Studies were carried out to examine the mechanism of action of estrogen on intestinal calcium absorption in the rat. Three-month-old Wistar rats were sham-operated or ovariectomized (OVX). They were fed a diet containing 0.4% Ca, 0.4% P, and 2000 IU vitamin D3/kg. Eight weeks after operation, both OVX and sham-operated rats were randomly assigned to eight treatment groups. Five groups received per 100 g of body weight 12.5 ng calcitriol (1, 25-dihydroxyvitamin D3); 7.5 microg of estradiol-benzoate; 7.5 microg of estradiol-benzoate and 0.1 mg of ICI 182780; 12.5 ng of calcitriol and 0.1 mg of ICI 182780; and 0.1 mg of ICI 182780, respectively. Three groups received the various vehicles used. Intestinal calcium absorption was measured in vivo using single pass perfusion of the duodenum. OVX did not change intestinal calcium absorption. A pharmacological dose of estradiol-benzoate caused a significant increase in intestinal absorption of calcium, which was comparable to that of a pharmacological dose of calcitriol in both OVX and sham-operated rats. Estrogen-induced rise in intestinal calcium absorption was completely blocked to basal level by the pure estrogen receptor (ER) antagonist ICI 182780. In contrast, ICI 182780 did not antagonize calcitriol-enhanced intestinal calcium absorption. Our findings suggest that estrogen stimulates intestinal calcium absorption via an ER.

SummaryOBJECTIVE Impaired intestinal calcium absorption in postmenopausal women is often indirectly linked to decreased serum 1,25(OH) 2 D or to intestinal resistance to its action rather than directly to low circulating oestrogen levels following the menopause. The purpose of this clinical study was to investigate the short-term effect of oral 17b-oestradiol on intestinal calcium absorption, with strontium as a marker. DESIGN

In order to determine body fluid shifts between the intra- and extra-cellular spaces, multifrequency impedance measurement is performed. According to the Cole-Cole extrapolation, lumped values of intra- and extra-cellular conduction can be estimated which are commonly expressed in resistances Ri and Re respectively. For this purpose the magnitude and phase of the impedance under study are determined at a number of frequencies in the range between 5 kHz and 1 MHz. An approach to determine intra- and extra-cellular conduction on the basis of Bode analysis is presented in this article. On this basis, estimation of the ratio between intra- and extra-cellular conduction could be performed by phase measurement only, midrange in the bandwidth of interest. An important feature is that the relation between intra- and extra-cellular conduction can be continuously monitored by phase measurement and no curve fitting whatsoever is required. Based on a two frequency measurement determining Re at 4 kHz and phi(max) at 64 kHz it proved possible to estimate extra-cellular volume (ECV) more accurately compared with the estimation based on extrapolation according to the Cole-Cole model in 26 patients. Reference values of ECV were determined by sodium bromide. The results show a correlation of 0.90 with the reference method. The average error of ECV estimation was -3.6% (SD 8.4), whereas the Cole-Cole extrapolation showed an error of 13.2% (SD 9.5). An important feature of the proposed approach is that the relation between intra- and extra-cellular conduction can be continuously monitored by phase measurement and no curve fitting whatsoever is required.

An approach to determine intra- and extracellular conduction on the basis of Bode analysis is presented. Estimation of the ratio between intra- and extracellular conduction could be performed by phase measurement only, midrange in the bandwidth of interest. An important feature is that the relation between intra- and extracellular conduction can be continuously monitored by phase measurement and no curve fitting whatsoever is required. Based on a two-frequency measurement determining Re at 4 kHz and phi max at 64 kHz, it proved possible to estimate extracellular volume (ECV) in 23 patients. Reference values on ECV were determined by sodium bromide. The results show a good correlation (r = 0.90) with the reference method. The average error of ECV estimation was -3.6% (SD 8.4).

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