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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

^* Author for correspondence (e-mail: jsoengas{at}uvigo.es)

Accepted 24 January 2008

The aim of this study was to obtain evidence in rainbow trout for a role of lactate in glucose homeostasis as well as in the function of glucosensing tissues. In a first set of experiments, trout were injected, either (1) intraperitoneally (N=8) with 5 ml kg^–1 of Cortland saline alone (control) or saline containing L-(+)-lactate (22.5 mg kg^–1 or 45 mg kg^–1), oxamate (22.5 mg kg^–1) or D-glucose (500 mg kg^–1), or (2) intracerebroventricularly (N=11) with 1 µl 100 g^–1 body mass of Cortland saline alone (control) or containing D-glucose (400 µg µl^–1) or L-(+)-lactate (400 µg µl^–1), with samples being obtained 6 h after treatment. In a second set of experiments, hypothalamus, hindbrain and Brockmann bodies were 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 oxamate, 1 mmol l^–1 DIDS, 1 mmol l^–1 dichloroacetate, 10 mmol l^–1 2-deoxy-D-glucose, 1 mmol l^–1 -cyano-4-hydroxy cinnamate or 10 mmol l^–1 D-glucose. The response of parameters assessed (metabolite levels, enzyme activities and glucokinase expression) in tissues provided evidence for (1) a role for lactate in the regulation of glucose homeostasis through changes not only in brain regions but also in liver energy metabolism, which are further reflected in changes in plasma levels of metabolites; (2) the possible presence in trout brain of an astrocyte–neuron lactate shuttle similar to that found in mammals; and (3) the lack of capacity of lactate to mimic in vitro (but not in vivo) glucose effects in fish glucosensing regions.

Key words: rainbow trout, glucosensor, lactate, glucose homeostasis, hypothalamus, hindbrain, Brockmann bodies