Normal Phosphate Levels Research Articles

Parabiosis suggests a humoral factor is involved in X-linked hypophosphatemia in mice.

Reduced renal tubular reabsorption of phosphate of unknown etiology is characteristic of X-linked hypophosphatemia in both humans and mice. To test whether a humoral abnormality is involved in the renal effect, parabiosis was performed between Hyp and normal mice at 4 weeks of age. The normal mice joined to Hyp mice showed a progressive diminution of plasma phosphate over the next 3 weeks to approach the level of the Hyp mice. These normal mice had a greater renal phosphate excretion index (urine P/plasma P/urine creatinine) than normal-normal pairs, thus suggesting a reduced renal tubular reabsorption of phosphate. At the same time the expected rises in plasma calcium and plasma 1,25-dihydroxyvitamin D did not occur. There was a significant reduction in their femoral mineral content but not in their femoral length or body growth relative to normal-normal pairs. This change in renal handling of phosphate was specific since the urinary losses of potassium and magnesium were not significantly changed. Separation of normal-Hyp pairs 3 or 6 weeks after parabiosis caused the normal mice to achieve normal plasma phosphate levels within 24 h. At 48 h and 7 days after separation these normal mice had plasma phosphate levels higher than normal mice separated from normal-normal pairs. In summary, the data suggest the presence of a phosphaturic factor in the Hyp mice that can cross a parabiotic union into normal mice and induce many of the symptoms of X-linked hypophosphatemia.

Sorbitol Generation and Its Inhibition by Sorbinil® in the Aging Normal Human and Rabbit Lens and Human Diabetic Cataracts

Fresh intact human cataracts (derived from patients with mature-onset diabetes mellitus and from nondiabetic patients), normal human lenses between 2 and 71 years old and lenses derived from 1.5- to 5-kg rabbits were incubated in Earle's media containing enriched 13C-glucose (5 and 15 mM). 31P NMR organophosphate profiles were obtained at the start and end of each incubation. Sorbinil was added to one of each pair of selected lenses, both incubated with 13C-glucose. All the lenses were frozen after 4h of incubation and were subsequently assayed by 13C NMR spectroscopy. The results demonstrate significant sorbitol generation only in young lenses which can be inhibited by Sorbinil. None of the older normal and cataractous human lenses or the mature-onset diabetic cataracts were capable of generating measurable sorbitol levels although they all showed active glucose metabolism and their organophosphate profiles demonstrated normal high-energy phosphate levels. Increased sugar phosphate levels were usually found in the mature-onset diabetic cataracts. Although our NMR spectroscopy is only sensitive to 10(-3) M levels, such concentrations of sorbitol are required to exert their osmotic effects. These data indicate that high sorbitol levels can only be generated in young human and rabbit lenses and correlate well with the age-related changes in aldose reductase activity in these lenses.

Repeated short periods of regional myocardial ischemia: effect on local function and high energy phosphate levels.

The effect of recurrent periods of ischemia on the myocardium was investigated in 15 open-chest dogs. Ischemia was produced by 3 minutes of proximal occlusion of the left anterior descending coronary artery. Each occlusion was followed by reperfusion of 3 minutes duration. Forty occlusions with a total of 120 minutes of ischemia were performed, and regional function (sonomicrometry) as well as high energy phosphates (needle biopsies) were determined at the end of the 5th, 20th, and 40th period of ischemia and reperfusion. The first periods of ischemia had a cumulative effect both on regional postischemic function (44% and 59% respectively of preischemic control after 20 occlusions) and on the ATP content, but with increasing number of occlusions the additive effects became smaller (ATP reduction/mumol/g w w/per occlusion). The ATP breakdown per occlusion was diminished with increasing number of periods of ischemia, and no significant adenosine was measured in the ischemic myocardium. Higher than normal postischemic creatine phosphate levels (9.1 mumol/g w w at the 40th reperfusion vs. 6.7 mumol/g w w control) indicated a functioning oxidative phosphorylation in the presence of an ATP utilization problem at the sarcomere level, because indicators of the cellular energy level (energy charge, free energy change of ATP hydrolysis) quickly normalized during reperfusion. Stunned myocardium is therefore not a problem of energy supply but rather of energy utilization. Reduced ATP utilization and regional dysfunction are the expressions of the same cellular defect which resides either in the ATP-splitting contractile apparatus or in the electromechanical coupling. Contractile dysfunction during reperfusion protects the heart against subsequent periods of ischemia because ATP turnover is reduced.

