Ontogenic development of lamb intestinal sodium‐glucose co‐transporter is regulated by diet.

Abstract

SUMMARY1. The ontogenic development of the intestinal Na+-glucose co-transporter was measured in lambs as a function of diet. Transport activity was assayed in brushborder membrane vesicles and the expression of transport protein in the brushborder membrane determined by Western analysis.2. Na+-dependent D-glucose transport increased to a maximum (300-700 pmol mg' s') within the first 2 weeks of birth and then declined to negligible amounts (< 10 pmol mg-' s-1) over the next 8 weeks. There was no further change over the next 2-3 years. Early changes were associated with modifications in both the maximum velocity Vma. for transport and expression of carrier protein in the brush-border plasma membrane.3. Maintaining lambs on a milk replacer diet beyond the normal weaning period prevented the normal decline in the expression of Na+-glucose co-transport. At 5 weeks the transport rate was 433 + 150 pmol mg-' s-I in lambs maintained on milk replacer, but only 79 + 40 pmol mg-' s-I in normally reared control lambs.4. Infusing the proximal intestine of 2-to 3-year-old sheep with 30 mM-D-glucose for four days increased the rate of transport 40-to 80-fold above that found in control animals perfused with mannitol. A similar but smaller increase was observed in one animal perfused with the non-metabolizable sugar a-methyl-D-glucopyranoside. The induced increase in glucose transport was correlated with the expression of the co-transporter protein in the brush-border plasma membrane.5. It is concluded that the age-related decline in Na+-glucose co-transport in the sheep intestine is directly due to the decrease in D-glucose (and D-galactose) reaching the small intestine after development of the rumen. These results further suggest that luminal sugar substrates for the co-transporter promote both the maintenance and the up-regulation of the brush-border transport protein and it is the intact sugar itself which controls gene expression during enterocyte maturation. MS 8905 S. P. SHIRAZI-BEECHEY AND OTHERS

Ontogenetic expression and regulation of Na+-d-glucose cotransporter in jejunum of domestic chicken

“…This value was well correlated with the decline observed in methyl ␣-D-glucopyranoside transport (40%) and corroborates the decrease in phlorizin binding during chicken development reported by Vá zquez et al (29). Similarly, an age-related reduction in transport rates that could be explained by a decrease in the density of transporters was found in mice (7) and lambs (23).…”

“…The molecular mass was very similar to that in adult chickens (11) and to those reported (13,23,26) for SGLT1 in various species. These results indicate that there were no age-related structural changes in SGLT1 that could explain the reduction in methyl ␣-D-glucopyranoside transport.…”

“…The maximal capacity per tissue weight to transport monosaccharides is reached the day after hatch and declines afterward until attainment of adult levels at the age of 5 wk (18,25). This pattern occurs not only in chickens (19,29) but also in various species of mammals (2,23).…”

“…Shirazi-Beechey et al (23) suggested that in lambs the decrease observed in transport capacity and SGLT1 expression was regulated directly by luminal D-glucose concentration resulting from dietary changes. In the present study, no dietary changes were introduced, since the diet composition was kept constant from hatch until the 5th wk of age.…”

Gene expression in the digestive tissues of ruminants and their relationships with feeding and digestive processes

“…More definitively, measurement of SGLT1 mRNA by Northern blot and protein expression by Western blot in jejunum of lambs and calves during the transition from a pre-ruminant to ruminant state revealed significant declines in both SGLT1 mRNA and protein after establishment of a functional rumen (Wood et al, 2000), presumably due to limited quantities of six-carbon sugars reaching the intestine after fermentation (Shirazi-Beechey et al, 1991). Furthermore, analysis of SGLT1 protein expression in jejunum of six ruminant species varying in their carbohydrate intake showed a strong positive correlation between dietary carbohydrate content and SGLT1 protein expression (Wood et al, 2000).…”