Relation between bone mineralization, Ca absorption, and plasma Ca in phosphonate-treated rats.

Area of Science:

• Biochemistry
• Pharmacology
• Calcium Homeostasis

Background:

• Disodium ethane-1-hydroxy-1,1-diphosphonate (EHDP) inhibits calcium phosphate crystallization in vitro.
• In vivo, EHDP at high doses impairs skeletal mineralization, reduces calcium absorption, and causes hypercalcemia.

Purpose of the Study:

• To investigate the relationship between bone mineralization, intestinal calcium absorption, and plasma calcium regulation.
• To define the effects of EHDP and 13 other phosphonates on calcium homeostasis in rats.

Main Methods:

• Rats were administered EHDP or other phosphonates subcutaneously at 10 mg P/kg/day for 7 days.
• In vitro crystallization inhibition and in vivo skeletal mineralization were assessed.
• Intestinal calcium absorption and plasma calcium levels were measured.

Main Results:

• All phosphonates inhibiting skeletal mineralization in vivo also inhibited crystallization in vitro.
• A strong correlation was observed between inhibited skeletal mineralization, decreased intestinal calcium absorption, and mild hypercalcemia.
• Dose-response studies confirmed this correlation.

Conclusions:

• Phosphonates primarily affect bone mineralization, leading to secondary impairment of intestinal calcium absorption.
• Elevated plasma calcium fractions may mediate this homeostatic response.
• These findings clarify the mechanisms of phosphonate-induced calcium dysregulation.