Alterations in parathyroid dynamics in lithium-treated subjects

Area of Science:

• Endocrinology
• Pharmacology
• Psychiatry

Background:

• Lithium (Li) is a key treatment for bipolar disorder, but its effects on calcium (Ca) and parathyroid hormone (PTH) regulation are debated.
• Previous in vitro studies suggested lithium shifts the PTH set-point, but in vivo data are limited.

Purpose of the Study:

• To investigate the in vivo effects of chronic lithium therapy on the calcium-PTH axis.
• To characterize PTH dynamics in patients with bipolar disorder undergoing lithium treatment.

Main Methods:

• Utilized a calcium and citrate infusion protocol in seven female patients on chronic lithium therapy and seven controls.
• Measured baseline and dynamic changes in ionized calcium (Cai) and intact PTH (iPTH) levels.
• Defined an inverse sigmoidal curve to analyze the Cai-iPTH relationship and determine the set-point.

Main Results:

• Lithium-treated patients exhibited significantly higher baseline ionized calcium (Cai) levels (5.2 vs. 4.9 mg/dL) and PTH levels (38.4 vs. 21.2 pg/mL).
• A significant rightward shift in the iPTH set-point was observed in the lithium group (5.08 vs. 4.88 mg/dL).
• Despite higher Cai levels during infusions, iPTH levels did not differ significantly between groups, indicating altered PTH dynamics.

Conclusions:

• Chronic lithium therapy causes a significant rightward shift in the PTH set-point in vivo.
• This shift suggests an altered calcium-PTH relationship, with higher calcium levels required to suppress PTH in lithium-treated patients.
• These findings clarify lithium's impact on mineral metabolism and the PTH axis.