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Results for “HYPOPHOSPHATEMIA, FAMILIAL”

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PubMed1980

Altered vitamin D, cyclic nucleotide and trace mineral metabolism in the X-linked hypophosphatemic mouse.

Hyp mice have a defective control system for the synthesis of 1,25-(OH)2-vitamin D that does not respond to a low phosphate stimulus. While the plasma levels of 25-OH-vitamin D are reduced somewhat, this seems to be not a serious defect since plasma 1,25-(OH)2-vitamin D levels are normal. Hyp kidneys synthesize and excrete elevated levels of cyclic AMP and cyclic GMP. The elevated tissue levels of trace minerals suggests increased food intake with normal intestinal absorption of the minerals. In addition there is the reduced renal tubular reabsorption of phosphate caused by a change in the brush border transport of phosphate. This leads to hypophosphatemia, osteomalacic bone disease and altered Mg metabolism. There is intestinal resistance to 1,25-(OH)2-vitamin D stimulation. Many of these defects seem unrelated to the reduced renal tubular reabsorption of phosphate. Yet all are derived from one mutation in the Hyp gene. The underlying explanation must account for all abnormalities by a single mutation in a single gene product. The near normal phosphate levels in soft tissues and the multiple defects argue against a genetic change in the phosphate pump as an ultimate explanation. Still to be explored are possible changes in a phosphate recognition site on a cell membrane or a change in an as yet unknown phosphate regulating system.

Animals↗
PubMed1978

Disturbances in acid-base balance during hypophosphatemia and phosphate depletion.

Phosphate depletion leads to bone resorption, resulting in the accession of alkali to the blood and urine. There may also be a release of lactic acid from liver, resulting from ATP depletion and intracellular alkalosis. In general, the net result of these tissue effects is an alkali load discharged into the extracellular fluid. In the kidneys, phosphate depletion causes impaired proximal tubular reabsorption of bicarbonate, and perhaps other substrates, owing in all likelihood to both intracellular alkalosis and depletion of ATP. This impaired proximal capacity to reclaim bicarbonate results in hyperchloremic acidosis. The distal nephron may contribute to acidosis by virtue of inability to produce titratable acid (phosphate-free urine) and perhaps impaired ammonia production. Severe phosphate depletion, therefore, tends to produce hyperchloremic acidosis as a result of a diminished capacity for bicarbonate reclamation in the proximal tubule and probably some impairment of bicarbonate regeneration in the distal nephron. These effects, when marked, ultimately outweigh the contribution of alkali coming from bone breakdown. In the liver, phosphate depletion may stimulate lactic acid production by reducing hepatic ATP stores (Pasteur effect) and producing intracellular alkalosis. ATP depletion may also limit hepatic uptake of lactate. Finally, in muscle cells ATP depletion, resulting from either profound hypophosphatemia or the metabolism of massive fructose loads, may eventuate in frank rhabdomyolysis.

Acid-Base Imbalance↗