DIET, OVERFEEDING, AND MODERATE DIETARY RESTRICTION IN CONTROL SPRAGUE-DAWLEY RATS .2. EFFECTS ON AGE-RELATED PROLIFERATIVE AND DEGENERATIVE LESIONS

This study compared the effects of ad libitum (AL) overfeeding and mod erate dietary restriction (DR) of 2 different diets on Sprague-Dawley (SD) rat survival and spontaneous, age-related proliferative and degen erative lesions. SD rats were fed Purina Rodent Chow 5002 or a modifie d Rodent Chow 5002-9 containing lower protein, fat, metabolizable ener gy, and increased fiber by AL or by DR at 65% of the AL amount by meas urement or time (6.5 hr). At 106 wk, rats fed the 5002-9 diet AL did n ot have significantly improved survival over rats fed the 5002 diet AL . The 5002 diet fed DR by time (6.5 hr) improved survival for males bu t not females. Only DR by measurement of both diets resulted in lower mortality for both sexes. By 106 wk rats fed either diet by AL had the same brain weights as DR fed rats, but AL fed rats had greater body w eight, body fat content, and increased heart, lung, kidney, liver, adr enal, thyroid, and pituitary weights that correlated with an increased incidence and severity of degenerative and/or proliferative lesions i n these organs. Moderate DR delayed the progression of chronic nephrop athy by delaying the early development of glomerular hypertrophy that initiates the development of glomerular sclerosis and nephron loss in AL overfed rats. Moderate DR lowered the incidence, severity, and prog ression of cardiomyopathy and other degenerative, age-related lesions and appeared to delay the development of reproductive senescence in SD females. The conclusion from this study is that moderate DR delayed o nset and progression of degenerative lesions, and death due to cardiov ascular or renal disease, and thus potentially improves the bioassay t o detect compound-specific chronic toxicity.