Function of GH/IGF-I axis in aging: Multicenter study in 152 healthy elderly subjects with different degrees of physical activity
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We evaluated somatotropic function in 142 healthy elderly subjects (54 men and 88 women), aged 60–90 years and in 10 non-professional, but regularly training elderly distance runners (7 men and 3 women), aged 60–71 years. In the healthy elderly, basal plasma growth hormone (GH) and insulin-like growth factor-I (IGF-I) median levels were 0.6 μg/L (25th and 75th centiles = 0.3, 1.3) and 100.5 μg/L (25th and 75th centiles = 63, 140), respectively. About 53% of the elderly had plasma IGF-I levels within the 3rd–97th centiles of young-adult subjects. Basal GH and IGF-I were not correlated with each other nor, with the degree of physical activity, evaluated by a self-administered questionnaire; however, basal GH showed a very weak positive correlation with age while IGF-I showed a highly significant negative correlation. The peak GH response to GHRH (1 μg/kg, iv), did not correlate with age, BMI and physical activity in 87/142 subjects investigated, but was highly correlated with basal GH levels. Correlation coefficients of plasma growth hormone binding protein (GHBP) with basal GH levels and peak GH levels following GHRH were r=-0.29 and r=-0.36, respectively, but statistical significance was not reached. In the “runners”, median values of both basal and GHRH-induced GH peak were higher than those recorded in the healthy elderly, but IGF-I levels were not significantly different and they too declined with age. These data suggest that: 1) plasma IGF-I rather than basal or stimulated GH is a better index for evaluating the effect of aging on the GH/IGF system; 2) while usual physical activity in itself does not influence somatotropic function, endurance training is related to higher basal GH levels, but fails to oppose the age-related decline of plasma IGF-I levels.
Key wordsAging growth hormone insulin-like growth factor-I multicenter study physical activity
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