Effect of Hypophosphatemia on Diaphragmatic Contractility in Patients with Acute Respiratory Failure

We studied the effects of hypophosphatemia on diaphragmatic function in eight patients with acute respiratory failure who were artificially ventilated. Their mean serum phosphorus level was 0.55 +/- 0.18 mmol per liter (normal value, 1.20 +/- 0.10). The contractile properties of the diaphragm were assessed by measuring the transdiaphragmatic pressure generated at functional residual capacity during bilateral supramaximal electrical stimulation of the phrenic nerves. Diaphragmatic function was evaluated in each patient before and after correction of hypophosphatemia, which was achieved by administration of 10 mmol of phosphorus (as KH2PO4) as a continuous infusion for four hours. After phosphate infusion, the mean serum phosphorus level increased significantly (1.33 +/- 0.21 mmol per liter, P less than 0.0001). The increase in serum phosphorus was accompanied by a marked increase in the transdiaphragmatic pressure after phrenic stimulation (17.25 +/- 6.5 cm H2O as compared with 9.75 +/- 3.8 before phosphate infusion, P less than 0.001). Changes in the serum phosphorus level and transdiaphragmatic pressure were well correlated (r = 0.73). These results strongly suggest that hypophosphatemia impairs the contractile properties of the diaphragm during acute respiratory failure, and they emphasize the importance of maintaining normal serum inorganic phosphate levels in such patients.

Effect of hypophosphatemia on diaphragmatic contractility in patients with acute respiratory failure.

We studied the effects of hypophosphatemia on diaphragmatic function in eight patients with acute respiratory failure who were artificially ventilated. Their mean serum phosphorus level was 0.55 +/- 0.18 mmol per liter (normal value, 1.20 +/- 0.10). The contractile properties of the diaphragm were assessed by measuring the transdiaphragmatic pressure generated at functional residual capacity during bilateral supramaximal electrical stimulation of the phrenic nerves. Diaphragmatic function was evaluated in each patient before and after correction of hypophosphatemia, which was achieved by administration of 10 mmol of phosphorus (as KH2PO4) as a continuous infusion for four hours. After phosphate infusion, the mean serum phosphorus level increased significantly (1.33 +/- 0.21 mmol per liter, P less than 0.0001). The increase in serum phosphorus was accompanied by a marked increase in the transdiaphragmatic pressure after phrenic stimulation (17.25 +/- 6.5 cm H2O as compared with 9.75 +/- 3.8 before phosphate infusion, P less than 0.001). Changes in the serum phosphorus level and transdiaphragmatic pressure were well correlated (r = 0.73). These results strongly suggest that hypophosphatemia impairs the contractile properties of the diaphragm during acute respiratory failure, and they emphasize the importance of maintaining normal serum inorganic phosphate levels in such patients.

A new case of phosphoglycerate kinase deficiency: PGK Creteil associated with rhabdomyolysis and lacking hemolytic anemia

A new case of phosphoglycerate kinase (PGK) deficiency is described. The propositus displayed episodes of rhabdomyolysis crises and acute renal failure but did not exhibit any sign of hemolysis. A severe deficiency in phosphoglycerate kinase was revealed in muscle and was also found in erythrocytes, white cells and platelets. A partial defect in the same enzyme was present in the mother's and the two daughters' erythrocytes, indicating a X-linked recessive genetic transmission of the enzyme defect. In the propositus, erythrocyte ATP concentration was normal, although 2,3-diphosphoglycerate and triose phosphate levels were moderately increased. Lactate production from glucose, in vitro, was close to normal in intact red cells. The partial PGK was characterized by an increased Km for ADP and more especially for ATP, reduced thermostability, and diminished electrophoretic mobility. Lack of this enzyme, which is a key step in the glycolytic process (generation of one molecule of ATP), is thought to be responsible for rhabdomyolysis, a fact that has not been reported previously.

