Laser microprobe mass spectrometric identification of cyclosporin-induced intrarenal microliths in rat

Using laser microprobe mass analysis (LAMMA), the composition of 'micro-calcifications (dystrophic type)' or 'metastatic calcifications', previously described in rats given high doses of cyclosporin, have been identified. Female Wistar rats given 12.5, 25 or 50 mg kg-1 per day of cyclosporin in olive oil by gastric gavage developed intrarenal calcifications detected by silver nitrate staining (von Kossa) in the outer medulla after two weeks. The calcifications stained red with periodic acid-Schiff reagent and appeared to be intraluminal microliths with concentric laminations. They could be identified by LAMMA as calcium phosphate (hydroxyapatite), indistinguishable from undecalcified bone. These studies indicate that intraluminal obstruction by calcium phosphate microliths, similar to that seen with magnesium depletion or high phosphate diets, may contribute to renal damage in rats given high-dose cyclosporin. LAMMA appears to be an appropriate technique for identifying both the elemental and organic moieities of intrarenal calcium deposits.