Glucose-dependent insulinotropic peptide
Encyclopedia
Gastric inhibitory polypeptide (GIP), also known as the glucose-dependent insulinotropic peptide is a member of the secretin family of hormone
s.
GIP, along with glucagon-like peptide-1
(GLP-1), belongs to a class of molecules referred to as incretin
s.
and the jejunum
of the gastrointestinal tract
.
Like all endocrine hormones, it is transported by blood.
Gastric inhibitory polypeptide receptor
s are seven-transmembrane proteins found on beta-cells in the pancreas
.
from acid damage, reduce the rate at which food
is transferred through the stomach
, and inhibit the GI motility and secretion of acid. However, this is incorrect, as it was discovered that these effects are achieved only with higher-than-normal physiological level, and that these results naturally occur in the body through a similar hormone
, secretin
.
It is now believed that the function of GIP is to induce insulin
secretion, which is stimulated primarily by hyperosmolarity of glucose
in the duodenum. After this discovery, some researchers prefer the new name of glucose-dependent insulinotropic peptide, while retaining the acronym "GIP." The amount of insulin secreted is greater when glucose is administered orally than intravenously.
GIP is also thought to have significant effects on fatty acid metabolism
through stimulation of lipoprotein lipase
activity in adipocyte
s. GIP release has been demonstrated in the ruminant animal and may play a role in nutrient partitioning in milk production (lipid metabolism). GIP is secreted in response to the first maternal feed (colostrum) in goat kids - GIP being measured via umbilical vein before its closure. For ethical reasons, GIP secretion has been demonstrated in humans only at approx 10 days of age. With respect to the role of GIP in lipid metabolism, supraphysiological levels have shown a lipogenic action, however the action of collagenase in experimental protocols is known to degrade GIP/ GIP receptors. GIP is part of the diffuse endocrine system and, as a consequence, difficult to demonstrate physiological or clinical effects. In comparison to insulin its effects are very subtle.
are not responsive to GIP and have lower levels of GIP secretion after a meal when compared to non-diabetics. In a research involving knockout mice, it was found that absence of the GIP receptors correlates with resistance to obesity
.
Hormone
A hormone is a chemical released by a cell or a gland in one part of the body that sends out messages that affect cells in other parts of the organism. Only a small amount of hormone is required to alter cell metabolism. In essence, it is a chemical messenger that transports a signal from one...
s.
GIP, along with glucagon-like peptide-1
Glucagon-like peptide-1
Glucagon-like peptide-1 is derived from the transcription product of the proglucagon gene. The major source of GLP-1 in the body is the intestinal L cell that secretes GLP-1 as a gut hormone. The biologically active forms of GLP-1 are: GLP-1- and GLP-1-NH2...
(GLP-1), belongs to a class of molecules referred to as incretin
Incretin
Incretins are a group of gastrointestinal hormones that cause an increase in the amount of insulin released from the beta cells of the islets of Langerhans after eating, even before blood glucose levels become elevated. They also slow the rate of absorption of nutrients into the blood stream by...
s.
Synthesis and transport
GIP is derived from a 153-amino acid proprotein encoded by the GIP gene and circulates as a biologically active 42-amino acid peptide. It is synthesized by K cells, which are found in the mucosa of the duodenumDuodenum
The duodenum is the first section of the small intestine in most higher vertebrates, including mammals, reptiles, and birds. In fish, the divisions of the small intestine are not as clear and the terms anterior intestine or proximal intestine may be used instead of duodenum...
and the jejunum
Jejunum
The jejunum is the middle section of the small intestine in most higher vertebrates, including mammals, reptiles, and birds. In fish, the divisions of the small intestine are not as clear and the terms middle intestine or mid-gut may be used instead of jejunum.The jejunum lies between the duodenum...
of the gastrointestinal tract
Gastrointestinal tract
The human gastrointestinal tract refers to the stomach and intestine, and sometimes to all the structures from the mouth to the anus. ....
.
Like all endocrine hormones, it is transported by blood.
Gastric inhibitory polypeptide receptor
Gastric inhibitory polypeptide receptor
The gastric inhibitory polypeptide receptor also known as the glucose-dependent insulinotropic polypeptide receptor is a protein that in humans is encoded by the GIPR gene...
s are seven-transmembrane proteins found on beta-cells in the pancreas
Pancreas
The pancreas is a gland organ in the digestive and endocrine system of vertebrates. It is both an endocrine gland producing several important hormones, including insulin, glucagon, and somatostatin, as well as a digestive organ, secreting pancreatic juice containing digestive enzymes that assist...
