Plasma calcium and parathyroid hormone responses to EDTA infusion in the cow

Abstract

Continuous EDTA infusion into cows at a rate comparable to the Ca outflow into milk elicited a homeostatic response in plasma Ca. Plasma Ca fell rapidly for the 1st 3-7 hr. of infusion but then the rate of plasma Ca decline decreased. After another 4-68 hr. of infusion, plasma Ca fell rapidly again until the infusion was terminated. Plasma parathyroid hormone increased within 15 min. of starting the EDTA infusion and was inversely pro-protional to the plasma Ca concentration regardless of whether plasma Ca was falling or rising. Parathyroid hormone is continuously secreted at a rate inversely proportional to plasma Ca within the range studied (1.5-5.4 mEq/liter). EDTA infusion into a parathyroidectomized cow produced no detectable response in plasma parathyroid hormone and plasma Ca fell at a constant rate for 13 hr.