Impact of growth hormone administration on other hormonal axes

Growth hormone regulates several other hormonal systems and vice versa. The present review focusses on the effect of GH administration in adults on selected hormonal systems. Growth hormone treatment has been linked to development of central hypothyroidism in hypopituitary children. We now know that GH enhances the extra-thyroidal conversion of T(4) to T(3). Lowering of T(4) during GH treatment therefore reflects biochemical unmasking of subclinical central hypothyroidism. In normal adults GH administration does not affect the pituitary-gonadal axis. There is, however, evidence to suggest that GH substitution in hypopituitary adults enhances peripheral actions of sex steroids (males) and stimulates gonadal function (females). Both increased, unchanged and reduced basal and ACTH stimulated glucocorticoid levels have been reported during GH treatment. Several groups have recorded reduced levels of cortisol binding globulin with unchanged free cortisol concentrations. Regular assessment of thyroid and glucocorticoid status during GH substitution in GH-deficient patients is recommended.