.
Function
It has traditionally been called gastrointestinal inhibitory peptide or gastric inhibitory peptide and was believed to neutralize stomach acid to protect the small intestineSmall intestine
The small intestine is the part of the gastrointestinal tract following the stomach and followed by the large intestine, and is where much of the digestion and absorption of food takes place. In invertebrates such as worms, the terms "gastrointestinal tract" and "large intestine" are often used to...
from acid damage, reduce the rate at which food
Food
Food is any substance consumed to provide nutritional support for the body. It is usually of plant or animal origin, and contains essential nutrients, such as carbohydrates, fats, proteins, vitamins, or minerals...
is transferred through the stomach
Stomach
The stomach is a muscular, hollow, dilated part of the alimentary canal which functions as an important organ of the digestive tract in some animals, including vertebrates, echinoderms, insects , and molluscs. It is involved in the second phase of digestion, following mastication .The stomach is...
, and inhibit the GI motility and secretion of acid. However, this is incorrect, as it was discovered that these effects are achieved only with higher-than-normal physiological level, and that these results naturally occur in the body through a similar hormone
Hormone
A hormone is a chemical released by a cell or a gland in one part of the body that sends out messages that affect cells in other parts of the organism. Only a small amount of hormone is required to alter cell metabolism. In essence, it is a chemical messenger that transports a signal from one...
, secretin
Secretin
Secretin is a hormone that controls the secretions into the duodenum, and also separately, water homeostasis throughout the body. It is produced in the S cells of the duodenum in the crypts of Lieberkühn...
.
It is now believed that the function of GIP is to induce insulin
Insulin
Insulin is a hormone central to regulating carbohydrate and fat metabolism in the body. Insulin causes cells in the liver, muscle, and fat tissue to take up glucose from the blood, storing it as glycogen in the liver and muscle....
secretion, which is stimulated primarily by hyperosmolarity of glucose
Glucose
Glucose is a simple sugar and an important carbohydrate in biology. Cells use it as the primary source of energy and a metabolic intermediate...
in the duodenum. After this discovery, some researchers prefer the new name of glucose-dependent insulinotropic peptide, while retaining the acronym "GIP." The amount of insulin secreted is greater when glucose is administered orally than intravenously.
GIP is also thought to have significant effects on fatty acid metabolism
Fatty acid metabolism
Fatty acids are an important source of energy and adenosine triphosphate for many cellular organisms. Excess fatty acids, glucose, and other nutrients can be stored efficiently as fat. Triglycerides yield more than twice as much energy for the same mass as do carbohydrates or proteins. All cell...
through stimulation of lipoprotein lipase
Lipoprotein lipase
Lipoprotein lipase is a member of the lipase gene family, which includes pancreatic lipase, hepatic lipase, and endothelial lipase. It is a water soluble enzyme that hydrolyzes triglycerides in lipoproteins, such as those found in chylomicrons and very low-density lipoproteins , into two free...
activity in adipocyte
Adipocyte
However, in some reports and textbooks, the number of fat cell increased in childhood and adolescence. The total number is constant in both obese and lean adult...
s. GIP release has been demonstrated in the ruminant animal and may play a role in nutrient partitioning in milk production (lipid metabolism). GIP is secreted in response to the first maternal feed (colostrum) in goat kids - GIP being measured via umbilical vein before its closure. For ethical reasons, GIP secretion has been demonstrated in humans only at approx 10 days of age. With respect to the role of GIP in lipid metabolism, supraphysiological levels have shown a lipogenic action, however the action of collagenase in experimental protocols is known to degrade GIP/ GIP receptors. GIP is part of the diffuse endocrine system and, as a consequence, difficult to demonstrate physiological or clinical effects. In comparison to insulin its effects are very subtle.
Pathology
It has been found that Type 2 diabeticsDiabetes mellitus type 2
Diabetes mellitus type 2formerly non-insulin-dependent diabetes mellitus or adult-onset diabetesis a metabolic disorder that is characterized by high blood glucose in the context of insulin resistance and relative insulin deficiency. Diabetes is often initially managed by increasing exercise and...
are not responsive to GIP and have lower levels of GIP secretion after a meal when compared to non-diabetics. In a research involving knockout mice, it was found that absence of the GIP receptors correlates with resistance to obesity
Obesity
Obesity is a medical condition in which excess body fat has accumulated to the extent that it may have an adverse effect on health, leading to reduced life expectancy and/or increased health problems...
.
External links
- http://web.indstate.edu/thcme/mwking/peptide-hormones.html#gastrin