Acromegaly and insulin-like growth factors]

The insulin-like growth factors (IGF) I and II are structural homologues of insulin with a molecular weight of 7500. In contrast to insulin, their insulin-like effects are not suppressible by insulin antibodies. They are mainly produced by the liver under the influence of growth hormone and are bound to specific carrier proteins in the circulation. According to the somatomedin concept, they mediate the effects of growth hormone on growth. IGF I is identical to somatomedin A and somatomedin C. In acromegalic patients oversecretion of growth hormone is accompanied by a significant increase in the serum IGF I level, whereas IGF II levels are normal. IGF I can, therefore, serve as a useful additional laboratory index in the diagnosis of acromegaly and in evaluating successful surgery and/or radiotherapy of this disease. Bromocriptine therapy often improves the clinical symptoms of acromegaly and lowers growth hormone levels without normalizing IGF I. In most of these patients, however, suppression of growth hormone under oral glucose load is not normal. In our opinion the determination of IGF I should not replace growth hormone determinations during an oral glucose tolerance test; rather, it should be performed to complement this test, above all when its results cannot be unambiguously interpreted.