Daily expression of sodium-dependent glucose cotransporter-1 protein in jejunum during rat ontogeny

It is widely known that intestinal capacities such as the enzymatic hydrolysis of carbohydrates, lipids and proteins, and the subsequent absorption of the hydrolyzed products, are evolutionary matched to dietary loads and feeding behaviors. In this study, we demonstrate that the protein expression of apically located sodium-dependent glucose cotransporter-1 (SGLT-1) throughout rat ontogeny is daily adjusted to afford glucose uptake when the load of this metabolically essential monosaccharide in the intestinal lumen is maximum. The jejunal expression of SGLT-1 protein in 14 one-day-old suckling pups was found to increase at dark and early light phase (P < 0.05), when they have a better access to mother milk. In weaning 21-d-old and juvenile 28-d-old rats, the cotransporter expression was high throughout the entire day (P < 0.05). Finally, adult 90-d-old rats showed a well-developed circadian rhythm for SGLT-1 protein (P < 0.05), whose expression increased at late light and dark phase when the highest intestinal glucose load was achieved. To our knowledge, these results are the first reporting the daily profile of SGLT-1 expression during rat early developmental stage and may contribute to understand the biological significance of a well-established molecular capacity to deal with the crucial increase of glucose load in the diet during the weaning process.