Fig. 1. The response of isolated vessels to hypoxia (N₂) or H₂S (1 mmol l^–1) is temporally and spatially similar, but vessel-specific. (A) Lamprey dorsal aorta (DA), (B) rat thoracic aorta (TA), (C) rat pulmonary artery (PA) pre-contracted with 10^–6 mol l^–1 norepinephrine (NE), (D) bovine pulmonary artery (PA) pre-contracted with 10^–7 mol l^–1 U-46619. A slight relaxation of bovine PA often precedes the hypoxic contraction; the H₂S contraction appears mono-phasic, but it also is multi-phasic (see Fig. 2). Horizontal lines=10 min; vertical lines=0.5 g tension; W=wash. (1), (2) and (3) in C, indicate stages in the multiphasic response. (A) N₂ trace adapted from (Olson et al., 2001), with permission; (C) H₂S trace adapted from Dombkowski et al. (Dombkowski et al., 2005), with permission.