The insulin-like growth factor (IGF) system appears to be important in the regulation
of adrenal growth and hormone synthesis. As IGF-binding proteins (IGFBPs) modify IGF
bioactivity, we investigated the expression of IGFBP 1-6 genes in different adrenal
tumors and hyperplasias to further clarify the role of the IGF system in adrenal pathophysiology.
IGFBP-1 mRNA levels were too low to be detected by Northern blot analysis, but could
be found by RT-PCR in some tumors and hyperplastic adrenals. Other IGFBPs were detected
by Northern blotting. IGFBP-3 mRNA levels were very low in normal adrenals. In adrenal
tumors and hyperplastic adrenals, IGFBP-3 mRNA expression was usually higher than
in normal adrenals. In hormonally active adrenocortical carcinomas, IGFBP-2, -4, -5
and -6 mRNA levels were lower than in nonfunctional carcinomas and normal adrenals.
The low IGFBP mRNA expression in the hormone-producing carcinomas was associated with
high IGF-II mRNA content. In adrenocortical adenomas from patients with Cushing's
or Conn's syndrome, mean IGFBP mRNA levels were higher than in normal adrenals or
in hormonally inactive adenomas. In nodular and bilateral hyperplasias, IGFBP-2, -3
and -4 mRNA expression was on average higher than in normal adrenals but varied substantially,
as did IGFBP mRNA levels in pheochromocytomas. In comparison to normal adrenals, pheochromocytomas
expressed on average higher levels of IGFBP-2 and -4 but less IGFBP-5 and -6 mRNAs.
Our data show that the six IGFBPs 1-6 are expressed at variable level in adrenal tumors
and hyperplasias. The low level of IGFBP mRNAs in hormonally active adrenocortical
carcinomas was of particular interest.
Key words
Insulin-Like Growth Factor Binding Protein - IGFBP - Adrenal - Adrenocortical - Pheochromocytoma
