Lactate kinetics of rainbow trout during graded exercise: do catheters affect the cost of transport?

摘要

Changes in lactate kinetics as a function of exercise intensity have never been measured in an ectotherm. Continuous infusion of a tracer is necessary to quantify rates of lactate appearance (R-a) and disposal (R-d), but it requires double catheterization, which could interfere with swimming. Using rainbow trout, our goals were to: (1) determine the potential effects of catheters and blood sampling on metabolic rate ((M) over dot(O2)), total cost of transport (TCOT), net cost of transport (NCOT) and critical swimming speed (U-crit), and (2) monitor changes in lactate fluxes during prolonged, steady-state swimming or graded swimming from rest to U-crit. This athletic species maintains high baseline lactate fluxes of 24 mu mol kg(-1) min(-1) that are only increased at intensities >2.4 body lengths (BL) s(-1) or 85% U-crit. As the fish reaches U-crit, R-a is more strongly stimulated (+67% to 40.4 mu mol kg(-1) min(-1)) than R-d (+41% to 34.7 mu mol kg(-1) min(-1)), causing a fourfold increase in blood lactate concentration. Without this stimulation of R-d during intense swimming, lactate accumulation would double. By contrast, steady-state exercise at 1.7 BL s(-1) increases lactate fluxes to similar to 30 mu mol kg(-1) min(-1), with a trivial mismatch between R-a and R-d that only affects blood concentration minimally. Results also show that the catheterizations and blood sampling needed to measure metabolite kinetics in exercising fish have no significant impact on (M) over dot(O2) or TCOT. However, these experimental procedures affect locomotion energetics by increasing NCOT at high speeds and by decreasing U-crit.