RETICULOENDOTHELIAL SYSTEM UPTAKE OF INFUSED I-125 TRYPSIN IN NEWBORNAND ADULT-RATS

Previous studies have demonstrated enhanced intestinal trypsin uptake and decreased liver clearance of trypsin in newborn rats compared to a dults. In order to examine the effectiveness of the reticuloendothelia l system (RES) in clearing trypsin, bovine trypsin (1.25 mg/100 g body weight) plus trace I-125-trypsin were injected into the portal vein o f 2-week-old (n = 57) and adult (n = 44) control rats or following RES stimulation using intraperitoneally injected lipopolysaccharide or RE S suppression with intraperitoneally injected oleic acid emulsion. Pla sma, liver and spleen I-125 activities were assessed at 1, 5 or 15 min following infusion in control, stimulated and suppressed animals. New born control rats had significantly increased I-125 plasma levels with decreased liver and spleen I-125 activity compared to control adults. RES stimulation in the newborns did not lead to any change in liver o r plasma levels although splenic values increased while adults had a d ecrease in liver I-125 activity. RES suppression in the newborns led t o increased plasma and decreased spleen I-125-trypsin values while adu lt rat levels were unchanged. The immature reticuloendothelial system in newborns is poorly responsive to RES stimulation although it can be made even further inefficient by RES suppression. The combination of RES immaturity and lack of response to stimulation may make newborns s usceptible to proteolytic damage, especially during times of increased systemic levels of proteolytic enzymes.