Response of lobar vessels to hypoxic pulmonary hypertension.

Lobar pulmonary arteries demonstrate increased production of extracellular matrix components in response to hypertension, but biosynthetic changes in lobar veins have not been described. We report here that steady-state levels of mRNAs for tropoelastin and type I procollagen in proximal lobar veins were decreased in calves with hypoxic pulmonary hypertension relative to levels detected in veins from normotensive animals. In contrast, transcript levels were elevated in lobar arteries from hypertensive calves. Histologically, medial thickening and hypertrophy were apparent in distal lobar arteries from pulmonary hypertensive calves, but at this level no structural changes were observed in veins. These results indicate that the synthetic response to hypoxic pulmonary hypertension is complex, with different alterations in the expression of extracellular matrix components in the pulmonary arterial and venous circulations.