Activin and inhibin
Encyclopedia
Activin and inhibin are two closely related protein
complexes that have almost directly opposite biological effects. Activin enhances FSH
biosynthesis
and secretion
, and participates in the regulation of the menstrual cycle
. Many other functions have been found to be exerted by activin, including roles in cell proliferation, differentiation
, apoptosis
, metabolism
, homeostasis
, immune response
, wound repair
, and endocrine
function. Conversely inhibin down regulates FSH synthesis and inhibits FSH secretion.
Activin is a dimer
composed of two identical or very similar beta subunits. Inhibin is also a dimer wherein the first component is a beta subunit similar or identical to the beta subunit in activin. However, in contrast to activin, the second component of the inhibin dimer is a more distantly-related alpha subunit. Activin, inhibin and a number of other structurally related proteins such as anti-Müllerian hormone
, bone morphogenetic protein
, and growth differentiation factor
belong to the TGF-β
protein superfamily.
The alpha and beta subunits share approximately 25% sequence similarity, whereas the similarity between beta subunits is approximately 65%.
In mammals, four beta subunits have been described, called activin βA, activin βB, activin βC and activin βE. Activin βA and βB are identical to the two beta subunits of inhibin. A fifth subunit, activin βD, has been described in Xenopus laevis
. Two activin βA subunits give rise to activin A, one βA, and one βB subunit gives rise to activin AB, and so on. Various, but not all theoretically possible, heterodimers have been described. The subunits are linked by a single covalent disulfide bond.
The βC
subunit is able to form activin heterodimers with βA or βB subunits but is unable to dimerize with inhibin α.
s, pituitary gland
, placenta
, and other organs:
production and GnRH
release from the hypothalamus. However, the overall mechanism differs between the genders:
, placenta
and other organs.
In women, FSH stimulates the secretion of inhibin from the granulosa cell
s of the ovarian follicles in the ovaries
. In turn, inhibin suppresses FSH.
Inhibin secretion is diminished by GnRH
, and enhanced by insulin-like growth factor
-1 (IGF-1).
s, located in the seminiferous tubules
inside the testes. Androgens stimulate inhibin production; this peptide
may also help to locally regulate spermatogenesis
.
activities in their cytoplasmic domains:
Activin binds to the Type II receptor and initiates a cascade reaction that leads to the recruitment, phosphorylation, and activation of Type I activin receptor. This then interacts with and then phosphorylates SMAD2
and SMAD3
, two of the cytoplasmic SMAD
proteins.
Smad3 then translocates to the nucleus and interacts with SMAD4
through multimerization, resulting in their modulation as transcription factor
complexes responsible for the expression of a large variety of genes.
, and a decreased estriol
) is suggestive of the presence of a fetus with Down syndrome
. As a screening test, abnormal quad screen test results need to be followed up with more definitive tests.
It also has been used as a marker for ovarian cancer
.
Inhibin B may be used as a marker of spermatogenesis
function and male infertility
. The mean serum inhibin B level is significantly higher among fertile men (approximately 140 pg/mL) than in infertile men (approximately 80 pg/mL). In men with azoospermia
, a positive test for inhibin B slightly raises the chances for successfully achieving pregnancy through testicular sperm extraction
(TESE), although the association is not very substantial, having a sensitivity of 0.65 (95% confidence interval [CI]: 0.56–0.74) and a specificity of 0.83 (CI: 0.64–0.93) for prediction the presence of sperm in the testes in non-obstructive azoospermia.
Protein
Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...
complexes that have almost directly opposite biological effects. Activin enhances FSH
Follicle-stimulating hormone
Follicle-stimulating hormone is a hormone found in humans and other animals. It is synthesized and secreted by gonadotrophs of the anterior pituitary gland. FSH regulates the development, growth, pubertal maturation, and reproductive processes of the body. FSH and Luteinizing hormone act...
biosynthesis
Biosynthesis
Biosynthesis is an enzyme-catalyzed process in cells of living organisms by which substrates are converted to more complex products. The biosynthesis process often consists of several enzymatic steps in which the product of one step is used as substrate in the following step...
and secretion
Secretion
Secretion is the process of elaborating, releasing, and oozing chemicals, or a secreted chemical substance from a cell or gland. In contrast to excretion, the substance may have a certain function, rather than being a waste product...
