Reduced relaxant potency of nitroprusside on pulmonary artery preparations taken from rats during the development of hypoxic pulmonary hypertension.

摘要

1. Relaxant responses to nitroprusside were examined on U46619-contracted pulmonary artery ring preparations from rats exposed to hypoxia, in chambers containing 10% oxygen, for 1, 3, or 14 days, or for 14 days followed by 12 days in room air. Control rats were housed in room air. 2. After 3 days of hypoxia (but not 1 day), rats had elevated pulmonary artery pressure, right ventricular hypertrophy and polycythemia. After 14 days of hypoxia there was, in addition, hypertrophy of the pulmonary artery. In rats returned to room air for 12 days after 14 days of hypoxia, there was still some right ventricular and vascular hypertrophy but no increase in pulmonary artery pressure or polycythemia. 3. The potency (neg log EC50) of nitroprusside on pulmonary arteries taken from rats after 3 or 14 days of hypoxia was significantly less than on preparations from control rats (3 and 11 fold, respectively). This was not seen after 1 day of hypoxia or after 14 days of hypoxia followed by 12 days in room air. Removal of the endothelium from the preparations had no effect on the potency of nitroprusside in control or hypoxic rats (14 days). 4. In preparations from hypoxic, but not control, rats (14 days), the maximum response to nitroprusside was > 100% (177% reversal of the U46619 contraction) in the absence, but not in the presence, of the endothelium, indicating that pulmonary arteries from hypoxic rats had inherent tone which could be counteracted by a relaxing factor from the endothelium. 5. Exposure of rats to hypoxia (14 days) did not affect the potency of nitroprusside on aorta or trachea.(ABSTRACT TRUNCATED AT 250 WORDS)