Effects of partial and total colectomy on mineral and acid-base homoeostasis in the rat: magnesium deficiency, hyperphosphaturia and osteopathy, in the presence of high serum 1,25-dihydroxyvitamin D but normal parathyroid hormone.
The effects of colectomy on acid-base status, extra-osseous and bone minerals, calciotropic hormones and bone morphology have not yet been studied. To rectify this, groups of normally fed male rats were subjected to distal (n=11), proximal (n=12) or total (n=12) colectomy. Sham-operated rats (n=12) served as controls. At 112 (+/-2) days after colectomy the following changes were noted: (1) weight gain was delayed; (2) faecal excretion of calcium and phosphorus was normal, whereas that of magnesium was increased; (3) intestinal calcium secretion and absorption of calcium and phosphorus were normal, but magnesium absorption was decreased; (4) urinary excretion of magnesium was also decreased, that of phosphorus was increased, and that of pyridinium and deoxypyridinium tended to be high; (5) the serum levels of ionized magnesium, total calcium, 25-hydroxyvitamin D and parathyroid hormone were normal, while that of 1,25-dihydroxyvitamin D was markedly elevated; and (6) bone magnesium and phosphorus content were decreased, but bone calcium was normal, and thus the bone calcium/phosphorus ratio was high. These abnormalities were associated with moderate metabolic acidosis, as reflected by high urinary ammonium, low citrate and low total CO(2), but normal blood gases. Significant structural abnormalities of bone were not detectable, but trabecular bone tended to show rarefication. Distal colectomy had the least effect, whereas proximal and total colectomies had a distinct effect, on these parameters. It is concluded that colectomy in the rat causes: (1) a syndrome of magnesium deficiency of intestinal origin, compensated metabolic acidosis, urinary phosphorus loss, and high circulating 1,25-dihydroxyvitamin D levels, with the degree depending on the extent of surgical resection; and (2) brittle bones, a feature characteristic of low bone magnesium and more generalized magnesium deficiency. The mechanisms leading to this syndrome are unknown, but altered tissue levels of magnesium and phosphorus may play a key role. (+info)
Calcium acetate versus calcium carbonate in the control of hyperphosphatemia in hemodialysis patients.
CONTEXT: Hyperphosphatemia has an important role in the development of bone and mineral abnormalities in end-stage renal disease (ESRD). OBJECTIVE: To compare the phosphorus binding power and the hypercalcemic effect of calcium acetate and calcium carbonate in hemodialysis patients. TYPE OF STUDY: Crossover, randomized, double-blind study. PLACE: A private hospital dialysis center. PARTICIPANTS: Fifty-two patients who were undergoing regular hemodialysis three times a week ([Ca++] dialysate = 3.5 mEq/L). PROCEDURES: Half of the patients were started on 5.6 g/day of calcium acetate and, after a 2 week washout period, received 6.2 g/day of calcium carbonate. The other half followed an inverse protocol. MAIN MEASUREMENTS: Clinical interviews were conducted 3 times a week to monitor for side effects. Determinations of serum urea, calcium, phosphorus, hematocrit, Kt/V and blood gas analysis were obtained before and after each treatment. RESULTS: Twenty-three patients completed the study. A significant increase in calcium plasma levels was only observed after treatment with calcium carbonate [9.34 mg/dl (SD 0.91) vs. 9.91 mg/dl (SD 0.79), P < 0.01]. The drop in phosphorus levels was substantial and significant for both salts [5.64 mg/dl (SD 1.54) vs. 4.60 mg/dl (SD 1.32), P < 0.01 and 5.89 mg/dl (SD 1.71) vs. 4.56 mg/dl (SD 1.57), P < 0.01, for calcium acetate and calcium carbonate respectively]. The percentage reduction in serum phosphorus (at the end of the study) per milliequivalent of salt administered per day tended to be higher with calcium acetate but statistical significance was not found. CONCLUSION: Calcium acetate can be a good alternative to calcium carbonate in the handling of hyperphosphatemia in ESRD patients. When calcium acetate is used, control of hyperphosphatemia can be achieved with a lower administration of calcium, perhaps with a lower risk of hypercalcemia. (+info)
Management of hyperphosphataemia of chronic kidney disease: lessons from the past and future directions.
