Abstract
Adaptive changes of carbohydrate and lipid metabolism induced by 7, 15, 30, 60, 90, 150 and 200 days of fasting were investigated in red tilapia (Oreochromis sp.). Plasma glucose, lactate and free fatty acids (FFA) levels, liver and muscle glycogen and total lipid contents and rates of FFA release from mesenteric adipose tissue (MAT) were measured. Plasma glucose levels showed significant differences only after 90 days of fasting, when glycemia was 34% lower (50±5mg.dL-1) than fed fish values (74±1mg.dL-1), remaining relatively constant until 200 days of fasting. The content of liver glycogen ("15%) in fed tilapia fell 40% in 7 days of food deprivation. In 60, 90 and 150 days of fasting, plasma FFA levels increased 49%, 64% and 90%, respectively, compared to fed fish values. In agreement with the increase in plasma FFA, fasting induced a clear increase in lipolytic activity of MAT incubated in vitro. Addition of isobutylmethylxanthine (cAMP-phosphodiesterase inhibitor) and isoproterenol (non selective beta adrenergic agonist) to the incubation medium induced a reduction of lipolysis in fasted fish, differently to what was observed in mammal adipose tissue. This study allowed a physiological assessment of red tilapia response to starvation.
Highlights
IntroductionFish present a relative efficiency in lipid and protein digestion (Clements and Raubenheimer 2006)
The ability to use carbohydrate for energy varies greatly among fish species and it is generally related to the feeding habitats of the species (NRC 2011).In contrast, fish present a relative efficiency in lipid and protein digestion (Clements and Raubenheimer 2006)
A significant fall in the condition factor was observed after 60 days of fasting (Table I)
Summary
Fish present a relative efficiency in lipid and protein digestion (Clements and Raubenheimer 2006) In this way, in general fish use preferentially lipids and proteins as main source of energy, because carbohydrates are usually metabolized very slowly and are not so well absorbed from the diet Despite the presence of appreciable amounts of organized fat tissue in several species, information about the regulation of the lipolytic activity in fish species when compared to mammals are sparse (Albalat et al 2005). Migliorini et al (1992) found that the in vitro lipolytic activity of Hoplias malabaricus adipose tissue was markedly increased in the presence of cAMP analogues or xanthine derivatives, which inhibit cAMPphosphodiesterase, increasing the intracellular concentration of cAMP.
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