, and participates in the regulation of the menstrual cycle
Menstrual cycle
The menstrual cycle is the scientific term for the physiological changes that can occur in fertile women for the purpose of sexual reproduction. This article focuses on the human menstrual cycle....
. Many other functions have been found to be exerted by activin, including roles in cell proliferation, differentiation
Cellular differentiation
In developmental biology, cellular differentiation is the process by which a less specialized cell becomes a more specialized cell type. Differentiation occurs numerous times during the development of a multicellular organism as the organism changes from a simple zygote to a complex system of...
, apoptosis
Apoptosis
Apoptosis is the process of programmed cell death that may occur in multicellular organisms. Biochemical events lead to characteristic cell changes and death. These changes include blebbing, cell shrinkage, nuclear fragmentation, chromatin condensation, and chromosomal DNA fragmentation...
, metabolism
Metabolism
Metabolism is the set of chemical reactions that happen in the cells of living organisms to sustain life. These processes allow organisms to grow and reproduce, maintain their structures, and respond to their environments. Metabolism is usually divided into two categories...
, homeostasis
Homeostasis
Homeostasis is the property of a system that regulates its internal environment and tends to maintain a stable, constant condition of properties like temperature or pH...
, immune response
Immune system
An immune system is a system of biological structures and processes within an organism that protects against disease by identifying and killing pathogens and tumor cells. It detects a wide variety of agents, from viruses to parasitic worms, and needs to distinguish them from the organism's own...
, wound repair
Wound healing
Wound healing, or cicatrisation, is an intricate process in which the skin repairs itself after injury. In normal skin, the epidermis and dermis exists in a steady-state equilibrium, forming a protective barrier against the external environment...
, and endocrine
Endocrine system
In physiology, the endocrine system is a system of glands, each of which secretes a type of hormone directly into the bloodstream to regulate the body. The endocrine system is in contrast to the exocrine system, which secretes its chemicals using ducts. It derives from the Greek words "endo"...
function. Conversely inhibin down regulates FSH synthesis and inhibits FSH secretion.
Activin is a dimer
Protein dimer
In biochemistry, a dimer is a macromolecular complex formed by two, usually non-covalently bound, macromolecules like proteins or nucleic acids...
composed of two identical or very similar beta subunits. Inhibin is also a dimer wherein the first component is a beta subunit similar or identical to the beta subunit in activin. However, in contrast to activin, the second component of the inhibin dimer is a more distantly-related alpha subunit. Activin, inhibin and a number of other structurally related proteins such as anti-Müllerian hormone
Anti-müllerian hormone
Anti-Müllerian hormone also known as AMH is a protein that, in humans, is encoded by the AMH gene. It inhibits the development of the Müllerian ducts in the male embryo. It has also been called Müllerian inhibiting factor , Müllerian-inhibiting hormone , and Müllerian-inhibiting substance...
, bone morphogenetic protein
Bone morphogenetic protein
Bone morphogenetic proteins are a group of growth factors also known as cytokines and as metabologens . Originally discovered by their ability to induce the formation of bone and cartilage, BMPs are now considered to constitute a group of pivotal morphogenetic signals, orchestrating tissue...
, and growth differentiation factor
Growth differentiation factor
Growth differentiation factors are a subfamily of proteins belonging to the transforming growth factor beta superfamily that have functions predominantly in development.-Types:...
belong to the TGF-β
TGF beta
Transforming growth factor beta is a protein that controls proliferation, cellular differentiation, and other functions in most cells. It plays a role in immunity, cancer, heart disease, diabetes, Marfan syndrome, and Loeys–Dietz syndrome....
protein superfamily.
Structure
The activin and inhibin protein complexes are both dimeric in structure, and, in each complex, the two monomers are linked to one another by a single disulfide bond. In addition, both complexes are derived from the same family of related genes and proteins but differ in their subunit composition. Below is a list of the most common inhibin and activin complexes and their subunit composition:
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The alpha and beta subunits share approximately 25% sequence similarity, whereas the similarity between beta subunits is approximately 65%.
In mammals, four beta subunits have been described, called activin βA, activin βB, activin βC and activin βE. Activin βA and βB are identical to the two beta subunits of inhibin. A fifth subunit, activin βD, has been described in Xenopus laevis
African clawed frog
The African clawed frog is a species of South African aquatic frog of the genus Xenopus. Its name is derived from the three short claws on each hind foot, which it uses to tear apart its food...
