Proteohormones represent the largest group of hormones with various functions in the organism. They are composed of chains of amino acids linked by peptide bonds and are all water-soluble.
What are proteohormones?
Proteohormones are composed of peptide chains of amino acids. Among them are long-chain proteins with a chain length of more than 100 amino acids and short- and medium-chain peptides with a chain length of up to 100 amino acids. All proteohormones are water soluble. Within the chemical classification of hormones, they represent the largest hormone group. As hormones, they are so-called messenger substances, which are formed in endocrine glands or special cells and cause a corresponding effect in target organs. They can be transported to the respective target site via the bloodstream or act in the immediate environment. The long-chain proteohormones include the growth hormone somatotropin, thyrotropin (regulates the formation of thyroid hormones) or luteotropin (LH), which is responsible for ovulation in women or sperm maturation in men. Medium-chain proteohormones of less than 100 amino acids include insulin or glucagon, for example, while short-chain proteohormones of nine amino acids each include the hormones oxytocin or vasopressin.
Function, effects, and roles
The proteohormones, like the other hormones of the organism, perform different functions. All body functions such as blood sugar regulation, food intake, regulation of water balance and mineral metabolism, digestion, sexual function, brood care, calcium metabolism, and many others depend on the influence of proteohormones along with other hormones. The proteohormone insulin, for example, regulates blood sugar levels by ensuring the transport of glucose into the individual cells of the body. To perform this function, it docks onto special receptors for insulin, preparing the cell for glucose uptake. Insulin’s counterpart is glucagon, which ensures the breakdown of glucogen stored in the liver into glucose when blood glucose levels are low. Other proteohormones such as leptin or ghrelin regulate food intake by acting on the hunger center. Thus, the influence of leptin produced in fat cells lowers the feeling of hunger, while appetite is increased by ghrelin. Vasopressin, made up of nine amino acids, is responsible for regulating water balance in the body. Oxytocin, also with nine amino acids, is in turn secreted for the induction of labor. It also regulates brood care and behavior between mother and child and between couples. It is also thought to have an overall influence on social behavior. Another proteohormone, gastrin, controls the formation of gastric acid and the secretion of the enzyme pepsin and is thus responsible for gastric function. The medium-chain peptides parathyroid hormone and calcitonin raise or lower blood calcium concentrations and are thus the hormones that regulate calcium and bone metabolism.
Formation, occurrence, properties, and optimal levels
Proteohormones, like all other hormones, are produced in specialized endocrine glands or specific hormone-producing cells. Important endocrine glands that also produce proteohormones include the pancreas, thyroid gland, parathyroid gland, or pituitary gland. Hormone-producing cells also exist in the stomach, liver, nervous system and other organs. For the proteohormones, synthesis works in the same way as for the other proteins. The DNA contains the genetic code for the corresponding proteins or peptides. When required, this is read in the responsible cell, resulting in the synthesis of the corresponding proteohormone. For example, the hormones insulin and glucagon are produced in the islet cells of Langerhans in the pancreas. Insulin lowers blood glucose levels, while its counterpart glucagon causes blood glucose levels to rise. Leptin is produced in the fat cells. The counterpart ghrelin is synthesized in the gastric mucosa or pancreas. Vasopressin and oxytocin are produced in the nerve cells of the hypothalamus and stored there. Their release then occurs when needed. Gastrin is a hormone of the gastrointestinal tract and is also produced there for gastric function.In turn, the hormones calcitonin and parathyroid hormone, which are responsible for calcium metabolism, are produced in the thyroid and parathyroid glands.
Diseases and disorders
Deficiency or overproduction of certain proteohormones can lead to serious diseases. Well-known and frequently described is the influence of insulin on the regulation of blood glucose levels. If insulin is missing or its effectiveness is reduced due to poorly functioning insulin receptors, a so-called diabetes develops. Type 1 diabetes mellitus is always caused by the absence or deficiency of insulin, for example by destruction of the pancreatic islet cells of Langerhans. Type 2 diabetes mellitus is usually caused by insulin resistance (poorly functioning insulin receptors), which can later lead to a true insulin deficiency. It is well known that diabetes, if poorly controlled, leads to various diseases, including arteriosclerosis and lipometabolic disorders. If, on the other hand, the hormones calcitonin or parathormone do not function effectively, calcium metabolism is disturbed. Among many other health problems, this can also lead to bone loss. The deficiency of another hormone, vasopressin, leads to a disturbance in water balance. If vasopressin is missing, the so-called diabetes insipidus occurs, in which the body loses up to 20 liters of water daily through urine output. This loss must then be compensated by drinking the same amount of water.
