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Eur J Clin Invest. 1993 Sep;23(9):546-53.

Cica-clamp technique: a method for quantifying parathyroid hormone secretion: a sequential citrate and calcium clamp study.

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1
Department of Clinical Chemistry, Hvidovre Hospital, University of Copenhagen, Denmark.

Abstract

Objectives of the present study were to establish and investigate a standardized method for quantifying of intact parathyroid hormone secretion during sequential induction of hypo- and hypercalcaemia, and to explore the applicability to these data of a mathematical model derived from in vitro studies as presented in the literature. Twenty-two healthy volunteers aged 20-80 years participated in one or more experiments. The experiments comprised three different protocols of sequential induction of a regular hypocalcaemic (citrate) clamp followed by increases in blood ionized calcium, ending in a regular hypercalcaemic (calcium) clamp. During protocol I, the induction of hypocalcaemia, blood ionized calcium 0.21 mmol l-1 (SD 0.01, n = 76) below baseline, the release of serum parathyroid hormone rapidly increased to a concentration of four to seven times above baseline. The serum parathyroid hormone declined gradually to a steady state of about two to three times above baseline. During stepwise increases in blood ionized calcium, the serum parathyroid hormone rapidly declined to new steady state concentrations. When a hypercalcaemia of 0.20 mmol l-1 (SD 0.02, n = 76) above baseline was reached, serum parathyroid hormone was suppressed to about one-fourth of baseline concentration. Protocol II, the Cica-clamp, and protocol III, are short versions of protocol I using a slow and gradual increase in blood ionized calcium from hypo- to hypercalcaemia.(ABSTRACT TRUNCATED AT 250 WORDS).

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