Adrenocortical Hormone Biosynthesis
- All adrenocortical hormones, known as Corticosteroids, are steroid hormones. As with all steroid hormones, biosynthesis of corticosteroids is based on sequential enzymatic modification of cholesterol. The three different subtypes of adrenocortical hormones are achieved by different pathways of enzymatic modification, yielding hormones with different chemical side groups. Because each zone of the adrenal cortex expresses a different set of modifying enzymes, different hormones are produced in each zone.
- The overall pathway for adrenocortical hormone biosynthesis is presented in the diagram above. Note that cholesterol is the starting material for all the hormones. Each zone of the adrenal cortex possesses only those enzymes necessary to synthesize its particular hormone; thus, no zone possess all of the enzymes shown. The only enzyme which is shared by all the zones is Cholesterol Desmolase which is required to activate cholesterol for any further chemical modification. Expression of cholesterol desmolase depends on the presence of ACTH a hypothalamic hormone; therefore, in the absence of ACTH no adrenocortical hormones are produced.
- Not all enzymes are displayed but the three clinically important enzymes of 17-α-hydroxylase, 21-hydroxylase, and 11-hydroxylase are displayed. These are enzymes which are mutated, resulting in the syndromes of Congenital Adrenal Hyperplasia.