. Two activin βA subunits give rise to activin A, one βA, and one βB subunit gives rise to activin AB, and so on. Various, but not all theoretically possible, heterodimers have been described. The subunits are linked by a single covalent disulfide bond.
The βC
INHBC
Inhibin beta C chain is a protein that in humans is encoded by the INHBC gene.-Further reading:...
subunit is able to form activin heterodimers with βA or βB subunits but is unable to dimerize with inhibin α.
Activin
Activin is produced in the gonadGonad
The gonad is the organ that makes gametes. The gonads in males are the testes and the gonads in females are the ovaries. The product, gametes, are haploid germ cells. For example, spermatozoon and egg cells are gametes...
s, pituitary gland
Pituitary gland
In vertebrate anatomy the pituitary gland, or hypophysis, is an endocrine gland about the size of a pea and weighing 0.5 g , in humans. It is a protrusion off the bottom of the hypothalamus at the base of the brain, and rests in a small, bony cavity covered by a dural fold...
, placenta
Placenta
The placenta is an organ that connects the developing fetus to the uterine wall to allow nutrient uptake, waste elimination, and gas exchange via the mother's blood supply. "True" placentas are a defining characteristic of eutherian or "placental" mammals, but are also found in some snakes and...
, and other organs:
- In the ovarian follicleOvarian follicleOvarian follicles are the basic units of female reproductive biology, each of which is composed of roughly spherical aggregations of cells found in the ovary. They contain a single oocyte . These structures are periodically initiated to grow and develop, culminating in ovulation of usually a single...
, activin increases FSH binding and FSH-induced aromatizationAromaticityIn organic chemistry, Aromaticity is a chemical property in which a conjugated ring of unsaturated bonds, lone pairs, or empty orbitals exhibit a stabilization stronger than would be expected by the stabilization of conjugation alone. The earliest use of the term was in an article by August...
. It participates in androgenAndrogenAndrogen, also called androgenic hormone or testoid, is the generic term for any natural or synthetic compound, usually a steroid hormone, that stimulates or controls the development and maintenance of male characteristics in vertebrates by binding to androgen receptors...
synthesis enhancing LHLuteinizing hormoneLuteinizing hormone is a hormone produced by the anterior pituitary gland. In females, an acute rise of LH called the LH surge triggers ovulation and development of the corpus luteum. In males, where LH had also been called interstitial cell-stimulating hormone , it stimulates Leydig cell...
action in the ovaryOvaryThe ovary is an ovum-producing reproductive organ, often found in pairs as part of the vertebrate female reproductive system. Ovaries in anatomically female individuals are analogous to testes in anatomically male individuals, in that they are both gonads and endocrine glands.-Human anatomy:Ovaries...
and testisTesticleThe testicle is the male gonad in animals. Like the ovaries to which they are homologous, testes are components of both the reproductive system and the endocrine system...
. In the male, activin enhances spermatogenesisSpermatogenesisSpermatogenesis is the process by which male primary germ cells undergo division, and produce a number of cells termed spermatogonia, from which the primary spermatocytes are derived. Each primary spermatocyte divides into two secondary spermatocytes, and each secondary spermatocyte into two...
.
- Activin is strongly expressed in wounded skinSkin-Dermis:The dermis is the layer of skin beneath the epidermis that consists of connective tissue and cushions the body from stress and strain. The dermis is tightly connected to the epidermis by a basement membrane. It also harbors many Mechanoreceptors that provide the sense of touch and heat...
, and overexpression of activin in epidermis of transgenicGenetically modified organismA genetically modified organism or genetically engineered organism is an organism whose genetic material has been altered using genetic engineering techniques. These techniques, generally known as recombinant DNA technology, use DNA molecules from different sources, which are combined into one...
miceMouseA mouse is a small mammal belonging to the order of rodents. The best known mouse species is the common house mouse . It is also a popular pet. In some places, certain kinds of field mice are also common. This rodent is eaten by large birds such as hawks and eagles...
improves wound healing and enhances scarScarScars are areas of fibrous tissue that replace normal skin after injury. A scar results from the biological process of wound repair in the skin and other tissues of the body. Thus, scarring is a natural part of the healing process. With the exception of very minor lesions, every wound results in...
formation. Its action in wound repair and skin morphogenesisMorphogenesisMorphogenesis , is the biological process that causes an organism to develop its shape...
is through stimulation of keratinocyteKeratinocyteKeratinocytes are the predominant cell type in the epidermis, the outermost layer of the human skin, constituting 95% of the cells found there. Those keratinocytes found in the basal layer of the skin are sometimes referred to as "basal cells" or "basal keratinocytes"...
s and stromal cellStromal cellIn cell biology, stromal cells are connective tissue cells of any organ, for example in the uterine mucosa , prostate, bone marrow, and the ovary. They are cells that support the function of the parenchymal cells of that organ...
s in a dose-dependent manner.
