Saline- and glycerol-induced acute renal failure: 'protection' occurs after insult.

To determine whether chronic saline ingestion is required for protection against acute renal failure, we examined the effect of the time at which saline was offered. Water-drinking rats developed severe azotemia (BUN 115 +/- 6 mg/dl; 41 +/- 2 mmol/l) 24 h after 50% glycerol i.m. Chronic saline ingestion for 30 days conferred protection only if continued after the insult (BUN 49 +/- 4 mg/dl; 18 +/- 1 mmol/l; p less than 0.01) but not if saline was withdrawn (BUN 110 +/- 8 mg/dl; 38 +/- 3 mmol/l). Moreover, saline offered only after the insult conferred equivalent protection (BUN 57 +/- 6 mg/dl; 32 +/- 2 mmol/l). Fluid intake, arterial blood pressure and plasma volume were better sustained in saline-drinking rats.