Researchers at the University of Saskatchewan in Canada compared how pigs and fish absorb glucose (i.e. sugar) from the diet. They did this by measuring how well glucose moves across the intestinal wall. Their findings appear in the American Journal of Physiology – Regulatory, Integrative and Comparative Physiology.
Transport of dietary glucose from the gut to the blood is facilitated by glucose transporters that pick up glucose and move it across cell membranes. There are two main types found in the gut, ones that move glucose along with sodium, SGLTs, and those that just move glucose (GLUTs). To cross an entire cell, glucose usually has to get help from both SGLTs (found on the intestine side) and GLUT2 (found on the blood side). Variations in SGLTs and GLUTs can understandably lead to variations in how well cells move glucose into the body.
In this new study, the research team wanted to know whether it was possible that other glucose transporters helped out SGLTs on the intestinal side of the cells when glucose concentrations were high enough in the diet to overwhelm the SGLTs. While there was some evidence in rodents and humans that GLUT2 could move from the blood to the intestinal side of the cells to pick up the slack when SGLTs are full, there was no evidence on whether something similar happens in fish or other mammals.
The research team chose to examine this in pigs because their gut physiology is similar to humans. They chose Nile tilapia (Oreochromis niloticus) and rainbow trout (Oncorhynchus mykiss) because they were familiar with the SGLT transporters in these species. What they found is that pigs are able to constantly absorb glucose from the diet with the help of two pathways (SGLT and GLUT2) whereas the two fish species only relied on one pathway. Having two pathways helps pigs absorb more glucose than the fish, which do not normally ingest much glucose in the diet.
This research has implications for humans as well since we too are able to take up glucose into the body with the help of two pathways. It also means that therapies aimed at reducing glucose uptake from the diet should consider targeting both pathways.
M Subramaniam, CB Enns, K Luu, LP Weber, ME Loewen. Comparison of intestinal glucose flux and electrogenic current demonstrates two absorptive pathways in pig and one in Nile tilapia and rainbow trout. American Journal of Physiology – Regulatory, Integrative and Comparative Physiology. 318(2): R245-R255, 2020.