A comparison of the effects of lactose and of two chemically modified waxy maize starches on mineral metabolism in the rat

Diets containing 30% by weight of waxy maize starch, lactose monohydrate, acetylated distarch phosphate (EEC No. 1414) or acetylated distarch adipate (EEC No. 1422) were fed to weanling female Specified Pathogen-Free Sprague-Dawley rats for 1 yr and to similar 9-month-old rats for 34 wk. Behaviour and general health were unaffected by the different diets and there were no diet-related differences in food consumption. AT the end of the experiment with 9-month-old rats the mean body weight of the animals receiving lactose was significantly lower than that of the controls receiving starch. The animals receiving the modified starches were slightly but not significantly heavier than the controls at the end of both experiments. The main treatment-related changes in rats on the three test diets were (1) caecal enlargement, (2) increased urinary excretion of calcium, (3) increased renal calcification as measured by chemical analysis of renal tissue obtained at autopsy and (4) increased medullary and pelvic nephrocalcinosis as assessed histopathologically. Acetylated distarch adipate had a slightly greater effect on the above parameters than acetylated distarch phosphate but both modified starches had less effect than lactose. The calcium content of the kidneys, as measured by chemical analysis or histopathology, increased with age, even in the animals receiving the control diet. This change may be due to excessively high concentrations of calcium and phosphorus in all the diets, including the control diet. Cortico-medullary mineral deposits were not a feature in these studies possibly because the diets were not deficient in magnesium. The importance of correct dietary formulation in long-term toxicity studies is emphasized.

Solubility of calcium oxalate in human urine, simulated urine, and water

The main factors that determine the amount of oxalate that can be held in solution in urine were found to be the ionic strength and the calcium and magnesium concentrations. Citrate seemed to be relatively unimportant at normal urine pH. Urea, pyrophosphate, chondroitin-4-sulphate, and chondroitin-6-sulphate were without effect at the concentrations normally found in urine.

Effects of calcium deprivation and orchidectomy on bone composition in the rat

The effects of calcium deprivation and of orchidectomy, separately and combined, on body growth and bone composition have been examined in mature male rats. Calcium deprivation had no significant effect on the rate of body growth but femoral bone weight, bone ash weight and total calcium and phosphorus contents of the femora were reduced while the water content increased. However, there were no significant changes in the ratio of bone weight to body weight, in the amounts of calcium or phosphorus per unit weight of bone, or in the ratio of calcium to phosphorus in the bone. Orchidectomy reduced the rate of body growth, the mean weight of the femora and the ratio of bone weight to body weight. There was a 60% decrease in bone water and a 30--35% reduction in the calcium and phosphorus content of the femora but the amounts of ash, calcium and phosphorus per unit weight of bone fell by only 6--10%. The combination of orchidectomy and calcium deprivation had no greater effect on body weight, bone weight or bone composition than had orchidectomy alone. It is concluded that calcium deprivation and orchidectomy both cause osteoporosis in mature rats but the effects of orchidectomy are more severe than those of calcium deprivation and there appears to be some demineralization of the bone remaining after orchidectomy.

Vitamin D and magnesium absorption in man

1. The effects of vitamin D and its hydroxylated derivatives on calcium and magnesium absorption have been examined in 47 balance studies on patients with various disorders of calcium or bone metabolism. 2. Vitamin D significantly increased the mean net absorption of calcium and also the calcium balance. The mean net absorption of magnesium was also significantly increased although the rise was much less than that of calcium and the mean magnesium balance was unaffected. 3. It is suggested that the slight effect of vitamin D on magnesium absorption may be incidental to its stimulation of active calcium transport, since the latter system has weak affinities for other alkaline earth ions including strontium, barium and magnesium.

Composition of urinary tract calculi from some developing countries

The composition of 142 calculi from Sudan, Thailand, Indonesia and Saudi Arabia has been determined by qualitative and quantitative chemical analysis. Calcium oxalate was the commonest constituent of both kidney and bladder stones, followed by magnesium ammonium phosphate, ammonium acid urate, calcium phosphate, uric acid and cystine in that order. Calcium oxalate was also the main constituent of the nucleus of most kidney and bladder stones, calcium phosphate, magnesium ammonium phosphate, and ammonium acid urate occurring most frequently in the outer layers of the stones. Most endemic bladder stones appear to originate as aggregates of calcium oxalate crystals in the kidney, which subsequently descend to the bladder, where they may acquire secondary deposits of calcium phosphate, magnesium ammonium phosphate or ammonium acid urate.

