Changes in plasma endothelin-1 concentration during blood volume depletion and expansion: role of the cardiopulmonary baroreflex.

To study the relationship between blood volume and the plasma level of endothelin-1 (ET-1), we examined the effects of blood volume depletion and expansion on the plasma ET-1 level in the rat. Anesthetized Wistar rats were subjected to hemorrhage (7 ml/kg), blood transfusion (7 ml/kg), or sham treatment. The same blood volume depletion and expansion were performed in other groups of rats, after bilateral cervical vagotomy or administration of intravenous atropine, to examine the role of the cardiopulmonary baroreflex. Hemorrhage produced mild decreases in the central venous pressure and arterial blood pressure, and an increase in the heart rate. Blood transfusion caused the opposite responses. The plasma ET-1 level was significantly higher in the volume-depleted rats (4.7 +/- 0.4 pg/ml, mean +/- SE, p < 0.05 vs. control), and was lower in the volume-expanded rats (2.6 +/- 0.2 pg/ml, p < 0.05) than in the control group (3.5 +/- 0.3 pg/ml). In the vagotomized rats, the blood volume depletion decreased and the volume expansion increased the central venous pressure and the arterial pressure, but they did not change the heart rate or the plasma ET-1 level. Vagal efferent inhibition with atropine did not affect the volume-induced changes in the plasma ET-1 level. These results indicate that the plasma level of ET-1 increases with blood volume depletion, and decreases with volume expansion. The cardiopulmonary baroreflex may play an important role in the regulation of plasma ET-1 levels when the blood volume is altered.