Sustained Growth Hormone (GH) and insulin-like growth factor I responses to prolonged high-dose twice-daily GH-releasing-hormone stimulation in middle-aged and older men

Abstract

Postulated mechanisms underlying the relative hyposomatotropism of aging include reduced hypothalamic drive by GHRH. To test this notion, we administered 1 mg (n = 11) vs. 4 mg (n = 11) recombinant human GHRH-1,44-amide sc twice daily for 3 months in a double-blind, parallel-cohort design to 22 healthy men (ages, 53-68 yr). After 3 months, GHRH elevated: overnight GH concentrations from 0.71 ± 0.19 to 1.74 ± 0.39 μg/liter (P < 0.001; 1 mg) and from 0.80 ± 0.15 to 5.12 ± 0.40 μg/liter (P < 0.001; 4 mg) and IGF-I concentrations from 117 ± 14 to 234 ±20 μg/liter (P = 0.007; 1 mg) and from 147 ± 13 to 286 ± 22 μg/liter (P < 0.001; 4 mg). Only the higher GHRH dose also increased total body water (tritium space; P = 0.024) and fat-free mass (dual-energy x-ray absorptiometry; P = 0.021), and reduced total abdominal adiposity (computed axial tomography scan; P = 0.042). Both supplementation schedules shortened the time required to walk 30 m and ascend four flights of stairs (P < 0.025 each). Lower extremity strength, aerobic capacity, and bone mineral density did not change. Local injection site reactions were common. We conclude that sc administration of a large dose of GHRH (4 mg) twice daily for 3 months elevates GH and IGF-I concentrations, increases total body water and fat-free mass, reduces total abdominal adiposity, and enhances certain performance measures in healthy aging men but causes local skin reactions.