Calcium excretion and

Thiazide diuretics decrease urinary calcium excretion and may decrease bone turnover. However, their effects on bone mineral density and fracture rates have not been studied in controlled trials. Thiazide diuretics are not recommended solely for potential beneficial effects in osteoporosis. 

Glucocorticoids decrease bone formation through decreased proliferation and differentiation, and enhanced apoptosis of osteoblasts. They also increase bone resorption, decrease calcium absorption, increase renal calcium excretion, and result in secondary hyperparathyroidism. 

Table VII. Calcium Excretion and Retention as Affected by Orthophosphate, Hexametaphosphate (Polyphospate), and Calcium...

While our data using this technique are still preliminary, we have observed that 25 yU/ml insulin inhibits the rate of calcium efflux from renal slices (28). This effect of insulin was gradually reduced at the higher concentrations of insulin. The effects of insulin on calcium exchange appear to be localized in the mitochondrial compartment. Further work is needed to determine whether insulin affects specific enzyme systems which are known to play a role in renal calcium transport, and which cellular or subcellular compartments are involved. This would substantially increase our understanding of the regulation of urinary calcium excretion, and of ways in which excessive loss of calcium by this route might be avoided. 

Pharmacology Thiazide diuretics increase the urinary excretion of sodium and chloride in approximately equivalent amounts. They inhibit reabsorption of sodium and chloride in the cortical thick ascending limb of the loop of Henie and the early distal tubules. Other common actions include Increased potassium and bicarbonate excretion, decreased calcium excretion and uric acid retention. At maximal therapeutic dosages all thiazides are approximately equal in diuretic efficacy. 

Glucocorticoid hormones alter bone mineral homeostasis by antagonizing vitamin D-stimulated intestinal calcium transport, by stimulating renal calcium excretion, and by blocking bone formation. Although these observations underscore... 

Sodium cellulose phosphate (Calcisorb) binds calcium in the gut, reduces urinary calcium excretion and may benefit calcium stone-formers. 

After persistent hypercalciuria, osteopenia can develop, causing metabolic bone disease, pathological fractures, and immobilization. Hypercalciuria can also lead to nephrolithiasis and nephrocalcinosis, factors that can impair renal function. Intravenous chlorothiazide has been successfully used for its hypocalciuric effect, with remarkable effect over a period of 6 months in a 13-year-old child who had received parenteral nutrition for 6 years. Calcium excretion and tubular reabsorption of phosphate returned to normal (48). What is not clear from this study is whether the drug actually has a positive long-term beneficial effect on metabolic bone disease. 

Diuretics have been shown to have variable effects in relationship to urinary calcium excretion and supersaturation, most notably including loop diuretic induced hypercalciuria and attenuation of urinary calcium excretion by thiazide diuretics. The factors contributing to nephrotoxicity are most commonly associated with multiple factors that favor calcium salt or uric acid deposition at the tubulo-interstitial level. Management of renal stone formation and nephrocalcinosis therefore presents a unique clinical challenge, balancing factors that increase risk for abnormal calcium salt deposition or crystallization, and factors that reduce this risk. 

Features of lithium-induced hyperparathyroidism include a) a low urinary calcium excretion and the absence of nephrolithiasis b) normal urinary cyclic adenosine monophosphate excretion and c) normal plasma inorganic phosphate [32]. In lithium-induced hypercalcemia, a higher frequency of conduction defects has been noted [47]. Lithium also inhibits par-... 

Peak BMD is generally achieved in a woman s mid-thirties and then gradually declines, with 30% of bone loss occurring after menopause in the absence of HRT. A BMD T score of -1 or higher is considered normal. A score of -1 to -2.5 indicates osteopenia, and a score of -2.5 or lower indicates osteoporosis. Therefore, ED has osteopenia. ED s previous chronic use of steroids is likely to have contributed to her reduced BMD. Steroids increase renal calcium excretion and bone resorption by parathyroid hormone. They also decrease bone collagen synthesis. 

