Relationship between some biochemical measurements and histopathological changes in age-related kidney lesions of rats

Histopathological observations were made on the spontaneous age-related kidney lesion in relation to some biochemical measurements for renal function using male SD rats from 82 to 560 days of age. Although all the rats examined were appearently healthy and had no gross lesions in the kidneys, several renal changes were detected histopathologically in the kidneys. The lesions occurred initially in renal tubules and then in glomerulus and in interstitial tissues successively increasing in severity with age. There was a correlation between the degree of the histopathological changes and the excreted amount of protein and sodium in the urine. The urinary protein was first detected at 34 days of age increasing with age. For rats of over 395 days of age, the urinary protein was greatly variable in amount among individuals. The negative correlation between urinary protein levels and those of serum albumin and urinary potassium was significant.