Exercise Decreases Insulin Production

Insulin is a necessary hormone for humans and many other living things. Its most well-known function is to regulate sugar metabolism. Its operation is well understood. Much less is known about how insulin-producing cells and, as a result, insulin secretion is regulated. A team from Julius-Maximilians-Universität (JMU) Würzburg in Bavaria, Germany, has published research on this topic in the scholarly journal Current Biology. The fruit fly Drosophila melanogaster was utilized as the study object by Dr. Jan Ache's group. Surprisingly, this fly secretes insulin after eating. However, unlike in humans, the hormone in the fly is released by nerve cells in the brain rather than the pancreas.

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Insulin-Producing Cells During Exercise

The JMU team discovered that the fly's physical activity has a significant impact on its insulin-producing cells. The researchers assessed the activity of these cells electrophysiologically in walking and flying Drosophila for the first time.

As a result, when Drosophila begins to walk or fly, its insulin-producing cells are blocked right away. When the fly stops moving, the activity of the cells quickly increases and exceeds normal levels.

“We hypothesize that the low activity of insulin-producing cells during walking and flight contributes to the provision of sugars to meet the increased energy demand,” says Dr. Sander Liessem, first author of the publication. “We suspect that the increased activity after exercise helps to replenish the fly's energy stores, for example in the muscles.”

The JMU team was also able to show that brain pathways actively govern the rapid, behavior-dependent regulation of insulin-producing cells. “It is mainly independent of changes in the sugar concentration in the blood of the fly,” co-author Dr. Martina Held adds.

To avoid dramatic changes in blood sugar levels, it makes a lot of sense for the organism to anticipate a higher energy need in this way.

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Insulin Has Not Changed Much Over Time

Can inferences be drawn about people based on the findings? Probably. “Although the release of insulin in fruit flies is mediated by different cells than in humans, the insulin molecule and its function have hardly changed in the course of evolution,” says Jan Ache.

Many fundamental problems have already been answered using Drosophila as a model organism over the last 20 years, which may lead to a better understanding of metabolic diseases in humans and associated disorders like diabetes or obesity.

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Less Insulin Equals Longer Life

“One exciting point is that reduced insulin activity contributes to healthy aging and longevity,” Sander Liessem tells us. This has already been shown in flies, mice, humans, and other species. The same applies to an active lifestyle. “Our work shows a possible link explaining how physical activity could positively affect insulin regulation via neuronal signaling pathways.”

Jan Ache's team intends to examine whether neurotransmitters and neural circuits are responsible for the activity fluctuations found in fly insulin-producing cells. This will most likely be difficult: Neuromodulatory processes involve a myriad of messenger chemicals and hormones, and individual substances can have opposed or complementary effects when combined.

The researchers are currently investigating the various ways in which insulin-producing cells process external input. They are also looking into other factors that could affect the functioning of these cells, such as the age of the fly or its nutritional status.

“In parallel, we are investigating the neuronal control of walking and flight behaviour,” explains Jan Ache. His group's long-term goal, he explains, is to combine these two study questions: How does the brain manage walking and other behaviors, and how does the nervous system keep the energy balance in check?

Source-Medindia