A LOW-MOLECULAR-WEIGHT (25-KDA) IGF-BINDING PROTEIN IS INCREASED WITHGROWTH-INHIBITION IN THE FASTING STRIPED BASS, MORONE-SAXATILIS

The effect of fasting on circulating IGFBPs in the striped bass was as sessed in relation to changes in growth and metabolism. Thirty-day-fas ted (30DF) and 60-day-fasted (60DF) fish, and 60DF fish refed for 14 a dditional days (REFED), were compared with control, fed fish. Growth a nd metabolic status of each animal were assessed by determining body l ength (BL) and body weight (BW) changes, hepatosomatic index (HSI), co ndition factor (CF), and serum glucose concentration, and by assaying for incorporation of [S-35]sulfate (proteoglycan synthetic activity) a nd [H-3]thymidine (mitotic activity) in cerato-branchial cartilage exp lants in vitro. Serum IGFBP concentrations were assessed by a Western ligand blot procedure using I-125-labeled human IGF-I tracer. Both 30D F and 60DF fish exhibited hypoglycemia and reduced HSI and CF, and the ir BL and BW growth rates were significantly inhibited. Strongly corre lated with the inhibited body growth indices were significantly depres sed levels of cartilage [S-35]sulfate incorporation in both 30DF and 6 0DF animals. The 60DF group also exhibited reduced [H-3]thymidine inco rporation. Associated with this growth inhibition was a dramatic incre ase in the serum levels of a 25-kDa IGFBP (sbIGFBP-1). A 35-kDa IGFBP (sbIGFBP-3), on the other hand, was not significantly altered with fas ting. All fasting-induced changes in growth, metabolism, and IGFBP lev els were restored in the REFED group. These results demonstrate that a n IGFBP of low molecular weight is increased with growth inhibition in the fasting striped bass, suggesting that a teleost fish counterpart to mammalian IGFBP-1 may exist. (C) 1996 Academic Press, Inc.