- Activin also regulates the morphogenesisMorphogenesisMorphogenesis , is the biological process that causes an organism to develop its shape...
of branching organs such as the prostateProstateThe prostate is a compound tubuloalveolar exocrine gland of the male reproductive system in most mammals....
, lungLungThe lung is the essential respiration organ in many air-breathing animals, including most tetrapods, a few fish and a few snails. In mammals and the more complex life forms, the two lungs are located near the backbone on either side of the heart...
, and especially kidneyKidneyThe kidneys, organs with several functions, serve essential regulatory roles in most animals, including vertebrates and some invertebrates. They are essential in the urinary system and also serve homeostatic functions such as the regulation of electrolytes, maintenance of acid–base balance, and...
. Activin A increased the expression level of type-I collagenType-I collagenType-I collagen is the most abundant collagen of the human body.It is present in scar tissue, the end product when tissue heals by repair.It is found in tendons, the endomysium of myofibrils and the organic part of bone.- See also :* Collagen...
suggesting that activin A acts as a potent activator of fibroblastFibroblastA fibroblast is a type of cell that synthesizes the extracellular matrix and collagen, the structural framework for animal tissues, and plays a critical role in wound healing...
s.
- Lack of activin during development results in neural developmental defects.
Inhibin
In both females and males, inhibin inhibits FSHFollicle-stimulating hormone
Follicle-stimulating hormone is a hormone found in humans and other animals. It is synthesized and secreted by gonadotrophs of the anterior pituitary gland. FSH regulates the development, growth, pubertal maturation, and reproductive processes of the body. FSH and Luteinizing hormone act...
production and GnRH
Gonadotropin-releasing hormone
Gonadotropin-releasing hormone , also known as Luteinizing-hormone-releasing hormone and luliberin, is a tropic peptide hormone responsible for the release of follicle-stimulating hormone and luteinizing hormone from the anterior pituitary. GnRH is synthesized and released from neurons within...
release from the hypothalamus. However, the overall mechanism differs between the genders:
In females
Inhibin is produced in the gonads, pituitary glandPituitary gland
In vertebrate anatomy the pituitary gland, or hypophysis, is an endocrine gland about the size of a pea and weighing 0.5 g , in humans. It is a protrusion off the bottom of the hypothalamus at the base of the brain, and rests in a small, bony cavity covered by a dural fold...
, placenta
Placenta
The placenta is an organ that connects the developing fetus to the uterine wall to allow nutrient uptake, waste elimination, and gas exchange via the mother's blood supply. "True" placentas are a defining characteristic of eutherian or "placental" mammals, but are also found in some snakes and...
and other organs.
In women, FSH stimulates the secretion of inhibin from the granulosa cell
Granulosa cell
A granulosa cell or follicular cell is a somatic cell of the sex cord that is closely associated with the developing female gamete in the ovary of mammals.-Anatomy and function:...
s of the ovarian follicles in the ovaries
Ovary
The ovary is an ovum-producing reproductive organ, often found in pairs as part of the vertebrate female reproductive system. Ovaries in anatomically female individuals are analogous to testes in anatomically male individuals, in that they are both gonads and endocrine glands.-Human anatomy:Ovaries...
. In turn, inhibin suppresses FSH.
- Inhibin B reaches a peak in the early- to mid-follicular phaseMenstrual cycleThe menstrual cycle is the scientific term for the physiological changes that can occur in fertile women for the purpose of sexual reproduction. This article focuses on the human menstrual cycle....
, and a second peak at ovulationOvulationOvulation is the process in a female's menstrual cycle by which a mature ovarian follicle ruptures and discharges an ovum . Ovulation also occurs in the estrous cycle of other female mammals, which differs in many fundamental ways from the menstrual cycle...
.
- Inhibin A reaches its peak in the mid-luteal phaseMenstrual cycleThe menstrual cycle is the scientific term for the physiological changes that can occur in fertile women for the purpose of sexual reproduction. This article focuses on the human menstrual cycle....
