Growth hormone is a peptide hormone that stimulates growth, development and regeneration. This peptide hormone is made up of 191 amino acids that form a long, single-chain polypeptide. Growth hormone is synthesized in the somatotropic cells, which are found in the anterior pituitary gland. These cells are also responsible for storing and releasing the hormone.

Types of growth hormone

• Somatotropin is the other name for growth hormone 1, which is produced naturally in animals.

• Somatropin is the synthetic form of growth hormone that is synthesized using recombinant DNA technologies. It is also referred to under the brand name Humatrope.

Functions and uses

Growth hormone is used widely in medicine to help treat growth disorders in children and growth hormone deficiency in adults. Growth hormone encourages growth and development in children and adolescents. It is also involved in regulating bodily fluids, sugar and fat metabolism and maybe even heart function.

Many of the functions of human growth hormone are still unknown. However, studies have shown that growth hormone can decrease body fat, while it increases muscle mass and bone density. Energy levels are consequently raised and the skin’s tone and texture is also improved. Due to these properties, this hormone has been used by sports competitors since the 1970s and has now been banned by the IOC and NCAA.

Regulation of release and secretion

The release of growth hormone is controlled by growth hormone-releasing hormone (somatocrinin) and growth hormone-inhibiting hormone (somatostatin), both of which are released by the neurosecretory nuclei of the hypothalamus. These regulatory hormones are released into the hypophyseal portal venous blood that surrounds the pituitary. The release of growth hormone in the pituitary is governed by these two hormones, which are affected by many external stimulatory and inhibitory factors.

Several factors can stimulate or inhibit the release of growth hormone.

Some examples of growth hormone stimulators include:

• Growth hormone-releasing hormone (GHRH) that acts by binding to growth hormone-releasing hormone receptor (GHRHR)

• Ghrelin acts by binding to growth hormone secretagogue receptors (GHSR)

• Sex hormones such as androgens and estrogen stimulate the secretion of growth hormone during puberty

• Fasting, low blood sugar and vigorous exercise can also stimulate the release of growth hormone

Some inhibitors of growth hormone secretion include:

• Somatostatin released from the periventricular nucleus of the hypothalamus

• Negative feedback on the pituitary and hypothalamus, as determined by the blood levels of growth hormone and insulin like growth factor 1

Dihydrotestosterone

The synthesis and release of growth hormone occurs in a pulsed manner throughout the day. There are peaks in secretion every three to five hours. The biggest peak generally occurs around an hour after the onset of sleep.