Collecting duct function in cis-platinum nephrotoxicity.

Microcatheterization was used to study the effect of cis-platinum nephrotoxicity on inner medullary collecting duct function in anaesthetized rats. Osmolality of collecting duct fluid increased from the beginning to the end (papillary tip) of the collecting duct by only 69 +/- 11 mosmol/kg in cis-platinum treated rats (at 5-6 days) compared with 306 +/- 75 mosmol/kg in sham controls (p less than 0.01). Tubular fluid to plasma inulin concentration ratio was reduced at the beginning and end of the collecting duct. Tubular fluid sodium, chloride, and potassium concentrations were lower at the papillary tip in cis-platinum treated rats (p less than 0.01). The results indicate that collecting duct water reabsorption is reduced, but electrolyte reabsorption is normal (or even increased) in cis-platinum nephrotoxicity. Papillary tissue sodium chloride concentration was reduced in cis-platinum treated rats. We conclude that the characteristic decrease in urine concentrating ability in cis-platinum nephrotoxicity is not primarily the result of an intrinsic abnormality in collecting duct function but is secondary to decreased papillary hypertonicity resulting from impaired function in more proximal nephron segments, presumably the pars recta of the proximal tubule and the loop of Henle where previous studies have demonstrated abnormal function.