Effects of homologous pituitary hormone treatment on serum insulin-like growth-factor-binding proteins (IGFBPs) in hypophysectomized tilapia, Oreochromis mossambicus, with special reference to a novel 20-kDa IGFBP

In the circulation, insulin-like growth factors (IGFs) bind to high-affinity-binding proteins. Insulin-like growth-factor-binding proteins (IGFBPs) appear to be present in all vertebrates, To examine the hormonal regulation of serum IGFBPs in a fish, tilapia (Oreochromis mossambicus) were hypophysectomized (Hx) and then treated with homologous tilapia growth hormone (tGH) or either form of tilapia prolactin (tPRL(177), tPRL(188)). Hormones were administered at three doses: 15, 150, and 500 ng/g of body weight. Serum IGFBP profiles were analyzed by SDS-PAGE and Western ligand blotting using I-125-rhIGF-I as a probe. A prominent IGFBP (ca 20 kDa), termed IGFBP-20K, appeared after hypophysectomy. Administration of tGH at all dose levels suppressed this BP and restored levels back to these seen in sham-operated control fish. tPRL(177) and tPRL(188) were also effective in lowering IGFBP-20K levels. Levels of the 29-kDa IGFBP (termed IGFBP-29K) increased after hypophysectomy; tGH at all doses and tPRL(177) at the two lower doses further increased these levels. All doses of tGH, tPRL(177), and tPRL(188) significantly increased levels of the 32-kDa IGFBP (termed IGFBP-32K). Hypophysectomy significantly lowered levels of the 40-kDa IGFBP (termed IGFBP-40K) below levels seen in the sham-operated controls, tGH treatment significantly raised IGFBP-40K levels at all doses examined, but not to the levels seen in intact tilapia. The 42-kDa IGFBP (termed IGFBP-42K) was not affected by hypophysectomy or hormone replacement. Our data suggest that the novel 20-kDa IGFBP and the 40-kDa IGFBP species may be similar in function to mammalian IGFBP-1 and IGPBP-3, respectively. (C) 2000 Academic Press.