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First published online March 14, 2008
Journal of Experimental Biology 211, 1075-1086 (2008)
Published by The Company of Biologists 2008
doi: 10.1242/jeb.014050

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Involvement of lactate in glucose metabolism and glucosensing function in selected tissues of rainbow trout

Sergio Polakof and José L. Soengas^*

Laboratorio de Fisioloxía Animal, Departamento de Bioloxía Funcional e Ciencias da Saúde, Facultade de Bioloxía, Universidade de Vigo, 36310 Vigo, Spain

View larger version (23K): [in this window] [in a new window]   Fig. 1. Glucose (A), lactate (B) and -amino acid (C) levels in plasma of rainbow trout sampled 6 h after intraperitoneal injection (IP treatment) of 5 ml kg–1 of Cortland saline alone (control, C) or saline containing L-(+)-lactate (L22.5, 22.5 mg kg–1 or L45, 45 mg kg–1), sodium oxamate (OXA, 22.5 mg kg–1) or D-glucose (GLU, 500 mg kg–1), or 6 h after intracerebroventricular injection (ICV treatment) into the third ventricle of 1 µl 100 g–1 body mass of Cortland saline alone (control, C) or containing D-glucose (GLU, 400 µg µl–1) or L-(+)-lactate (L400, 400 µg µl–1). Results are shown as percentages of control values (control=100%). Each value is the mean ± s.e.m. of N=11 (IP treatment) or N=8 (ICV treatment) fish per group. Different letters indicate significant differences among treated groups within each treatment (one-way ANOVA, P<0.05).

View larger version (10K): [in this window] [in a new window]   Fig. 2. Relative abundance of glucokinase (GK) mRNA expression in liver (A), hypothalamus (B), hindbrain (C) and Brockmann bodies (D) of rainbow trout sampled 6 h after intracerebroventricular injection into the third ventricle of 1 µl 100 g–1 body mass of Cortland saline alone (control, C) or containing D-glucose (GLU, 400 µg µl–1) or L-(+)-lactate (L400, 400 µg µl–1). Results are shown as percentages of control values (control=100%). Relative abundance of RT–PCR products is presented in arbitrary units as mean ± s.e.m. (N=4) between GK and 18s expression. Different letters indicate significant differences among treated groups within each treatment (one-way ANOVA, P<0.05).

View larger version (22K): [in this window] [in a new window]   Fig. 3. Glucose (A), glycogen (B) and -amino acid (C) levels in hindbrain (Hb), hypothalamus (Hy), and Brockmann bodies (BB) of rainbow trout sampled 6 h after intraperitoneal injection (IP treatment) of 5 ml kg–1 of Cortland saline alone (control, C) or saline containing L-(+)-lactate (L22.5, 22.5 mg kg–1 or L45, 45 mg kg–1), sodium oxamate (OXA, 22.5 mg kg–1) or D-glucose (GLU, 500 mg kg–1), or 6 h after intracerebroventricular injection (ICV treatment) into the third ventricle of 1 µl 100 g–1 body mass of Cortland saline alone (control, C) or containing D-glucose (GLU, 400 µg µl–1) or L-(+)-lactate (L400, 400 µg µl–1). Results are shown as percentages of control values (control=100%, dotted line). Each value is the mean ± s.e.m. of N=11 (IP treatment) or N=8 (ICV treatment) fish per group. Different letters indicate significant differences among treated groups within each tissue (one-way ANOVA, P<0.05). *Significantly different from control (dotted line) in IP treatments (P<0.05); significantly different from control (dotted line) in ICV treatments (P<0.05).

View larger version (16K): [in this window] [in a new window]   Fig. 4. Activities of glucokinase (A), and low Km hexokinase (B) in hindbrain (Hb), hypothalamus (Hy) and Brockmann bodies (BB) of rainbow trout sampled 6 h after intraperitoneal injection (IP treatment) of 5 ml kg–1 of Cortland saline alone (control, C) or saline containing L-(+)-lactate (L22.5, 22.5 mg kg–1 or L45, 45 mg kg–1), sodium oxamate (OXA, 22.5 mg kg–1) or D-glucose (GLU, 500 mg kg–1), or 6 h after intracerebroventricular injection (ICV treatment) into the third ventricle of 1 µl 100 g–1 body mass of Cortland saline alone (control, C) or containing D-glucose (GLU, 400 µg µl–1) or L-(+)-lactate (L400, 400 µg µl–1). Results are shown as percentages of control values (control=100%, dotted line). Each value is the mean ± s.e.m. of N=11 (IP treatment) or N=8 (ICV treatment) fish per group. Different letters indicate significant differences among treated groups within each tissue (one-way ANOVA, P<0.05). *Significantly different from control (dotted line) in IP treatments (P<0.05); significantly different from control (dotted line) in ICV treatments (P<0.05).

