Hormone linked to inhibited weight loss discovered in new study
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Let's dive into a groundbreaking study that sheds light on a hidden role of growth hormone (GH) during weight loss. Researchers at the University of São Paulo have unearthed an unexpected function of GH in energy conservation, adding a fascinating twist to our understanding of metabolic responses.
GH, a hormone we've known about for decades, is primarily associated with bone growth and maintaining organs and tissues. But what if I told you that this well-respected hormone might've had a secret role up its sleeve?
José Donato Junior and his team have uncovered a new side to GH: energy conservation during weight loss. They recently published their findings in a renowned journal.
When calories intake drops, the body responds by conserving energy. This mechanism is crucial, as in the wild, it helps animals survive when food is scarce. Sadly, it also makes weight loss after dieting a challenging battle.
Hormones and Weight Loss
Scientists already recognized that leptin, another hormone, has a part in the body's response to weight loss. Fat cells produce leptin, which suppresses hunger. When we lose weight, the amount of leptin in our blood decreases, making us hungrier.
Some individuals may develop leptin resistance, meaning they no longer respond to the hormone and continue to feel hungry more frequently.
As Donato points out, "Leptin has commonly been considered the main hormone that conserves energy when we're struggling with hunger."
However, despite our growing comprehension of leptin, it hasn't led to successful weight-loss interventions. The latest study asks if GH might be one of the missing pieces to the puzzle.
"GH receptors are found in large quantities in muscle and tissue, in the liver, and in organs directly involved in growth metabolism," says Donato. "However, we discovered that the brain is also brimming with GH receptors. That's brand new information."
The scientists discovered that leptin levels decrease in response to a restriction in caloric intake, while GH levels increase.
Where are the GH Receptors?
The scientists found a wealth of GH receptors in the hypothalamus, a region that governs the autonomic nervous system and regulates important bodily functions such as breathing and digestion.
The hypothalamus also plays a significant role in controlling energy homeostasis, which refers to the regulation of energy expenditure and food intake.
In the hypothalamus, there is a small group of neurons that produce Agouti-related protein (AgRP). When these neurons release AgRP into the body, appetite increases, and the body holds onto its energy stores more tightly.
The scientists found that GH receptors in the hypothalamus activate these neurons, triggering the release of AgRP.
To understand the extent of GH's influence on AgRP neurons, the researchers created a strain of genetically modified mice that lacked the AgRP-specific GH receptor (AgRP GHR KO mice).
In a series of experiments, the scientists restricted food intake and assessed the mice's energy expenditure.
The control mice, which still had the GH receptor, responded to restricted food intake as expected by reducing their energy expenditure to save energy.
However, in the AgRP GHR KO mice, the decrease in energy expenditure was significantly less pronounced. Consequently, these mice lost more weight over the course of the study, as they experienced a higher loss of energy-dense fat deposits and some loss of lean mass (which includes muscle, bone, organs, and fluids).
Blocking Growth Hormone
In a separate experiment, the researchers used mice that did not have the GH receptor blocked using a drug called pegvisomant. Once again, with food deprivation, the energy expenditure of these mice decreased significantly less than it did in the mice that had not received pegvisomant.
"GH is not only important for growth metabolism, but it plays a crucial role in the metabolic responses that conserve energy when we're hungry or dieting," concludes Donato.
"In other words, we discovered that weight loss stimulates increased GH levels in the hypothalamus, leading to a heightened sense of hunger. That's the same function leptin serves."
Lead author José Donato Junior
The authors concluded that GH does not significantly impact energy balance when animals have access to adequate food. Instead, it acts as a signal for energy deficiency to the brain, triggering neuroendocrine responses to conserve energy stores.
Donato suggests that this explains why weight-loss interventions based solely on leptin have been ineffective – they only address part of the mechanism.
In the future, the authors believe that compounds that target GH receptors could "represent a promising approach to facilitate weight loss and improve the efficacy of obesity treatments."
- The role of growth hormone (GH) in weight loss has been redefined, as researchers from the University of São Paulo found GH plays a role in energy conservation.
- Despite leptin being recognized as the main hormone for energy conservation during weight loss struggles, it has not led to successful weight-loss interventions.
- The latest study on GH suggests that it might be one of the missing pieces to the puzzle of weight-management, as GH receptors are found in abundance in parts of the body involved in growth metabolism and energy homeostasis.
- When food intake is restricted, GH levels increase in response, which stimulates the hypothalamus to release Agouti-related protein (AgRP), leading to an increased appetite and conservation of energy stores.
- As Donato suggests, targeting GH receptors could represent a promising approach for facilitating weight loss and improving the efficacy of weight-management and obesity treatments, as these compounds could address part of the metabolic mechanism that has thus far proven elusive in weight-loss interventions.
