The 1994 National Institutes of Health Technology Conference on bioelectrical impedance analysis (BIA) did not support the use of BIA under conditions that alter the normal relationship between the extracellular (ECW) and intracellular water (ICW) compartments. To extend applications of BIA to these populations, we investigated the accuracy and precision of seven previously published BIA models for the measurement of change in body water compartmentalization among individuals infused with lactated Ringer solution or administered a diuretic agent. Results were compared with dilution by using deuterium oxide and bromide combined with short-term changes of body weight. BIA, with use of proximal, tetrapolar electrodes, was measured from 5 to 500 kHz, including 50 kHz. Single-frequency, 50-kHz models did not accurately predict change in total body water, but the 50-kHz parallel model did accurately measure changes in ICW. The only model that accurately predicted change in ECW, ICW, and total body water was the 0/infinity-kHz parallel (Cole-Cole) multifrequency model. Use of the Hanai correction for mixing was less accurate. We conclude that the multifrequency Cole-Cole model is superior under conditions in which body water compartmentalization is altered from the normal state.

Hypocalcemia, rickets, and osteomalacia are major phenotypic abnormalities in vitamin D receptor (VDR)-null mice. In an attempt to understand the abnormal regulation of calcium metabolism in these animals, we examined the expression of calbindins (CaBP) as well as calcium handling in the intestine and kidney of VDR null mice. In adult VDR-null mice, intestinal and renal CaBP-D9k expression was reduced by 50 and 90%, respectively, at both the mRNA and protein levels compared with wild-type littermates, whereas renal CaBP-D28k expression was not significantly changed. Intestinal calcium absorption was measured by the rate of (45)Ca disappearance from the intestine after an oral dose of the isotope. (45)Ca absorption was similar in VDR-null and wild-type mice, but the amount of (45)Ca accumulated in the serum and bone was 3-4 times higher in wild-type mice than in VDR-null mice. Despite the hypocalcemia, the urinary excretion of calcium in VDR-null mice was not different from that in wild-type mice. Moreover, 1 wk of a high-calcium diet treatment that normalized the serum ionized calcium level of VDR-null mice increased the urinary calcium level of these mutant mice to twofold higher than that of wild-type mice on the same diet, suggesting impaired renal calcium conservation in VDR-null mice. These data demonstrate that renal CaBP-D9k, but not CaBP-D28k, is highly regulated by the VDR-mediated action of 1,25-dihydroxyvitamin D(3). Furthermore, the results also suggest that impaired calcium conservation in the kidney may be the most important factor contributing to the development of hypocalcemia in VDR-null mice, and CaBP-D9k may be an important mediator of calcium reabsorption in the kidney.

We compared the intestinal absorption of cholecalciferol and 25-hydroxycholecalciferol in patients with Crohn's disease and resections of the small bowel. Patients were subgrouped into those with small (less than 100 cm), intermediate (100-300 cm), and large (greater than 300 cm) resections. [3H]cholecalciferol or [3H]25-hydroxycholecalciferol were given orally and serial blood samples were taken for measurement of plasma radiolabeled vitamin. Absorption of both forms of the vitamin decreased with extent of resection but 25-hydroxycholecalciferol absorption was always greater than that of cholecalciferol. When compared with normal control subjects, 25-hydroxycholecalciferol absorption in these patients was better maintained than that of cholecalciferol. These data indicate that vitamin D malabsorption reflects the extent of distal small-bowel resection in Crohn's disease. Treatment with oral cholecalciferol is sufficient in those with small or moderate resections but oral 25-hydroxycholecalciferol supplementation may be preferred in those with a severe short-bowel syndrome.