View larger version (22K): [in this window] [in a new window]   Fig. 5. Lactate (A) levels, lactate dehydrogenase oxidase (B) and lactate dehydrogenase reductase (C) activities in hindbrain (Hb), hypothalamus (Hy) and Brockmann bodies (BB) of rainbow trout sampled 6 h after intraperitoneal injection (IP treatment) of 5 ml kg–1 of Cortland saline alone (control, C) or saline containing L-(+)-lactate (L22.5, 22.5 mg kg–1 or L45, 45 mg kg–1), sodium oxamate (OXA, 22.5 mg kg–1) or D-glucose (GLU, 500 mg kg–1), or 6 h after intracerebroventricular injection (ICV treatment) into the third ventricle of 1 µl 100 g–1 body mass of Cortland saline alone (control, C) or containing D-glucose (GLU, 400 µg µl–1) or L-(+)-lactate (L400, 400 µg µl–1). Results are shown as percentages of control values (control=100%, dotted line). Each value is the mean ± s.e.m. of N=11 (IP treatment) or N=8 (ICV treatment) fish per group. Different letters indicate significant differences among treated groups within each tissue (one-way ANOVA, P<0.05). *Significantly different from control (dotted line) in IP treatments (P<0.05); significantly different from control (dotted line) in ICV treatments (P<0.05).

View larger version (52K): [in this window] [in a new window]   Fig. 6. Glucose (A), glycogen (B) and lactate (C) levels, and glucokinase (D) and lactate dehydrogenase reductase (E) activities in hypothalamus of rainbow trout incubated in vitro for 1 h at 15°C in modified Hanks' medium containing 2, 4 or 8 mmol l–1 L-(+)-lactate alone (control) or with 50 mmol l–1 sodium oxamate, 1 mmol l–1 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid disodium salt hydrate (DIDS), 1 mmol l–1 sodium dichloroacetate (DCA), 10 mmol l–1 2-deoxy-D-glucose (2-DG), 1 mmol l–1 -cyano-4-hydroxy cinnamate (4-CIN) or 10 mmol l–1 D-glucose. Each value is the mean ± s.e.m. of ten (control) or three (treatments) independent experiments carried out with pools of tissues from three to four different fish (21 pools per experiment: seven treatments times three glucose concentrations). Different letters indicate significant differences (P<0.05) among treatments within each lactate concentration. #Significantly different from groups incubated with 2 mmol l–1 lactate within the same treatment (P<0.05); significantly different from groups incubated with 4 mmol l–1 lactate within the same treatment (P<0.05).

View larger version (53K): [in this window] [in a new window]   Fig. 7. Glucose (A), glycogen (B) and lactate (C) levels, and glucokinase (D) and lactate dehydrogenase reductase (E) activities in hindbrain of rainbow trout incubated in vitro for 1 h at 15°C in modified Hanks' medium containing 2, 4 or 8 mmol l–1 L-(+)-lactate alone (control) or with 50 mmol l–1 sodium oxamate, 1 mmol l–1 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid disodium salt hydrate (DIDS), 1 mmol l–1 sodium dichloroacetate (DCA), 10 mmol l–1 2-deoxy-D-glucose (2-DG), 1 mmol l–1 -cyano-4-hydroxy cinnamate (4-CIN) or 10 mmol l–1 D-glucose. Each value is the mean ± s.e.m. of ten (control) or three (treatments) independent experiments carried out with pools of tissues from three to four different fish (21 pools per experiment: seven treatments times three glucose concentrations). Different letters indicate significant differences (P<0.05) among treatments within each lactate concentration. #Significantly different from groups incubated with 2 mmol l–1 lactate at the same treatment (P<0.05); significantly different from groups incubated with 4 mmol l–1 lactate at the same treatment (P<0.05).

View larger version (37K): [in this window] [in a new window]   Fig. 8. Glucose (A), glycogen (B) and lactate (C) levels, and glucokinase (D) activities in Brockmann bodies of rainbow trout incubated in vitro for 1 h at 15°C in modified Hanks' medium containing 2, 4 or 8 mmol l–1 L-(+)-lactate alone (control) or with 50 mmol l–1 sodium oxamate, 1 mmol l–1 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid disodium salt hydrate (DIDS), 1 mmol l–1 sodium dichloroacetate (DCA), 10 mmol l–1 2-deoxy-D-glucose (2-DG), 1 mmol l–1 -cyano-4-hydroxy cinnamate (4-CIN) or 10 mmol l–1 D-glucose. Each value is the mean ± s.e.m. of ten (control) or three (treatments) independent experiments carried out with pools of tissues from three to four different fish (21 pools per experiment: seven treatments times three glucose concentrations). Different letters indicate significant differences (P<0.05) among treatments within each lactate concentration; #significantly different from groups incubated with 2 mmol l–1 lactate at the same treatment (P<0.05); significantly different from groups incubated with 4 mmol l–1 lactate at the same treatment (P<0.05).

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