The effect of oophorectomy on plasma oestrone and androstenedione levels in the rat

Plasma oestrone and androstenedione levels have been measured in oophorectomized and sham-operated rats by means of radioimmunoassay. The mean oestrone level in the oophorectomized animals was approximately two-thirds of that in the intact animals while the androstendione levels were about half of those in the intact rats. A direct relationship was observed between the plasma oestrone and androstenedione levels in the control animals and to a lesser extent in the oophorectomized animals. The results indicate that approximately 50% of circulating androstenedione and 30% of circulating oestrone originate in the ovaries in the female adult rat.

Oxalic acid metabolism in the rat

Feeding experiments indicated that approximately 15% of dietary oxalate is adsorbed in the rat intestine and that dietary oxalate accounts for about one third of the oxalic acid normally excreted in rat urine. Oxalate excretion increased by about 40% when a low calcium diet was fed, decreased by 65% when a low protein diet was fed and increased by 100% when a high protein diet was fed. Fasting for 24 hours resulted in a fall in calcium excretion but phosphate and creatinine excretion increased. Oxalate excretion also tended to increase. Between 60% and 70% of activity was recovered in the urine, faeces and body tissues after 14C-oxalic acid had been administered intraperitoneally. Recoveries of 14C-labeled compounds as urinary 14C-oxalic acid decreased in the following order: glyoxylic acid greater than ascorbic acid greater than citric acid greater than glycollic acid greater than tryptophan greater than hydroxyproline greater than glycine. It is suggested that conversion of citrate to oxalate in the rat may occur via the "glyoxylate cycle." It is concluded that a higher proportion of dietary oxalate is absorbed in the rat intestine compared with man, and that dietary oxalate accounts for a higher proportion of urinary oxalate in the rat than in man. Intestinal secretion and bacterial degradation of oxalate also appear to be proportionately greater in the rat than in man.

Effect of oophorectomy and calcium deprivation on bone mass in the rat

1. The effects of a low calcium diet and of oophorectomy, separately and together, on cortical and trabecular bone mass, have been examined in mature female rats. 2. Calcium deprivation caused a significant decrease of weight, cortical cross-sectional area and ratio of cortical to total area in the femur, it significantly reduced the volume of trabecular bone and increased the percentage of osteoid surface in the tail vertebrae, and in addition increased the urinary excretion of phosphate and, initially, of hydroxyproline. 3. Oophorectomy caused similar though smaller changes in trabecular bone and urine, whereas the effects of oophorectomy on cortical bone were greater on a low calcium intake than on a normal intake. 4. The ash weight of the femora, expressed as a percentage of the total dry weight, was unaffected by calcium deprivation or oophorectomy alone but was significantly reduced when the two occurred together. 5. The percentage of resorption surfaces in the vertebrae tended to increase on the low calcium diet and after oophorectomy on the normal diet but decreased after oophorectomy on a low calcium diet. 6. It is concluded that oophorectomy and calcium deficiency each reduce bone mass in the adult rat but the greatest effect is seen when they are combined.

Evidence of increased oxalate absorption in patients with calcium-containing renal stones

1. The possible roles of the diet and of intestinal absorption in the increased excretion of oxalate by patients with renal calcium stones have been studied. 2. Dietary surveys showed that the mean daily intake of oxalic acid by stone-formers was not significantly different from that of non-stone-formers. 3. The mean urinary excretion of oxalate, expressed as an oxalate/creatinine molar ratio, was significantly reduced by fasting, the change being more marked in the stone-formers than in the normal subjects. Moreover, fasting abolished the difference in mean oxalate/creatinine ratios between stone-formers and control subjects. 4. These results are compatible with the hypothesis that the small increases in urinary oxalate excretion which occur in some idiopathic calcium oxalate stone-formers are due to increased absorption of oxalate from the intestine, which may be due to a reduction in intraluminal calcium concentration.

Composition of urinary tract calculi in children of different ages

The composition of urinary tract calculi in children in relation to their age has been examined and comparisons have been made with other published series. It is concluded that paediatric stone disease can be divided into two main types: (1) infection stones, composed largely of magnesium ammonium phosphate and occurring mainly in children under 5 years of age, (2) calcium stones, occurring mainly in older children.

Seasonal variations in the composition of urine from normal subjects: a longitudinal study

The volume, pH and composition of 24-h urine samples, collected by 13 healthy male adults, were followed over a period of one year. Significant and systematic variations in urine pH, calcium, phosphate, oxalate, uric acid, potassium and magnesium were observed. A significant but non-sinusoidal variation in sodium excretion was found but there were no significant changes in urinary volume, creatinine or hydroxyproline. Many of the observed changes could be attributed to variations in the pattern of food consumption throughout the year but calcium, phosphate and oxalate were exceptions in that seasonal variations in these parameters appeared to be due to the effects of sunlight (or vitamin D) rather than to the diet.

