Natural Steroids and Steroid Hormones

Cholesterol (Greek solid bUe) is the most important steroid of vertebrate animals (the zoosterols ). It is a central intermediate in the biosynthesis of steroids. 

Isolated for the first time in 1775 from gallstones by the physician Benjamin Gottlob Friedrich Conradi (Jena, Germany), cholesterol occurs everywhere in the human body. With high levels especially in the brain, the spinal cord and the suprarenal glands, the total amount of cholesterol in an adult adds up to some 240 grams. Invertebrates, on the other hand, synthesise in addition 24-dehydro-cholesterol in considerable quantity. 

In most fungi, lichens and algae, ergosterol (mycosterol) occurs. This was isolated from ergot fungus (most prominent member Claviceps purpurea) in 1889 by the Parisian apothecary Gharles Tanret (1847-1917). It is the main sterol in baker s yeast Saccharomyces cerevisiae), and acts as provitamin D (Fig. 6.5). [7] 

An important raw material for the partial synthesis of steroid hormones (and Vitamin D) is cholesterol, which (prior to the BSE crisis) was isolated from the spinal cord of cattle. Another important source is the fat in sheep s wool (lanolin), which contains around 15 % of cholesterol. Among the plant sterols, stigmasterol is of great economic significance as the starting material for the partial synthesis of steroids. It is contained from 12 to 25 % in the non-hydrolysable 

Steroid hormones play a critical role in a whole range of vital processes like sexuality, reproduction and stress (Fig. 6.6). They can be differentiated into four physiological categories  

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