Other methods used to decrease the recurrence of urolithiasis include dietary modifications that decrease calcium excretion and promote diuresis. Changing the diet from alfalfa to grass or oat hay decreases the calcium intake and should decrease the urinary excretion of calcium, since fecal calcium excretion is relatively constant in horses. Although this dietary change should decrease the total calcium excretion, it may also decrease the urinary excretion of nitrogen and the daily urine volume. The latter changes could enhance the supersaturation of urine. In theory, diuresis could be promoted further by the addition of loose salt (50-75 g per day) to the concentrate portion of the diet. However, in one study where ponies were fed sodium chloride (1, 3 or 5% of the total diet dry matter (1% is approximately 75 g sodium chloride for a 500 kg horse)), there were no differences in water intake, urine production or calcium excretion. 

Regular use of antacids containing calcium carbonate should be avoided by patients taking thiazide diuretics, as these reduce calcium excretion and hypercalcaemia may result... 

For those patients with normal to moderately impaired renal function, the cornerstone of initial treatment of hypercalcemia is volume expansion to increase urinary calcium excretion (see Table 49-6). Patients with severe renal insufficiency usually do not tolerate volume expansion they may be initiated on therapy with calcitonin. Patients with symptomatic hypercalcemia are often dehydrated secondary to vomiting and polyuria thus rehydration with saline-containing fluids is necessary to interrupt the stimulus for sodium and calcium reabsorption in the renal mbule. ° Rehydration can be accomplished by the infusion of normal saline at rates of 200 to 300 mL/h, depending on concomitant conditions (primarily cardiovascular and renal) and extent of hypercalcemia. Adequacy of hydration is assessed by measuring fluid intake and output or by central venous pressure monitoring. Loop diuretics such as furosemide (40 to 80 mg IV every 1 to 4 hours) or ethacrynic acid (for patients with sulfa allergies) may also be instiffited to increase urinary calcium excretion and to minimize the development of volume overload from the administration of saline (see Table 49-6). Loop diuretics such as furosemide... 

Adverse effects of oral calcium and vitamin D supplementation include hypercalcemia and hypercalciuria, especially in the hy-poparathyroid patient, in whom the renal calcium-sparing effect of parathyroid hormone is absent. Hypercalciuria may increase the risk of calcium stone formation and nephrolithiasis in susceptible patients. One maneuver to help prevent calcium stones is to maintain the calcinm at a low normal concentration. Monitoring 24-hour urine collections for total calcium concentrations (goal <300 mg/24 h) may also minimize the occurrence of hypercalciuria. The addition of thiazide dinretics for patients at risk for stone formation may result in a reduc-tionof both urinary calcium excretion and vitamin D requirements." ... 

In patients with hypercalcemia, treatment with a loop diuretic plus saline promotes calcium excretion and helps lower serum calcium. In patients with intact regulatory function, increases in calcium resorption promoted by thiazides have minor impact on serum calcium due to buffering in bone and gut. However, thiazides can unmask hypercalcemia that occurs in diseases that disrupt normal calcium regulation (eg, hyperparathyroidism, sarcoidosis, carcinoma). 

Garland, H.O., A.G. Porshaw, and C.P. Sibley. 1997. Dietary essential fatty acid supplementation, urinary calcium excretion and reproductive performance in the diabetic pregnant rat. J. Endocrinol. 153(3) 357-363. 

Since excess dietary protein and excess phosphorus have opposing effects on urinary calcium, the natural association of these nutrients in the human diet tends to ameliorate the effect of both on calcium excretion and bone loss. Whether the relative amounts of protein and phosphorus in high protein diets are always compatible with calcium homeostasis is unclear. This question is not amenable to study in rodents because feeding excess protein has no effect on calcium balance. Excess phosphorus causes bone loss irrespective of the protein content of the diet. Hence, adult rodents and adult humans differ with respect to their skeletal response to both excess protein and excess phosphorus. 

Hunter, D., De Lange, M., Snieder, H., et al. 2001. Genetic contribution to bone metabolism, calcium excretion, and vitamin D and parathyroid hormone regulation. J Bone Miner Res, 16 371-8. 

Collectively, the possible effects of high dietary intakes of protein and phosphate on urinary calcium excretion and enhanced bone resorption, respectively, along with the possibility of reduced calcium absorption with advancing age, argue for recommending an ample intake of calcium. 

Epidemiologic studies have consistently documented that increased potassium intake is associated with greater bone mineral density. In trials, supplemental potassium bicarbonate reduced bone turnover as manifest by less urinary calcium excretion and by biochemical evidence of greater bone formation and reduced bone resorption. However, no trial has tested the effect of increased potassium or diets rich in potassium on bone mineral density or clinical outcomes related to osteoporosis. 

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