HANCOCK, T.V.*; CROCKER, C.E.; GLEESON, T.T.: Contributions to elevated metabolic rates during recovery, the excess post-exercise oxygen consumption (EPOC), in the desert iguana (Dipsosaurus dorsalis).
Metabolism remains elevated for some time following vigorous activity in Dipsosaurus. This excess O2 consumption may be quantified as EPOC, a volume of O2 representing metabolic costs of recovery. To analyze these costs, Dipsosaurus (n=25) were run at a maximal treadmill intensity (2.4 m/s) for 15 sec while VO2 was monitored. Animals were removed and sacrificed at rest, directly post-exercise or following 3, 10 or 60 min of recovery. Hindquarters were immediately freeze-clamped and the gastrocnemius (GAS), red iliofibularis (rIF) and white iliofibularis (wIF) were analyzed for ATP, phosphocreatine (PCr), and lactate (LA) using HPLC. GAS resting levels measured 8.7 mM ATP, 40.3 mM PCr and 4.0 mM LA and were more similar to wIF than rIF in all measures. Post-exercise ATP decreased 13%, PCr decreased 78% and LA increased 966%. ATP showed the greatest decrease in wIF, while PCr showed the greatest decrease in rIF. PCr and ATP returned to resting levels within 3-10 min, while LA remained above resting levels for the entire 60 min. VO2 recovery required 44 min and EPOC measured 0.104 ml O2/g. Modeling of individual components of EPOC indicate the majority of energetic outlay may be due to phosphagen replenishment (28%); glyconeogenic lactate removal (42%); and catecholamine stimulation (17%). Phosphagen replenishment is complete during the first 10 min of EPOC and would require 67% of O2 consumption during this time. Glyconeogenesis likely does not begin until after this time and would account for 72% of EPOC from 10 to 44 min. This model is sensitive to assumptions of % active muscle, P:O ratios and lactate fate which will be discussed. NSF#97240140.
