Nyctohemeral growth hormone profiles in young and aged men: correlation with somatomedin-C levels.

The effects of aging on GH secretion and somatomedin-C (SM-C) levels were studied in 10 young (22-45 yr) and 10 elderly (65-85 yr) men. Plasma GH levels were measured in samples obtained at 20-min intervals for 1300 min. Plasma SM-C levels were measured in samples obtained at 0600, 1100, 1600, 2100, and 0200 h. In the elderly men the mean basal plasma GH level was similar to that in the young men, but the total GH peak area as well as the amplitude of the peaks were significantly (p less than 0.01) lower than those in young men during both the day and the night. Plasma SM-C levels were significantly lower in the elderly men and were correlated with the total integrated GH levels and total GH peak areas, but not with basal plasma GH levels, suggesting that the GH peaks determine SM-C levels and that the decreased GH secretion in elderly men has biological significance.