INDUCTION OF AN ACUTE-PHASE RESPONSE IN LAMBS CAUSES AN INCREASE IN PLASMA-LEVELS OF GH AND IGF-I

GH and IGF-I plasma concentrations were measured in lambs during an ac ute phase response induced by an intrathoracic injection of yeast. The acute phase response was indicated by reduced feed intake, weight los s and an increase in plasma concentrations of the acute phase protein haptoglobin. Intensive blood sampling on day 1 revealed elevated basal concentrations of GH in the yeast-injected group compared with concen trations in pair weight and ad libitum fed control lambs. This suggest s that at the beginning of an acute phase response there is an increas e in either GH secretion or the half life of GH. No evidence of a spec ific GH-binding protein in sheep plasma could be detected. IGF-I conce ntrations in the yeast-injected group remained constant for 3 days the n increased to a peak level at day 6. In contrast, plasma IGF-I concen trations were depressed from days 3 to 6 in the pair weight control gr oup and they were unchanged in the ad libitum fed controls. When the I GF-I concentrations were elevated in the yeast-injected group, this gr oup had a higher daily weight gain despite their lower feed intake com pared with the ad libitum fed controls. These results suggest that IGF -T may be associated with the increase in weight in the late stage of an acute phase response during recovery from an infection or injury. D ay 1 GH peak amplitude concentrations in the yeast-injected lambs were negatively correlated with IGF-I concentrations on the following 2 da ys yet in the pair weight lambs the correlation was in a positive dire ction suggesting that the relationship between GH and IGF-I is differe nt between animals that lose weight during an acute phase response and animals that lose weight because of feed restriction.