Trained anoles move leucine to surprising areas Free

Your body is capable of something miraculous, distributing the energy you get from your diet to the right places to make sure that you function properly. When we exercise, some parts of the body need more energy than others to function, so energy and nutrients need to be distributed differently. Areas that are using the most energy are prioritized, while less energy is directed towards other bodily functions. This is also true in other animals. When running away is more important than reproducing, their bodies provide extra energy to the muscles to help them live another day. But what happens if an animal isn't getting enough energy from their diet to maintain their high activity levels? Jerry Husak of the University of St Thomas, USA, and Simon Lailvaux of the University of New Orleans, USA, were curious about where the nutrients go when a green anole (Anolis carolinensis) is training like an athlete but their diet isn't keeping up, and whether they might be taking energy away from other functions such as reproduction.

To do so, Husak and a group of undergraduates undertook the herculean task of exercise training 80 lizards. For 9 weeks, they trained some anoles for endurance by running them on a treadmill while training others to sprint on a racetrack. At the same time, they provided some anoles with three crickets each time they were fed while giving others only one cricket each time. After the training was over, Husak gave the anoles a radiolabelled amino acid called leucine. By measuring how much of the leucine was in each tissue, the team could track where nutrients were going inside the lizard's body. So where do the nutrients go? That depends on a number of different things. Male lizards that only ate one cricket three times per week routed more leucine to their liver than lizards that were fed more. This suggests that these lizards needed to use the leucine for fuel to power their energetic exercise. Surprisingly, sprint-trained anoles also routed more leucine to their livers compared with other lizards, though the researchers expected them to route the leucine to their muscles instead. The sprint-trained male lizards also routed more leucine to their spleens compared with untrained lizards, potentially to produce more red blood cells, allowing the anoles to deliver more oxygen to their cells.

The female anoles did things slightly differently. Both types of training caused the lizards to shuttle more leucine to their livers, but only if they were fed one cricket per week. Females that were sprint trained and on the restricted diet also channelled more leucine to their spleens than other female anoles. However, the most surprising finding is that these same female lizards sent more leucine to their gonads than other female lizards, suggesting that they were investing energy into reproduction even though their bodies may have needed that to power their exercise training instead.

So, instead of the leucine going to their muscles as the researchers expected, the anoles directed the radiolabelled amino acid to their liver and spleen. ‘We suspect that after 9 weeks of training, the lizards’ gains had plateaued, much like we see in human weightlifters’, says Husak. The scientists go on to explain that the anoles may have routed more leucine to their muscles earlier in their training as the leg muscles of trained anoles were larger than those of lizards that didn't train. Whether the lizards direct the leucine to their muscles or to other organs during training, understanding how training and diet impact where nutrients go can provide us with a better understanding of how this happens in our own bodies as well.