Aging and urinary excretion of epidermal growth factor

The aging process in man leads to some loss of kidney mass and function. The kidney produces epidermal growth factor (EGF), a polypeptide involved in the repairing process of epithelial cells. Human urine contains high concentrations of EGF, derived from its production in the kidney It is not known if aging alters urinary EGF production in humans. This study investigates the possibility of decreased urinary EGF in elderly people. Urine samples were collected from 70 healthy subjects of various ages and measured for EGF by the technique of radioimmunoassay. The studied urine samples were divided into five age groups (3 to 10, 11 to 20, 21 to 60, 61 to 70, and 71 to 80 years). Urinary EGF (corrected for the urine creatinine concentration and measured as ng per mg creatinine) was highest in the two youngest groups, 78.5 +/- 14.3 and 76.2 +/- 18.8 (mean +/- standard error of the mean), respectively, and decreased with age so that the lowest urinary EGF was observed in the oldest group (27.0 +/- 8.8 ng per mg creatinine). In addition, a significant inverse relationship exists between urinary EGF in all 70 subjects and their respective age (P < 0.001). These findings show that normal values of urinary EGF should take age into account. The reduced production of EGF by the kidney in the elderly may have functional significance in retarding the repair process in the kidney.