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Do androgens regulate growth hormone-binding protein in adult man?
T P Ip1, D M Hoffman, A J O'Sullivan
1Garvan Institute of Medical Research, St. Vincent's Hospital, Sydney, New South Wales, Australia.
The Journal of Clinical Endocrinology and Metabolism
|April 1, 1995
Summary
Serum growth hormone-binding protein (GHBP) levels are normal in hypogonadal men. Testosterone treatment significantly reduces GHBP, indicating a pharmacological effect independent of growth hormone (GH) mediation.
Area of Science:
- Endocrinology
- Andrology
Background:
- Serum growth hormone-binding protein (GHBP) is a key regulator of growth hormone (GH) bioavailability.
- The role of androgens in regulating GHBP levels in adult men remains incompletely understood.
Purpose of the Study:
- To investigate whether serum GHBP concentrations in adult men are influenced by androgen levels.
- To determine the effect of testosterone replacement therapy on GHBP levels in hypogonadal men.
Main Methods:
- Serum GHBP and insulin-like growth factor I (IGF-I) levels were measured using a ligand immunofunctional assay.
- Comparisons were made between normal men and hypogonadal men (with and without GH deficiency) before and after testosterone enanthate treatment.
Main Results:
- Untreated hypogonadal men had normal serum GHBP levels compared to normal men, but lower IGF-I levels.
- Testosterone treatment in hypogonadal men led to a significant decrease in serum GHBP levels.
- IGF-I levels increased with testosterone treatment in GH-sufficient hypogonadal men, but not in GH-deficient men.
Conclusions:
- Serum GHBP levels are not directly regulated by endogenous androgen status in adult men.
- Testosterone administration exerts a direct pharmacological effect on GHBP levels, independent of endogenous growth hormone secretion.
- These findings suggest a complex interplay between androgens, GHBP, and IGF-I.