What Is AMH Hormone?
Anti-Müllerian Hormone or AMH is a glycoprotein hormone involved in folliculogenesis and differentiation. This hormone is closely associated structure-wise to activin and inhibin belonging to the transforming growth factor beta superfamily.
In humans, the fetus develops two sets of ducts after nearly 2 weeks of conception. Out of the two sets, one can develop into the male reproductive tract and the other into the female reproductive tract. If the fetus is a male genetically i.e., presence of XY chromosome, then the embryonic test carried out on the foetus will produce the amh or anti-müllerian hormone. This action leads to the disappearance of the female duct (Müllerian). This is why it is referred to as the anti-Müllerian hormone.
Simultaneously, the testes produce the testosterone causing the male ducts(Wollfian) to thrive. These male ducts form the future parts of the male reproductive system such as the vas deferens, the epididymis, the prostate gland and the seminal vesicles. Similarly, in the female fetus, lack of testosterone causes the disappearance of Wollfian ducts while the Müllerian duct goes on to develop into the uterus, fallopian tubes, cervix and the upper vaginal portion.
What Does AMH level Indicate?
They are a helpful marker of the ovarian reserve as Anti-Müllerian hormone or AMH plasma levels indicate the continuous non-cyclic growth of small follicles reflecting the size of the resting primordial follicle pool. Seemingly, in healthy women, this hormone is the best endocrine marker to assess the age-related decline of ovarian pool. Thereby, it has the capability in predicting the probable future-reproductive lifespan. AMH measurements are significant before the initiation of in vitro fertilization as these hormones can be predictive of ovarian responses such as hyper and poor responses. Recently, the use of AMH was also highlighted in a range of pathological conditions related to the ovaries which includes granulosa cell tumors, polycystic ovary syndrome and also in premature ovarian failure.
In addition, the anti-Müllerian hormone can have a role in adult testes and ovaries and also in checking sex steroid production in puberty. The AMH in ovaries seems to be significant during the initial phases of follicular development which are crucial in containing and assisting the eggs before fertilization. AMH can be determined in bloodstream to examine the count of remaining follicles in a woman’s ovaries, the ovarian reserve as the more the ovarian follicles a woman possesses, the more the AMH her ovaries produce.
What Is Ovarian Reserve?
Ovarian reserves represent the size of the ovarian follicle pool and the quality of the oocytes. It diminishes as the woman ages causing a decline in the functioning of the reproductive system of a woman. As chronological age is not a good indicator of the reproductive aging process and hence the ovarian reserve as there is a considerable amount of variation in age when it comes to menopause and in subfertility.
Activation of AMH
Male fetus has sertoli cells which possess SOX9 that activates the anti-Müllerian hormone. When these are expressed, it obstructs the development of the Müllerian ducts or female reproductive tract in the male embryo thus hindering the development of the female reproductive parts such as the uterus, fallopian tube, upper vagina.
Expression of AMH is pivotal in differentiation of sex at a particular time while fetus is developing. Seemingly, it is checked closely by transcription GATA factors, nuclear receptor SF-1, FSH (follicle-stimulating hormone), sex-reversal gene DAX1 etc.
In women, the AMH is a product of granulosa cells of small antral and preantral follicles. AMH is only found in the ovary until a woman reaches menopause. AMH production checks the phenomena of folliculogenesis as it inhibits follicular recruitment from the resting pool to select the dominant follicle post which the AMH production declines.
Structure Of AMH
Possessing a molar mass of 140 kDa, the hormone is a dimeric glycoprotein. It is composed of two identical subunits associated by sulfide bridges and distinguished by C-terminal dimer and N-terminal dimer. Under the TGF beta signalling pathway, the type I receptor is phosphorylated as the AMH binds to its Type 2 receptor AMHR2.
Function Of AMH
In the reproductive years, the AMH is expressed by the granulosa cells of the ovary, inhibiting excessive follicular recruitment by the FSH thereby limiting the primary follicular formation. The expression of AMH is the most in the recruitment phase of folliculogenesis in the small antral and preantral follicles and expression declines as follicles develop and enter into the selection phase where expression of FSH increases.
AMH averts the development of the female ducts in male mammals into the uterus and other structures of the female reproductive system. It has an ipsilateral effect wherein each of the testis subdues the Müllerian development on its side only. This action in humans occurs in the first 8 weeks of gestation period. In the event of no hormone being produced from the gonads, the female duct develops automatically and the Wolffian ducts(male reproductive duct) on the other hand dissolves
The hormone works when it interacts with particular receptors on the surface of the target tissue cells. Apoptosis or programmed cell death of target tissues i.e., the fetal Müllerian ducts is the most specific effect, best-known that is moderated through the AMH Type II receptors.
Some Other Functions
In males, testis possess sertoli cells which produce the AMH. It’s levels are known to stay high all through one’s childhood. But once he hits puberty to enter adult life, the levels diminish. The AMH is known to check the sex hormone production. The fluctuating levels of the AMH can be involved in the onset of puberty in both males and females.
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