The effects of different levels of dietary restriction on aging and survival in the Sprague-Dawley rat: Implications for chronic studies

A study was undertaken to determine the effects of incremental levels of di etary restriction (DR) in rats. Survival, growth, reproductive, and dietary intake (DI) variables were monitored in a chronic study in which male Spra gue Dawley (SD) rats (NCTR colony) were fed their ration ad libitum (AL), o r DR. The main objectives were to determine if low levels of DR could be us ed to increase the survival rate of SD rats in the chronic bioassay, and to identify the survival characteristics of a long-lived SD rat strain (NCTR colony). The average life span of AL rats was 115 months. At 104 weeks on s tudy (110 weeks of age), the survival rate for the AL and 10%, 25%, and 40% DR groups was 63.4, 87.5, 87.5, and 97.5%, respectively. The largest incre ase in survival (24.1%) occurred between AL and 10% DR, indicating that ver y low levels of DR have a significant effect on survival. Whole-body, liver , prostate, and epididymis weights and body length were decreased by DR, wh ereas brain weight, testicular weight, and skull length were not altered by DR. Rats from the NCTR colony were found to be ideal for chronic studies b ecause they are much longer-lived than other SD stocks. Although the 104-we ek survival rate for these SD, non-obese AL rats exceeds the FDA's "Redbook " survival guideline (> 50%) for chronic bioassays, the use of DR is advoca ted because it reduces individual variability in body weight. (C) 2001, Edi trice Kurtis.