Renal clearance, metabolic clearance rate, and half-life of human growth hormone in young and aged subjects.

We studied the renal clearance, MCR, and half-life of the synthetic 22K form of human GH [recombinant hGH (rhGH)] in seven healthy young and five aged men by means of the constant iv infusion technique. rhGH was infused at a rate of 2 micrograms/kg.2 mL/h for 150 min, after which its disappearance was followed for 50 min. Changes in GH levels in plasma and urine were measured by a highly sensitive enzyme immunoassay. The mean (+/- SD) renal clearance of GH was significantly greater in the aged group than in the young group (14.3 +/- 2.5 vs. 4.2 +/- 1.0 microL/min; P < 0.05). The mean MCR was greater in the young group than in the aged group (187.1 +/- 43.7 vs. 120.5 +/- 39.5 mL/min; P < 0.05), but the MCR adjusted for body weight was not different between the two groups (2.9 +/- 0.6 vs. 2.3 +/- 0.8 mL/min.kg). No difference was noted in the half-life of GH between the two groups (13.8 +/- 0.9 vs. 14.2 +/- 0.4 min). These findings indicate that GH reabsorption from the renal tubule may be impaired in elderly subjects, but the disappearance rate of GH is not influenced by age.