Effect of hypoxia on plasma immunoreactive endothelin-1 concentration in anesthetized rats

The present study was designed to examine the possible influence of hypoxia on plasma immunoreactive (ir) endothelin-1 concentrations in anesthetized rats. Plasma ir-endothelin-1 concentration, blood pressure, heart rate, and arterial gas levels were measured 1 and 2 hours after exposure to normoxic (20% O2), mildly hypoxic (16% O2), and severely hypoxic (12% O2) gas. Mean blood pressure and heart rate were significantly decreased and the plasma ir-endothelin-1 concentration was significantly increased in severely hypoxic rats after both 1 and 2 hours. In mildly hypoxic rats, the plasma ir-endothelin-1 concentration was also increased, but this value was not statistically significant. The plasma ir-endothelin-1 concentration was inversely correlated with arterial blood PO2 in the three study groups (normoxic, mildly hypoxic, and severely hypoxic rats) after 1 hour (n = 18, r = -.74, P less than .01), and after 2 hours (n = 18, r = .71, P less than .01). Our results indicate that severe hypoxia increased the plasma ir-endothelin-1 level in anesthetized rats. The observed increase in plasma ir-endothelin-1 level may represent a compensatory mechanism against the blood pressure reduction associated with severe hypoxia.