5reductasa

5-reductase, or 5-alpha-reductase, refers to a group of microsomal enzymes that convert testosterone into dihydrotestosterone (DHT), a more potent androgen. The reaction, which uses NADPH as a cofactor, is a key step in androgen metabolism and affects the activity of androgen receptors in various tissues. DHT plays a major role in the development and maintenance of androgen-dependent tissues, including the prostate, skin, and hair follicles.

Three human isoforms have been identified: type 1 (SRD5A1), type 2 (SRD5A2), and a third isoform (SRD5A3). Type 2 is the predominant form in the prostate and genital skin, while type 1 is widely expressed in the skin and liver. The distribution and function of type 3 are less clearly defined, though it has been described in humans and may participate in certain steroid-metabolic processes.

Physiologically, 5-reductase enzymes contribute to fetal male genital development and to adult processes such as hair growth and sebaceous gland activity. They also influence prostate growth and function. Clinically, genetic variants in SRD5A2 can cause 5-alpha-reductase deficiency, leading to undervirilized external genitalia in 46,XY individuals and variable puberty-related virilization.

Pharmacologically, inhibitors of 5-reductase are used to treat conditions such as benign prostatic hyperplasia and androgenic alopecia. Finasteride predominantly targets type 2, while dutasteride inhibits both type 1 and type 2. Potential adverse effects include sexual dysfunction, and handling considerations are advised for pregnant individuals.