Longevity of the Stroke-Prone Hypertensive rats is influenced by the source and amount of dietary protein

Abstract

Longevity was studied in the Stroke-Prone Spontaneously Hypertensive (SHRSP) rats fed diets containing either three levels of casein protein (10, 20 and 40%) or two sources of protein (casein and soybean protein isolate, SPI, each providing 40% protein). All diets contained 10% soybean oil and required levels of other nutrients. The diets and water (containing 1% NaCl) were provided ad libitum during the entire study. Animals were observed for the following symptoms leading to death such as laboured respiration (dyspnoea), development of edema, lethargy and low response to stimuli, as well as nasal and ocular secretions (red). If an animal was in pain or judged to be unable to live for 24 h, euthanasia was performed. Death or severe symptoms leading to euthanasia were attributed to stroke, confirmed by necropsies. Mean survival rates of SHRSP rats fed 10% casein, 20% casein, 40% casein and 40% SPI diets were 77.2 ± 5.5, 95.9 ± 9.3, 98.8 ± 20.9 and 140.0 ± 37.3 days, respectively. Death due to stroke was significantly (P <0.001) earlier in the animals fed 10% casein protein diet compared to those fed the other diets. The death rates of the SHRSP rats fed the 20 and 40% protein casein diets were not different but the survival rate of the animals fed the SPI diet (40% protein) was significantly (P <0.001) longer than of those fed the casein diets. Since the SHRSP rat is one of the most suitable models for stroke in humans, our data would suggest that dietary protein may also play a role in the incidence of stroke in humans.