Recent studies from our laboratory have demonstrated that the in vitro addition of 1,25-dihydroxycholecalciferol [1,25(OH)2D3] rapidly (seconds to minutes) stimulated membrane phosphoinositide turnover, translocated protein kinase C from the cytosolic to particulate fraction, increased cytosolic calcium ([Ca2+]i), and decreased cytoplasmic pH (pHi) via inhibition of Na(+)-H+ exchange in rat colonic epithelium of dietary vitamin D-sufficient rats and in Caco-2 cells. In contrast to these prior findings, in the present experiments, 1,25(OH)2D3 failed to elicit any of these colonic biochemical responses in vitamin D-deficient animals. Bethanechol chloride also failed to alter this signal transduction pathway, [Ca2+]i, or pHi. In vivo administration of this hormone for 5-7 days, moreover, to vitamin D-deficient animals restored the rapid biochemical effects of in vitro 1,25(OH)2D3 and bethanechol chloride. These studies, therefore, indicate that alterations in the vitamin D status of rats modulate the action of 1,25(OH)2D3 and other agents on the colonic phosphoinositide signal transduction system and on [Ca2+]i, which, in turn, may influence important cellular processes in this organ such as Na(+)-H+ exchange.

Our laboratory has previously demonstrated that 1,25-dihydroxyvitamin D 3 (1,25[OH] 2 D 3 ) rapidly stimulated polyphosphoinositide (PI) hydrolysis, raised intracellular Ca 2 ϩ , and activated two Ca 2 ϩ -dependent protein kinase C (PKC) isoforms, PKC-␣ and -␤ II in the rat large intestine. We also showed that the direct addition of 1,25(OH) 2 D 3 to isolated colonic membranes failed to stimulate PI hydrolysis, but required secosteroid treatment of intact colonocytes, suggesting the involvement of a soluble factor. Furthermore, this PI hydrolysis was restricted to the basal lateral plasma membrane of these cells. In the present studies, therefore, we examined whether polyphosphoinositide-phospholipase C-␥ (PI-PLC-␥ ), a predominantly cytosolic isoform of PI-PLC, was involved in the hydrolysis of colonic membrane PI by 1,25(OH) 2 D 3 . This isoform has been shown to be activated and membrane-associated by tyrosine phosphorylation. We found that 1,25 (

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We have studied the intestinal absorption of physiological amounts of vitamin D and 25-hydroxyvitamin D [25(OH)D3] in vivo from jejunal sacs in rats with thoracic and bile duct cannulas. Under all test conditions, absorption of 25(OH)D was greater than absorption of vitamin D. The majority of absorbed vitamin D and 25(OH)D was transported from the intestine in portal blood rather than lymph. When the luminal fluid contained 2.5 mM oleic acid and monoolein, the presence of taurocholate did not affect total intestinal absorption of vitamin D or 25(OH)D but increased recovery of vitamin in lymph. When luminal fat content was increased to 10 mM oleic acid and monoolein, total absorption of both vitamin D and 25(OH)D was enhanced by taurocholate. No significant metabolism of vitamin D or 25(OH)D occurred during absorption and transport in lymph. Fifty-three percent of lymph vitamin D was found in the chylomicron fraction, compared with only 13% of 25(OH)D. Inhibition of chylomicron synthesis by cycloheximide decreased vitamin D absorption by 46% but diminished 25(OH)D absorption by only 30%. These differences in behavior of vitamin D and 25(OH)D during absorption may explain the superior absorption of 25(OH)D in patients with malabsorption.

Postprandial levels of copper, ceruloplasmin, iron, total iron binding capacity, cholesterol, vitamin A, carotene, folic acid, vitamin C, albumin, and total globulins in plasma, of 25-OH-vitamin D in serum, and of glutathione reductase activity, an index of riboflavin status, in erythrocytes were determined in a group of 18 juvenile cystic fibrosis patients receiving specialized outpatient care with attention to diet, vitamin supplementation, and pancreatic enzyme replacement. Bone mineralization was assessed by radiographic and photon beam technique. In the plasma of cystic fibrosis patients, levels were elevated for copper, ceruloplasmin, total globins, and total proteins and were depressed for iron, vitamin D, vitamin A, carotene, and albumin. Cortical thickness was diminished in the patients, but bone density was not. For patients with cystic fibrosis, a relation was established between forced vital capacity and certain biochemical indices in plasma. As forced vital capacity decreased, plasma levels increased for copper, total globulins and total proteins and decreased for albumin.