuations in the composition of renal tubular fluid through the nephron in the initiation of Randall's plugs and calcium oxalate crystalluria in a computer model of renal function.
This article describes an updated computer model which attempts to simulate known renal reabsorption and secretion activity through the nephron (NEPHROSIM) and its possible relevance to the initiation of calcium-containing renal stones. The model shows that, under certain conditions of plasma composition, de novo nucleation of both calcium oxalate (CaOx) and calcium phosphate (CaP) can take place at the end of the descending limb of the Loop of Henle (DLH), particularly in untreated, recurrent idiopathic CaOx stone-formers (RSF). The model incorporates a number of hydrodynamic factors that may influence the subsequent growth of crystals nucleated at the endincreases in plasma oxalate concentration, crystallisation only takes place in the CD and leads to the formation of small crystals which are comfortably passed in the urine and, secondly, that for slightly greater increases in the filtered load of oxalate, spontaneous and/or heterogeneous nucleation of CaOx may occur both at the end of the DLH and in the CD. This latter situation leads to the passage in the final urine of a mixture of large crystals of CaOx (arising from nucleation at the end of the DLH) and small crystals of CaOx (as a result of nucleation originating in the CD). As a result of the higher calcium and oxalate concentrations in the urine of RSF, these patients have an increased probability of initiating CaOx crystallisation in the