Insulin-like growth factor binding proteins in the human adrenal gland

Insulin-like growth factors (IGFs) are thought to be important regulators of adrenocortical growth and steroidogenesis. IGFs are usually complexed with a family of specific IGF-binding proteins (IGFBPs) in serum, other body fluids, and in conditioned media of a variety of cell types. IGFBPs may either inhibit or potentiate the effects of IGFs. In the present study we have investigated the gene expression of the IGFBPs and IGF receptors in human fetal (HFA) and adult (HAA) adrenals. Northern blotting and/or reverse transcription polymerase chain reaction (RT-PCR) methods were used. IGFBP secretion into the cell culture medium was studied in primary cell cultures by Western ligand blotting and by radioimmunoassays. IGFBP-1 mRNA expression was low in adrenals: Northern blots were negative, but RT-PCR revealed IGFBP-1 mRNA in HFA. IGFBP-2 mRNA was equally expressed in both HFA and HAA with no differences in signal intensities by Northern blotting. IGFBP-3 mRNA was detected in HFA but not in HAA by Northern blotting. IGFBP-4 mRNA was expressed equally in both HFA and HAA. IGFBP-5 and -6 mRNA expression was more abundant in HAA than in HFA. IGF-I and type I and type II IGF receptor mRNAs were equally expressed in both HFA and HAA. 12-O-tetradecanoyl phorbol-13-acetate (TPA), a protein kinase regulator, upregulated IGFBP-1 in HFA cultures as determined by RIA, but ACTH was without effect. IGFBP-2 was not regulated by TPA or ACTH neither at protein nor at mRNA level. IGFBP-3 was downregulated by TPA both at protein and mRNA levels, but it was not affected by ACTH.(ABSTRACT TRUNCATED AT 250 WORDS)