Parathyroid hormone response to hypocalcaemia following hypercalcaemia

Abstract

Experiments were designed to study the ability of Ca infusions to suppress parathyroid hormone (PTH) responses to hypocalcemia, induced by i.v. infusions of ethylene-glycol-bis(.beta.-aminoethylether)N,N''-tetraacetate (EGTA). When plasma Ca was raised for 60 min to levels > 2.6 mmol/l, PTH responses to a subsequent fall of Ca due to EGTA infusions for 7 min were significantly reduced (P < 0.02) or abolished when compared to PTH responses during 7-min EGTA infusions in normocalcemia animals. CaCl2 infusions lasting for only 10 min did not cause a significant reduction of PTH responses to subsequent 7-min EGTA infusions. The results apparently demonstrate that raised Ca reduces PTH available for immedite release. This effect was time-dependent since it was only seen when CaCl2 was infused for more than 10 min prior to the EGTA administration.