INFLAMMATORY EDEMA AND MIGRATION OF LEUKOCYTES BUT NOT PHAGOCYTOSIS ARE REDUCED IN YOUNG-RATS

1. Newborn and old individuals are more susceptible to infection. In t his study vascular permeability as well as the migration of neutrophil s and mononuclear cells were determined in male Wistar rats aged 3, 8 and 16 weeks (N = 5-7 animals per group). The increase in vascular per meability induced by the ip injection of carrageenin in 3-week old rat s was 2-fold lower than observed for 8- or 16-week old animals. 2. The migration of neutrophils and mononuclear cells into the peritoneal ca vity induced by carrageenin and thioglycollate was lower in 3-week old rats (1.4 +/- 0.4 x 10(6) and 1.22 +/- 0.27 x 10(6)) compared to 8-we ek (4.5 +/- 0.25 x 10(6) and 4.16 +/- 0.38 x 10(6)) and 16-week old an imals (5.75 +/- 1.0 x 10(6) and 5.5 +/- 0.5 x 10(6)), respectively. Th e number of resident cells in the peritoneal cavity of 3-week old rats was also only 15% of that observed for the older rats. The reduced ce ll migration in younger rats was not the result of leucopenia since th e white cell counts of these animals were significantly higher than th at of animals aged 8 or 16 weeks (15 +/- 2 x 10(6) vs 8 +/- 1 x 10(6) and 7 +/- 1 x 10(6)/ml of blood, respectively). 3. Although the chemot actic response was lower in 3-week old rats compared to 16-week old an imals, the ability of both neutrophils and macrophages from young rats to phagocytose zymosan was similar to that of older animals (60-80%). 4. These results suggest that newborn susceptibility to infection may be due to the reduced ability of leucocytes to accumulate at the infl ammatory site, rather than to their reduced phagocytic activity.