What are gonadotropins?
Gonadotropins are hormones that control the function of the gonads, also known as the sex glands. In men, these are the testicles, and in women, the ovaries. The two most important gonadotropins are luteinizing hormone (LH) and follicle-stimulating hormone (FSH).
Both hormones are produced in the pituitary gland (hypophysis) and play a central role in regulating testosterone production and sperm formation. Together with the hypothalamus, they form the hormonal regulatory circuit of the HPG axis (hypothalamus-pituitary-gonadal axis).
Measuring gonadotropins is one of the most important laboratory tests for investigating testosterone deficiency or fertility disorders.
What gonadotropins are there?
In men, two gonadotropins are particularly important:
- LH (luteinizing hormone)
- FSH (follicle-stimulating hormone)
Both hormones are controlled by the hormone GnRH (gonadotropin-releasing hormone) from the hypothalamus.
Although LH and FSH work closely together, they perform different functions.
What functions does LH have?
LH stimulates the so-called Leydig cells in the testicles.
This stimulates the production of testosterone. The testosterone produced affects numerous bodily functions, including:
- Libido
- Muscle building
- Bone health
- Energy balance
- Mood
- Sexual function
If testosterone production is reduced, the pituitary gland usually increases LH secretion to stimulate the testicles more strongly.
What functions does FSH have?
FSH acts mainly on the Sertoli cells in the testicles.
It supports spermatogenesis, i.e., the formation and maturation of sperm. Thus, FSH plays a crucial role in male fertility. You can read more about the relationship between hormones and fertility in our article Testosterone and Fertility.
Together with testosterone, FSH ensures the normal development and function of sperm cells.
How are gonadotropins regulated?
Gonadotropins are released via the HPG axis.
The hormonal process can be simplified as follows:
- The hypothalamus produces GnRH.
- GnRH stimulates the pituitary gland to release LH and FSH.
- LH and FSH act on the testicles.
- The testicles produce testosterone and sperm.
- Testosterone and estradiol inhibit further secretion of GnRH, LH, and FSH through a negative feedback mechanism.
This regulatory system ensures that the hormonal balance remains as constant as possible.
When are gonadotropins measured?
Measuring LH and FSH is an important part of hormonal diagnostics.
Typical reasons for measurement include:
- Suspected testosterone deficiency
- Investigation of hypogonadism
- Fertility disorders
- Reduced libido
- Erectile dysfunction
- Monitoring of hormonal disorders
The values are usually assessed together with testosterone and other hormones.
What do elevated gonadotropins mean?
Elevated LH and FSH levels often indicate that the testicles are not responding sufficiently to hormonal stimulation.
Typical causes include:
- Primary hypogonadism
- Hypergonadotropic hypogonadism
- Genetic disorders
- Testicular damage
- Age-related decline in testicular function
The elevated values represent the body's attempt to compensate for reduced testosterone production.
What do low gonadotropins mean?
Low or inappropriately normal LH and FSH levels in relation to reduced testosterone often indicate a disruption of the hormonal regulatory circuit in the brain.
Possible causes include:
- Secondary hypogonadism
- Hypogonadotropic hypogonadism
- Pituitary gland disorders
- Hypothalamus disorders
- Hyperprolactinemia
- Functional hypogonadism, for example in obesity or chronic illnesses
For the correct interpretation, gonadotropins are always assessed together with other laboratory values.
Conclusion
Gonadotropins are the hormones LH and FSH, which are produced in the pituitary gland and control the function of the testicles. They regulate testosterone production and sperm formation and are an important part of the HPG axis.
Measuring gonadotropins provides important clues as to whether the cause of testosterone deficiency lies in the testicles or in the hormonal control centers of the brain.