In the pituitary gland, three lobes are distinguished: anterior, middle and posterior; the first two are glandular, the third is of neuroglial origin. In the anterior lobe, the main tropic hormones are formed (ACTH, somatotropic, thyroid-stimulating, follicle-stimulating, luteinizing and lactogenic), in the middle – melanocyte-stimulating (all three types – alpha, beta, gamma), in the back – oxytocin and vasopressin. The latter are formed in the nuclei of the hypothalamus (paraventricular and supraoptic) and pass along the axons to the pituitary gland, which increments them into the blood.
The main property of oxytocin is its stimulating effect on the muscles of the uterus. This property is so characteristic that drugs that have this effect are often referred to as oxytocytic agents. Oxytocin and its synthetic analogs (demoxytocin) are widely used in obstetric and gynecological practice with insufficient functional activity of the myometrium.
Vasopressin, or antidiuretic hormone, is structurally similar to oxytocin, but slightly differs in the content and location of amino acid residues. The main effect of vasopressin is to regulate water reabsorption by the distal renal tubules. By increasing the permeability of the tubules, it promotes water reabsorption and decreases urine output. In large doses, vasopressin has a stimulating effect on smooth muscles (vessels, uterus, intestines). The increase in blood pressure caused by vasopressin is due to a direct myotropic effect on arterioles and capillaries. In medical practice, along with vasopressin, its synthetic analogues and homologues (desmopressin, terlipressin) are used.
Gonadotropins are protein-peptide hormones that stimulate the development and function of the male and female gonads. The synthesis and secretion of gonadotropins occurs under the influence of hypothalamic neurohormones (releasing factors). From the anterior lobe of the pituitary gland, three hormones are released that affect the functions of the gonads: follicle-stimulating (FSH), luteinizing (LH), prolactin. FSH promotes the development of the ovaries and the maturation of follicles in them, it is also necessary for the manifestation of the action of LH, in addition, it enhances spermatogenesis in the male gonads. LH in women promotes the transition of a developed follicle to the corpus luteum and lengthens the life of the latter. In men, this hormone stimulates the function of interstitial cells of the testes (it is also called a hormone that stimulates interstitial cells), the activation of spermatogenesis caused by it is mainly associated with an increase in testosterone synthesis, it also contributes to the descent of the testicles with cryptorchidism; under the influence of this hormone, the content of cholesterol in the blood increases; it has a fat-mobilizing effect. Prolactin enhances the hormonal function of the corpus luteum and the activity of progesterone, increases the secretion of milk in the mammary glands in the postpartum period.
In medical practice, menopausal gonadotropin (menotropins), as well as its homologues (urofollitropin, follitropin alpha, follitropin beta), are used as drugs with FSH activity. Menopausal gonadotropin is obtained from the urine of women who are in menopause. The drug with LH activity is chorionic gonadotropin obtained from the urine of pregnant women.
Antigonadotropins suppress the release of pituitary gonadotropic hormones (LH and FSH). Due to their antigonadotropic action, they are used in the treatment of endometriosis (danazol) with concomitant infertility, benign breast neoplasms (fibrocystic mastitis, etc.), premenstrual syndrome, gynecomastia and other diseases in which blockade of the increment of gonadotropins is indicated.
Other tropic hormones of the anterior lobe either activate the functions of the corresponding glands, or directly affect metabolic processes. ACTH and its analogs (corticotropin, tetracosactide) in the adrenal cortex increases the synthesis of glucocorticoids, somatotropin causes the growth of the skeleton and the whole organism (its release is controlled by the hypothalamus through the production of somatostatin, which inhibits the liberation of growth hormone; in medicine, synthetic substitutes for somatostatin, ltreotidine ), thyrotropin – stimulates the secretion of thyroxine, lactogenic – the development of mammary glands and lactation.
Below is a list of hormones of the hypothalamus, pituitary gland, gonadotropins and their antagonists:
- Menotropins (Menotropina)
- Chorionic gonadotropin
- Follitropin alpha
- Lutropin alpha
- Choriogonadotropin alpha
- Follitropin beta
- Corifollitropin alpha