Thymulin, zinc and insulin-like growth factor-I (IGF-I) activity before and during recombinant growth hormone (rec-GH) therapy in children and adults with GH deficiency

Plasma thymulin (active and total) levels, IGF-I and zinc concentrations were evaluated in 9 children and in 8 adults with GH deficiency (GHD) before and after 3-6 months of recombinant-GH treatment. Before therapy, GH deficient children had lower plasma active thymulin levels (1.0+/-0.3 log(-2)), not due to a peripheral defect in zinc saturation since plasma zinc levels were within the normal range, and total thymulin levels (1.3+/-0.3 log(-2)) than in the agematched control group. GH therapy significantly increased active thymulin (3rd month: 3.0+/-0.2 log(-2), 6th month: 4.0+/-0.2 log(-2)), total thymulin (3rd month: 3.3+/-0.3 log(-2), 6th month: 4.3+/-0.2 log(-2)) and IGF-I levels (3rd month: 283.3+/-7.2 mu g/L, 6th month: 411.2+/-44.2 mu g/L, vs basal: 144.3+/-11.5 mu g/L); at the 6th month of therapy, thymulin levels (active and total) were comparable to those found in controls. A positive correlation existed between zinc and plasma IGF-I levels (r=0.66, p<0.05). In adults with GHD, plasma active (1.9+/-0.3 log(-2)) and total thymulin levels (3.9+/-0.1 log(-2)), significantly lower (p<0.01 and 0.05, respectively) than in controls before treatment, increased after GH therapy (active thymulin, 3rd month: 3.0+/-0.2 log(-2), 6th month: 4.4+/-0.3 log(-2); total thymulin, 3rd month: 3.9+/-0.3 log(-2), 6th month: 4.71+/-0.2 log(-2)), being at 6th month of therapy no more different from the values recorded in the age-matched control group. In conclusion, children and adults with GHD have a marked impairment of the thymic endocrine activity, which can be restored by six months of GH treatment. The effects of GH on thymic functions may be mediated by IGF-I, through the modulation of zinc turnover, suggesting the possible existence of an interplay among GH, zinc, IGF-I and thymulin both in children and adults with GHD. (C) 1996, Editrice Kurtis