Effect of supra-physiological dose administration of rhGH on pituitary-thyroid axis in healthy male athletes

The effect of recombinant human growth hormone (rhGH) administration on hypothalamic-pituitary-thyroid (HPT) system in healthy trained humans still needs to be fully clarified. Furthermore, whether rhGH abuse could exert undesirable or noxious effect on health is still unclear. In order to evaluate changes in HPT axis variables in time after rhGH administration, 14 well-trained healthy male athletes were treated with rhGH (0.03mg/kg body weight/day, sc) administration, 6days/week for 3weeks. Morning blood samples were collected immediately before and 3, 4, 8, 15, and 21days after rhGH administration. A further set of blood samples was taken 3, 6 and 9days after drug withdrawal. Samples were analyzed for GH-IGF and HPT axis. Significant TSH serum decrease and IGF-I increase occurred early after rhGH administration, without FT 3 content modification and with FT 4 reduction delayed in time. Serum TSH concentrations negatively correlated with IGF-I, IGFBP-3 and IGF-I/IGFBP-3 ratios. rhGH short-term administration in healthy trained subjects induced an early TSH suppression - likely acting at central level through IGF-I - without thyroid function alteration. Further investigations in athletes are necessary to verify whether prolonged TSH suppression, i.e. rhGH intake for longer time, could induce pathologic condition, such as hypothyroidism.