Endotoxin alters hypoxic pulmonary vasoconstriction in isolated rat lungs

Hypoxic pulmonary vasoconstriction (HPV) is an important mechanism for maintaining oxygenation, which may be altered by endotoxin. We determined that acute endotoxemia alters the HPV response secondary to changes in endothelium-derived vasoactive products. Rats were treated with Salmonella typhimurium lipopolysaccharide (LPS; 15 mg/kg i.p.) either 1 to 6 h before lung isolation and compared with control rats (no LPS). Additional 6-h LPS-treated and control rats were pretreated with either indomethacin (15 mg/kg i.p.), a cyclooxygenase inhibitor, or bosentan (10 mg/kg po), a nonselective endothelin-receptor antagonist. The rats lungs were isolated and challenged with 3% O2 for 10 min to elicit HPV responses before and after nitric oxide (NO) synthase inhibition with N omega-nitro-L-arginine methyl ester (L-NAME; 100 microM). LPS (6 h) significantly increased the peak HPV responses by 108%. L-NAME had no significant effect in LPS-treated lungs but increased the peak HPV response in control lungs to levels equal to LPS-treated lungs. Bosentan increased the peak HPV response in all lungs, and indomethacin increased the peak HPV in LPS-treated lungs. The HPV response was sustained in control lungs at 10 min and in additional 20-min studies. In contrast, in LPS-treated lungs the HPV response faded after 10 min to levels equal to control, and in 20-min studies it faded by 82% to levels significantly less than in control lungs. The 10-min fade in LPS-treated lungs was attenuated by indomethacin (51%) and bosentan (80%) but not by L-NAME. In conclusion, acute endotoxemia with LPS increased the peak HPV response, but this effect was not sustained and by 20 min was nearly abolished. Inhibition of endogenous NO by LPS may explain the increased peak HPV response, but NO is not involved in the fade. The fade is at least partially due to increased vasodilating cyclooxygenase products and endothelins.