Influence of Testosterone on the GH—IGF-I Axis in Healthy Elderly Men

Numerous in vivo and in vitro animal studies attest to the complex interplay between gonadal steroids and the GHRH—somatostatin-GH—IGF-I axis in the male and female, a topic that has been excellently and extensively reviewed (1–3). In male rats, consensus exists that the daily secretion of growth hormone (GH) is severalfold greater than that of females; that males release GH in high-amplitude, regular pulses, with low interpulse GH concentrations, whereas females secrete GH in low-amplitude, irregular pulses, with higher interpulse GH levels; and that there are many gender-distinct differences in the central nervous system and peripheral regulatory components of the GH axis, both in the absence and presence of endogenous or exogenous testosterone (1–3).