Steroid Hormones Are Metabolized by Conjugation with Sulfates and GlucuronidesrWhich Makes Steroids Water Soluble
Hormone activity is limited by the metabolism of hormones. The metabolism of steroids usually involves reduction of the molecule, followed by conjugation with sulfates and glucuronides, which increases the water solubility of the steroids, allowing them to be excreted in urine.
The liver is the main organ responsible for this process. Iodine molecules are removed from thyroid hormones during metabolism. Protein hormones are cleaved by peptidases; this is preceded by reduction of disulfide bonds if this is a characteristic of the molecule. Although a metabolite is usually less biologically potent than the original molecule, some evidence suggests that conjugates of steroids can have significant biological activity. This raises the question of whether the conversion of hormones intracellularly, such as testosterone to dihydrotestosterone, represents metabolism, because dihydrotestosterone is more potent biologically than testosterone. Another example, the conversion of estradiol-17β to estrone by peripheral tissues, including adipose cells, is described as a form of metabolism; however, estrone is a natural, and relatively potent, estrogen.Although in some situations the rate of clearance of a hormone can change (e.g., decrease as a result of increased hormone-binding plasma proteins during pregnancy, or increase as the result of decreased hormone-binding plasma proteins in conjunction with liver disease), metabolism of hormones is relatively constant, and the concentration of a hormone usually reflects the other determinant of hormone activity: the rate Ofsynthesis of the hormone.
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