Facilitative glucose transporters in livestock species

Abstract

-The study of facilitative glucose transporters (GLUT) requires carefully done immunological experiments and sensitive molecular biology approaches to identify the various mechanisms which control GLUT expression at the RNA and protein levels. The cloning of species-specific GLUT cDNAs showed that GLUT4 and GLUT1 diverge less among species than other GLUT isoforms. The key role of GLUT in glucose homeostasis has been demonstrated in livestock species. In vitro studies have suggested specific roles of GLUT1 and GLUT3 in avian cells. In vivo studies have demonstrated a regulation of GLUTs (especially of GLUT4) by nutritional and hormonal factors in pigs and cattle, in lactating cows and goats and throughout the foetal life in the placenta and tissues of lambs and calves. All these results suggest that any changes in GLUT expression and activity (such as GLUT4 in muscles) could modify nutrient partitioning and tissue metabolism, and hence, the qualities of animal products (milk, meat).glucose transporter / pig / ruminant / poultry Résumé -Les transporteurs du glucose à diffusion facilitée chez les animaux de ferme. L'étude des transporteurs du glucose à diffusion facilitée (GLUT) nécessite des techniques en immunologie ou en biologie moléculaire précises et sensibles pour étudier la régulation de leur expression au niveau ARNm ou protéique. Le clonage d'ADNc des différents GLUT a montré que GLUT4 et GLUT1 divergent moins entre espèces que les autres isoformes de GLUT. Le rôle important des GLUT dans le contrôle de l'homéostasie du glucose a été démontré chez les animaux de ferme. Des études in vitro ont suggéré un rôle spécifique de GLUT1 et de GLUT3 dans les cellules aviaires. Des études in vivo ont mis en évidence une régulation des GLUT (notamment GLUT4) par des facteurs nutritionnels ou hormonaux chez le porc et le bovin, chez la vache ou la chèvre en lactation, et tout au long de la vie foetale dans le placenta et les tissus de l'agneau ou du veau. L'ensemble de ces résultats suggère que tout changement dans l'expression et l'activité des GLUT (tel que de GLUT4 dans les muscles) peut modifier la répartition des nutriments et le métabolisme tissulaire, et affecter ainsi la qualité des produits animaux (lait, viande).transporteur du glucose / porc / ruminant / volaille Reprod. Nutr. Dev. 40 (2000) 517-533 517

Prenatal developmental changes in glucose transporters, intermediary metabolism and hormonal receptors related to the IGF/insulin-glucose axis in the heart and adipose tissue of bovines

“…Moreover, the degree of maturity for muscle development at birth is similar in humans and bovines, but higher than for other mammals such as pigs [13]. The mechanism of insulin action in bovines is also similar to that in other species, although dietary supply of glucose is very low in ruminants after weaning, thereby modifying insulin secretion and action [8,14]. The insulin-sensitive glucose transporter GLUT4 was characterised in cattle by Hocquette et al [15] and Abe et al [16] at protein and mRNA levels respectively.…”

“…Several GLUT isoforms have been characterised, among them GLUT1 expressed in many tissues and especially erythrocytes, GLUT2 expressed in the liver and GLUT4 expressed in insulin-sensitive tissues (heart/muscle/fat) only. Heart, skeletal muscle and adipose tissue are of great physiological interest due to the regulation of their glucose transport rate by insulin [8,9]. This allows a regulation of glucose tolerance at the whole body level.…”

“…The expression of GLUT4 in muscles and adipose tissues increases at weaning in the rat [28] and in the pig [39], but not in cattle [40]. This may be explained by the fact that the fatrich diet of the suckled rat or the suckled pig is replaced by a carbohydrate-rich diet, whereas fat and carbohydrates of the calf milk replacer are replaced by volatile fatty acids originating from food fermentation by micro-organisms present in the rumen of herbivores from weaning onwards [8,41].…”

Responses to nutrients in farm animals: implications for production and quality

“…States of insulin resistance or of reduced potential of glucose use by muscles may impair growth, for instance in calves (for review, see Bauchart et al, 1996 also Hocquette andAbe, 2000). Many factors have been shown to be involved in the aetiology of insulin resistance.…”

“…Glucose oxidation is usually decreased in insulin-resistant human subjects. An increase in lactose intake increases insulin resistance in preruminant calves (for review, see Hocquette and Abe, 2000) as described in other species (for review, see Hocquette et al, 1998). By contrast, an increase in digestible protein intake at a constant protein-free energy intake decreases insulin resistance unlike the situation in humans.…”