METABOLISM Historical Perspective Definitions Methods Factors affecting Metabolic Rate

Antoine Lavoisier, 1773 heat produced by an animal is proportional to O2 consumed and CO2 produced so…“animal heat” is a byproduct of chemical reactions (metabolism)

Metabolic Rate = Total energy metabolized by an organism per unit time Maintenance, growth, reproduction, activity Food/fuel is oxidized to form ATP Metabolism = sum of all biological transformations of energy and matter Metabolic Rate = Total energy metabolized by an organism per unit time

Fuel + O2 CO2 + H2O + ATP + heat Energy Maintenance, growth, reproduction, activity Food/fuel is oxidized to form ATP Aerobic metabolism: Fuel + O2 CO2 + H2O + ATP + heat

Metabolic rate (MR, or E) = energy metabolism/time What does MR tell us? Overall rate of all physiological activities Resource needs Rate of production of new tissue

How can we measure MR? Fuel + O2 CO2 + H2O + ATP + heat Aerobic metabolism: Direct measures * Indirect measures

1. Direct measure of heat production = “direct calorimetry” Lavoisier & Laplace 79.9 cal melts 1 g ice (335 Joules)

How can we measure MR? Fuel + O2 CO2 + H2O + ATP + heat Aerobic metabolism: Direct measures * Indirect measures

X 2. Indirect measure of MR Fuel + 6O2 6CO2 + 6H2O + 2820 kJ food intake (fuel) O2 consumption CO2 production metabolic water X Complete oxidation of 1 mol glucose: Fuel + 6O2 6CO2 + 6H2O + 2820 kJ (C6H12O6) Amount of energy ingested, O2 consumed, or CO2 produced is directly related to amount of heat produced

Measuring O2 consumption: Closed system respirometry: Volume = 1 L Initial O2 = 21% 1000 mls 210 mls O2 Final O2 = 15% 150 mls O2 (1 hour) E = 0.06 L O2 /hr

Measuring O2 consumption: Open system respirometry (flow through): Constantly measure O2 consumption

Can be used to measure BOTH: Carbon Dioxide Production Respirometry: Open and Closed Can be used to measure BOTH: Oxygen consumption Carbon Dioxide Production

X 2. Indirect measure of MR Fuel + 6O2 6CO2 + 6H2O + 2820 kJ food intake (fuel) O2 consumption CO2 production metabolic water X Complete oxidation of 1 mol glucose: Fuel + 6O2 6CO2 + 6H2O + 2820 kJ (C6H12O6) Amount of energy ingested, O2 consumed, or CO2 produced is directly related to amount of heat produced BUT, heat production varies with foodstuff being oxidized…

BUT, heat production varies with foodstuff being oxidized… HEAT PRODUCTION (KJ) Per gram of food Per liter of O2 consumed Per liter of CO2 produced carbohydrates 17.1 21.1 21.1 38.9 19.8 27.9 lipids 17.6 18.7 23.3 Proteins (urea) Relatively constant, but not exact…

Heat produced per liter of O2 consumed (KJ/L) E = 0.06 L O2 /hr To convert to heat production: Use appropriate conversion factor (on left) - possible if you know food source -OR- 2) Use a “representative” conversion factor - 20.2 KJ/L Heat produced per liter of O2 consumed (KJ/L) Proteins (urea) lipids carbohydrates 21.1 19.8 18.7 Figure kJ from O2 example with mouse Thre is a more complicated method, but you need to measure both O2 consumption and CO2 production (rare)

How does energy use compare between lab and field? Values of MR in field are 3X higher than in lab!! Why? Field metabolic rate, (“FMR”) accounts for activity levels!

How can we measure FMR? Doubly labeled water: O H (Water) 18O H 3H dual isotope technique can use with free-ranging terrestrial animals no equipment attached to animal measures CO2 production O H (Water) 18O H 3H (Doubly-labeled water)

Doubly-labeled water 18O H 3H Inject into animal measure the “washout” rates of 3H and 18O 18O H 3H Inject into animal How does an animal lose hydrogens or oxygens? 3H lost as body water (urination, sweating, breathing…) 18O is lost as water and CO2 **Loss rate for 18O is steeper than for 3H

Doubly-labeled water isotope in body time 3H Initial sample 18O Final sample Convert to estimates of CO2 production…

Doubly-labeled water 3H : 18O inject a known quantity into animal let equilibrate, take blood sample release animal recapture, take 2nd blood sample isotope in body time 18O 3H Initial sample Final sample 3H : 18O

Doubly-labeled water Is it accurate? Limitations? 18O H 3H Predicts CO2 production w/in 3-8% Limitations? cost of analysis radioisotope use in field

What factors affect an animal’s metabolic rate? 1. Activity

What factors affect an animal’s metabolic rate? 2. Digestion: “specific dynamic action” = MR increase after a meal Amount Type Humans: 30% 1.4 kJ meal 5.6 kJ meal Why?

What factors affect an animal’s metabolic rate? 2. Digestion: “specific dynamic effect” = MR increase after a meal 3. Starvation Metabolic rate drops Why might this be adaptive?

What factors affect an animal’s metabolic rate? 4. Reproductive Status Humans: MR increases 30% near term -growth of fetus -fetal metabolic requirements -growth of mammary tissue Golden-mantled ground squirrels: - lactation takes up 1/3 of yearly energy budget!

What factors affect an animal’s metabolic rate? Many animals lower MR well below resting levels 5. Hibernation, Estivation, Torpor

6. Endothermy vs. Ectothermy Relatively high MR Relatively low MR

6. Endothermy vs. Ectothermy physiological correlates of huge MR difference Higher SA/V in lungs; complex, efficient heart Mitochondrial membrane SA ~4-5X bigger Greater enzyme activity

6. Endothermy vs. Ectothermy

What does measuring O2 consumption tell us? Endotherms: Ectotherms: basic metabolism basic metabolism thermoregulation digestion digestion activity activity reproduction/growth reproduction/growth “Basal MR” “Standard MR”

7. Temperature affects MR endotherms Basal Metabolic Rate: ?? Animal must be: “tnz” -in TNZ -resting -fasting BMR Thermoneutral zone = range of temps within which MR is unaffected by temp change

7. Temperature affects MR ectotherms temperature “Standard Metabolic Rate” Animal must be: SMR -fasting -resting * SMR is specific to body temp

7. Temperature affects MR ectotherms temperature MR temperature endotherms “tnz” SMR BMR BMR: -in TNZ -resting -fasting SMR: -fasting -resting -temperature specific

Metabolic Rate Summary What is MR and how can you measure it? Direct Colorimetry (heat production) Food Consumption Oxygen Consumption Carbon Dioxide Production Field metabolic rate Factors affecting metabolic rate: Activity Digestion Starvation Reproductive Status Hibernation, Estivation, Torpor Endothermy vs. Ectothermy Temperature

METABOLISM Historical Perspective Definitions Methods Factors affecting Metabolic Rate

BUT, heat production varies with foodstuff being oxidized… HEAT PRODUCTION (KJ) Per gram of food Per liter of CO2 produced Per liter of O2 consumed Proteins (urea) lipids carbohydrates 17.1 38.9 17.6 21.1 27.9 23.3 19.8 18.7 RQ 1.0 0.7 0.8 What if you aren’t sure what animal ate? “Respiratory Quotient” = Rate of CO2 production Rate of O2 production