Growth factors and the thyroid: effects of treatment for hyper- and hypothyroidism on serum IGF-I and urinary epidermal growth factor concentrations

We investigated the impact of thyroid hormone levels on serum concentrations of IGF-I and urinary epidermal growth factor (EGF) in hyper- and hypothyroid patients before and during medical treatment. Serum IGF-I levels measured with radioreceptor-assay decreased in 12 hyperthyroid patients from 1.25 (1.02-1.80) to 1.02 (0.77-1.78) X 10(3) U/l (P less than 0.01), whereas a non-significant increase in 8 hypothyroid patients--from 1.14 (0.85-1.40) to 1.39 (1.08-1.80) X 10(3) U/l was recorded. Urinary EGF, measured with radioimmunoassay decreased in 10 hyperthyroid patients from 68.0 (38.0-122.9) to 40.9 (23.6-100.3) micrograms/g creatinine (P less than 0.001) and increased in 7 hypothyroid subjects from 23.8 (17.5-35.8) to 36.1 (24.7-60.1) micrograms/g creatinine (P less than 0.05). In hyperthyroidism, but not in hypothyroidism, the urinary excretion of creatinine changed significantly from 0.66 (0.26-1.21) to 1.52 (0.81-2.59) g/l (P less than 0.001) during treatment, thus affecting the EGF excretion values. However, a comparison of untreated hyperthyroid with untreated hypothyroid patients showed a highly significant difference in EGF excretion (P less than 0.001) despite a non-significant difference in creatinine excretion between the two groups. FT4 I concentrations correlated significantly (r = 0.83) (P less than 0.001) to EGF values in untreated hyper- and hypo-thyroid patients. Data from the present study thus conform with the view that the growth promoting effect of thyroid hormones involves a stimulated synthesis or release of classic growth factors.