Functional development of phagocytic activity of the spleen.

The improvement of phagocytic activity of organs was studied in rats by means of 99mTc sulfur colloid uptake. This function was measured in the newborn rat, 1-, 2-, 3-, and 4-week-old baby rats and in adult rats. Organ distribution of the 99mTc-S-colloid showed marked phagocytic activity of the liver in all age groups including the newborn period. Phagocytosis in bone marrow was markedly increased and that in spleen markedly decreased at the time of birth. However, rapid improvement of phagocytic activity with age was prominent in the spleen.