Fig. 2. Inhibition of hypoxic responses by inhibitors of H₂S synthesis. (A) Three consecutive exposures to hypoxia (N₂) produce identical contractions in lamprey dorsal aorta (DA; left bars) whereas in parallel experiments the second and third hypoxic contractions are significantly (^*) inhibited after addition of hydroxylamine (H), an inhibitor of cystathionine β-synthase (CBS) and cystathionine -lyase (CSE). (B) Hypoxic relaxation of a norepinephrine-contracted (NE; 10^–6 mol l^–1) rat thoracic aorta (TA) is significantly (^*) inhibited by the CSE inhibitor propargyl glycine (P). (C) Hypoxic contractions of bovine pulmonary arteries (PA) are not affected by propargyl glycine (P) but are increasingly inhibited by the CBS inhibitor aminooxy acetate (A), hydroxylamine (H), or a combination of all three inhibitors (HPA). Means ± s.e.m.; responses are normalized to an initial KCl (80 mmol l^–1) or NE contraction. (Adapted from Olson et al., 2006.)