CALCIUM KINETICS WITH MICROGRAM STABLE-ISOTOPE DOSES AND SALIVA SAMPLING

Studies of calcium kinetics require administration of tracer doses of calcium and subsequent repeated sampling of biological fluids. This st udy was designed to develop techniques that would allow estimation of calcium kinetics by using small (mu g) doses of isotopes instead of th e more common large (mg) doses to minimize tracer perturbation of the system and reduce cost, and to explore the use of saliva sampling as a n alternative to blood sampling, Subjects received an oral dose (133 m u g) of Ca-43 and an i.v. dose (7.7 mu g) of Ca-46. Isotopic enrichmen t in blood, urine, saliva and feces was well above thermal ionization mass spectrometry measurement precision up to 170 h after dosing, Frac tional calcium absorptions determined from isotopic ratios in blood, u rine and saliva were similar, Compartmental modeling revealed that kin etic parameters determined from serum or saliva data were similar, dec reasing the necessity for blood samples, It is concluded from these re sults that calcium kinetics can be assessed with mu g doses of stable isotopes, thereby reducing tracer costs and with saliva samples, there by reducing the amount of blood needed.