title: Pregnanolone
text: # Pregnanolone
  
  Pregnanolone, also known as eltanolone, is an endogenous inhibitory neurosteroid which is produced in the body from progesterone. It is closely related to allopregnanolone, which has similar properties.
  
  ## Biological activity
  
  Pregnanolone is a positive allosteric modulator of the $GABA_A$ receptor, as well as a negative allosteric modulator of the glycine receptor.
  
  ## Biological function
  
  Pregnanolone has sedative, anxiolytic, anesthetic, and anticonvulsant effects. During pregnancy, pregnanolone and allopregnanolone are involved in sedation and anesthesia of the fetus.
  
  ## Biochemistry
  
  Pregnanolone is synthesized from progesterone via the enzymes 5β-reductase and 3α-hydroxysteroid dehydrogenase, with 5β-dihydroprogesterone occurring as a metabolic intermediate. The elimination half-life of pregnanolone is between 0.9 and 3.5 hours.
  
  ## Chemistry
  
  Pregnanolone, also known as 3α,5β-tetrahydroprogesterone (3α,5β-THP) or as 5β-pregnan-3α-ol-20-one, is a naturally occurring pregnane steroid and a derivative of progesterone. Related compounds include allopregnanolone (3α,5α-THP; brexanolone), epipregnanolone (3β,5β-THP), hydroxydione, isopregnanolone (3β,5α-THP), and renanolone.
  
  ## History
  
  Pregnanolone was first isolated from the urine of pregnant women in 1937. Its anesthetic properties were first demonstrated in animals in 1957.
  
  ## Research
  
  Pregnanolone was investigated for clinical use as a general anesthetic under the name eltanolone (INN), but produced unwanted side effects such as convulsions on occasion, and for this reason, was never marketed.
  
  