.
Inhibin secretion is diminished by GnRH
Gonadotropin-releasing hormone
Gonadotropin-releasing hormone , also known as Luteinizing-hormone-releasing hormone and luliberin, is a tropic peptide hormone responsible for the release of follicle-stimulating hormone and luteinizing hormone from the anterior pituitary. GnRH is synthesized and released from neurons within...
, and enhanced by insulin-like growth factor
Insulin-like growth factor
The insulin-like growth factors are proteins with high sequence similarity to insulin. IGFs are part of a complex system that cells use to communicate with their physiologic environment...
-1 (IGF-1).
In males
It is secreted from the Sertoli cellSertoli cell
A Sertoli cell is a 'nurse' cell of the testes that is part of a seminiferous tubule.It is activated by follicle-stimulating hormone and has FSH-receptor on its membranes.-Functions:...
s, located in the seminiferous tubules
Seminiferous tubules
Seminiferous tubules are located in the testes, and are the specific location of meiosis, and the subsequent creation of gametes, namely spermatozoa....
inside the testes. Androgens stimulate inhibin production; this peptide
Peptide
Peptides are short polymers of amino acid monomers linked by peptide bonds. They are distinguished from proteins on the basis of size, typically containing less than 50 monomer units. The shortest peptides are dipeptides, consisting of two amino acids joined by a single peptide bond...
may also help to locally regulate spermatogenesis
Spermatogenesis
Spermatogenesis is the process by which male primary germ cells undergo division, and produce a number of cells termed spermatogonia, from which the primary spermatocytes are derived. Each primary spermatocyte divides into two secondary spermatocytes, and each secondary spermatocyte into two...
.
Activin
As with other members of the superfamily, activins interact with two types of cell surface transmembrane receptors (Types I and II) which have intrinsic serine/threonine kinaseSerine/threonine-specific protein kinase
Serine/threonine protein kinases phosphorylate the OH group of serine or threonine .At least 125 of the 500+ human protein kinases are serine/threonine kinases .-Regulation:...
activities in their cytoplasmic domains:
- Activin type 1 receptorsActivin type 1 receptorsThe Activin type I receptors transduce signals for a variety of members of the Transforming growth factor beta superfamily of ligands. This family of cytokines and hormones include activin, Anti-müllerian hormone , bone morphogenetic proteins , and Nodal...
: ACVR1ACVR1Activin A receptor, type I also known as ALK-2 is a protein which in humans is encoded by the ACVR1 gene.- Function :...
, ACVR1BACVR1BActivin receptor type-1B is a protein that in humans is encoded by the ACVR1B gene.ACVR1B or ALK-4 acts as a transducer of activin or activin like ligands signals. Activin binds to either ACVR2A or ACVR2B and then forms a complex with ACVR1B. These go on to recruit the R-SMADs SMAD2 or SMAD3...
, ACVR1CACVR1CThe activin A receptor also known as ACVR1C or ALK-7 is a protein that in humans is encoded by the ACVR1C gene. ACVR1C is a type I receptor for the TGFB family of signaling molecules... - Activin type 2 receptorsActivin type 2 receptorsThe Activin type 2 receptors modulate signals for ligands belonging to the Transforming growth factor beta superfamily of ligands. These include: Activin , Bone morphogenetic proteins and Nodal. They are involved in a host of physiological processes including, growth, cell differentiation,...
: ACVR2AACVR2AActivin receptor type-2A is a protein that in humans is encoded by the ACVR2A gene.ACVR2A is an activin type 2 receptor.-Interactions:ACVR2A has been shown to interact with INHBA, SYNJ2BP and ACVR1B.-Further reading:...
, ACVR2BACVR2BActivin receptor type-2B is a protein that in humans is encoded by the ACVR2B gene. ACVR2B is an activin type 2 receptor.-Interactions:ACVR2B has been shown to interact with SYNJ2BP and ACVR1B.-Further reading:...
Activin binds to the Type II receptor and initiates a cascade reaction that leads to the recruitment, phosphorylation, and activation of Type I activin receptor. This then interacts with and then phosphorylates SMAD2
Mothers against decapentaplegic homolog 2
Mothers against decapentaplegic homolog 2 also known as SMAD family member 2 or SMAD2 is a protein that in humans is encoded by the SMAD2 gene. MAD homolog 2 belongs to the SMAD, a family of proteins similar to the gene products of the Drosophila gene 'mothers against decapentaplegic' and the C....
and SMAD3
Mothers against decapentaplegic homolog 3
Mothers against decapentaplegic homolog 3 also known as SMAD family member 3 or SMAD3 is a protein that in humans is encoded by the SMAD3 gene. SMAD3 is a member of the SMAD family of proteins.The human SMAD3 gene is located on chromosome 15...
