The IGF-I response to very low rhGH doses is preserved in human ageing

OBJECTIVES The activity of the GH/IGF‐I axis varies during life and is clearly reduced in the elderly. In fact, GH, IGF‐I and IGFBP‐3 levels in older people are clearly reduced and similar to those observed in patients with GH deficiency. The declining activity of the GH/IGF‐I axis with advancing age may contribute to changes in body composition, structure, function and metabolism. In fact, treatment with pharmacological doses of rhGH restored plasma IGF‐I levels, increased lean body mass and muscle strength while decreased adipose tissue mass in healthy elderly subjects. At present it is unclear whether peripheral GH sensitivity is preserved in aging. To clarify this point, we aimed to verify the effect of both single dose and short term treatment with very low rhGH doses on the IGF‐I levels in normal elderly subjects. Normal young adults were studied as controls. DESIGN We studied the IGF‐I response to rhGH administration after single (20 μg/kg s.c.) or repeated administrations (5 μg/kg s.c. for 4 days) in two groups of young and elderly subjects. SUBJECTS Twenty‐seven healthy elderly (ES, 14 F and 13 M, age mean ± SEM: 69.4 ± 1.3 years, BMI: 23.9 ± 0.5 kg/m2) and 21 young adult subjects (YS, 12 F and 9 M, 29.8 ± 1.2 years, 23.8 ± 0.5 kg/m2) were studied, divided into two groups. MEASUREMENTS Group 1: blood samples for IGF‐I and IGFBP‐3 assay were drawn basally and 12 h after rhGH administration (20 μg/kg). Group 2: blood samples for IGF‐I, IGFBP‐3, glucose and insulin assays were drawn basally, 12 h after the first and the last rhGH administration (5 μg/kg). Free T3 (fT3), free T4 (fT4) and TSH levels were also assayed basally and after the last rhGH administration; oestradiol and testosterone levels were measured basally. RESULTS Basal IGF‐I levels were lower in ES (whole group) than in YS (whole group) (123.1 ± 8.9 vs. 230.4 ± 16.1 μg/l, P