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

We have investigated the magnitude and duration of excess post-exercise oxy gen consumption (EPOC) in a lizard following a single bout of vigorous exer cise 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 ((V) over dot O-2) increased from 0.16 ml O-2 g(-1) h (-1) at rest to 1.3-1.6 ml O-2 g(-1) h(-1) during 5-60 s of running. EPOC d uration increased with activity duration, ranging from 35-63 min. EPOC volu me, the excess oxygen consumed post-exercise, doubled from 0.13 ml O-2 g(-1 ) following 5 s of activity to 0.25 ml O-2 gl 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 t hat these two processes are not causally related. Alpha- and beta-adrenergi c receptor blockade by phentolamine and propranolol had no effect on restin g (V) over dot O-2 but depressed excess post-exercise oxygen consumption vo lumes 25-40%. The extent of catechol stimulation post-exercise may be motiv ation or stimulus dependent. The data indicate that metabolic elevations po st-exercise represent the majority of activity costs in lizards. The study suggests that EPOC of ectothermic vertebrates is sensitive to exercise dura tion and catecholamine release post-activity, even when activity periods ar e less than 60 s in duration.