Characterization of endothelin receptors in newborn piglet lung

Endothelins (ET-1, ET-2, and ET-3) cause dilation and constriction as a result of binding to different ET receptors. ETA receptor is responsible for the vasoconstrictor response, while ETB receptors lead to vasodilation (ETB1) or vasoconstriction (ETB2). Although the effects of ETs have been described in the neonatal pulmonary vasculature, ET receptors have not been characterized extensively. Therefore, in newborn piglets we aimed to characterize ET receptors by studying 1) in isolated perfused lungs the effects of ET-1, ET-3, and the ETB receptor agonists sarafotoxin S6c (S6c) and BQ-3020 on perfusion pressure with or without an ETA antagonist, BQ-123, or an ETB1 antagonist, RES-701-1, and 2) the concentration-dependence of ET-1 and ET-3 on their binding to microsomes from arteries and veins of piglet lungs. ET-1, ET-3, S6c, and BQ-3020 cause an early-onset dilation followed by a late-onset constriction. The dilator response to ET-3 is blunted by RES-701-1 (P < 0.005), while the inhibition of the dilator response of ET-1 almost reaches significance (P = 0.06). BQ-123 inhibits incompletely (P < 0.05) the constrictor response to ET-1, while it does not alter the response to ET-3. This suggests that constriction may follow binding to ETA as well as ETB2 receptors. Binding studies reveal that ET receptors are abundant in pulmonary vessels. ETA receptors are predominant, but ETB1 and likely ETB2 receptors are also present. Also, receptor affinities are higher in veins than in arteries.(ABSTRACT TRUNCATED AT 250 WORDS)