Diurnal variation in serum insulin-like growth factor (IGF)-I and IGF binding protein-3 concentrations during daily subcutaneous injections of recombinant human growth hormone in GH-deficient adults

OBJECTIVE  Whereas there seems to be little, if any, circadian variation in circulating concentrations of IGF-I and IGFBP-3 in healthy subjects, there are conflicting reports on this issue in GH-deficient patients treated with GH as a daily subcutaneous injection. We have therefore investigated the 24-hour serum profiles of IGF-I and IGFBP-3 concentrations after one week and more than one year of GH treatment.
PATIENTS  Eleven subjects, with adult onset GH deficiency mainly caused by pituitary adenomas were included in the study.
DESIGN AND MEASUREMENTS  In an open study, six subjects (three women and three men; age (±SEM) 41.2±3.9 years) were investigated after one week of GH therapy and five subjects (three women and two men; age (±SEM) 61.4±3.3 years) were investigated after 13–40 months of GH therapy. The GH injections were given at 2000 h. The subjects were hospitalized for 24-hour blood sampling at 1-hour intervals and serum concentrations of GH, IGF-I and IGFBP-3 were determined.
RESULTS  There was a significant diurnal variation in serum IGF-I and IGFBP-3 concentrations both in the subjects who had received GH for one week and in those who had received GH treatment for more than one year. The serum concentrations of IGF-I and IGFBP-3 were highest in the morning and lowest during night-time and early morning. The molar IGF-I/IGFBP-3 ratio varied significantly with time in both groups of patients in a similar way as IGF-I and IGFBP-3 indicating a more pronounced variation in IGF-I compared with IGFBP-3 in response to the GH therapy.
CONCLUSION  Significant diurnal variations in serum IGF-I and IGFBP-3 concentrations occur after one week and more than one year of GH treatment with daily subcutaneous injections. The results indicate that the free fraction of IGF-I may exhibit a diurnal variation.