A historical look at research in hyperphosphataemia of chronic kidney disease over the last 40 years shows remarkable advances in our understanding of this abnormality and in the technology used to manage it. Phosphate binders, which have become a mainstay in the management of hyperphosphataemia, have evolved from the early use of aluminium gels to calcium salts, to novel, non-absorbed, aluminium-free, calcium-free agents such as sevelamer hydrochloride, and to magnesium-, iron-, and lanthanum-based compounds. With recent advances, clinical management of this complication of chronic renal disease is evolving from adequate care to optimal care, such that new standards in phosphorous management are being set, and various parameters of patient care are being integrated to optimize outcomes and minimize side effects. This paper provides a historical view of the clinical management of hyperphosphataemia, and looks to advances in treatment that are changing the course of renal bone disease management. (+info)
A prospective study of combination therapy for hyperphosphataemia with calcium-containing phosphate binders and sevelamer in hypercalcaemic haemodialysis patients.
INTRODUCTION: Hyperphosphataemia is predictive of death, in haemodialysis (HD) patients. Sevelamer is a mineral-free phosphate binder not limited by the hypercalcaemia often encountered when utilizing calcium-containing phosphate binders. Highly positive calcium balance is associated with ectopic calcification and potentially accelerated vascular disease. Unfortunately, exclusive use of sevelamer entails a large cost differential, limiting its use in many centres. We report on a strategy of partial replacement of calcium with sevelamer for the management of hyperphosphataemia in hypercalcaemic chronic HD patients. METHODS: We identified 23 HD patients with serum calcium >2.6 mmol/l. Dietary phosphate and calcium intake were assessed and baseline serum calcium, phosphate and 1alpha calcidol and elemental calcium dose recorded. Fifty per cent of this initial calcium dose was exchanged for sevelamer. Vitamin D doses were left unchanged. If serum calcium was still >2.6 mmol/l after 4 weeks a further 50% of calcium was exchanged. If serum phosphate was >2 mmol/l the sevelamer dose was increased by 25%. The patients were followed up for a further 4 weeks. RESULTS: Seven patients complained of gastrointestinal intolerance of sevelamer. Serum calcium fell from a mean value of 2.8+/-0.04 (2.64-3.54) mmol/l to 2.56+/-0.03 (2.4-2.9) mmol/l, P<0.0005. The hypercalcaemic percentage of patients fell from 100 to 26%. Mean serum phosphate was not significantly changed, 1.59+/-0.1 (0.57-2.6) mmol/l to 1.63+/-0.11 (0.55-2.68) mmol/l, 17-22% of patients having serum phosphate >2 mmol/l. Serum intact parathyroid hormone increased from 166+/-47 (12-933) ng/l to 276+/-104 (20-1013) ng/l, P=0.02. Mean sevelamer dose was 2.77+/-0.36 (0-5.6) g per day. Elemental calcium dose fell from 2.05+/-0.23 (0.5-4.5) g to 1.03+/-0.1 (0.5-2.5) g, P<0.0001. CONCLUSION: A regimen based on the combination of sevelamer and calcium is capable of effectively managing hyperphosphataemia, without hypercalcaemia, in the majority of hypercalcaemic HD patients. Such a minimally calcaemic approach might reduce the financial burden of sevelamer therapy, and enable a wider range of patients to be treated. (+info)
Hyperphosphataemia as a cardiovascular risk factor -- how to manage the problem.
