Epinephrine

Also known as adrenaline. It is secreted by the adrenal medulla in response to stress and acts on all body tissues. When produced in the body, it participates in the fight-or-flight response of the sympathetic nervous system by stimulating several physiological processes.

Norepinephrine

Also identified as noradrenaline. A fight-or-flight hormone that directly increases heart rate, triggers the release of glucose from energy stores, and increases blood flow to skeletal muscle. Norepinephrine serves a role in the suppression of appetite during acute stress.

Leptin

A hormone that has an important effect on regulation of body weight, metabolism and reproductive function. Leptin serves an important role in long-term regulation of body weight, which is controlled by the hypothalamus in the brain.

Neuropeptide-Y

A hormone involved in the regulation of energy balance and feeding behaviour, including food intake and preference. Neuropeptide-Y increases the proportion of energy stored as fat and thus may contribute to the development of obesity.

Corticotrophin-Releasing Hormone and Adrenocorticotrophic Hormone (CRH)

Secreted by the hypothalamus in response to stress. CRH is then transferred to the anterior lobe of the pituitary, where it stimulates the secretion of adrenocorticotrophic hormone (ACTH) and other biologically active substances. ACTH’s principal effects are increased production and release of cortisol from the adrenal cortex (outer layer of adrenal glands, which sit on top of the kidneys).

Cortisol

A steroid hormone secreted by the adrenal gland in response to stress. Cortisol increases blood sugar levels (when low and during endurance exercise) through a process called gluconeogenesis (formation of new glucose) that occurs in the liver. It suppresses the immune system and aids in fat, protein and carbohydrate metabolism. The amount of cortisol hormone present in the blood undergoes daily cyclic variation, with the highest levels present in the early morning (approximately 8:00 am), and the lowest levels present around midnight to 4:00 am, or 3–5 hours after the onset of sleep. Higher levels of cortisol are a contributing factor to the storage of body fat, particularly visceral, or intra-abdominal fat.