Effect of estrogen on intestinal strontium absorption in postmenopausal women.

OBJECTIVES: there is considerable uncertainty about the underlying cause of decreased intestinal calcium absorption that occurs in postmenopausal women. In a previous study, estrogen treatment did not result in an increased intestinal calcium absorption using strontium as a marker. A possible explanation could be that the calcium/strontium load given to the women was too high ( approximately 600 mg Ca), which might result in an insensitive test with respect to the possible stimulation of active strontium transport by estrogen. Therefore, the purpose of this study was to reinvestigate the effect of estrogen on active intestinal strontium absorption using a load of 2.5 mmol of strontium only. METHODS: the effect of estrogen on intestinal strontium absorption was measured in eight normal postmenopausal women. The study included two baseline strontium absorption tests, which were performed with an interval of 10 days for calculating the within subject variation (SER). Thereafter the effect of 2 months of estrogen treatment on intestinal strontium absorption was assessed. Fractional absorption (FC(240)) and the area under the concentration time curve (AUC) 4 h after an oral strontium load of 2.5 mmol were calculated. RESULTS: the within subject SER of FC(240) and AUC(0-240) were 2.3+/-0.76 and 1.2+/-0.41, respectively. FC(240) and AUC(0-240) of strontium were unchanged after treatment with estrogen. CONCLUSIONS: in normal postmenopausal women, we did not find a modulating effect of short-term treatment with a (supra) physiological dose of estrogen on intestinal calcium absorption as measured by the strontium absorption test.

Influence of ovariectomy on extracellular fluid volume in rats: assessment of extracellular fluid volume by means of bromide.

There is considerable evidence that the extracellular fluid volume (ECV) may change in disease states or during longitudinal Intervention studies. Therefore, the measurement of ECV is Important for studying body composition in patients and laboratory animals. We present a modified plasma bromide (Br-, non-radioactive) assay using anion-exchange chromatography, in which a small blood sample of 200 microL (100 microL of plasma) appeared to be enough to reproducibly measure ECV. The inter- and intra-assay accuracy of the Br- analysis ranged from -1.6% to 0.9% and from -0.5% to 0%, respectively. The inter- and intra-assay precision ranged from 1.3% to 1.7% and from 0.6% to 1.2%, respectively. This modified precise and accurate Br- analysis in a small blood sample was applied to investigate whether the ECV changed in rats after ovariectomy. Ovariectomy significantly (P < .05) reduced the ECV as compared with results in SHAM rats. This observation indicates that a change in clinical condition may change ECV, which has consequences for the determination of, for example, the fractional absorption and the relative bioavailability of compounds principally distributed through the ECV.

Strontium as a marker for intestinal calcium absorption: the stimulatory effect of calcitriol.

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 (SE(R)). Before the third test, 0.5 microg of calcitriol was given twice daily for 3 days. In each test, the fractional strontium absorption (Fc(240)) and the area under the concentration-time curve (AUC(0-240)) 4 h after an oral strontium load of 2.5 mmol were calculated. RESULTS: The within-subject SE(R) of Fc(240) and AUC(0-240) was 1.7 +/- 0.7 and 0.83 +/- 0.1, respectively. The stimulatory effect of calcitriol on Fc(240) and AUC(0-240) 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 AUC(0-240) and its sensitivity to calcitriol were better than those of Fc(240), the Fc(240) of strontium is preferred for a clinical test because of its simplicity, requiring only two instead of five blood samples.