The hypocalcemic response to protamine as a measure of bone resorption

The heparin antagonist protamine inhibits bone resorption. In the present study protamine was given i.v. at a dose of 10 mg/kg to goats and sheep in various stages of pregnancy and lactation. It is known that bone resorption increases as pregnancy progresses. In sheep maximum in bone resportion is reached at early lactation. The hypocalcemic response to protamine followed a similar course. The slightest decrease in serum calcium was obtained during early pregnancy and the greatest during late pregnancy and early lactation. Protamine increased serum inorganic phosphorus. The increase was most pronounced during early pregnancy. Protamine did not significantly change serum magnesium.Five lactating ewes were given 25000 i.u./kg of vitamin D3. Serum calcium increased and the hypocalcemic response to protamine was greater after vitamin D₃ administration than before.The results showed that the hypocalcemic response to protamine can be used as an indicator of the role of bone resorption in calcium homeostasis in various physiological situations.