17-Hydroxypregnenolone is a C21 steroid

Steroid

A steroid is a type of organic compound that contains a characteristic arrangement of four cycloalkane rings that are joined to each other. Examples of steroids include the dietary fat cholesterol, the sex hormones estradiol and testosterone, and the anti-inflammatory drug dexamethasone.The core...

 that is obtained by hydroxylation

Hydroxylation

Hydroxylation is a chemical process that introduces a hydroxyl group into an organic compound. In biochemistry, hydroxylation reactions are often facilitated by enzymes called hydroxylases. Hydroxylation is the first step in the oxidative degradation of organic compounds in air...

 of pregnenolone

Pregnenolone

Pregnenolone is a steroid hormone involved in the steroidogenesis of progesterone, mineralocorticoids, glucocorticoids, androgens, and estrogens. As such it is a prohormone. Pregnenolone sulfate is a GABAA antagonist and increases neurogenesis in the hippocampus.-Chemistry:Like other steroids,...

 at the C17α position. This step is performed by the mitochondrial cytochrome P450 enzyme

Cytochrome P450 oxidase

The cytochrome P450 superfamily is a large and diverse group of enzymes. The function of most CYP enzymes is to catalyze the oxidation of organic substances. The substrates of CYP enzymes include metabolic intermediates such as lipids and steroidal hormones, as well as xenobiotic substances...

 17α-hydroxylase (CYP17A1) that is present in the adrenal and gonad

Gonad

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. Peak levels are reached in humans at the end of puberty

Puberty

Puberty is the process of physical changes by which a child's body matures into an adult body capable of reproduction, as initiated by hormonal signals from the brain to the gonads; the ovaries in a girl, the testes in a boy...

 and then decline. High levels are also achieved during pregnancy

Pregnancy

Pregnancy refers to the fertilization and development of one or more offspring, known as a fetus or embryo, in a woman's uterus. In a pregnancy, there can be multiple gestations, as in the case of twins or triplets...

.

Prohormone

17-OH-pregnenolone is considered a prohormone

Prohormone

A prohormone is a substance that is a precursor to a hormone, usually having minimal hormonal effect by itself. The term has been used in medical science since the middle of the 20th century. The primary function of a prohormone is to enhance the strength of the hormone that already occurs in the...

 in the formation of dehydroepiandrosterone

Dehydroepiandrosterone

5-Dehydroepiandrosterone is a 19-carbon endogenous steroid hormone. It is the major secretory steroidal product of the adrenal glands and is also produced by the gonads and the brain. DHEA is the most abundant circulating steroid in humans....

 (DHEA), itself a prohormone of the sex steroid

Sex steroid

Sex steroids, also known as gonadal steroids, are steroid hormones that interact with vertebrate androgen or estrogen receptors. Their effects are mediated by slow genomic mechanisms through nuclear receptors as well as by fast nongenomic mechanisms through membrane-associated receptors and...

s.

This conversion is mediated by the enzyme 17,20 lyase. As such 17-OH-pregenolone represents an intermediary in the delta-5-pathway that leads from pregnenolone to DHEA. 17-hydroxypregneolone is also converted to 17-hydroxyprogesterone

17-Hydroxyprogesterone

17-Hydroxyprogesterone is a C-21 steroid hormone produced during the synthesis of glucocorticoids and sex steroids.As a hormone, 17OHP also interacts with the progesterone receptor.-Production:...

, a prohormone for glucocorticosteroids and androstenedione

Androstenedione

Androstenedione is a 19-carbon steroid hormone produced in the adrenal glands and the gonads as an intermediate step in the biochemical pathway that produces the androgen testosterone and the estrogens estrone and estradiol.-Synthesis:Androstenedione is the common precursor of male and female sex...

 through the activity of 3-hydroxysteroid dehydrogenase.

Neurohormone

There is some evidence that 17-OH-pregnenolone may have activity as a neurohormone

Neurohormone

A neurohormone is any hormone produced and released by neurons.Examples include:*Thyrotropin-releasing hormone *Gonadotropin-releasing hormone *Adrenocorticotropin-releasing hormone*Oxytocin*Antidiuretic hormone *Epinephrine...

.

Clinical use

Measurements of 17-OH-pregnenolone are useful in the diagnosis of certain forms of congenital adrenal hyperplasia

Congenital adrenal hyperplasia

Congenital adrenal hyperplasia refers to any of several autosomal recessive diseases resulting from mutations of genes for enzymes mediating the biochemical steps of production of cortisol from cholesterol by the adrenal glands ....

.
In patients with congenital adrenal hyperplasia due to 3 beta-hydroxysteroid dehydrogenase deficiency

Congenital adrenal hyperplasia due to 3 beta-hydroxysteroid dehydrogenase deficiency

3β-Hydroxysteroid dehydrogenase II deficient congenital adrenal hyperplasia is an uncommon form of CAH resulting from a mutation in the gene for one of the key enzymes in cortisol synthesis by the adrenal gland, 3β-hydroxysteroid dehydrogenase type II...

 17-OH-pregnenolone is increased, while in patients with congenital adrenal hyperplasia due to 17 alpha-hydroxylase deficiency

Congenital adrenal hyperplasia due to 17 alpha-hydroxylase deficiency

Congenital adrenal hyperplasia due to 17α-hydroxylase deficiency is an uncommon form of congenital adrenal hyperplasia resulting from a defect in the gene for the enzyme CYP17A1. It produces decreased synthesis of both cortisol and sex steroids, with resulting increase in mineralocorticoid production...

levels are low to absent.