Modification of hypoxic pulmonary vasoconstriction by antigen challenge in sensitized sheep

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Abstract
The effects of inhalation challenge with Ascaris suum extract on pulmonary resistance (RL), arterial blood gas composition and pulmonary vascular resistance (PVR) were measured in conscious sensitized sheep during 13% O2 breathing. Skin test negative, nonsensitized sheep challenged with A. suum aerosol and sheep challenged with carbachol aerosol served as controls. The breathing of 13% O2 produced comparable decreases in arterial O2 tension (PaO2) and increases in PVR in the 3 groups. Subsequent A. suum challenge in the sensitized sheep was characterized by a 49% increase in mean RL, a 24% decrease in mean PVR and a decrease in mean PaO2 from 48 to 42 Torr, whereas these parameters remained unchanged in the skin test negative, non-sensitized sheep. Carbachol produced a 340% increase in mean RL, but no changes in PaO2 and PVR. Pretreatment with the prostaglandin inhibitor indomethacin (2 mg/kg) prevented the decrease in PVR (but not the increase in RL) after A. suum challenge in sensitized sheep, but it did not modify the effects of carbachol challenge on PVR and RL. Hypoxic pulmonary vasoconstriction is apparently blunted by inhalation challenge with antigen in conscious sensitized sheep. This is not related to bronchoconstriction per se but seems to be mediated by vasodilator prostaglandins.