ABSTRACT
Dietary cholesterol mixes in the gastrointestinal tract with cholesterol from the bile and that furnished by de novo synthesis in the intestinal mucosa. It is important to note that the free cholesterol is not rigidly fixed in these compartments but can readily exchange from erythrocyte to lipoprotein and vice versa. A number of tissues are capable of synthesizing steroid hormones from cholesterol, but the adrenal cortex and gonads are the principal ones. In light of the lowered capacity of 19-iodocholesterol esters to undergo enzymatic hydrolysis and the failure of 19-iodocholesterol to undergo cholesterol side-chain cleavage, it is not surprising that 19-radioiodinated cholesterol selectively accumulates in adrenals and ovaries and can be employed to image these organs clinically. The pathway from cholesterol to pregnenolone is common to all steroid hormones. This conversion, known as the cholesterol side-chain cleavage reaction, has long been considered to be the rate-limiting step in steroid hormone production.
