Intrinsic microbicidal activity and pulmonary hypertension in isolated newborn piglet lungs

The lung appears to be one of the dominant sites of bacterial clearance from the blood of infant piglets. Part of the lung bacterial clearance involves activation of an oxygen radical bactericidal mechanism that may be central to induction of acute pulmonary hypertension. The present study determined whether this bactericidal activity was intrinsic to resident lung cells. Isolated piglet lung preparations perfused with blood-free salt solution were used to delineate the amount of group B streptococci (GBS) extracted and killed upon transit through pulmonary vasculature. Approximately 45% of infused GBS was deposited in the lung during a single pulmonary transit, whereas nearly 40% of the organisms sequestered in the lung were killed within a 30-min period. Pretreatment with dimethylthiourea, a scavenger of hydroxyl radical that inhibits GBS-induced pulmonary hypertension, attenuated both bacterial uptake and killing to similar extents. Along with its deposition in the lung, GBS also induced concentration-dependent increases in total pulmonary resistance, which were related principally to increases in upstream arterial resistance. Lung weight also increased in a concentration-dependent manner. Both the increase in total pulmonary resistance and lung weight were temporally related to elevation in perfusion medium content of the stable thromboxane degradation product, thromboxane B2. Pretreatment with indomethacin, a prostaglandin H synthase inhibitor, or sodium(E)-3[4-(1-imidazolyl-methyl)phenyl]-2-propenoic acid a thromboxane synthase inhibitor, reduced GBS-induced pulmonary hypertension and edema. These results suggest that, in isolated piglet lungs, GBS evokes an intrinsic bactericidal response residing within lung cells, probably pulmonary intravascular macrophages, which may be responsible for the initiation of pulmonary hemodynamic changes.(ABSTRACT TRUNCATED AT 250 WORDS)