Impaired hepatic reticuloendothelial bacterial clearance in fetal and newborn rats

Abstract

Sepsis is a major cause of morbidity and mortality in the neonate. This study evaluates the role of the hepatic reticuloendothelial system (RES) in removing blood-borne bacteria in fetal, newborn, and suckling rats as compared to older rats. Sprague-Dawley rats were placed in four groups: group I (n = 8) were fetuses studied at hysterotomy at 20 days' gestation (body wt. 5.1+/−0.4 g), group II (n = 10) 2-week-old suckling (body wt. 33.4+/−3.2 g), group III (n = 10) 4-week-old (body wt. 68.3+/−5.4 g), and group IV (n = 10) 6-week weanling rats (body wt. 140+/6 g). ³⁵S-radiolabeled viable Escherichia coli (10⁹ bacteria/ml) was injected according to body weight via the tail vein in groups II, III, and IV and via the umbilical vein in group I. At 10 min, bacterial distribution in the liver, spleen, kidneys, and lungs was determined. Tissue samples (50–100 mg) from each organ were processed for liquid scintillation counting. The final distribution of bacteria was calculated from the input specific activity (dpm/bacteria) and expressed as mean percentage of injected viable E. coli per g tissue and per total organ weight. The ability of the liver RES of fetal and neonatal rats to remove blood-borne bacteria was impaired (61.4+/−2, 53.8+/−8.2%, respectively) compared to controls (74.6+/−8.0, P <0.001). This was compensated for by an increase in lung localization of bacteria. The lung has a relatively poor capacity to kill sequestered bacteria, which may play a role in the occurrence of bacterial re-emregence and systemic sepsis in the neonate.