inhibitor, has been shown to mimic the effects of SSRI’s causing sexual dysfunction. Research has shown that 5α-reductase is the rate-limiting enzyme in neurosteroid synthesis, specifically in the conversion of progesterone to allopregnanolone, low levels of allopregnanolone has been tied to depression, anxiety and schizophrenia. Sleep deprivation can enhance 5α-reductase expression and activity in the prefrontal cortex, leading to mania-related symptoms in rats. It is also contested whether the use of 5α-reductase inhibitors is associated with suicidal ideation and depression in patient populations who use them for benign prostatic hyperplasia. These symptoms have been found during active use of inhibitors and in immediate followup. However, it is unknown if these symptoms arise naturally from benign prostatic hyperplasia. Hypothalamic–pituitary–adrenal axis dysfunction An alternative mechanism of cortisol regulation is regulated via 5α-reductase which catalyzes an A-ring reduction of cortisol, metabolizing the compound. Type 1 and 2 of 5α-reductase are the principal enzymes involved in cortisol clearance through the liver. Excess cortisol has been tied to non-alcoholic fatty liver disease (NAFLD), but in-vitro studies have found that an over expression of 5α-reductase type 2 can suppress lipogenesis. The key role of 5α-reductase in cortisol breakdown and fat buildup has elucidated some of the side effects of 5α-reductase inhibitors. In randomized studies on human volunteers it was found that 5α-reductase inhibition through the use of dutasteride and finasteride can lead to hepatic lipid accumulation in men. In critical illness, overstimulation of cortisol as part of a stress response can lead to decreased clearance of cortisol through the liver via 5α-reductase and kidneys via 11β-hydroxysteroid dehydrogenase type 2, longterm elevation of cortisol can lead to Cushing's syndrome. Nomenclature This enzyme belongs to the family of oxidoreductases, to be specific, those acting on the CH-CH group of donor with other acceptors. The systematic name of this enzyme class is 3-oxo-5α-steroid:acceptor Δ4-oxidoreductase. Other names in common use include: 5α-Reductase 3-Oxosteroid Δ4-dehydrogenase 3-Oxo-5α-steroid Δ4-dehydrogenase Steroid Δ4-5α-reductase Δ4-3-Keto steroid 5α-reductase Δ4-3-Oxo steroid reductase Δ4-3-Ketosteroid-5α-oxidoreductase Δ4-3-Oxosteroid-5α-reductase 3-Keto-Δ4-steroid-5α-reductase Testosterone 5α-reductase 4-Ene-3-ketosteroid-5α-oxidoreductase Δ4-5α-Dehydrogenase 3-Oxo-5α-steroid:(acceptor) Δ4-oxidoreductase See also Steroidogenic enzyme Acne vulgaris Cholestenone 5α-reductase Hirsutism Lower urinary tract symptoms Polycystic ovarian syndrome List of steroid metabolism modulators References Further reading External links EC 1.3.1