Somatomedin-C levels in healthy young and old men: relationship to peak and 24-hour integrated levels of growth hormone.

We investigated the relationship between growth hormone secretion and somatomedin levels as a function of age in normal healthy men. There was a substantial decrease with age in somatomedin levels from 0.95 +/- 0.06 (M +/- SEM) units/ml in young (23 to 27 years) men to 0.68 +/- 0.07 in old (58 to 82 years) men. The blood samples were taken throughout a 24-hour period, so it was possible to analyze the data for correlations between average somatomedin levels and various aspects of growth hormone secretion. There was a significant correlation of somatomedin level with the 24-hour integrated growth hormone level, and a nearly significant correlation with the sum of the highest three peaks, but no correlation with the highest nighttime peak or the basal level of growth hormone. These lower blood levels of somatomedin in the aged may be responsible, at least in part, for the catabolic effects on muscle and bone frequently associated with aging.