Blood ionic calcium response to hypocalcemia in the chicken induced by ethyleneglycol-bis-(B-aminoethylether) -N,N'-tetraacetic acid: role of the parathyroids.

Eight groups of cockerels were used to test an ethyleneglycol-bis-(B-aminoethylether)-N,N'-tetraacetic acid (EGTA) challenge as a possible means for estimating parathyroid function and responsiveness in birds. Intravenous injections of EGTA significantly depressed blood ionic calcium concentrations (hypocalcemia), and the recovery from this hypocalcemia was dependent upon the presence of parathyroid hormone (PTH). However, it also was demonstrated that a surge of PTH is not necessary for recovery from the EGTA-induced hypocalcemia. Therefore, in the bird, the EGTA challenge is a test of the ability of PTH target tissues (bone or soft tissues) to buffer ionic calcium in the blood. The EGTA challenge is not a quantitative means of testing parathyroid gland function or responsiveness.