Cecal ligation and puncture (CLP) has been extensively used as a model of sepsis in adult rats. It is not known if the response to sepsis is similar in young and adult rats. This investigation was done to compare hemodynamic and metabolic alterations in young (four to six weeks of age, 60 to 90 grams) and adult (12 to 14 weeks of age, 270 to 340 grams) rats after CLP. In one series of experiments, survival rate was determined for 96 hours, and in other experiments, mean arterial blood pressure (MAP), heart rate (HR), white blood cell count, hematocrit, platelets, plasma glucose, lactate, amino acids, blood urea nitrogen (BUN), blood and peritoneal cultures and resting energy expenditure (REE) were determined eight and 16 hours after CLP. Levels of glycogen in liver and muscle were determined 16 hours after CLP. Mortality rate was similar in young and adult rats. MAP was stable throughout the course of sepsis, with no significant differences between the two groups of rats. HR was higher in young rats at all times studied. The adult rats became hyperglycemic after CLP while the young were hypoglycemic eight hours after CLP but normalized at 16 hours. Plasma lactate and BUN were similar in the two groups of rats, and no alterations were seen during sepsis. Both young and adult rats became hypoaminoacidemic after CLP. The phenylalanine to tyrosine ratio increased in a similar manner during sepsis in both experimental groups. REE was higher in young than in adult rats, but no significant changes were observed during the course of sepsis in either group.(ABSTRACT TRUNCATED AT 250 WORDS)