Decreased pulmonary vascular responses in dogs with increased pulmonary blood flow

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Abstract
We wished to determine whether high pulmonary blood How alters the pulmonary vascular responses to the vasoconstrictors, hypoxia and prostaglandin F2α (PGF2α). Acute or chronic left pulmonary artery (PA) occlusion was performed in dogs in order to create high pulmonary blood How conditions. Right lung pulmonary vascular resistance (PVR) during normoxia was reduced by both acute and chronic left PA occlusion, suggesting passive vasodilatation. Increases in right lung PVR induced by hypoxia (10–15% O2) and PGF2α (0.8–4 μg kg−1min−1) were attenuated both in acute and chronic left PA occluded dogs. Since the reductions in responsiveness were similar with acute and chronic increases in blood flow, the attenuating effect of high blood How was not dependent upon morphologic changes in the vasculature. Pulmonary vascular responsiveness was probably reduced in these animals due to their dilated pulmonary vascular beds, consequent to the increased pulmonary blood How, thereby decreasing the effectiveness of smooth muscle contraction.