Effects of dietary protein restriction on nitrogen balance and cardiovascular functions in aged rats

Effects of aging and dietary protein restriction on nitrogen balance and cardiovascular functions were examined. Male Fischer 344 rats 6-7 months old were fed ad libitum until 24 or 25 months old with either a 12% or a 23% protein diet, respectively. The nitrogen balance measured at the age of 24 months old demonstrated a significant difference between the two groups: the group with the 23% protein diet had a negative balance, while the group with the 12% protein diet had a positive balance. Endothelium-dependent relaxation with acetylcholine of the thoracic aortas was impaired by age but to a lesser extent to the protein-restricted animals. In addition, increased ability of platelet aggregation according to aging was also significantly suppressed by protein restriction. These observations demonstrate that protein restriction delays the aging effects of nitrogen loss and reduced cardiovascular function.