Local inflammatory reactions in juvenile and adult rats

The present investigation was designed for the study of the early phases of local inflammatory reactions in juvenile and adult rats. A recently developed experimental model, based on continuous diffusion of an inflammation inducing agent, was applied. Thirty-five juvenile (6 weeks) and thirty-five adult (6 months) rats were used. Two sterile teflon tables were implanted subcutaneously on the back of each animal on each side of the midline. After three weeks, when a connective tissue capsula had developed, the tablets were replaced by one test tablet (containing lipopolysaccharide) and one fresh teflon tablet, respectively. In each group five animals were sacrificed on day 0 and fifteen animals on each of day 7 and 21. Biopsies comprising tablet and surrounding tissue were taken and exposed to routine histological treatment. The total number of cells was assessed in four defined areas in connection with each tablet. Cells classified as leukocytes were recorded separately. The analysis was performed at 1000x magnification in a light microscope. During the first seven days an increase in the number of leukocytes was seen in the tissue adjacent to the test tablets in both young and adult rats. After 21 days the number of leukocytes was still high in the adult group while in the juvenile group the number of leukocytes returned to the base-line level.