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 se lected hormonal systems. Growth hormone treatment has been linked to develo pment 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 st eroids (males) and stimulates gonadal function (females). Both increased, u nchanged and reduced basal and ACTH stimulated glucocorticoid levels have b een reported during GH treatment. Several groups have recorded reduced leve ls of cortisol binding globulin with unchanged free cortisol concentrations . Regular assessment of thyroid and glucocorticoid status during GH substit ution in GH-deficient patients is recommended. Copyright (C) 1999 S. Karger AG, Basel.