Depressed blood neutrophil response to lithium stimulation in newborn rats

The blood neutrophil response to lithium chloride challenge was determined in one-day-old and young adult rats to test the hypothesis that granulocytopoiesis is less efficient in neonates than in adults. Adult animals responded rapidly to lithium chloride treatment, showing a 134% increase in blood neutrophils on the second day of exposure and ultimately increasing by 260% by the tenth day. Newborn rats on the other hand, showed a 25% decrease in blood neutrophils after one day of treatment with lithium, then remained at that or at pretreatment levels throughout the subsequent 10 days. These observations suggest that hematopoietic tissue in the newborn is less responsive than is that of adults.