C- Reactive Protein (CRP)
13. Hormones of hypothalamus and hypophysis
Author: MUDr. Tomáš Franěk
Reviewers: doc. RNDR. Kristian Šafarčík, Ing. Vladimír Bartoš, Ph.D.
13.1. Prolactin
Prolactin is a polypeptide hormone produced in eosinophilic cells of the anterior pituitary, whose secretion is cen-trally inhibited from the hypothalamus through the action of prolactin-inhibiting hormone (PIH) and dopamine; con-versely, its secretion is stimulated by the effect of serotonergic neurons, prolactin-releasing hormone and some drugs.
Prolactin stimulates the transformation of lobuloalveolar epithelium in the mammary gland into the secretory type with subsequent breast milk formation. The action of prolactin on ovaries inhibits follicle maturation and aromatase activity with a subsequent decrease in oestradiol synthesis.
Indications for the prolactin assay include infertility, menstrual cycle disorders such as amenorrhoea, dysmenorr-hoea and galactorrdysmenorr-hoea, gynaecomastia in males, tumours and traumas in the sella turcica region, and signs of virili-zation.
Physiological elevated values can be found in pregnant women, postpartum lactation, extreme stress, prolactino-mas and ectopic production. Furthermore, prolactin secretion is stimulated by the following drugs: chlorpromazine, haloperidol, phenothiazines, cimetidine, tricyclic antidepressants and reserpine, metoclopramide.
13.2. FSH – Follicle Stimulating Hormone
FSH is a glycoprotein secreted by the basophilic gonadotrophic cells of the anterior pituitary. The function of FSH is to stimulate the growth and maturation of ovarian follicles; FSH together with LH support oestrogen secretion and participate in endometrium transformation in the proliferative phase of menstrual cycle. The stimulation of Sertoli cells by the FSH helps maintain male spermatogenic epithelium, and affects the synthesis of inhibin and binding protein for angrogens (SHBG) in seminiferous tubules.
Indications for the FSH assay include amenorrhoea, dysmenorrhoea, oligomenorrhoea, infertility, primary and se-condary hypogonadism, conditions following cytostatic treatment or radiation, atypical sexual maturation in children, pituitary traumas and tumours, gonadal dysgenesis, and hypothalamic-pituitary-gonadal axis disorders. The LH and FSH assay is also important for diagnosis in polycystic ovary syndrome where the FSH level decreases or is normal and the LH level increases, so that the LH/FSH ratio increases in contrast to healthy individuals.
Elevated values can be found in primary ovarian insufficiency, Turner syndrome, climacterium praecox, gonadotro-pinomas, and physiologically elevated values in the menopausal period and primary hypogonadism in males. Reduced levels can be found in pituitary traumas and endocrine-inactive tumours, anorexia nervosa, secondary ovarian insuffi-ciency and pseudopubertas praecox.
13.3. LH – Luteinizing Hormone
LH is a glycoprotein secreted by the basophilic gonadotropic cells of the adenohypophysis. The function of LH is to act on ovarian theca cells where stimulation of steroid synthesis takes place. With the assistance of FSH, the steroids subsequently transform into oestradiol. In addition, LH is responsible for the final ripening of the ovarian follicles and also induces ovulation and the early development of the corpus luteum with subsequent progesterone secretion. In males, LH stimulates testosterone synthesis in Leydig cells in the interstitial tissue of the testicles.
Indications for the LH assay include amenorrhoea, dysmenorrhoea, oligomenorrhoea, infertility, primary and se-condary hypogonadism, conditions following cytostatic treatment or radiation, atypical sexual maturation in children, pituitary traumas and tumours, gonadal dysgenesis, selected chromosome aberrations, and hypothalamic-pituitary--gonadal axis disorders.
Elevated values can be found in primary ovarian insufficiency, Turner syndrome, climacterium praecox, gonadotro-pinomas, and physiologically elevated values in the menopausal period and primary hypogonadism in males. Reduced levels can be found in pituitary traumas and tumours, anorexia nervosa, secondary ovarian insufficiency and pseudo-pubertas praecox.
