Intestinal strontium absorption: from bioavailability to validation of a simple test representative for intestinal calcium absorption

Abstract Calcium absorption tests have rarely been validated for being representative for absolute bioavailability (true absorption) or for intraindividual variation. Therefore, we investigated the reproducibility of the absolute bioavailability of strontium chloride, a marker for intestinal calcium absorption, in healthy male volunteers (n = 8) by measuring the area under the plasma strontium concentration-time curve after oral and intravenous administration of strontium. Subsequently, we selected a simple test variable as being representative of absolute bioavailability. The mean absolute bioavailability (+/- SD) was 25% +/- 7%. The best test variable appeared to be the fractional absorption at 240 min (Fc240) after oral intake, which demonstrated the highest correlation with absolute bioavailability (r = 0.66). The intraindividual variations of the data for this variable and for the absolute bioavailability are similar to those described for various absorption tests based on the use of calcium isotopes. Thus, the Fc240 of strontium offers the potential of a simple clinical test for use as a measure of intestinal calcium absorption and its modulation.

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Strontium as a Marker for Intestinal Calcium Absorption: The Stimulatory Effect of Calcitriol

Clinical Chemistry ◽

10.1093/clinchem/46.2.248 ◽

2000 ◽

Vol 46 (2) ◽

pp. 248-251 ◽

Cited By ~ 9

Author(s):

Marieke Dijkgraaf-ten Bolscher ◽

J Coen Netelenbos ◽

Rob Barto ◽

Wim J F van der Vijgh

Keyword(s):

Calcium Absorption ◽

Intestinal Calcium Absorption ◽

Clinical Test ◽

Time Curve ◽

Blood Samples ◽

Healthy Men ◽

The Third ◽

Healthy Humans ◽

Concentration Time ◽

Better Than

Abstract Background: Intestinal strontium absorption is becoming accepted as a clinical and diagnostic tool for assessing intestinal calcium absorption in humans. However, little is known about whether intestinal strontium absorption, like that of calcium, is stimulated by calcitriol in healthy humans. Methods: The effect of calcitriol on intestinal strontium absorption was measured in eight healthy men, ages 20–60 years. Before administration of calcitriol, two tests were performed with an interval of 10 days for calculating the within-subject variation (SER). Before the third test, 0.5 μg of calcitriol was given twice daily for 3 days. In each test, the fractional strontium absorption (Fc240) and the area under the concentration-time curve (AUC0–240) 4 h after an oral strontium load of 2.5 mmol were calculated. Results: The within-subject SER of Fc240 and AUC0–240 was 1.7 ± 0.7 and 0.83 ± 0.1, respectively. The stimulatory effect of calcitriol on Fc240 and AUC0–240 was 35% (21.8 ± 2.0 to 28.8 ± 2.4; P = 0.003) and 61% (8.97 ± 0.97 to 14.4 ± 1.3 mmol · L−1 · min; P = 0.001), respectively. Conclusions: Although the reproducibility of AUC0–240 and its sensitivity to calcitriol were better than those of Fc240, the Fc240 of strontium is preferred for a clinical test because of its simplicity, requiring only two instead of five blood samples.

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