Roles of lactate and catecholamines in the energetics of brief locomotion in an ectothermic vertebrate

Abstract.

We have investigated the magnitude and duration of excess post-exercise oxygen consumption (EPOC) in a lizard following a single bout of vigorous exercise of 5–60 s, common activity durations for many ectothermic vertebrates. Desert iguanas (Dipsosaurus dorsalis) were run for 5 s, 15 s, 30 s, or 60 s. Oxygen consumption ($\dot VO_2$ ) increased from 0.16 ml O₂ g^–1 h^–1 at rest to 1.3–1.6 ml O₂ g^–1 h^–1 during 5–60 s of running. EPOC duration increased with activity duration, ranging from 35–63 min. EPOC volume, the excess oxygen consumed post-exercise, doubled from 0.13 ml O₂ g^–1 following 5 s of activity to 0.25 ml O₂ g^–1 after 60 s. EPOC represented 91–98% of the total metabolic expense of the activity. EPOC durations were always shorter than the period required for lactate removal, illustrating that these two processes are not causally related. Alpha- and beta-adrenergic receptor blockade by phentolamine and propranolol had no effect on resting $\dot VO_2$ but depressed excess post-exercise oxygen consumption volumes 25–40%. The extent of catechol stimulation post-exercise may be motivation or stimulus dependent. The data indicate that metabolic elevations post-exercise represent the majority of activity costs in lizards. The study suggests that EPOC of ectothermic vertebrates is sensitive to exercise duration and catecholamine release post-activity, even when activity periods are less than 60 s in duration.