Regulation of Food Intake by the Endocrine System

&Disordered Eating

Michelle Auman

September 21, 2005

Current theories of how feeding behavior and hunger are regulated focus on:

• Neural signals from the digestive tract

• Blood borne signals related to energy stores

• Hormones(6)

Neural signals

• One way the brain evaluates the contents of the gut depends on vagal nerve fibers that carry on a conversation between gut and brain.

-Serotonin-CCK (cholecystokinin) -BDNF (Brain derived Neurotrophic

Factor)

Serotonin

A monoamine neurotransmitter that is a powerful vasoconstrictor and is found especially in the brain. Acts both as a chemical messenger that transmits nerve signals between nerve cells and that causes blood vessels to narrow. Also called 5-HT for 5-hydroxytryptamine.

CCK

A neuropeptide that stimulates the contraction of the gallbladder with release of bile and the secretion of pancreatic enzymes into the small intestine. CCK is secreted by cells lining the upper intestine and by the hypothalamus. Hypothalamic cholecystokinin is a neurotransmitter.

BDNF

Brain derived Neurotrophic Factor is the most abundant of neurotrophins in the brain. It is recognized as a critical regulator in the survival, differentiation, and outgrowth of select neurons during development and adulthood.

Blood Nutrients

At any time, blood levels of glucose, amino acids, and fatty acids provide information to the brain that may help adjust energy intake to energy output.

Leptin (Fatty Acid)

A peptide released by adipose cells that circulates at levels related to fat reserves. Serves as an indicator of the body’s total energy stores and provides a mechanism for controlling hunger.

Glucose

When we eat, blood glucose levels rise and glucose catabolism increases. Subsequent activation of glucose receptors in the brain depress eating. During fasting, this signal is absent, resulting in hunger.

Amino Acids

The building blocks of protein.

Elevated blood levels of amino acids depress eating, whereas low levels stimulate eating. The precise mechanism mediating these effects is unknown.

Hormones

Plasma concentrations of hormones help to initiate, maintain and control certain functions associated with food intake.

Ghrelin

A 28-amino-acid peptide hormone that is secreted primarily by stomach cells with lesser amounts secreted by other cells (as of the hypothalamus), that is a growth hormone that stimulates secretion (as by the stomach or pancreas), and that has been implicated in the stimulation of fat storage and food intake

T3

A crystalline iodine-containing hormone that is an amino acid derived from thyroxine (T4) and is used especially in the form of its soluble sodium salt in the treatment of hypothyroidism and metabolic insufficiency.

A protein hormone that promotes an increase in the sugar content of the blood by increasing the rate of breakdown of glycogen in the liver.

Glucagon

Insulin

A protein hormone that is synthesized in the pancreas from proinsulin, that is essential for the metabolism of carbohydrates, lipids, and proteins, that regulates blood sugar levels by facilitating the uptake of glucose into tissues, by promoting its conversion into glycogen, fatty acids, and triglycerides, and by reducing the release of glucose from the liver

TSH

Thyroid Stimulating Hormone: a hormone secreted by the adenohypophysis of the pituitary gland that regulates the formation and secretion of thyroid hormone -- called also thyrotropic hormone, thyrotropin

References1. Bariohay, B.; Bruno, L.; Moyse, E. and Jean, A. (2005). BDNF plays a

role as an anorexigenic factor in the dorsal vagal complex. Endocrinology. 10: 1-38.

2. Geary, N. (2004) Endocrine controls of Eating: CCK, leptin and ghrelin. Physiology and Behavior. 81: 719-733.

3. Grinspoon, S. and Klibanski, A. (2004). Effects of Estrogen and rILG-1 on ghrelin secretion in severe undernutrition. Journal of Clinical Endocrinology and Metabolism. 89(8): 3988-3993.

4. Grundy, D. (2005). Sensory signals from the GI tract. Journal of Pediatric Gastroenterology and Nutrition. 41: 57-59

5. Hashimoto, K. and Iyo, M. (2005). Role of BDNF in eating disorders: recent findings and it’s pathophysiological implications

References Cont.

6. Marieb, E. (2004). Human Anatomy and Physiology 6th ed. SanFransisco, Pearson.

7. Medline Plus. http://www2.merriam-webster.com/cgi-bin/mwmednlm. [Sept. 19, 2005].

8. Palmiero, M.; Fabrazzo, M. and Martiadis, V. (2004). Circulating BDNF is decreased in women with anorexia and bulimia but not in women with binge eating disorder. Psychological Medicine. 35: 897-905.