WEANING MARGINALLY AFFECTS GLUCOSE-TRANSPORTER (GLUT4) EXPRESSION IN CALF MUSCLES AND ADIPOSE TISSUES

The nutritional regulation of glucose transporter GLUT4 was studied in eight muscles and four adipose tissues from two groups of preruminant (PR) or ruminant (R) calves of similar age (170 d), empty body weight (194 kg) at slaughter, and level of net energy intake from birth onwa rds. Isocitrate dehydrogenase (EC 1.1.1.41) activity in muscles was no t different between PR and R except in masseter muscle from the cheek (+71 % in R; P < 0.003), which becomes almost constantly active at wea ning for food chewing. Basal and maximally-insulin-stimulated glucose transport rate (GTR) per g tissue wet weight in rectus abdominis muscl e were significantly higher in R calves (+31 and 41% respectively; P < 0.05). GLUT4 protein contents did not differ in muscles from PR and R except in masseter (+74% in R; P < 0.05) indicating that the increase d GTR in rectus abdominis cannot be accounted for by an enhanced GLUT4 expression. GLUT4 mRNA levels did not differ between the two groups o f animals in all muscles suggesting a regulation of GLUT4 at the prote in level in masseter. GLUT4 number expressed on a per cell basis was l ower in adipose tissue from R calves (-39 %; P < 0.05) and higher in i nternal than in peripheral adipose tissues. In summary, the regulation of GLUT4 in calves at weaning differs markedly from that previously d escribed in rodents (for review, see Girard et al. 1992). Furthermore, significant inter-individual variations were shown for metabolic acti vities in muscle and for biochemical variables in adipose tissue.