, two of the cytoplasmic SMAD
R-SMAD
R-SMAD stands for receptor-regulated SMAD. Smads are transcription factors that transduce extracellular TGF-ß superfamily ligand signaling from cell membrane bound TGF-ß receptors into the nucleus where they activate transcription TGF-ß target genes...
proteins.
Smad3 then translocates to the nucleus and interacts with SMAD4
Mothers against decapentaplegic homolog 4
SMAD family member 4, also known as SMAD4, is a protein that in humans is encoded by the SMAD4 gene.SMAD4 is a 552-amino acid protein involved in cell signaling. It belongs to the Darfwin family of proteins that modulate members of the TGFβ protein superfamily...
through multimerization, resulting in their modulation as transcription factor
Transcription factor
In molecular biology and genetics, a transcription factor is a protein that binds to specific DNA sequences, thereby controlling the flow of genetic information from DNA to mRNA...
complexes responsible for the expression of a large variety of genes.
Inhibin
In contrast to activin, much less is known about the mechanism of action of inhibin, but may involve competing with activin for binding to activin receptors and/or binding to inhibin-specific receptors.Clinical significance
Quantification of inhibin A is part of the prenatal quad screen that can be administered during pregnancy at a gestational age of 16–18 weeks. An elevated inhibin A (along with an increased beta-hCG, decreased AFPAlpha-fetoprotein
Alpha-fetoprotein is a protein that in humans is encoded by the AFP gene....
, and a decreased estriol
Estriol
Estriol is one of the three main estrogens produced by the human body.-Synthesis:Estriol is only produced in significant amounts during pregnancy as it is made by the placenta from 16-Hydroxydehydroepiandrosterone sulfate , an androgen steroid made in the fetal liver and adrenal glands.The human...
) is suggestive of the presence of a fetus with Down syndrome
Down syndrome
Down syndrome, or Down's syndrome, trisomy 21, is a chromosomal condition caused by the presence of all or part of an extra 21st chromosome. It is named after John Langdon Down, the British physician who described the syndrome in 1866. The condition was clinically described earlier in the 19th...
. As a screening test, abnormal quad screen test results need to be followed up with more definitive tests.
It also has been used as a marker for ovarian cancer
Ovarian cancer
Ovarian cancer is a cancerous growth arising from the ovary. Symptoms are frequently very subtle early on and may include: bloating, pelvic pain, difficulty eating and frequent urination, and are easily confused with other illnesses....
.
Inhibin B may be used as a marker of spermatogenesis
Spermatogenesis
Spermatogenesis is the process by which male primary germ cells undergo division, and produce a number of cells termed spermatogonia, from which the primary spermatocytes are derived. Each primary spermatocyte divides into two secondary spermatocytes, and each secondary spermatocyte into two...
function and male infertility
Male infertility
Male infertility refers to the inability of a male to achieve a pregnancy in a fertile female. In humans it accounts for 40-50% of infertility. Male infertility is commonly due to deficiencies in the semen, and semen quality is used as a surrogate measure of male fecundity.-Pre-testicular...
. The mean serum inhibin B level is significantly higher among fertile men (approximately 140 pg/mL) than in infertile men (approximately 80 pg/mL). In men with azoospermia
Azoospermia
Azoospermia is the medical condition of a male not having any measurable level of sperm in his semen. It is associated with very low levels of fertility or even sterility, but many forms are amenable to medical treatment...
, a positive test for inhibin B slightly raises the chances for successfully achieving pregnancy through testicular sperm extraction
Testicular sperm extraction
Testicular sperm extraction is the process of removing a small portion of tissue from the testicle under local anesthesia and extracting the few viable sperm cells present in that tissue for the purpose of intracytoplasmic sperm injection...
(TESE), although the association is not very substantial, having a sensitivity of 0.65 (95% confidence interval [CI]: 0.56–0.74) and a specificity of 0.83 (CI: 0.64–0.93) for prediction the presence of sperm in the testes in non-obstructive azoospermia.