Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0024523 (malabsorption)
 7,319 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

To determine whether the phosphaturic response to circulating parathyroid hormone (PTH) is exaggerated in patients with familial x-linked hypophosphatemic vitamin D-resistant rickets (FHR), we examined the phosphaturic response to parathyroid extract (PTE) (administered intravenously in the posthypercalcemic state) in two unrelated adult hemizygotes with FHR. In these two patients whose plasma concentration of PTH was normal (determined by radioimmunoassay). neither vitamin D nor phosphate therapy had been given during the past 10 yr. Two normal men and a hypophosphatemic man with intestinal malabsorption, hypocalcemia, and osteomalacia served as control subjects. In all subjects, calcium gluconate was adminstered intravenously from 6 p.m. to 12 midnight at a rate that maintained the concentration of serum calcium at 13-15 mg/100 ml during the administration of calcium. When normocalcemia had recurred the next morning, and the plasma PTH concentration and urinary excretion of cyclic 3', 5'-AMP were reduced. PTE was administered intravenously at successively increasing rates of 0.1, 0.4, and 0.8 U/kg per h, each rate lasting 90 min. Minutes after the initiation of PTE in the affected hemizygotes, fractional excretion of filtered phosphate increased from negligible values to values strikingly greater than those of similarly studied control subjects and plateaued at strikingly greater values throughout further administration of PTE. This phenomenon of exaggerated phosphaturia could not be attributed to volume expansion, decreases in serum concentration of calcium during the study, differences in percent of administered calcium retained, or hemodynamic changes. Only the phosphaturic response to PTE appeared to be exaggerated. At any cumulative dose of PTE, urinary excretion of cyclic 3', 5'-AMP in the hemizogytes was indistinguishable from that of control subjects. The findings in this study suggest that in patients with FHR, circulating PTH is required for the genetically transmitted abnormality to be physiologically expressed as a reduction in net renal reabsorption of phosphate, and that this physiological expression of the genetic abnormality is expressed fully at normal or nearly normal circulating levels of PTH.
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PMID:Exaggerated phosphaturic response to circulating parathyroid hormone in patients with familial X-linked hypophosphatemic rickets. 18 58

X-linked hypophosphatemic (Hyp) mice are a model for human X-linked (familial) hypophosphatemia (vitamin D-resistant rickets). In several studies, Hyp mice have been shown to exhibit either normal intestinal phosphate absorption or malabsorption of phosphate. These apparently conflicting reports led us to further investigate intestinal phosphate absorption. Isolated intestinal segments in vivo were used in C57BL/6J normal and Hyp mice, both male and female. 33P was placed in the segment in 2 mM Na2HPO4 + 150 mM NaCl, pH 7.2. Mice at 4, 7, and 12 weeks of age were used. No significant differences in phosphate absorption were found between the sexes. At 4 weeks of age, Hyp mice showed significant malabsorption of phosphate, with the jejunum being the most severely affected. Malabsorption was judged by significantly more 33P remaining in the lumen, less in the intestinal tissue, and less in the plasma. At 7 weeks of age, these same trends were seen but at a nonsignificant level. By the 12th week of life, the absorption of 33P was similar in Hyp and normal mice. Thus, phosphate malabsorption in Hyp mice is an age-related phenomena. These changes parallel the malabsorption of calcium in young Hyp mice and reflect the lowered plasma 1,25-dihydroxyvitamin D (1,25(OH)2D) levels of young Hyp mice.
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PMID:Malabsorption of phosphate by the intestines of young X-linked hypophosphatemic mice. 314 95

X-linked hypophosphatemic (Hyp) mice are a model for human sex-linked vitamin D-resistant rickets. We have reported intestinal malabsorption of calcium in young Hyp mice, and in this report we have explored the mechanism for it. To test for resistance of the intestine to 1,25(OH)2 vitamin D3, this hormone was continually infused via osmotic minipumps into 4-week-old normal and Hyp mice at 0, 17, 50 or 150 ng/kg/day. After 3 days, 45Ca and inorganic 32P were administered by gavage, and the mice were sacrificed on the fifth day. The Hyp mice showed responses to the hormone equivalent to the normal mice in terms of increased intestinal absorption of both 45Ca and 32P, increased plasma isotope levels, increased femoral isotope content, and increased duodenal and renal 9 kD vitamin D-dependent calcium-binding protein (calbindin-D9K; CaBP). Plasma 1,25(OH)2D was measured in these mice. There were significant correlations of plasma 1,25(OH)2D to the intestinal absorption of 45Ca and 32P and to duodenal and renal CaBP. Plasma 1,25(OH)2D was also measured in stock normal and Hyp mice and was found to be lower in 4-week-old Hyp mice than in 4-week-old normal mice (113 +/- 10 pM (n = 18) vs. 67 +/- 10 (n = 20), normal vs. Hyp, p less than .01), but unchanged at 13 weeks of age (77 +/- 13 (n = 13) vs. 70 +/- 15 (n = 15), NS). This observed difference in plasma 1,25(OH)2D between normal and Hyp mice at 4 weeks of age was sufficient to explain the observed normal-to-Hyp differences in intestinal absorption of 45Ca and duodenal and renal CaBP. It also explained 72 +/- 18% of the observed difference in 32P absorption. We conclude that Hyp mouse intestine is not resistant to 1,25(OH)2D and that the lower plasma 1,25(OH)2D of 4-week-old Hyp mice causes intestinal malabsorption of calcium and phosphate.
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PMID:Evidence that low plasma 1,25-dihydroxyvitamin D causes intestinal malabsorption of calcium and phosphate in juvenile X-linked hypophosphatemic mice. 345 58

Elucidation of the vitamin D endocrine system and the availability of potent metabolites have led to new approaches to vitamin D therapy. The traditional management of exogenous (sunlight) or endogenous (malabsorption) vitamin D deficiency without evidence of disordered vitamin D metabolism has not changed, since it consists of treatment with vitamin D itself--a therapy which preserves the normal intrinsic mechanisms for regulating the rate of production of 1,25-dihydroxycholecalciferol. 1,25-DHCC and the analogue compound 1 alpha-CC should be reserved for treatment of hypocalcemia consequent on chronic renal failure or hypoparathyroidism, where 1-hydroxylation is lacking or impaired. Hypophosphatemic rickets has been treated with 1-hydroxylated compounds, with promising results; this use of the latter metabolites warrants further investigation. The use of vitamin D metabolites and of pharmacological doses of vitamin D itself must be regarded as substitution of a hormone or hormone precursors. Therefore, careful monitoring of serum and urine calcium is required in every patient receiving these compounds, in order to avoid excessive dosage. Special attention must be paid to patients with sarcoidosis since they often develop hypercalcemia after vitamin D or UV-light exposure, as a result of an intrinsic regulation defect in 1,25-DHCC synthesis.
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PMID:[Therapy with vitamin D and D-metabolites]. 626 26