Aging Aging

Dietary Restriction 357important to allow true ad libitum feeding. However, one word of caution isneeded: Ensure the chow in food cups is fresh, as rodents tend to consume less ifthe food is stale, which would preclude accurate food consumption measurements,especially for small rodents.3. Continually collect, usually twice weekly, the average amount of food consumedfrom the ad libitum, control animals.4. During the animal’s rapid growth phase, adjust food allotment for the DR animals,twice weekly if necessary.3.3. Animal MonitoringAn animal’s morbidity and mortality are profoundly influenced by its nutritionalstatus. It is therefore imperative that the colony of experimental animalsbe closely monitored as follows:1. Check animal behavior and health conditions daily, paying close attention tospontaneous movements and eating and drinking habits.2. Inspect animals with increased frequency as they age (more than twice daily, ifpossible).3. Perform necropsy on all animals killed, fixing tissue specimens in a formulinsolution for a histological evaluation for the probable cause of death.3.4. Longevity Studies: Survival Data and AnalysisThe hallmark of DR is life extension. It is therefore important to carefullycollect and analyze survival data based on animal mortality.1. Prior to the start of the study, consider the number of animals needed to meet thestatistical requirements of your study based on power function analysis.2. If possible, allow animals to die naturally, using death as the endpoint for datacollection criterion.3. To construct survival data, register each death, noting age in days.4. Use data collected to calculate median life-span, 10% survival, and maximumlife-span.5. Another method used to analyze longevity data is to measure mortality rate doublingtime (MRDT) base on the Gompertzian equation. Some investigators considerMRDT a more reliable expression of the rate of aging or “biomarker” ofaging (11). Although DR intervention has been show to increase MRDT, thismethod has some inherent shortcomings as the Gompertzian derivation is basedon mortality rate (i.e., death) as an index of the rate of aging, which it is not inactuality.4. Notes4.1. Extent and Time of DR InterventionToday, the DR paradigm is the most powerful and reproducible interventionavailable to gerontologists to retard aging processes and suppress the patho-