Abstract
The effects of the pancreatic hormones, insulin and glucagon, on rates of lipid biosynthesis in liver removed from rainbow trout, Oncorhynchus mykiss, were evaluated in vitro. Livers were removed from animals fasted for 30–36h, cut into ca. 1 mm3 pieces, and incubated in the presence of various concentrations of salmon insulin (sINS), bovine insulin (bINS), or a combination of BINS and bovine/porcine glucagon (GLU). Lipid synthesis was evaluated by total lipid concentration, 3H2O incorporation into total lipid, and by fatty acid synthetase activity. Both mammalian and sINS tended to increase tissue total lipid concentration in hepatic tissue incubated for 5h. Insulin also stimulated 3H2O incorporation into total lipid in a dose-dependent manner. Bovine INS (2 × 10−6 M) stimulated de novo synthesis nearly 6-fold over control rates; sINS (2 × 10−6 M) stimulated label incorporation more than 7-fold over control rates. Glucagon inhibited INS-stimulated 3H2O incorporation; whereas, GLU alone had no effect on lipid synthesis in liver pieces incubated 5h. Lipid class analysis indicated that bINS significantly stimulated 3H2O incorporation into phospholipids, fatty acids, and triacylglycerols. The greatest accumulation of label was in the triacylglycerol fraction, where incorporation was stimulated 17-fold over control levels. Hepatic enzymatic analysis indicated that bINS also significantly stimulated lipogenic enzyme activity 9-fold above control levels. These results indicate that INS is an important regulator of lipid synthesis in the liver of trout.
Résumé
Les effecs des hormones pancréatiques, insuline et glucagon, sur le taux de biosynthèse des lipides dans le foie de truite arc-en-ciel (Oncorhynchus mykiss), ont été évalués in vitro. Les foies ont été prélevés sur des animaux mis à jeun depuis 30–36 heures, puis coupés en fragment d'un mm3 et incubés en présence de concentrations variables d'insuline de saumon (sINS), d'insuline bovine (BINS), ou d'une combinaison de BINS et de glucagon bovin/porcin (GLU). La synthèse lipidique est estiméee à partir de la concentration totale de lipides, par l'incorporation de 3H2O dans les lipides totaux, et par l'activité acides gras synthétase. Les insulines mammaliennes et de saumon ont tendance à augmenter la concentration totale de lipides du tissu hépa-tique incubé durant 5 heures. L'insuline stimule aussi l'incorporation de 3H2O dans les lipides totaux de manière dose-dépendante. La bINS (2 × 10−8 M) stimule près de six fois la synthèse de novo comparée à celle observée dans le contrôle, et la sINS (2 × 10−8 M) plus de 7 fois. Le glucagon inhibe la stimulation de l'incorporation de l'3H2O par l'insuline, alors que seul, il n'a aucun effet sur la synthèse lipidique des explants de foie incubés durant 5 heures. L'analyse des classes de lipides montre que la bINS stimule significativement l'incorporation de 3H2O dans les phospholipides, les acides gras et les triglyćerides. La plus grande accumulation a lieu dans la fraction des triglycérides, avec une stimulation augmentée de 17 fois. L'analyse des enzymes hépatiques indique que la bINS stimule 9 fois l'activité de l'enzyme lipogénique. Ces résultats montrent que l'insuline, est un important régulateur de la synthèse des lipides dans le foie.
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Cowley, D.J., Sheridan, M.A. Insulin stimulates hepatic lipogenesis in rainbow trout, Oncorhynchus mykiss . Fish Physiol Biochem 11, 421–428 (1993). https://doi.org/10.1007/BF00004592
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DOI: https://doi.org/10.1007/BF00004592