2023-10-11 20:31:50
To meet the high energy needs during the menstrual period, the brain may coordinate variations in insulin sensitivity throughout the body.
This is what researchers at the University of Tubingen, in Germany, discovered: women were more sensitive to the effects of insulin during the follicular phase of the menstrual cycle, and less sensitive during the luteal phase. Conclusions, published in the newspaper Nature Metabolismsuggest differences in the mechanisms of action of insulin on the brain depending on sex, with important implications for women’s health.
How did the study take place?
Using a technique called the hyperinsulinaemic euglycemic clamp, Julia Hummel and colleagues measured insulin sensitivity in 11 healthy women; twice during the follicular phase and twice during the luteal phase of their menstrual cycle. The technique consisted of nasal spraying with an insulin spray, which increased the level of insulin in the blood beyond the normal level. An intravenous glucose infusion was administered concomitantly at a rate adapted to counterbalance the effects of the administered insulin. The procedure aimed to determine the effectiveness of the tissue response to insulin.
The research team found that changes in glucose infusion rates induced by the insulin spray varied significantly between the two menstrual phases. Compared to placebo, a greater infusion of glucose was necessary during the follicular phase to maintain a plasma glucose concentration within normal values. However, this was not the case during the luteal phase.
The researchers then performed functional magnetic resonance imaging in 15 other women to assess the response of blood flow in the hypothalamus to the intranasal insulin spray. The results showed that insulin modulated hypothalamic activity – measured by a decrease in cerebral blood flow in the hypothalamus – during the follicular phase of the menstrual cycle, but not during the luteal phase.
Martin Heni, lead author, told Univadis.com: “During the follicular phase, it appears necessary for glucose to flow efficiently to areas of high energy demand, such as the thickening endometrium. Insulin sensitivity presents [également] a vital character for the maturation of preovulatory follicles. And it seems that it is the brain that guides and coordinates insulin. »
What are the mechanisms of action of insulin on the brain?
For a long time, it was thought that the brain was insensitive to insulin, but we now know that insulin receptors are present throughout the brain. Insulin is also an important regulator of brain metabolism. Likewise, it acts on different regions of the brain which influence behavior and systemic metabolism.
Besides regulating blood sugar levels, insulin also plays a role in cognitive control and restricts appetite by decreasing the attractiveness of food cues.
The action of insulin on the brain also improves insulin sensitivity throughout the body, ensuring more efficient metabolism of glucose and regulation of fat distribution.
What is insulin sensitivity in the brain?
Just like the body, the brain can develop insulin resistance. This resistance has repercussions on the metabolism of the entire body and might lead to poor fat distribution and weight gain in the long term, possibly resulting in prediabetes.
Martin Heni adds: “We focused on the functional consequences of the action of brain insulin on glucose metabolism throughout the body. We studied its impact on healthy women throughout their menstrual cycle. Our study shows that while brain insulin action may improve peripheral insulin sensitivity in women, these effects appear limited to the follicular phase of the menstrual cycle. The response may be attenuated by relative brain resistance to insulin during the luteal phase. »
Impact on women’s health
Vital to the female reproductive system, insulin plays a key role in the proliferation of the endometrium and the maturation of follicles before ovulation. Insulin sensitivity likely increases during the follicular phase of the menstrual cycle due to the high energy demand of the developing endometrium; and the brain might coordinate this increase. On the contrary, insulin sensitivity decreases during the luteal phase and might promote energy storage in adipose tissues.
“This cyclical shift in energy storage modulated by the brain might be a contributing factor to the well-known differences in fat distribution between the two sexes. The question of how these mechanisms may vary in obesity and diabetes remains unanswered, but further studies on the subject will certainly be carried out,” according to Mr. Heni.
Do these findings have any impact in clinical practice?
The study was carried out on a small group of healthy women, and provided a better understanding of these complex biological processes. However, the results still need to be validated in larger clinical trials before they can be applied to clinical practice.
Mr. Heni temporizes: “Our results must imperatively be considered with reasoned optimism. Direct clinical application cannot be done without other adequate studies that test potential approaches. Our study focused on how brain insulin action modifies insulin sensitivity in the rest of the body. It will provide a better understanding of the contribution of this mechanism to food intake, food choices, body weight and the distribution of adipose mass. Well-designed research in this direction, with a specific focus on gender differences, is imperative to be carried out in order to clarify the possible clinical importance of presumed gender differences on the action of insulin on the brain. . »
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