Etiocholanolone

Endogenous 5-beta epimer of androsterone; a GABA-A positive allosteric modulator and the archetypal steroid endogenous pyrogen.

Etiocholanolone is a normal endogenous steroid metabolite and, at physiological concentrations, is benign and without androgenic effect. Its documented adverse profile derives almost entirely from historical experimental use, in which the unconjugated steroid was injected intramuscularly to induce controlled fever and inflammation for research. Such injections produced fever, chills, malaise, neutrophilic leukocytosis, an acute-phase response, and frequently a painful sterile inflammatory reaction at the injection site. It is not an approved therapeutic agent and is not sold as a dietary supplement, so no oral dosing is established. In routine clinical endocrinology it is encountered only as a measured urinary or plasma 17-ketosteroid marker of androgen metabolism rather than as an administered compound.

Etiocholanolone was characterized in the 1930s as one of the urinary 17-ketosteroids that reflect metabolism of testosterone and adrenal androgens. Interest intensified in the late 1950s when Bondy, Cohn and colleagues at Yale proposed that elevated unconjugated plasma etiocholanolone might underlie certain unexplained periodic fevers, and developed methods to separate and measure the pyrogenic steroids in plasma. In 1968 to 1970 Bodel and Dillard demonstrated that etiocholanolone stimulates human leukocytes to produce endogenous pyrogen in vitro, cementing its status as a model endogenous pyrogen, and investigators at the United States National Institutes of Health used it as a reproducible experimental fever stimulus.

A 1969 study by George and Wolff, however, failed to confirm a consistent causal association between plasma unconjugated etiocholanolone and idiopathic periodic fever, tempering the original hypothesis. The compound's GABAergic and anticonvulsant properties as an androstane neurosteroid were established later, most prominently by Kaminski and Rogawski in 2005 and through the electrophysiological work of Akk, Steinbach and colleagues.

Within nootropics and supplement circles etiocholanolone is obscure and is not used as a self-administered compound. It is best known to endocrinologists as a urinary 17-ketosteroid index of androgen turnover and to immunologists and historians of medicine as a foundational endogenous pyrogen from the pre-cytokine era of fever research. Contemporary academic attention treats it primarily as a mechanistic probe of neurosteroid action at GABA-A receptors and as a member of the 5-beta-dihydrosteroid family whose formation and properties continue to be studied.