Interstitial focal fibrosis and reduction in proximal tubular length in adult rats after lithium treatment.

Seven adult male and eight adult female rats were treated with lithium for 16 weeks. The kidneys were fixed by vascular perfusion with glutaraldehyde and investigated by morphometric methods. Plasma lithium was in the therapeutic range. All treated animals showed a significant increase in interstitial volume as a result of focal interstitial fibrosis (from 6.6% to 9.8% in males and from 5.2% to 8.4% in females) and a significant reduction in proximal tubular length in male rats (from 292 to 181 m/kidney). Two rats had elevated plasma urea at the end of the experiment. A few animals that were treated for 8 months showed even more significant structural changes. The findings in the present study demonstrate that lithium treatment also in the adult rat leads to focal interstitial fibrosis in the renal cortex.