A New Case of Phosphoglycerate Kinase Deficiency: PGK Creteil Associated With Rhabdomyolysis and Lacking Hemolytic Anemia

Abstract A new case of phosphoglycerate kinase (PGK) deficiency is described. The propositus displayed episodes of rhabdomyolysis crises and acute renal failure but did not exhibit any sign of hemolysis. A severe deficiency in phosphoglycerate kinase was revealed in muscle and was also found in erythrocytes, white cells and platelets. A partial defect in the same enzyme was present in the mother's and the two daughters' erythrocytes, indicating a X-linked recessive genetic transmission of the enzyme defect. In the propositus, erythrocyte ATP concentration was normal, although 2,3-diphosphoglycerate and triose phosphate levels were moderately increased. Lactate production from glucose, in vitro, was close to normal in intact red cells. The partial PGK was characterized by an increased Km for ADP and more especially for ATP, reduced thermostability, and diminished electrophoretic mobility. Lack of this enzyme, which is a key step in the glycolytic process (generation of one molecule of ATP), is thought to be responsible for rhabdomyolysis, a fact that has not been reported previously.

The Effect of Treatment on Growth and Deformity in Hypophosphatemia Vitamin D-Resistant Rickets

Vitamin D-resistant rickets is characterized by short stature, lower extremity deformities, and defective mineralization of bone. While basic biochemical defects vary among involved individuals, all patients show a failure of the proximal tubule of the kidney to resorb inorganic phosphate. Laboratory findings consist of low serum phosphorus, elevated alkaline phosphatase, and abnormal serum calcium. Previously recommended treatment programs of high doses of vitamin D have effected some roentgenographic improvement in the rachitic lesions, but no related increase in height or severity of deformities has been associated with significant complications resulting from vitamin D toxicity. Daily administration of low doses of vitamin D and oral phosphates has more recently been suggested to be beneficial in promoting growth and preventing deformities. Thirteen children with documented vitamin D-resistant rickets were treated with oral phosphate and low doses of vitamin D for a mean of five years, and followed for a mean of ten years. Partial roentgenographic resolution of rachitic lesions was similar to those who received vitamin D alone. While the majority had consistently lowered alkaline phosphatases, no patient had consistently normal phosphate levels. No patient exceeded the third percentile in height. One half required osteotomies of the lower extremities. All osteotomies (eight) performed before maturity required revision, whereas those done after maturity (12) did not. Since no apparent clinical roentgenographic benefit can be documented by the addition of oral phosphate to low doses of vitamin D, we would not recommend continually doing so at this time.

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.

Oxygen availability from the blood and the effect of phosphate replacement on erythrocyte 2,3-diphosphoglycerate and haemoglobin-oxygen affinity in diabetic ketoacidosis.

Eleven patients with diabetic ketoacidosis were given intravenous phosphate in doses (mean 118 mmol; range 83--320 mmol) adequate to maintain normal plasma phosphate, in addition to a standard treatment regime. Prevention of hypophosphataemia stimulated recovery of the initially low red-cell 2,3-diphosphoglycerate concentrations (10.6 +/- 5.8 (SD) mumol/g Hb) after twenty-four hours. In ten control patients (initial concentration 8.1 +/- 4.4 mumol/g Hb) treated without phosphate replacement, significantly lower red-cell 2,3-diphosphoglycerate concentrations were found between 2 and 6 days after admission (forty-eight hour value for control patients 14.6 +/- 1.6 and for phosphate-treated patients 18.9 +/- 4.1 mumol/g Hb; p less than 0.01). However, no effect on in vivo p 50 or on the availability of oxygen from the blood resulted from the higher 2,3-diphosphoglycerate levels. Maintenance of normal plasma phosphate levels by intravenous phosphate is, therefore, not indicated to improve tissue oxygenation in diabetic ketoacidosis.

The influence of insulin on glucose and fatty acid metabolism in the isolated perfused rat hind quarter.

