Fig. 2. Heart rate (A; f_H) and mean circulatory filling pressure (B; MCFP) in untreated, prazosin-treated (1 mg kg^–1) and atropine+prazosin treated trout (1 mg kg^–1 and 1.2 mg kg^–1, respectively) during control conditions (white bars), post-(grey bars) and pre-branchial occlusion (black bars). Control heart rate represents pooled mean values + S.E.M. of 120 s prior to occlusion. Heart rate during post- and pre-branchial occlusion are mean values + S.E.M. of the last 20 s of the 30 s occlusion. MCFP is measured in unstimulated fish and immediately following 30 s of stimulation with post- or pre-branchial occlusion. Statistically significant difference ^*from the control within each treatment and for control values between treatments (Px0.05).