Hyperphosphataemia is a frequent and important cardiovascular risk factor in patients with chronic kidney disease (CKD). High phosphate levels may influence vascular calcifications by two separate mechanisms: by worsening secondary hyperparathyroidism, which in turn facilitates calcification, and by promoting calcium phosphate deposition in pre-formed endothelial plaques and in the arterial wall. Recent studies have shown that hyperphosphataemia induces the proliferation and differentiation of endothelial vascular cells into osteoblast-like cells, promoting vascular calcification. High phosphate levels also increase the risk of mortality in patients with CKD. To reduce the negative impact of high phosphate, serum phosphate levels should be <5 mg/dl and serum calcium <10 mg/dl. This allows the calcium x phosphate product to be maintained at < or =50 mg(2)/dl(2), reducing the risk of vascular, valvular, and extraskeletal calcification. A multiple-factor approach can be used to reduce serum phosphate: (i). decrease bone resorption by maintaining adequate serum parathyroid hormone levels; (ii). reduce phosphorous intake in the diet, (iii). use phosphate binders efficiently; and (iv). avoid under-dialysis. The patient's diet should be high in nutrition but with the lowest possible phosphorous content. Doses of phosphate binders should be tailored to individual dietary habits and must be taken during meals in a dose proportional to the phosphorous content of the meal. Because of the risk of increased extraskeletal calcification, calcium-containing phosphate-binder intake should not exceed 2-3 g/day. Sevelamer hydrochloride, a non-calcium and non-aluminium phosphate binder with a potency similar to that of calcium salts has shown beneficial effects on lipid profiles. Better control of serum phosphate is achieved in patients on continuous ambulatory peritoneal dialysis than in those on haemodialysis. Removal of phosphate is directly correlated with duration and frequency of dialysis sessions. Thus, it is advisable not to reduce the duration of dialysis sessions to <4 h three times per week. (+info)
Decreased absorption of calcium, magnesium, zinc and phosphorus by humans due to increased fiber and phosphorus consumption as wheat bread.
During a 20 day period of high fiber consumption in the form of bread made partly from wheaten wholemeal, two men developed negative balances of calcium, magnesium, zinc and phosphorus due to increased fecal excretion of each element. The fecal losses correlated closely with fecal dry matter and phosphorus. Fecal dry matter, in turn, was directly proportional to fecal fiber excretion. Balances of nitrogen remained positive. Mineral elements were well-utilized by the same subjects during a 20-day period of white bread consumption. (+info)
Molecular targets of hyperphosphataemia in chronic renal failure.
Dietary phosphate restriction can prevent or retard the progress of chronic renal failure (CRF) and secondary hyperparathyroidism. The klotho gene is involved in the development of a syndrome resembling human ageing, and klotho mutant mice show abnormal calcium/vitamin D metabolism, developing hyperphosphataemia and vascular calcification. Phosphate retention rescues the phenotype of klotho mice. The level of expression of klotho RNA was greatly reduced in the kidneys of all CRF patients. Dietary P(i) restriction induced klotho expression, which enhances the beneficial effect of P(i) restriction in patients with CRF and/or on haemodialysis. (+info)
Hyperphosphataemia and treatment with sevelamer in haemodialysis patients.
More than 60% of patients on chronic haemodialysis (HD) have a serum phosphate level above 5.5 mg/dl (1.75 mmol/l), which recently has been recommended as an appropriate target in patients with end-stage renal disease (ESRD). Preventing hyperphosphataemia and elevated Ca x P product not only ameliorates the progression of secondary hyperparathyroidism and bone disease, but also appears to reduce cardio-vascular morbidity and mortality from vascular calcifications. Dietary phosphate restriction and the administration of aluminium and calcium salts have been the principal means of phosphate control over the last decade. Unfortunately, the protean disturbances of toxic aluminium accumulation in the body virtually eliminated aluminium from clinical practice. Calcium-based therapy, although well tolerated, results in frequent hypercalcaemia when administered concurrently with vitamin D analogues, despite a decrease in the concentration of dialysate calcium. Sevelamer (Renagel((R))) has been a novel, non-absorbable calcium- and aluminium-free synthetic polymer. In initial studies, sevelamer reduced serum phosphate, Ca x P product and parathyroid hormone (PTH) in a manner comparable with calcium acetate therapy. However, the effect on PTH levels may prove to be inconsistent. It seems somewhat less effective in binding phosphate than aluminium, although no direct comparisons have been made. In a recent study, it attenuated the progression of vascular calcification in HD patients. It also binds bile acids, resulting in substantially lower low-density lipo-protein cholesterol levels. The major obstacle to its current use is a substantial increase in the cost associated with sevelamer therapy. (+info)