Acute parathyroid hormone response: sensitivity, relationship to hypocalcemia, and rapidity.

Abstract

Studies were designed to determine die relationship between acute hypocalcemia obtained with ethylene-glycol-bis (α-aminoethyl-ether)-N,N'tetraacetate (EGTA) infusions and im-munoreactive PTH (iPTH) responses seen in cows. In addition, the sensitivity and the rapidity of the iPTH responses were evaluated. During EGTA infusions the plasma ionized calcium decreased in proportion to the total calcium (Ca), whereas the magnesium did not change. A significant response of 0.2 ng⁄ml iPTH (Δ4–8 min, p < 0.02) was already observed with a A Ca of 0.1 mg⁄100 ml (Δ4-8 min, p < 0.005). The magnitude of the early iPTH responses was determined by decrements of Ca of up to 1.2 mg/100 ml (A4-8 min). When the Δ Ca 4-8 min was greater, peak iPTH responses did not rise further. The total incremental iPTH output (ng/ml × min) was also increased in a nonlinear manner to the total decremental change of Ca (mg/100 ml × min). After subtraction of the circulation-time (measured by Evans Blue), iPTH started to rise at 20 sec or les...