Coping with an exogenous glucose overload: glucose kinetics of rainbow trout during graded swimming

Abstract

This study examines how chronically hyperglycemic rainbow trout modulate glucose kinetics in response to graded exercise up to critical swimming speed (Ucrit), with or without exogenous glucose supply. Our goals were 1) to quantify the rates of hepatic glucose production (Ra glucose) and disposal (Rd glucose) during graded swimming, 2) to determine how exogenous glucose affects the changes in glucose fluxes caused by exercise, and 3) to establish whether exogenous glucose modifies Ucrit or the cost of transport. Results show that graded swimming causes no change in Ra and Rd glucose at speeds below 2.5 body lengths per second (BL/s), but that glucose fluxes may be stimulated at the highest speeds. Excellent glucoregulation is also achieved at all exercise intensities. When exogenous glucose is supplied during exercise, trout suppress hepatic production from 16.4 ± 1.6 to 4.1 ± 1.7 μmol·kg(-1)·min(-1) and boost glucose disposal to 40.1 ± 13 μmol·kg(-1)·min(-1). These responses limit the effects of exogenous glucose to a 2.5-fold increase in glycemia, whereas fish showing no modulation of fluxes would reach dangerous levels of 114 mM of blood glucose. Exogenous glucose reduces metabolic rate by 16% and, therefore, causes total cost of transport to decrease accordingly. High glucose availability does not improve Ucrit because the fish are unable to take advantage of this extra fuel during maximal exercise and rely on tissue glycogen instead. In conclusion, trout have a remarkable ability to adjust glucose fluxes that allows them to cope with the cumulative stresses of a glucose overload and graded exercise.

Lean, mean, lipolytic machines: lipid mobilization in rainbow trout during graded swimming

“…The observed changes in COT with increasing speed (Fig. 2) are consistent with previous studies on doubly cannulated trout when metabolite kinetics were quantified (Choi and Weber, 2016;Teulier et al, 2013). In all cases, rainbow trout showed the highest COT at low swimming speeds before falling to minimal values above 1 BL s −1 .…”

“…1A). It is unlikely that U crit was underestimated here, however, because lower U crit were measured in previous studies on doubly cannulated trout of the same size, tested with the same swimming protocol, but accompanied by elevated blood lactate concentrations [U crit =2.9±0.2 BL s −1 (N=7) (Omlin et al, 2014), 2.8±0.1 BL s −1 (N=7) (Teulier et al, 2013) and 2.3± 0.1 BL s −1 (N=10) (Choi and Weber, 2016)]. The observed changes in COT with increasing speed (Fig.…”

How the expression of green fluorescent protein and human cardiac actin in the heart influences cardiac function and aerobic performance in zebrafish Danio rerio

“…() using mass spectroscopy for metabolomic analyses suggested that the expression of eGFP in transgenic mice caused changes in the maintenance of glucose delivery to the tissues as indicated by reduced levels of glycogen and glucose in the liver of eGFP mice. In addition, experiments by Choi & Weber () on rainbow trout Oncorhynchus mykiss (Walbaum 1792) have demonstrated that the C T at high levels of aerobic exercise decreased when the fish were supplied with exogenous glucose. But that the U crit was not affected.…”

Unexpected effect of insulin on glucose disposal explains glucose intolerance of rainbow trout

“…3B and 4B). Downregulating hepatic glucose production can be achieved by reducing glycogen breakdown, gluconeogenesis, or both (6,7). The weaker R a response of trout could be explained by the fact that insulin impairs glycogen breakdown in mammals but may not do so in fish.…”