Glucose and fatty acid metabolism of resting skeletal muscle were studied by perfusion of the isolated rat hind leg with a hemoglobin-free medium. Tissue integrity was demonstrated by normal ATP, ADP and creatine phosphate levels, by a sufficient oxygen supply, and by a normal appearance of perfused muscle specimens under the electron microscope. The rates of glucose and fatty acid uptake, and of lactate, alanine, glycerol and fatty acid release were constant over a perfusion period of 60 min. Insulin (1 unit/l) caused a more than threefold increase in glucose uptake, a stimulation of lactate production, and a 20% increase in the muscular glycogen levels. Fatty acids and alanine release were significantly diminished by insulin, but glycerol release did not change. The uptake of oleate by the rat hind leg was dependent on the medium concentration in a range of 0.7-1.9mM oleate, and was stimulated by insulin. Glucose uptake was not influenced by oleate, whether sodium was present or not. When the leg was perfused with [1-14C]oleate, 75% of the incorporated fatty acids were found in muscle lipids, 10% were oxidized to CO2, and 5% were recovered in bone lipids. The absolute amount of oleate oxidation was not altered by insulin. In all experiments with and without glucose in the medium, 70-80% of the 14C label incorporated into muscle lipids was found in the triglyceride fraction. In the presence of glucose, insulin significantly increased the incorporation of [1-14C]oleate into muscle triglycerides, whereas no insulin effect, either on fatty acid uptake or on triglyceride formation, could be observed when glucose was omitted from the perfusate. The present results indicate that a "glucose-fatty acid cycle" as found in rat heart muscle does not operate in resting peripheral skeletal muscle tissue. They also demonstrate that the stimulating effect of insulin on muscular fatty acid uptake and triglyceride synthesis is dependent on glucose supply. This finding can be intrepreted as a stimulation of fatty acid esterification by sn-glycerol 3-phosphate derived from an increased glucose turnover, which is in turn due to insulin.

Hereditary fructose intolerance.

Abstract. The clinical and metabolic aspects of hereditary fructose intolerance (HFI) are reviewed and some new observations on children with HFI are reported. The acute rise in plasma FFA level which was earlier shown to follow an acute exposure to fructose in these patients, was found to be associated with an increase in epinephrine excretion and a decrease in plasma TG level. Abolition of the fructose induced hypoglycemia by an infusion of glucose after injection of fructose prevented the rise in plasma FFA, but did not modify the increase in plasma lactate or urate concentration. Maintaining normal or high plasma inorganic phosphate levels after fructose injection by infusion of phosphate buffer did not alter the fructose‐induced changes in blood glucose or lactate, or in plasma FFA or urate concentration. The hyperuricemia and hyperuricosuria after fructose were larger in HFI patients than in normal children. Administration of fructose in the small doses of 0.33‐1.3 g/kg daily for 3–5 days brought about a gradual fall in plasma cholesterol level, and a rise in the excretion of urate and 17‐ketogenic steroids, but no increase in proteinuria.

Defective intestinal phosphate absorption in familial and non-familial hypophosphataemia.

With an oral phosphate tolerance test a primary defect in intestinal phosphate absorption was found in patients with untreated familial and non-familial hypophosphataemia. It is suggested that this plays a major part in the aetiology of rickets and osteomalacia in these disorders. Vitamin D was shown to have a beneficial effect on intestinal transport of phosphate, though defective absorption was not completely corrected. If intestinal phosphate absorption is normal, oral phosphate supplements will maintain normal plasma phosphate levels even in the presence of a pronounced renal phosphate leak.In familial and non-familial hypophosphataemia the phosphate tolerance test may be a more sensitive index of genetic abnormality than a low plasma phosphate. It may be helpful in distinguishing several syndromes at present classified under non-familial hypophosphataemia, as well as assessing the response to treatment with vitamin D and in investigating intestinal transport of phosphate.

Bizarre Clinical Findings-Reply

To the Editor:— There was no intent on my part to imply that hyperparathyroidism might be at the basis of the patient's symptoms. My reason for not including the disorder was the absence of the usual clinical manifestations and laboratory findings. You will note that my answer makes reference to equivocal laboratory results. Though I was aware of the slight rise in serum calcium (12 mg.%), I could not interpret the significance of this slight change in view of the normal serum inorganic phosphate level (3.7 mg.%). Dr. Hunter may be correct in not dismissing this so readily, since a high phosphorus intake or renal impairment, factors which we do not know about in this patient, conceivably could mask a hypophosphatemia. None of the patient's symptoms resemble those of hyperparathyroidism. Indeed, the muscle tightness complained of is opposite to the usual muscle flaccidity and weakness. As I stated in my