13.4. Oxytocin
Oxytocin is a peptide hormone formed primarily in the paraventricular nuclei of the hypothalamus, from where it is transported and deposited in the granules of posterior pituitary nerve endings. The function of this hormone is to act on myoepithelial cells lining mammary gland outlets, which causes milk to be ejected from the mammary gland.
Another important function is the effect on the smooth muscles of the uterus during pregnancy, by which it enhances labour at the end of pregnancy. Assays for this hormone are not common as their importance for diagnosis is low.
13.5. ADH – Antidiuretic Hormone
ADH or vasopressin is another hormone stored in the posterior pituitary. This hormone is composed of 9 amino acids. The basic physiological action of ADH is water retention in the body, and ADH thus participates in the home-ostasis of the body. ADH is secreted as a result of an increase in blood plasma osmolality, and its function is to incre-ase the permeability of distal tubules and collecting ducts in the kidneys so thatwater can enter the hypertonic renal interstitium. Secretion disorders, or disorders at the peripheral receptor level, will manifest themselves as diabetes insipidus with the inability of the kidneys to concentrate urine, with specific clinical impacts. The opposite situation occurs following some traumas or bleeding in the CNS when ADH overproduction occurs with normal blood plasma osmolality. This condition is referred to as inappropriate ADH secretion (SIADH). Indications for the ADH assay include diabetes insipidus and SIADH.
13.6. TSH – Thyroid-Stimulating Hormone or Thyrotropin
TSH is a peptide hormone synthesized by thyrotrope cells in the anterior pituitary gland. The function of this hor-mone is to stimulate thyroid cells to produce peripheral horhor-mones, i.e. thyroxine and triiodothyronine. Secretion of this tropic hormone is partly regulated by direct inhibitory (negative) feedback caused by a high thyroid hormone level in the blood, which inhibits the adenohypophysis. A partial role is also played by neural mechanisms acting through the hypothalamus.
The assay for this hormone is essential for the diagnosis of thyroid gland disorders. Elevated levels can be found in hypothyroidism, subclinical hypothyroidism, following thyroidectomy, or pituitary adenoma producing TSH. Reduced levels can be found in hyperthyroidism, hypopituitarism and some non-thyroidal diseases such as febrile conditions, myocardial infarction, serious traumas and operations.
13.7. ACTH – Adrenocorticotropic Hormone
ACTH is a hormone synthesized in adenohypophysis cells in the form of a precursor, pro-opiomelanocortin (POMC).
This precursor is subsequently cleaved by enzymes into several physiologically active peptides, one of them being ACTH. This hormone is the main hormone that regulates the production of glucocorticoid hormones in the adrenal cortex. Assays for this hormone are not common due to specific and complicated pre-analytical factors, and are solely used in the diagnosis of adrenal cortex function disorders, in particular to distinguish between a primary and secondary disorder of cortisol secretion.
Elevated levels can be found in primary hypercorticalism, Addison’s disease, adrenogenital syndrome, Cushing’s disease and adrenal damage. Reduced levels can be found in Cushing’s syndrome, when feedback ACTH inhibition occurs.
13.8. STH – Somatotropin (GH – growth hormone)
STH is a polypeptide hormone produced by acidophil cells in the adenohypophysis. Secretion is regulated from the hypothalamus by regulatory hormones such as somatoliberin and somatostatins. The function of this hormone is to control and stimulate growth due to different effects on metabolism. Major effects include the stimulation of proteo-synthesis and inducing a positive nitrogen balance; furthermore, STH has anti-insulin effects and increases the content of free fatty acids in the blood plasma. Peripheral effects of this hormone depend on the production of peptide growth factors known as somatomedins (IGF-1 and IGF-2).
Indications for the STH assay include growth disorders, nanism or acromegaly. Elevated levels can be found in gi-gantism, endocrine-active pituitary tumours and acromegaly. Reduced levels can be seen in nanism.