Acetylcholine-induced inhibition of responses to field stimulation in rabbit pulmonary artery is unaffected by endothelium removal.

Acetylcholine (0.01-10 mumol litre-1) relaxed normal rings (endothelium-retained) of rabbit pulmonary artery precontracted with clonidine (10 mumol litre-1) while preparations with the endothelium removed responded with contraction only. Removal of the endothelium had no effect on contractions of the preparation to clonidine or field stimulation of the adventitial nerves (2 Hz, 10 s). Furthermore, the inhibitory effect of acetylcholine (0.3 and 1.0 mumol litre-1) on contractions induced by field stimulation was not influenced by the vascular endothelium.