Obesity, Appetite, and the PYY Hormone

PYRROLINE AND THE GHRELIN AGENDA

The human body produces two hormones which are related to the appetite: Growth Hormone (GH) and Insulin-Like Growth Factor 1 (IGF1). Both of these hormones play a major role in regulating growth, development, metabolism, bone health and many other functions. They affect our physical appearance, moods and behavior.

Both of them have been shown to increase appetite through several mechanisms. One of them is through activation of the hypothalamus-pituitary-adrenal axis (HPA), which controls many physiological processes such as growth, reproduction, immune system activity and energy expenditure.

Another mechanism involves the release of hormones from adipose tissue into the bloodstream. These include leptin and resistin. Leptin is secreted mainly by fat cells while resistin is produced primarily by white blood cells called macrophages.

Leptin and resistin are both secreted by fat cells. Leptin is a protein which binds to receptors located throughout the brain and spinal cord. Resistin is another hormone secreted by adipose tissue. It binds to receptors found throughout the central nervous system (CNS). Both of these hormones influence appetite by influencing the amount of food consumed or burned during periods of satiety, or when there is no need for increased energy expenditure.

Both hormones influence hunger signals which are received by the hypothalamus, a region of the brain that controls the release of several neurotransmitters which control various bodily functions. The amount of leptin or resistin in the blood is a measure of the body’s fat reserves. Since many factors can cause these levels to be either higher or lower, this can lead to changes in weight.

Hormones that increase hunger will trigger hunger signals to the brain and cause the subject to feel hungry. The opposite also holds true as hormones that decrease hunger will have a suppressing effect and can decrease appetite.

Ghrelin is a peptide hormone produced by the stomach that increases hunger. Ghrelin works by binding to receptors in the hypothalamus. The effect of ghrelin on hunger can be blocked by administering octreotide, a long lasting octapeptide drug. Ghrelin was found to promote growth in children and activate the hypothalamic hunger center. Ghrelin levels have been observed to increase before mealtimes and decrease after a meal.

OXYTOCIN AND THE APPETITE

Oxytocin is another peptide hormone that has an effect on appetite. It was traditionally considered to be involved in pregnancy and mother-child bonding but experimental data suggests it also increases appetite.

Sources & references used in this article:

Gut hormones and appetite control: a focus on PYY and GLP-1 as therapeutic targets in obesity by A De Silva, SR Bloom – Gut and liver, 2012 – ncbi.nlm.nih.gov

Obese adolescents show impaired meal responses of the appetite‐regulating hormones ghrelin and PYY by SD Mittelman, K Klier, S Braun, C Azen, ME Geffner… – …, 2010 – Wiley Online Library

Gut hormones as mediators of appetite and weight loss after Roux-en-Y gastric bypass by CW le Roux, R Welbourn, M Werling, A Osborne… – Annals of …, 2007 – journals.lww.com