Cardiovascular effects of endothelin in chronic hypoxic rats

This study was undertaken to investigate the effects of endothelin (ET) on cardiovascular function in chronic hypoxic rats (HA) and sea level controls (SL). Catheters were placed in femoral and pulmonary arteries for measurements of mean systemic arterial pressure (Psa) and mean pulmonary arterial pressure (Ppa). The cardiac output was measured by thermodilution method. It is very interesting to find that intravenous injection of ET (0.2 and 1 nmol/kg) caused a decrease in pulmonary arterial pressure (from 44 +/- 2.6 to 36 +/- 1.9 mmHg, p < 0.05) which sustained for about 10 min while the systemic arterial pressure rise (1 nmol/kg) or no significant change (0.2 nmol/kg) in the HA rats. The depressor action of ET is mainly resulted from the drop of cardiac output in HA rats, since the pulmonary vascular resistance resisted to the action of ET in those chronic hypoxic rats could be due to a simple loss of reaction to ET or the release of vascular dilators which balance the ET vasoconstrictive action. This report also found indomethacin and saralasin did not involve the action of ET on pulmonary arterial depression.