The growth hormone (GH), also known as somatotropin, is a single-chain polypeptide or protein hormone composed of 191 amino acids that are synthesized, stored, and secreted by cells called somatotropin cells within the anterior pituitary gland. It is responsible for several complex physiological processes such as metabolism, growth, cell regeneration, and cell reproduction in humans that is why it’s important in human development. Growth hormone is a stress hormone that increases the concentration of free fatty acids and glucose. It also triggers the production of IGF-1.
The production of growth hormone in the pituitary gland is managed by the neurosecretory nuclei of the hypothalamus. The hypothalamus is an area of the brain that regulates the production of hormones from the pituitary gland which is located below it. The cells in the hypothalamus release the growth hormone-inhibiting hormone (GHIH or somatostatin) and growth hormone-releasing hormone (GHRH or somatocrinin) into the hypophyseal opening venous blood that is surrounding the pituitary gland. The balance of these peptides primarily determines the production of the growth hormone in the pituitary gland along with other factors like physiological stimulators such as sleep, nutrition, and exercise and the inhibitors of the production of growth hormone such as free fatty acids.
Somatostatin (SS, SOM, or SST) is also called somatotropin release inhibiting hormone (SRIH), somatotropin release inhibiting factor (SRIF), or growth hormone inhibitory hormone (GHIH). Somatostatin is a peptide hormone produced by several tissues in the body, particularly in the digestive and nervous systems. It is responsible for regulating various physiological functions and suppresses the secretion of secondary hormones such as the growth hormone, the accelerated reproduction of normal and tumor cells, and the activity of the gastrointestinal tract. Somatostatin acts as a neurotransmitter.
Somatostatin that comes from the hypothalamus suppresses the secretion of some other hormones found in the pancreas such as glucagon and insulin. Somatostatin can also be released in the gastrointestinal tract where it is responsible for reducing gastrointestinal pain and gastric secretion and also for inhibiting the secretion of secretin and gastrin which are both hormones found in the gastrointestinal tract.
Scientists have created chemically altered counterparts of somatostatin which are used to control the hypersecretion of hormones in patients diagnosed with acromegaly and other conditions involving the endocrine and also to treat a number of tumors and gastrointestinal diseases.
While somatostatin inhibits or controls the secretion of some hormones in the body, several hormones also function by controlling the production or secretion of somatostatin. The production of somatostatin is increased by heightened levels of these hormones and is reduced by low levels of these hormones.
The pancreas also secretes somatostatin as a response to factors that are related to the intake of food such as high blood levels of amino acids and glucose.
Glucose and Insulin
Glucose is a type of sugar that a person gets when eating. It is needed by the body for energy. It comes from foods that are rich in carbohydrates like fruits, bread, and potatoes. When you eat, the food travels down the esophagus up to the stomach. The enzymes and acids inside the esophagus and stomach break down the food into tiny pieces. Glucose is released during the breaking down of food. The intestines absorb the glucose as it goes into it. From the intestines, glucose passes into the bloodstream. Once glucose is in the blood, insulin helps it travel to the cells.
Insulin is a hormone that helps glucose travel from the blood into the cells for storage and energy. The body is designed to keep the level of glucose in the blood constant. Beta cells in the pancreas monitor the blood sugar level every few seconds. When the blood glucose increases after eating, the beta cells release insulin into the bloodstream. Insulin acts like a key that unlocks fat, liver, and muscle cells in order for glucose to get inside of them.
How Glucose inhibits Growth Hormone
A high blood glucose level usually inhibits the body in producing growth hormone. High blood levels of glucose result in the secretion of somatostatin in the pancreas and somatostatin suppress the production of growth hormone. Somatostatin inhibits the secretion of growth hormone as a response to the growth hormone-releasing hormone (GHRH) and to other stimulatory factors.
This is the reason why glucose is used in diagnosing an individual with gigantism or acromegaly. Glucose is used in Oral Glucose Tolerance Test (OGTT) which is administered to patients who are suspected to have gigantism or acromegaly. In this procedure, the doctor gives the patient a glucose drink for the patient to consume immediately. The doctor measures the blood levels in the growth hormone before and after drinking the glucose drink. The glucose drink instantly suppresses the growth hormone levels. For a normal person, the growth hormone levels drop instantly after doing the OGTT but for someone with acromegaly, the growth hormone levels don’t drop or remain high.