Age-related changes of GH-IGF1 axis function

BackgroundThere is a reduction in the GH-IGF1 axis activity with increasing age, but there is evidence that the pool of GH available for release is not diminished in elderly subjects. We investigated whether there are differences among healthy young-middle aged and old aged subjects in the 24 hour secretory profiles of GH and IGF1.MethodsThe study was carried out on 15 healthy young-middle aged subjects (age range 36–55 years) and 15 healthy old aged subjects (age range 67–79 years). GH, IGF1, melatonin and cortisol serum levels were measured on blood samples collected every four hours for 24 hours. The fractional variation between single time point GH and IGF1 serum levels, mean photoperiod (06:00h–10:00h–14:00 h) and scotoperiod (18:00h–22:00h–02:00 h) values and the presence of circadian rhythmicity were evaluated.ResultsA normal circadian rhythmicity was recognizable for GH, melatonin and cortisol secretion in young-middle aged and old aged subjects, MESOR of cortisol was higher in the elderly (P = 0.002) and the acrophase of cortisol was advanced in the group of old aged subjects (P = 0.03), whereas the amplitude of IGF1 was higher in the group of young-middle-aged subjects (P < 0.01). Old aged subjects presented higher mean GH levels in the photoperiod (P = 0.01), but lack of variability of GH and IGF1 fractional variations, whereas young-middle aged subjects presented significant variability of GH and IGF1 factional variations (P = 0.05 and P = 0.003, respectively) and increased fractional variation of nocturnal GH and IGF1 serum levels in respect to older subjects (P = 0.03 and P = 0.05, respectively). There was no statistically significant difference between mean melatonin serum levels in the photoperiod (P = 0.937) and in the scotoperiod (P = 0.494). There was no statistically significant difference between mean cortisol serum levels in the photoperiod (P = 0.235), whereas mean cortisol serum levels were higher in old aged subjects in the scotoperiod (P = 0.04). Linear regression evidenced a statistically significant negative trend between age and the 24 h mean of GH (P < 0.01) and a statistically significant positive trend between age and the 24 h mean of cortisol (P < 0.001).ConclusionsAging is associated with an altered pattern of GH secretion and IGF1 production.