The objective of these studies was to examine the effects of early dietary protein restriction on disease progression and survival in the DBA/2FG-pcy (pcy) mouse model of polycystic kidney disease. Male pcy mice of 70 days of age were fed either a normal protein (NP, 25% casein) or a low-protein (LP, 6% casein) diet for 105 days. At the end of the dietary treatment, kidney weight, kidney weight relative to body weight and kidney water contents were almost 50% lower, and relative renal phospholipid and triglyceride contents were almost 50% higher, in mice fed the LP diet, indicating a marked reduction in the progression of cystic disease. Morphometric analyses also revealed a lower total and percent cyst area in kidneys derived from mice on the LP compared with the NP diet. There were no significant differences in final body weight, urine volume and osmolality, GFR, proteinuria, or plasma levels of protein and urea between these two groups. In a second study, it was found that all mice fed an NP diet from 70 days of age onward had died by 310 days of age, compared with a 42% survival rate in LP-fed mice at this age. Overall, the mean lifespan for pcy mice on the LP diet was 24% longer than that for those mice on the NP diet (310 +/- 20 versus 251 +/- 16 days; P < 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)