Impaired glomerular and tubular function as a short-term effect of sirolimus treatment in the rat.

Aims: To investigate acute and short-term effects of sirolimus (SRL) on glomerulo-tubular function, blood pressure (BP), and renal morphology in the rat. Methods: Male Sprague-Dawley rats, weighing initially 140–180 g were treated with SRL in three series: SRL 0.2, 0.4, or 0.8 mg/kg/day intraperitoneally for up to 28 days after skin allo-transplantation from Lewis donors (to establish a dosage with significant immunosuppressive effect). SRL 0.4 mg/kg intravenously (acute effects). SRL 0.4 mg/kg/day intraperitoneally for 7 days (short-term effects). Inulin, lithium (CLi) and sodium clearance, and intra-arterial BP were measured in conscious catheterized rats. Morphological kidney studies were completed after post-mortem fixation. Results: Maximum immunosuppressive effect was achieved with SRL 0.4 mg/kg/day. SRL acutely increased GFR and CLi, whereas fractional proximal reabsorption (PFR) declined. In the short-term study SRL had opposite effects on GFR and CLi, unaffected proximal tubular reabsorption and PFR, raised BP, diminished food consumption, and slower increase in body weight. Morphological changes were non-specific. Conclusion: In a dosage giving maximum immunosuppressive effect, SRL revealed acute effects on glomerular and proximal tubular function thus indicating increased outflow from the proximal tubules whereas one week of SRL treatment produced a change resembling the known nephrotoxic effects of the calcineurine inhibitors.