Gonadotropin releasing hormone (GnRH)

GnRH is delivered pulsatile, i.e. rhythmically, every 60-120 minutes by the hypothalamus and causes LH and FSH to be produced and released from the frontal lobe of the pituitary gland. Due to this mechanism, GnRH is considered to be one of the stimulating (“releasing”) hormones of the hypothalamus. The measurement of the gonadotropin-releasing hormone (GnRH) is normally of no clinical relevance, since only in the connecting veins (portal veins) between the hypothalamus and the pituitary gland are sustained levels found.

Gonadotropins (LH and FSH)

The control hormones LH (luteinizing hormone) and FSH (follicle-stimulating hormone) are also pulsatiously secreted (released) by the front lobe of the pituitary gland (pituitary gland) when stimulated by GnRH. Because of their primary effect on the gonads, i.e. the sex glands, they are also called gonadotropins. The release of LH and FSH begins at puberty, as this is when the stimulating (“releasing”) hormone (GnRH) is released from the hypothalamus.

The two hormones LH and FSH from the front lobe of the pituitary gland stimulate the ovaries and thus stimulate the production of the female sex hormones.There is a so-called negative feedback between the gonadotropins LH and FSH and the level of the female sex hormones. This means that both a high estrogen level and a high progesterone level reduce the release of LH and FSH from the pituitary gland. When the levels of estrogen and progesterone in the blood are low, the release of LH and FSH increases with the aim of boosting the level of female sex hormones again.

In this case one speaks of a positive feedback. In the middle of the female cycle there is a rapid increase in estrogen concentration, which in turn triggers a peak in the release of LH. This large release of LH, also known as the “LH peak”, is responsible for the onset (ovulation).

During menopause, the release of LH and FSH is no longer slowed down by the actual sex hormones as usual, as the production of estrogens and progesterone is steadily decreasing. Thus, feedback mechanisms lead to a significant increase in blood levels of LH and FSH. After the menopause, the control hormones of the pituitary gland also decrease again, but remain elevated compared to the time before the menopause.

In contrast to the GnRH level, the FSH level can be determined in the blood without any problems. The normal values depend on the stage of life the woman is in. During puberty, an FSH level of 2-3 mIE/ml is considered normal.

At sexual maturity, it must be differentiated in which phase of the cycle the blood was taken. In the follicular phase (the time between the onset of menstruation and ovulation) values of 2-10 mIE/ml are considered normal, in the ovulation phase (the time around ovulation) a level of 8-20 mIE/ml is normal, and in the luteal phase (the time between ovulation and the onset of the next menstruation) a level of 2-8 mIE/ml is considered normal. In the postmenopause, FSH levels of > 20 mIE/ml and LH concentrations in the blood between 20 and 100 mIE/ml are found.