Function of Calcitonin in the Body
Calcitonin is a hormone secreted by the C-cells of the thyroid gland that primarily acts on bone to inhibit osteoclast activity, causing a rapid, transient, and reversible inhibition of bone resorption, which helps regulate calcium homeostasis in the body. 1, 2
Primary Functions
- Calcitonin acts as a powerful inhibitor of osteoclast activity, causing marked transient inhibition of ongoing bone resorptive processes 1, 3
- With prolonged use, calcitonin creates a persistent decrease in bone resorption rate, associated with decreased number of osteoclasts and apparent reduction in their resorptive activity 1, 2
- In vitro studies show that calcitonin causes inhibition of osteoclast function with loss of the ruffled osteoclast border responsible for bone resorption 1
- Calcitonin participates with parathyroid hormone in the homeostatic regulation of blood calcium - high blood calcium levels trigger increased calcitonin secretion, which inhibits bone resorption 1
Effects on Calcium Metabolism
- In normal adults with relatively low bone resorption rates, exogenous calcitonin administration results in slight decreases in serum calcium within normal range 1, 2
- In patients with more rapid bone resorption (children, Paget's disease patients), decreases in serum calcium are more pronounced in response to calcitonin 1
- Calcitonin increases the excretion of filtered phosphate, calcium, and sodium by decreasing their tubular reabsorption in the kidneys 1, 2
Physiological Role
- Calcitonin protects against the development of hypercalcemia by opposing the resorptive actions of parathyroid hormone and vitamin D 4
- It serves as a protective mechanism for the skeleton against excessive resorption 5
- Calcitonin secretion is stimulated by increases in serum calcium concentration and by gastrointestinal hormones such as gastrin 4
Clinical Applications
- Calcitonin has documented efficacy in treating Paget's disease, with effects of a single injection potentially lasting for months 6
- It has shown effectiveness in treating bone destruction associated with malignancy 6
- Calcitonin has been studied extensively for treatment of high-turnover osteoporosis, with some studies suggesting significant reduction in bone resorption 6
- For patients with acute osteoporotic spinal compression fractures, calcitonin can provide significant pain relief 6
- Calcitonin may be helpful in various cases of bone pain and as a second-line treatment for some neuropathic conditions 7
Pharmacological Considerations
- The bioavailability of calcitonin varies by administration route - approximately 66% for intramuscular injection and 71% for subcutaneous injection 2
- After subcutaneous administration, peak plasma levels are reached in approximately 23 minutes 2
- The terminal half-life is approximately 58 minutes for intramuscular administration and 59-64 minutes for subcutaneous administration 2
- Nasal calcitonin has better tolerability compared to injectable forms, with side effects being rare and generally negligible 3
Potential Mechanisms Beyond Bone
- Some evidence suggests calcitonin may have effects on the gastrointestinal tract, including decreases in the volume and acidity of gastric juice and pancreatic secretions 2
- Calcitonin has an analgesic action, possibly mediated through β-endorphins and central modulation of pain perception 8
- It may exert a protective action on cartilage and could be useful in managing osteoarthritis 8
Clinical Considerations
- Main side effects of calcitonin include hypersensitivity reactions, nausea, and altered serum levels of calcium and phosphorus 7
- Assessment of calcium and phosphorus may be advisable when using calcitonin therapeutically 7
- Calcitonin has the unique ability to uncouple bone turnover, reducing bone resorption without affecting bone formation at certain doses, potentially increasing bone mass and improving bone quality 8