Which statement about lithium and calcium homeostasis is true?

Which statement about lithium and calcium homeostasis is true?

• A. Lowers threshold for calcium suppression
• B. Has no effect
• C. Increases PTH suppression
• D. Raises threshold for calcium suppression of PTH secretion

Answer: (D)

Lithium alters calcium homeostasis by antagonizing the calcium-sensing receptor (CaSR) in the parathyroid gland, which shifts the PTH response curve to the right. Normally, when extracellular calcium rises, CaSR activation suppresses PTH release. If CaSR signaling is reduced by lithium, a higher extracellular calcium level is needed to achieve that suppression, so the threshold for calcium to inhibit PTH is increased. This is why the statement about raising the threshold for calcium suppression of PTH secretion is true. Clinically, chronic lithium can lead to mild hypercalcemia or hyperparathyroidism because PTH remains секретed until calcium levels reach higher points. The other options don’t fit because lowering the threshold would mean PTH is suppressed at lower calcium, having no effect ignores the known CaSR interference, and increasing PTH suppression would imply the opposite shift in the PTH-calcium set-point.

Lithium alters calcium homeostasis by antagonizing the calcium-sensing receptor (CaSR) in the parathyroid gland, which shifts the PTH response curve to the right. Normally, when extracellular calcium rises, CaSR activation suppresses PTH release. If CaSR signaling is reduced by lithium, a higher extracellular calcium level is needed to achieve that suppression, so the threshold for calcium to inhibit PTH is increased. This is why the statement about raising the threshold for calcium suppression of PTH secretion is true. Clinically, chronic lithium can lead to mild hypercalcemia or hyperparathyroidism because PTH remains секретed until calcium levels reach higher points. The other options don’t fit because lowering the threshold would mean PTH is suppressed at lower calcium, having no effect ignores the known CaSR interference, and increasing PTH suppression would imply the opposite shift in the PTH-calcium set-point.