title: Cica-clamp technique: a method for quantifying parathyroid hormone secretion: a sequential citrate and calcium clamp study.
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)
authors.affiliation: Department of Clinical Chemistry, Hvidovre Hospital, University of Copenhagen, Denmark.
authors.forename: P
authors.initials: P
authors.lastname: Schwarz
authors.forename: H A
authors.initials: HA
authors.lastname: Sørensen
authors.forename: P
authors.initials: P
authors.lastname: McNair
authors.forename: I
authors.initials: I
authors.lastname: Transbøl
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002118:Calcium / Q000097:blood*; D002951:Citrates; D019343:Citric Acid; D005260:Female; D006801:Humans; D006934:Hypercalcemia / Q000097:blood* / Q000139:chemically induced; D006996:Hypocalcemia / Q000097:blood* / Q000139:chemically induced; D008297:Male; D008875:Middle Aged; D008954:Models, Biological; D010281:Parathyroid Hormone / Q000378:metabolism*
chemical_list: D002951:Citrates; D010281:Parathyroid Hormone; D019343:Citric Acid; D002118:Calcium