In Vitro Secretion of Insulin-like Growth Factor-Binding Proteins from Liver of Striped Bass, Morone saxatilis

Abstract

In vitro secretion of insulin-like growth factor-binding proteins (IGFBPs) from liver of striped bass (sb: Morone saxatilis) was studied using a simple organ culture system. Liver cubes (1 mm 3) were cultured in minimum essential medium with Earle's salts containing 0.1% bovine serum albumin and 100 U/ml penicillin in 5% CO 2/95% O 2 at 16°. The amount of double-stranded DNA in these cultured liver cubes did not change by 192 hr in the culture, but decreased by 216 hr. Four IGFBPs (a 23- to 24-kDa protein, a 28- to 30 kDa protein, a 35 to 39-kDa protein, and an 85- to 90-kDa protein) were identified in striped bass serum by Western ligand blotting; two of these IGFBPs, 23-24 kDa (sbIGFBP-1) and 28-30 kDa (sbIGFBP-2), were consistently detected in culture media by Western ligand blot analysis. The intensity of the blot for sbIGFB-2 was consistently greater than that of sbIGFBP-1, which was no longer secreted after 96 hr in culture. The effects of hormones and growth factors on IGFBP secretion by liver tissue were measured after 48 hr in culture. sbIGFBP-1 in the medium was significantly decreased by adding ovine prolactin (10 μg/ml), bovine insulin (100 μg/ml), and bovine IGF-I (100 ng/ml), but was increased by 17β-estradiol (E 2: 5 and 50 ng/ml). sbIGFBP-2 in the medium was significantly decreased by glucagon (100 μg/ml), thyroxine (0.1 and 1 n M), and IGF-I (10 and 100 ng/ml) and increased by ovine growth hormone (1 μg/ml), triiodothyronine (1 n M), E 2 (0.5 and 5 ng/ml), and epidermal growth factor (10 and 100 ng/ml). These results suggest that the secretion of two IGFBPs by striped bass liver is regulated by several hormones and growth factors.