Effects of changes in pH and CO2 on pulmonary arterial wall tension are not endothelium dependent

Department of Human Anatomy and Physiology, University College, Dublin 2, Ireland We examined the changes in isolated pulmonary artery (PA) wall tension on switching from control conditions (pH 7.38 ± 0.01, P CO 2 32.9 ± 0.4 Torr) to isohydric hypercapnia (pH change 0.00 ± 0.01, P CO 2 change 24.9 ± 1.1 Torr) or normocapnic acidosis (pH change 0.28 ± 0.01, P CO 2 change 0.3 ± 0.04 Torr) and the role of the endothelium in these responses. In rat PA, submaximally contracted with phenylephrine, isohydric hypercapnia did not cause a significant change in mean (± SE) tension [3.0 ± 1.8% maximal phenylephrine-induced tension (P o )]. Endothelial removal did not alter this response. In aortic preparations, isohydric hypercapnia caused significant ( P