Endotoxin administration decreases plasma insulin-like growth factor (IGF)-I and IGF-binding protein-2 in Angus × Hereford steers independent of changes in nutritional intake

Abstract

Abstract Endotoxemia and sepsis cause severe shifts in metabolism towards catabolic events. The objective of the research was to determine whether endotoxin administration changes plasma concentrations of IGF-I and IGF-binding protein-2 (IGFBP-2) in Angus × Hereford steers. In Experiment 1, mean feed intake in endotoxin-treated steers (n=6) decreased 60% within the first 24 h after endotoxin and averaged, for the duration of the 96 h test period, an intake 35·5% lower than the mean ad libitum intake recorded prior to endotoxin. Plasma concentrations of IGF-I averaged 182 ng/ml in steers before endotoxin (E. coli, 055:B5, 0·2 μg/kg, i.v. bolus) and decreased an average of 24·2% at 24 to 96 h after endotoxin. In Experiment 2, a paired feeding strategy was used to determine whether the reduced feed intake was a significant factor in changing plasma concentrations of IGF-I and IGFBP-2 after endotoxin challenge. Steers were divided into endotoxin (0·2 μg/kg, i.v., n=6) or control (saline, n=6) n=3) treatments. Each of three endotoxin-treated steers was paired to a specific control. In this fashion, the adjusted feed intake of each endotoxin-treated steer was fed to it's paired control every 24 h through 96 h after endotoxin. After endotoxin, plasma concentrations of tumour necrosis factor-α (TNF) and cortisol peaked at one and three hours, respectively. TNF returned to baseline by 8 h while cortisol returned to baseline by 24 h. Feed intake declined 60% at 24 h in endotoxin-treated steers but returned to normal by 96 h. Plasma IGF-I remained more than 28% lower in endotoxin-treated steers than in control steers through 96 h (P<0·05). IGFBP-2 was 61% lower in endotoxin-treated than control steers at 24 h (P<0·05) and gradually returned to normal levels by 96 h. The level and duration of feed offered pair-fed control steers did not affect any measured parameter. The data suggest that decreases in plasma IGF-I and IGFBP-2 which occur after endotoxin administration are not fully explained by transient changes in nutrient intake and may constitute a part of the mechanism underlying shifts in metabolism that accompany endotoxemia. The partitioning of IGFs to tissues by altered patterns of IGFBPs may be another mechanism through which the classical anabolic character of IGF-I is modified during acute disease stress. Journal of Endocrinology (1995) 144, 109–117