When it comes to human sex hormones, estrogens, progestins, and testosterone are most often mentioned first. However, in addition to these, there is the group of gonadotropins, proteohormones that have an equally crucial influence on ovaries, testes and endocrine functions. This group of hormones includes, for example, FSH, LH, prolactin, and hCG.
What are gonadotropins?
Gonadotropins are hormones with a protein structure that promote the development of the male and female gonads and influence hormone balance in the body. A distinction is made between pituitary gonadotropins, which are produced in the pituitary gland, and extrapituitary gonadotropins, which are produced in other glands. However, most of the hormones in the gonadotropin group are produced in the cells of the anterior pituitary gland, where they are released into the bloodstream. Follicle-stimulating hormone (FSH), for example, is a gonadotropin produced in the adenohypophysis that stimulates follicle maturation in women and spermatogenesis in men. Another pituitary sex hormone is luteinizing hormone (LH), which is responsible for the maturation of gametes in both men and women. Human chorionic gonadotropin (hCG) is also a gonadotropin. It ensures the maintenance of pregnancy. Prolactin from the pituitary gland serves the growth of the female mammary gland during pregnancy and the secretion of milk after the birth of the child.
Function, effects, and roles
LH stimulates the formation and release of sex hormones, ie, androgens and estrogens, respectively, in the gonads. In males, it promotes synthesis and secretion of testosterone in the testes. In women, LH plays a significant role in the menstrual cycle, especially in the second half of the month. This is because a steep rise in LH concentrations occurs in the middle of the cycle, which triggers ovulation. In men, FSH stimulates the sertoli cells in the testes, in or between which spermatogenesis takes place. In a woman in the early phase of her cycle, the main effect of FSH is the maturation of follicles from the primordial follicle to the tertiary follicle ready to jump. During pregnancy, hCG maintains the corpus luteum, which in turn produces the hormone progesterone, which is important for maintaining pregnancy. Furthermore, hCG promotes the synthesis of steroid hormones. In women, prolactin promotes milk production in the mammary gland, especially during pregnancy. On the other hand, the hormone has an inhibitory effect on follicle maturation, since no further follicles capable of fertilization are supposed to mature during pregnancy. Prolactin is also thought to play a role in post-orgasm fatigue.
Formation, occurrence, properties, and optimal levels
Both prolactin and LH and FSH are formed in the pituitary gland. Their release is stimulated by another hormone, called gonadotropin-releasing hormone (GnRH) from the hypothalamus. Both hormones in turn inhibit the secretion of GnRH to prevent their own overproduction. LH and FSH as well as hCG have identical alpha subunits, which means that the specific biological function of the hormones is based on the different structures of their beta subunits. The normal values for both LH and FSH are 2-8 U/l in pre-menopausal women, depending on the cycle, and then over 20 U/l (FSH) or 30 U/l (LH) after menopause. Unlike FSH, LH and prolactin, hCG is synthesized outside the pituitary gland. Under the influence of the chorion, the female placenta produces hCG during pregnancy, with the highest hormone level being reached in the second to third month. Prolactin, on the other hand, is produced in the anterior pituitary from the eighth week of pregnancy. Regulation of its release occurs primarily via inhibition by dopamine from the hypothalamus. A synthesis-increasing effect is attributed to estrogen. The normal value of the prolactin concentration in the blood is considered to be around 2-25 μg/l for women. Values above 25 to 200 μg/l are to be classified as elevated, and all even higher concentrations indicate a pathological change. During pregnancy, more prolactin is produced and released in response to a sucking stimulus by the child. In men, prolactin concentrations usually range from 3.0-14.7 μg/l.
Diseases and disorders
Decreased LH concentrations may occur in women as a result of, among other things, secondary ovarian hypofunction secondary to a disorder in the hypothalamus or pituitary gland. This is the case, for example, in anorexia.In men, they may analogously be a consequence of secondary testicular hypofunction or testosterone supplementation. Elevated LH levels are present in women with primary ovarian insufficiency, premature menopause or polycystic ovaries, and in men with primary testicular hypofunction or androgen resistance due to defective androgen receptors. hCG is best known for its function in detecting pregnancy. This is because an elevated urinary hCG level, as measured by standard pregnancy tests, is a relatively sure sign of pregnancy. In the early stages, hCG levels are also used to monitor the progress of a pregnancy. If highly elevated concentrations are detected, these are indications of a multiple pregnancy or a chromosomal abnormality, such as Down syndrome, in the embryo. Excessively low or falling hCG levels can be caused, for example, by an ectopic pregnancy, an impending premature birth or miscarriage. Outside of pregnancy, increased hCG levels can be an indication of ovarian carcinomas, testicular, renal cell and bronchial carcinomas, and hepatocellular carcinomas. Certain medications, such as the neuropletic drug amisulpride, can cause excessive prolactin concentrations in the blood, known as hyperprolactinemia. These can lead to absence of menstruation, spontaneous leakage of breast milk, and infertility. In men, abnormal growth of the mammary glands may occur as a result.
