Influence of the plasma ET-1 level on the vascular and respiratory systems of the pig

In this study the changes induced by the intravenous administration of ET-1 (50 ng/Kg) as a bolus injection or as an infusion to anesthetized spontaneously breathing pigs were correlated with plasma ET-1 levels. Both bolus administration and infusion of ET-1 caused statistically significant increases in arterial plasma ET-1 like immunoreactivity (ir) levels. Plasma Et-1-ir disappeared from the systemic circulation with a half-life of 1.5-1.9 min. Bolus administration of ET-1 caused a significant increase in mean pulmonary arterial pressure (MPAP) at 15 min. at which time the ET-1 plasma levels had returned to pre-injection values. This effect was not observed when the peptide was infused. ET-1 given by i.v. infusion increased total pulmonary vascualr resistances. The peptide caused a slight change in breathing pattern and passive compliance without significant changes in passive resistance. Our results suggest that in the pig ET-1 is a more potent constrictor of vascular than bronchial smooth muscle. However, changes in plasma ET-1 levels are not contemporary with altered vascular functions.