As frogs develop, their intestines become shorter and the cells on the inner lining of the intestine change. Researchers have suspected that these changes help the animals transition from a diet consisting of mainly algae as a tadpole to a carnivorous diet in adulthood. This was the subject of a recent study published in the American Journal of Physiology – Regulatory, Integrative and Comparative Physiology, which examined how the intestine changes throughout metamorphosis in African clawed frogs, Xenopus laevis.
Sodium is very important in the absorption of many nutrients in the gut. Take dietary glucose, for example. To get glucose into the body, it must first cross the cells that line the gut. Because sodium concentrations are higher in the gut than the cells, it moves easily down its concentration gradient into the cells. In other words, it is moving from an area of high concentration to an area of low concentration. Glucose, on the other hand, is higher in the tissues than the gut. It moves across these cells with the help of special transporters that move sodium down its concentration gradient and allow glucose to tag along. Because of the role of sodium in nutrient absorption, it was thought that dietary sodium helped control how well other molecules could be absorbed. However, research has shown that gut levels of sodium in omnivorous humans and mice are constant. Similarly, the researchers found that the sodium levels in the gut of tadpoles and frogs are consistent regardless of how much sodium was in their diet. So, if the diet is low in sodium (like in freshwater tadpoles), how does it get into the lumen of their gut?
Research shows that tadpoles absorb sodium through their gills from the surrounding water. Some of the sodium is then added to the lumen of the gut with the help of special pores found between the intestinal cells that allow sodium to pass through. The sodium that is added to the gut can then help other molecules get into the body.
Source:
N Ishizuka, M Nagahashi, Y Mochida, W Hempstock, N Nagata, H Hayashi. Na+-dependent intestinal glucose absorption mechanisms and its luminal Na+ homeostasis across metamorphosis from tadpoles to frogs. American Journal of Physiology – Regulatory, Integrative and Comparative Physiology. 324(5): R645-R655, 2023.
Categories: Diet and Exercise, Nature's Solutions
Tags: American Journal of Physiology, American Physiological Society, digestion, frog, glucose, sodium, Xenopus
Life Lines by Dr. Dolittle 
