biology

Pregnenolone

Pregnenolone is a biology topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Pregnenolone rather than just read about it. In short: Pregnenolone (P5), or pregn-5-en-3β-ol-20-one, is an endogenous steroid and precursor/metabolic intermediate in the biosynthesis of most of the steroid hormones, including the progestogens, androgens, estrogens, glucocorticoids, and mineralocorticoids. In addition, pregnenolone is biologically active in its own right, acting as a neurosteroid.

Key takeaways

Pregnenolone belongs to biology; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Pregnenolone to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Pregnenolone from memory before moving on to harder problems.

Reference excerpt

Pregnenolone (P5), or pregn-5-en-3β-ol-20-one, is an endogenous steroid and precursor/metabolic intermediate in the biosynthesis of most of the steroid hormones, including the progestogens, androgens, estrogens, glucocorticoids, and mineralocorticoids. In addition, pregnenolone is biologically active in its own right, acting as a neurosteroid. In addition to its role as a natural hormone, pregnenolone has been used as a medication and supplement; for information on pregnenolone as a medication or supplement, see the pregnenolone (medication) article.

Biological function Pregnenolone and its 3β-sulfate, pregnenolone sulfate, like dehydroepiandrosterone (DHEA), DHEA sulfate, and progesterone, belong to the group of neurosteroids that are found in high concentrations in certain areas of the brain, and are synthesized there. Neurosteroids affect synaptic functioning, are neuroprotective, and enhance myelinization. Pregnenolone and its sulfate ester may improve cognitive and memory function. In addition, they may have protective effects against schizophrenia.

Biological activity

Neurosteroid activity Pregnenolone is an allosteric endocannabinoid, as it is a negative allosteric modulator of the CB1 receptor. Pregnenolone is involved in a natural negative feedback loop against CB1 receptor activation in animals. It prevents CB1 receptor agonists like tetrahydrocannabinol, the main active constituent in cannabis, from fully activating the CB1. A related compound AEF0117 has been derived from pregnenolone and is more specific for this type of activity. Pregnenolone has been found to bind with high, nanomolar affinity to microtubule-associated protein 2 (MAP2) in the brain. In contrast to pregnenolone, pregnenolone sulfate did not bind to microtubules. However, progesterone did and with similar affinity to pregnenolone, although unlike pregnenolone, it did not increase binding of MAP2 to tubulin. Pregnenolone was found to induce tubule polymerization in neuronal cultures and to increase neurite growth in PC12 cells treated with nerve growth factor. As such, pregnenolone may control formation and stabilization of microtubules in neurons and may affect both neural development during prenatal development and neural plasticity during aging. Although pregnenolone itself does not possess these activities, its metabolite pregnenolone sulfate is a negative allosteric modulator of the GABAA receptor as well as a positive allosteric modulator of the NMDA receptor. In addition, pregnenolone sulfate has been shown to activate the transient receptor potential M3 (TRPM3) ion channel in hepatocytes and pancreatic islets causing calcium entry and subsequent insulin release.

Nuclear receptor activity Pregnenolone has been found to act as an agonist of the pregnane X receptor. Pregnenolone has no progestogenic, corticosteroid, estrogenic, androgenic, or antiandrogenic activity.

Biochemistry

Biosynthesis Pregnenolone is synthesized from cholesterol. This conversion involves hydroxylation of the side chain at the C20 and C22 positions, with cleavage of the side chain. The enzyme performing this task is cytochrome P450scc, located in the mitochondria, and controlled by anterior pituitary trophic hormones, such as adrenocorticotropic hormone, follicle-stimulating hormone, and luteinizing hormone, in the adrenal glands and gonads. There are two intermediates in the transformation of cholesterol into pregnenolone, 22R-hydroxycholesterol and 20α,22R-dihydroxycholesterol, and all three steps in the transformation are catalyzed by P450scc. Pregnenolone is produced mainly in the adrenal glands, the gonads, and the brain. Although pregnenolone is also produced in the gonads and brain, most circulating pregnenolone is derived from the adrenal cortex. To assay conversion of cholesterol to pregnenolone, radiolabeled cholesterol has been used. Pregnenolone product can be separated from cholesterol substrate using Sephadex LH-20 minicolumns.

Distribution Pregnenolone is lipophilic and readily crosses the blood–brain barrier. This is in contrast to pregnenolone sulfate, which does not cross the blood–brain barrier.

Metabolism Pregnenolone undergoes further steroid metabolism in one of several ways:

Pregnenolone can be converted into progesterone. The critical enzyme step is two-fold using a 3β-hydroxysteroid dehydrogenase and a Δ5-4 isomerase. The latter transfers the double bond from C5 to C4 on the A ring. Progesterone is the entry into the Δ4 pathway, resulting in production of 17α-hydroxyprogesterone and androstenedione, precursor to testosterone and estrone. Aldosterone and corticosteroids are also derived from progesterone or its derivatives. Pregnenolone can be converted to 17α-hydroxypregnenolone by the enzyme 17α-hydroxylase (CYP17A1). Using this pathway, termed Δ5 pathway, the next step is conversion to dehydroepiandrosterone (DHEA) via 17,20-lyase (CYP17A1). DHEA is the precursor of androstenedione. Pregnenolone can be converted to androstadienol by 16-ene synthase (CYP17A1). Pregnenolone can be converted to pregnenolone sulfate by steroid sulfotransferase, and this conversion can be reversed by steroid sulfatase.

Levels Normal circulating levels of pregnenolone are as follows:

Men: 10 to 200 ng/dL Women: 10 to 230 ng/dL Children: 10 to 48 ng/dL Adolescent boys: 10 to 50 ng/dL Adolescent girls: 15 to 84 ng/dL Mean levels of pregnenolone have been found not to significantly differ in postmenopausal women and elderly men (40 and 39 ng/dL, respectively). Studies have found that pregnenolone levels are not significantly changed after surgical or medical castration in men, which is in accordance with the fact that pregnenolone is mainly derived from the adrenal glands. Conversely, medical castration has been found to partially suppress pregnenolone levels in premenopausal women. Similarly, an adrenalectomized premenopausal woman showed incompletely diminished circulating pregnenolone levels.

Chemistry

… excerpt ends here. Continue reading the full article.

Illustrations

Worked examples

Example 1 — a first encounter with Pregnenolone

Start with the simplest possible case. Write down what Pregnenolone claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In biology, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Pregnenolone before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Pregnenolone ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Pregnenolone

In research: Pregnenolone appears in biology research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Pregnenolone in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Pregnenolone is common in secondary-school and first-year university syllabi. It links to neighbouring topics CB1 receptor antagonists, CB1 receptor negative allosteric modulators, Glycine receptor agonists, so understanding it makes those chapters shorter.
In everyday life: Look for Pregnenolone outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Pregnenolone in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Pregnenolone means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Pregnenolone out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Pregnenolone in simple terms?

Why does Pregnenolone matter?

Because it connects several biology ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Pregnenolone?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Pregnenolone.