The effects of dexamethasone treatment on immunoreactive and bioactive insulin-like growth factors (IGFs) and IGF-binding proteins in normal male volunteers

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Abstract
Glucocorticoids inhibit somatic growth in man and laboratory animals, and have long been regarded as suppressors of both stimulated GH secretion and insulin-like growth factor (IGF) activity. Recent evidence suggests, however, that glucocorticoids can be potent GH secretagogues in their own right with concomitant increases in circulating IGF-I levels. IGFs circulate tightly bound to a group of high-affinity binding proteins (IGFBPs) which modulate their actions. In order to investigate the effects of glucocorticoids on serum levels of IGFs and IGFBPs, normal male volunteers were sampled over 24-h periods before and directly after treatment with dexamethasone (2 mg twice daily) for 96 h. Following dexamethasone administration, all volunteers showed a marked increase in mean± s.e.m. IGF-I levels over the 24-h sampling period (292·2±31·8 before dexamethasone, 425·9 ±37 μg/l after dexamethasone, PP= 0·002) and IGFBP-1 was significantly suppressed (42·9±8·2) before dexamethasone, 28·0±7·9 μg/l after dexamethasone, PP=0·002), and there was a significant increase in IGFBP-3 levels from 3·24 ±0·25 to 3·67±0·32 mg/l (P=0·0153). Mean IGF bioactivity over the sampling period after dexamethasone was reduced by approximately 60% (0·93 ±0·39 before dexamethasone, 0·39 ±0·05 U/ml after dexamethasone, P Journal of Endocrinology (1993) 136, 525–533

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