In vivoregulation of rainbow trout lipolysis by catecholamines

Abstract

SUMMARYLipolysis provides fatty acids that support key life processes by functioning as membrane components, oxidative fuels and metabolic signals. It is commonly measured as the rate of appearance of glycerol (R a glycerol). Its in vivo regulation by catecholamines has been thoroughly investigated in mammals, but little information is available for ectotherms. Therefore, the goals of this study were, first, to characterize the effects of the catecholamines norepinephrine (NE) and epinephrine (Epi) on the lipolytic rate of intact rainbow trout (Oncorhynchus mykiss) and, second, to determine whether the plasma glycerol concentration is a reliable index of R a glycerol. Our results show that baseline R a glycerol (4.6±0.4 μmol kg -1 min -1) is inhibited by NE (-56%), instead of being stimulated, as in mammals, whereas Epi has the same activating effect in both groups of vertebrates (+167%). NE-induced inhibition of fish lipolysis might play a particularly important role during aquatic hypoxia, when survival often depends on regulated metabolic depression. The plasma glycerol concentration is a poor predictor of R a glycerol, and it should not be used as an index of lipolysis. Trout maintain a particularly high baseline lipolytic rate because only 13% of the fatty acids provided are sufficient to support total energy expenditure, whereas the remaining fatty acids must undergo reesterification (87%).

Effects of environmental hypoxia on cardiac energy metabolism and performance in tilapia

“…NEFA are a metabolically dynamic lipid fraction of the blood and are important for fatty acid oxidation (24). A ϳ80% decrease in NEFA supply to tissues, as seen in this study, could therefore significantly reduce substrate oxidation and Ṁ O 2 of tissues and, as also suggested by Magnoni et al (32), may contribute to metabolic rate depression. It may also lessen potential effects of impaired fatty acid oxidation in hypoxia.…”

Molecular Analysis, Tissue Profiles, and Seasonal Patterns of Cytosolic and Mitochondrial GPDH in Freeze-Resistant Rainbow Smelt (Osmerus mordax)

“…The activity of cGPDH in the muscle of salmon (10% of smelt liver) was the next highest of all tissues evaluated but was not matched to a temperature-associated increase in glycerol accumulation. The elevated levels of cGPDH activity in salmon muscle may be related to a high ratio of lipolytic rate to metabolic rate, as exists in the trout (Magnoni et al 2008), and, as such, might reflect high rates of lipid recycling rather than a specific role in glycerol production. This explanation leads to the concept that glycerol production in smelt liver may involve cycling tbrough the triglycéride pool as opposed to a direct dephosphorylation of G3P, as previously proposed , This issue is beyond tbis study, and, regardless, botb of the aforementioned potential pathways to glycerol require cGPDH, The seasonal profile of cGPDH transcript levels in smelt tracking ambient water temperature confirms that presented by Liebscber et al, (2006) and extends tbe findings, witb tbe inclusion of fisb beld at a non-glycerol-producing temperature.…”

Metabolic fuels: regulating fluxes to select mix

“…This process of lipolysis can be quantified in vivo by monitoring the rate of appearance of glycerol in the circulation (R a glycerol). Measurements of R a glycerol in salmonids (Bernard et al, 1999;Magnoni et al, 2008b) and migratory birds (Vaillancourt and Weber, 2007) reveal that they have the ability to support much higher lipolytic rates than other animals, even in the resting state. Migratory birds preferentially mobilize fatty acids with more double bonds Relative contributions of lipids, carbohydrates (CHO) and proteins to total heat production in adult humans with normal glycogen reserves during low-and high-intensity shivering [2.3 and 3.5ϫ resting metabolic rate (RMR)].…”