Serum somatomedin activity and cartilage metabolism in acutely fasted, chronically malnourished, and refed rats.

Serum somatomedin activity (SM-act) and cartilage metabolism were compared in acutely fasted, marasmic (M), and marasmic kwashiorkor (MK) rats. SM-act was estimated in the porcine bioassay. In vitro uptake of [35S]sulfate and [3H]methylthymidine in costal cartilage of the experimental animals during an incubation in medium immediately after sacrifice, called endogenous activity, and the effect of incubation in 20% normal human plasma after a preincubation of 22 h in medium only, called plasma responsiveness", were determined. Acutely fasted rats had lowered SM-act and a circulating heat-labile inhibitor. Endogenous activity and responsiveness of cartilage were depressed. MK rats (fed ad libitum a 0.5% casein, isocaloric food) showed a profound depression of growth and cartilage endogenous activity despite only partially reduced SM-act and increased responsiveness. M rats received normal food and were pair-fed with MK rats, consuming approximately 0.08 g/g BW . day. They showed very depressed SM-act and low endogenous activity, and responsiveness was increased, though less than in the MK rats. On refeeding M rats, SM-act and cartilage responsiveness increased, followed by an increase of endogenous activity. Catch-up growth was best related to [3H]methylthymidine incorporation by cartilage (endogenous activity). In conclusion, these two types of experimental chronic malnutrition induce a more diversified pattern than does acute fasting. During malnutrition, cartilage metabolism does not reflect bioassayable SM-act of serum but rather the other effects of the nutritional insult. On refeeding, the expected relationship of SM-act and cartilage metabolism is rapidly restored.