Effects of a three-hour calcium clamp on calcium, phosphate, magnesium and zinc concentrations of human parotid saliva.

Ionized (saliva-Ca2+) and total calcium (saliva-CaT), inorganic phosphate (saliva-P), magnesium (saliva-Mg), and zinc (saliva-Zn) levels in parotid saliva were studied in eight healthy volunteers during a 3-h calcium infusion, directly regulated to obtain a pre-settled standardized blood calcium level. Frequent determinations of whole blood ionized calcium (B-Ca2+) were used for continuous adjustments of the calcium infusion rate ('calcium clamp'). Basal B-Ca2+ (1.26 +/- 0.04 mmol X l-1, mean +/- SD) was thus elevated to and maintained at 1.51 +/- 0.05 mmol X l-1 from +30 to +180 min. Saliva samples were taken prior to the infusion and at regular intervals during the infusion period. Saliva-Ca2+ decreased from 0.38 +/- 0.06 to 0.33 +/- 0.05 mmol X l-1 (P less than 0.01) and saliva-Ca2+ as a percentage of saliva CaT from 63 +/- 7% to 53 +/- 10% (P less than 0.001) during the infusion. No changes could be observed in saliva-CaT, saliva-P, saliva-Mg, saliva-Zn, saliva-Na and saliva-K. Possible mechanisms behind these findings might be decreased parathyroid hormone and increased calcitonin concentrations in serum.