Hormone levels may be controlled not only by the rate of synthesis of the hormone but also by the rate of destruction. The enzymes that destroy polypeptide hormones seem to be involved in controlling hormone concentration. There is evidence that these enzymes may control the destruction of insulin, glucagon, parathyroid hormone, and possibly calcitonin. Published reports indicate that two types of degradative control mechanisms exist. One mechanism tends to keep hormone levels constant; the other tends to keep constant some physiological variable controlled by the hormone. The first type of control system opposes any and all changes in hormone levels, tending to maintain hormone concentration within a narrow range. The second opposes changes in some physiological variable by manipulating hormone concentrations appropriately. Mechanisms which control hormone destruction would tend to oppose the over and under production of hormone seen in various endocrine diseases. However, a loss of control over destruction might be a primary cause of endocrine disease.
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