Releasing hormones are those hormones that are produced in a specific area of the brain, the hypothalamus. They are releasing hormones and neuropeptides that are released from the brain into the blood, from where they travel to the pituitary gland. There, the releasing hormones induce the release of other hormones by the pituitary gland.
What are releasing hormones?
Releasing hormones control the release of other hormones. They are also called hypophysiotropic or hypothalamic hormones. These releasing hormones, which are produced by the hypothalamus, are a number of hormones. They include corticotropin-releasing hormone, tyrotropin-releasing hormone, growth hormone-releasing hormone, and gonadotropin-releasing hormone. Two other hormones belong to this class, but they have an inhibitory effect on the release of other hormones. These are the release-inhibiting hormones. These are somatostatin and dopamine. The following text will deal with the releasing hormones and will not discuss the release-inhibiting hormones in detail.
Function, action, and roles
Tyrotropin-releasing hormone (TRH) causes the pituitary gland to induce the formation and release of thyroid-stimulating hormone (TSH) and prolactin. In addition, TSH then leads to the release of the thyroid hormones T3 and T4. TRH is released when body temperature decreases and allows the TSH and subsequent release to stimulate metabolism. Indirectly, it acts on gastric acid production and peristaltic movement of the intestine. The TRH increases the heartbeat and also the blood pressure. It also has a regulatory effect on insulin production. Corticotropin-releasing hormone (CRH) also acts in the anterior pituitary, where it activates cAMP-dependent protein kinase A. This induces the release of adrenocorticotropic hormone and this has an activating effect on the sympathetic nervous system. The CRH ensures the release of cortisone which takes place due to inflammatory processes in the body. Growth hormone-releasing hormone, also known as somatoliberin, regulates the release of somatotropin. Somatotropin is the growth hormone that is also released from the anterior pituitary. Gonadotropin-releasing hormone, which is also called follicle-stimulating hormone-releasing hormone, stimulates the pituitary gland to release follicle-stimulating hormone (FSH) and luteinizing hormone. These hormones are gonadotropins, which are also called sex hormones. They regulate the function of the ovaries and testes in the human body. FSH stimulates egg growth in the female and Luteinizing Hormone assists ovulation in the female and maturation of sperm in the male. However, in addition to the pituitary gland, gonadotropin-releasing hormone also acts directly on tissues such as the mammary gland, ovaries, lymphocytes and prostate.
Formation, occurrence, properties, and optimal levels
Tyrotropin-releasing hormone (TRH) is produced in the hypothalamus when the signal from adrenergic or serotoninergic neurons reaches the hypothalamus. TRH is then produced and transported via the hypothalamic-pituitary portal system. Secretion is subject to a circadian rhythm due to regulation by the nucleus suprachiasmaticus. The highest release occurs at midnight and the lowest amount is present in the afternoon. This type of release is also influenced by the limbic system to prepare the body for stress but also to regulate the rhythm between sleep phases and phases during which the person is awake. It also serves to regulate the temperature of the body and suppress pain. It also inhibits food and fluid intake. Corticotropin-releasing hormone is secreted in a circadian rhythm. In the morning, there is an increased release of this hormone compared to the evening. The release of corticotropin-releasing hormone is regulated by negative feedback through its own release. In addition, its release is also regulated by interleukin-1beta and tumor necrosis factor (TNF). Growth hormone-releasing hormone is produced in the nucleus arcuatus of the hypothalamus.Gonadotropin-releasing hormone is also produced by special types of cells in the hypothalamus and then passed on to the pituitary gland by the circulating blood. This release occurs approximately every 2 hours in the human body and is controlled by the nucleus arcuatus of the hypothalamus. This rhythmic release of the hormone is important for the production of gonadotropin in the pituitary gland.
Diseases and disorders
In a defective pituitary gland, which is called anterior pituitary insufficiency, the anterior lobe of this gland can no longer respond adequately to TRH. As a result, TSH secretion is too low for the body. No T3 and T4 can be produced and released. This is called secondary hypothyroidism. Tertiary hypothyroidism, or Pickardt syndrome, occurs because the vascular system between the hypothalamus and pituitary gland is disturbed. In the case of growth hormone-releasing hormone, pancreatic carcinoma may cause a release of this hormone. In case of an excessive production of the hormone, the so-called giant growth can occur. If there is a lack of release of gonadotropin-releasing hormone, this is called hypogonadotropic hypogonadism. In this case, there is a low release of luteinizing hormone and FSH due to an insufficient concentration of gonadotropin-releasing hormone. This can occur due to a dysfunction of the hypothlamus, which is also called tertiary hypogonadism. As in the case of tyrotropin-releasing hormone, the low release of gonadotropin-releasing hormone may also be due to a disturbance in the transport of blood from the hypothalamus to the pituitary gland. Also, prolonged anorexia may lead to a defect in gonadotropin-releasing hormone release.
