A low-molecular-weight (25-kDa) IGF-binding protein is increased with growth inhibition in the fasting striped bass, Morone saxatilis.

The effect of fasting on circulating IGFBPs in the striped bass was assessed in relation to changes in growth and metabolism. Thirty-day-fasted (30DF) and 60-day-fasted (60DF) fish, and 60DF fish refed for 14 additional days (REFED), were compared with control, fed fish. Growth and metabolic status of each animal were assessed by determining body length (BL) and body weight (BW) changes, hepatosomatic index (HSI), condition factor (CF), and serum glucose concentration, and by assaying for incorporation of [35S]sulfate (proteoglycan synthetic activity) and [3H]thymidine (mitotic activity) in ceratobranchial cartilage explants in vitro. Serum IGFBP concentrations were assessed by a Western ligand blot procedure using 125I-labeled human IGF-I tracer. Both 30DF and 60DF fish exhibited hypoglycemia and reduced HSI and CF, and their BL and BW growth rates were significantly inhibited. Strongly correlated with the inhibited body growth indices were significantly depressed levels of cartilage [35S]sulfate incorporation in both 30DF and 60DF animals. The 60DF group also exhibited reduced [3H]thymidine incorporation. Associated with this growth inhibition was a dramatic increase 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 fasting. All fasting-induced changes in growth, metabolism, and IGFBP levels were restored in the REFED group. These results demonstrate that an 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.