Testosterone administration increases insulin-like growth factor-I levels in normal men

Area of Science:

• Endocrinology
• Androgen research
• Metabolic studies

Background:

• Testosterone (T) administration is known to increase insulin-like growth factor-I (IGF-I) in hypogonadal men.
• The effect of androgens on IGF-I in eugonadal (normal) men remains unexamined.
• Investigating this relationship is crucial for understanding the anabolic mechanisms of androgens.

Purpose of the Study:

• To determine if testosterone administration increases IGF-I levels in normal men.
• To compare the effects of testosterone enanthate (TE) and nandrolone decanoate (ND) on IGF-I and related factors.
• To explore the potential role of IGF-I in the anabolic effects of androgens.

Main Methods:

• A randomized, double-blinded, cross-over study involving 11 normal men.
• Subjects received either TE (300 mg/week) or ND (300 mg/week) for 6 weeks, followed by a washout period and then the alternate treatment.
• Serum IGF-I and IGF-binding protein-3 (IGF-BP3) were measured using RIA; GH, total T, and estradiol levels were also analyzed.

Main Results:

• Testosterone enanthate (TE) treatment significantly increased serum IGF-I levels after 6 weeks.
• Nandrolone decanoate (ND) treatment did not significantly alter serum IGF-I levels.
• ND treatment significantly decreased IGF-binding protein-3 (IGF-BP3), potentially increasing bioavailable IGF-I, while TE did not change IGF-BP3.
• GH levels showed a trend towards increase with TE but not with ND.
• Serum total testosterone and estradiol levels increased with TE and decreased with ND.

Conclusions:

• Testosterone enanthate administration leads to increased serum IGF-I levels in normal men.
• Nandrolone decanoate does not affect serum IGF-I but may increase bioavailable IGF-I by reducing IGF-BP3.
• These findings suggest that increased IGF-I contributes to the anabolic effects of testosterone in normal men.