D-Glucose uptake in fish hepatocytes: mediated by transporter in rainbow trout (Oncorhynchus mykiss), but only by diffusion in prespawning lamprey (Lampetra fluviatilis) and in RTH-149 cell line

Metabolomic profiles and pathways of praziquantel in crucian carp

Praziquantel (PZQ) is a drug commonly used to treat some parasitic infections in animals. This study aimed to apply a reliable and simple method to identify important biological metabolites relevant to PZQ in crucian carp (Carassius auratus) to decipher the metabolic pathways and provide a basis for developing new anti-parasite drugs. The experimental group of crucian carp was administered oral PZQ at a dose of 10 mg kg^-1 via a stomach feed tube. All biological blood samples were analysed using liquid chromatography electrospray ionization/quadrupole time-of-flight mass spectrometry (LC ESI/Q-TOF MS). MetPA analysis was used to identify relevant pathways for PZQ in crucian carp. Thirty-five potential metabolic pathways were revealed by MetPA network software. Furthermore, the chemical structures of the related metabolites and pathways were identified by comparison with data obtained from free online databases. Forty-four significantly differentially abundant endogenous metabolites were found in the PZQ-treated crucian carp. The changes in metabolomic profiles and pathways induced by PZQ played a role in inhibiting pathogenesis.

Comparison of intestinal glucose flux and electrogenic current demonstrates two absorptive pathways in pig and one in Nile tilapia and rainbow trout

The mucosal-to-serosal flux of ¹⁴C 3-O-methyl-d-glucose was compared against the electrogenic transport of d-glucose across ex vivo intestinal segments of Nile tilapia, rainbow trout, and pig in Ussing chambers. The difference in affinities (K_m "fingerprints") between pig flux and electrogenic transport of glucose, and the absence of this difference in tilapia and trout, suggest two absorptive pathways in the pig and one in the fish species examined. More specifically, the total mucosal-to-serosal flux revealed a super high-affinity, high-capacity (sHa/Hc) total glucose transport system in tilapia; a super high-affinity, low-capacity (sHa/Lc) total glucose transport system in trout and a low-affinity, low-capacity (La/Lc) total glucose transport system in pig. Comparatively, electrogenic glucose absorption revealed similar K_m in both fish species, with a super high-affinity, high capacity (sHa/Hc) system in tilapia; a super high-affinity/super low-capacity (sHa/sLc) system in trout; but a different K_m fingerprint in the pig, with a high-affinity, low-capacity (Ha/Lc) system. This was supported by different responses to inhibitors of sodium-dependent glucose transporters (SGLTs) and glucose transporter type 2 (GLUT2) administered on the apical side between species. More specifically, tilapia flux was inhibited by SGLT inhibitors, but not the GLUT2 inhibitor, whereas trout lacked response to inhibitors. In contrast, the pig responded to inhibition by both SGLT and GLUT2 inhibitors with a higher expression of GLUT2. Altogether, it would appear that two pathways are working together in the pig, allowing it to have continued absorption at high glucose concentrations, whereas this is not present in both tilapia and trout.

Limited effects of exogenous glucose during severe hypoxia and a lack of hypoxia-stimulated glucose uptake in isolated rainbow trout cardiac muscle

We examined whether exogenous glucose affects contractile performance of electrically paced ventricle strips from rainbow trout under conditions known to alter cardiomyocyte performance, ion regulation and energy demands. Physiological levels of d-glucose did not influence twitch force development for aerobic preparations (1) paced at 0.5 or 1.1 Hz, (2) at 15 or 23°C, (3) receiving adrenergic stimulation or (4) during reoxygenation with or without adrenaline after severe hypoxia. Contractile responses to ryanodine, an inhibitor of Ca(2+) release from the sarcoplasmic reticulum, were also not affected by exogenous glucose. However, glucose did attenuate the fall in twitch force during severe hypoxia. Glucose uptake was assayed in non-contracting ventricle strips using 2-[(3)H] deoxy-d-glucose (2-DG) under aerobic and hypoxic conditions, at different incubation temperatures and with different inhibitors. Based upon a lack of saturation of 2-DG uptake and incomplete inhibition of uptake by cytochalasin B and d-glucose, 2-DG uptake was mediated by a combination of facilitated transport and simple diffusion. Hypoxia stimulated lactate efflux sixfold to sevenfold with glucose present, but did not increase 2-DG uptake or reduce lactate efflux in the presence of cytochalasin B. Increasing temperature (14 to 24°C) also did not increase 2-DG uptake, but decreasing temperature (14 to 4°C) reduced 2-DG uptake by 45%. In conclusion, exogenous glucose improves mechanical performance under hypoxia but not under any of the aerobic conditions applied. The extracellular concentration of glucose and cold temperature appear to determine and limit cardiomyocyte glucose uptake, respectively, and together may help define a metabolic strategy that relies predominantly on intracellular energy stores.

Regulation of hepatic estrogen receptor isoform mRNA expression in rainbow trout (Oncorhynchus mykiss)

The complete nuclear estrogen receptor family in rainbow trout consists of two subtypes (ERalpha and ERbeta) each of which consists of two isoforms (alpha1/alpha2 and beta1/beta2). Transcription rate and mRNA stability of ERalpha1 is affected by 17beta-estradiol (E2) but no information on estrogen regulation exists for the other isoforms. The objective of this study was to compare the mRNA expression patterns of the four ER isoforms in the liver of male trout and in immortalized trout hepatocyte lines (RTH-149 and SOB-15) treated with E2 or 17alpha-ethynylestradiol (EE2) using quantitative RT-PCR. To determine the in vivo dose-response, isogenic male trout were injected intra-peritoneally with 0, 1.5, 15 or 150 microg E2 or an equimolar amount of EE2 and the liver sampled 24 h later. Treatment with either E2 or EE2 significantly (p<0.05) increased the level of ERalpha1 mRNA at all doses tested compared to vehicle, while the response of mRNAs for the other three isoforms did not change. The in vitro dose-response was tested by treating both cell lines with 0, 0.1, 1.0 or 10.0 microM E2 for 48 h. In RTH-149 cells, ERalpha1, ERalpha2 and ERbeta2 mRNAs were significantly higher in cells incubated with 10 microM E2 as compared to cells treated with only vehicle (p<0.05). In SOB-15 cells, ERalpha2 and ERbeta1 mRNAs were significantly higher in cells incubated with 1.0 microM E2 as compared to cells incubated with only vehicle (p<0.05). These results support the conclusion that the mRNAs for the four ER isoforms respond differentially to estrogen regulation.