Fig. 3. Plasma levels of adrenaline (filled columns) and noradrenaline (open columns) during acute hypoxia (40 mmHg=5.3 kPa) in rainbow trout (Oncorhynchus mykiss) previously infused (0.2 ml min^–1) with nicotine (1.3x10^–5 mol kg^–1 h^–1) for 60 min under conditions of normoxia. To block specific receptors or enzymes, injections were administered at 40 min (20 min prior to hypoxia) using saline (control; N=17), atropine (muscarinic receptor antagonist; 1 µmol kg^–1; N=9), methysergide (serotonin receptor antagonist; 10^–8 mol kg^–1; N=9) or lisinopril (angiotensin-converting enzyme inhibitor; 10^–4 mol kg^–1; N=20). Values are shown as means + S.E.M. A dagger indicates a statistically significant difference (P<0.05) from the control value.