title: Induced hypocalcaemia controlled by a citrate clamp technique, and the intact parathyroid hormone response obtained.
abstract: In order to investigate (1) the possibility of controlled induction and maintenance of hypocalcaemia, and (2) the intact parathyroid hormone (PTH(1-84)) response obtained thereby, 14 healthy individuals were administered an i.v. infusion of trisodiumcitrate. The reproducibility of the method established was assessed in five of the 14 individuals. Aiming at a steady-state level of blood ionized calcium (B-Ca2+) = 1.00 mmol/l, obtained within 30 min and subsequently maintained for 90 min, the infusion was guided by frequent determinations B-Ca2+. The method established was as follows: infusion of 0.85 mmol citrate/kg body weight/h during the first 10 min, followed by 0.44 mmol citrate/kg body wt h 1.26 exp. ((actual B-Ca2(+)--target B-Ca2+)/0.02) mmol/l, until B-Ca2+ = 1.00 mmol/l. In the steady-state period the infusion rate was 0.29 mmol citrate/kg body wt. h 1.26 exp. ((actual B-Ca2(+)--target B-Ca2+)/0.02) mmol/l. The method showed reproducibility by an overall difference in B-Ca2+ measurements of -0.03 mmol/l, which did not statistically differ from zero (p less than 0.05). No severe side effects were observed during a total of 21 infusions. Intact serum parathyroid hormone concentrations (S-PTH(1-84)) obtained during induced hypocalcaemia rose to a peak within 5-10 min, and then declined to a steady-state level about three times the initial. The serum (S) PTH(1-84) response could be caused by a burst of S-PTH(1-84) from a depot source while the steady-state level may indicate a stimulated secretion from parathyroid glands. The S-PTH(1-84) response was shown to be reproducible by an overall difference in S-PTH(1-84) measurements of -0.52 pmol/l, which did not statistically differ from zero (p less than 0.10).
authors.affiliation: Department of Clinical Chemistry, Hvidovre Hospital, Denmark.
authors.forename: P
authors.initials: P
authors.lastname: Schwarz
authors.forename: H A
authors.initials: HA
authors.lastname: Sørensen
authors.forename: I
authors.initials: I
authors.lastname: Transbøl
authors.forename: P
authors.initials: P
authors.lastname: McNair
mesh_terms: D002118:Calcium / Q000097:blood*; D002951:Citrates / Q000494:pharmacology*; D019343:Citric Acid; D005260:Female; D006801:Humans; D008297:Male; D010281:Parathyroid Hormone / Q000097:blood*
chemical_list: D002951:Citrates; D010281:Parathyroid Hormone; D019343:Citric Acid; D002118:Calcium