Fig. 6. Tension recordings showing the effect of ACh on the crocodile right aorta with the endothelium intact (A) and with the endothelium removed (B). Haematoxylin and Eosin staining was used to verify that the endothelium was present or removed (see inset). The preparations were exposed to ET-1 (10^-8 mol l^-1) until a maximum constriction was achieved, and then ACh (10^-5 mol l^-1) was added. Acetylcholine only induced a vasodilation in the vessels with the endothelium intact (N=5).