Uric acid disorders in patients with calcium stones

Plasma and uric acid levels were measured in 132 men with calcium-containing renal stones and in 24 healthy men of similar ages. Fasting resulted in a significant fall in the mean plasma uric acid level of normal subjects. Intermittent hyperuricaemia was observed in 7% of fasting patients. Intermittent hyperuricosuria was found in 17% of non-fasting patients but in only 2 to 6% of fasting subjects. Most of the uric acid abnormalities in patients with calcium stones therefore appear to be due to diet and may be prevented by reducing the consumption of purine-rich foods. A direct relationship was observed between uric acid excretion and urine flow at normal flow rates. It is suggested that the apparent increase in stone incidence, which occurs with rising living standards, may be due partly to increased consumption of purine-rich foods.

Changes in the composition of urinary tract stones

An increase in the average calcium oxalate content and decrease in average calcium phosphate content of stones received for analysis has been noted in a 9-year study. These changes appear to be due to a progressive increase in the number of patients with noninfected upper urinary tract stone and to the gradual elimination of phosphatic stones as a result of improved diagnosis and treatment. Some of the conditions associated with calcium phosphate stones are examined, particularly primary hyperparathyroidism, renal tubular acidosis, and medullary sponge kidney. These results further emphasize the importance of calcium oxalate in idiopathic stone disease and the need for a fuller understanding of the factors influencing calcium oxalate crystallization.

Relations between oxalic acid, calcium, magnesium and creatinine excretion in normal men and male patients with calcium oxalate kidney stones

1. The daily excretion of oxalate, calcium, magnesium and creatinine was determined in fifty-two normal men and sixty-five male patients with calcium oxalate-containing renal stones.

2. Direct relationships were found between calcium and oxalate excretion, magnesium and oxalate excretion and calcium and magnesium excretion in both normal subjects and stone-formers. The significance of these relationships is discussed.

3. The mean excretion of calcium and oxalate was significantly higher in the stone-formers, compared with the controls, both calcium and oxalate excretion being raised by about 20%.

4. The effect of oral ingestion of glucose and casein on the rate of excretion of calcium, magnesium, oxalate and phosphate was examined. Glucose increased the rate of calcium and magnesium excretion but had no effect on oxalate excretion and suppressed phosphate excretion. Casein also increased calcium excretion but had little or no effect on magnesium or oxalate excretion, and it increased phosphate excretion.

5. The association of high calcium excretion with high oxalate excretion, in both normal subjects and stone-formers, results in a high degree of supersaturation of the urine with respect to calcium oxalate. The implication of these findings with respect to the cause and treatment of calcium oxalate stones is discussed.

Plasma oxalate concentration and renal excretion of oxalate in man

1. The concentration of oxalate in plasma was determined by an isotopic method involving the simultaneous measurement of [14C]oxalate activities in plasma and urine and the concentration of stable oxalate in the urine.

2. Plasma oxalate concentrations ranged from 1.3 to 1.6 μmol/l (11.8–14.3 μg/100 ml) in three normal men; in fifteen male patients with renal calcium oxalate stones the mean value was 1.73 μmol/l (15.6 μg/100 ml), SD = 0.55 μmol/l (4.98 μg/100 ml).

3. The renal clearance of [14C]oxalate ranged from 162 to 358 ml/min (mean = 249 ml/min) in the normal subjects and from 95 to 315 ml/min (mean = 201 ml/min) in the patients. A direct and statistically significant relationship was observed between the oxalate and creatinine clearances.

4. The oxalate/creatinine clearance ratio ranged from 1.42 to 2.60 (mean = 1.95) in the normal subjects and from 1.04 to 2.33 (mean = 1.76) in the patients, implying a net renal tubular secretion of oxalate. However, oxalate excretion was unaffected by probenecid, a drug known to inhibit the active tubular transport of organic anions.

5. Possible errors in the determination of plasma oxalate concentration and oxalate clearance by chemical and isotopic methods are discussed.

6. Intravenous administration of [14C]oxalate to eight subjects allowed estimations of the miscible oxalate pool [mean = 53.3 μmol (4.80 mg); SD = 18.7 μmol (1.68 mg)], the volume of distribution of [14C]oxalate (mean = 45.2% of body weight; SD = 5.65) and the biological half-life of [14C]oxalate (mean = 91.10 min; SD = 13.89).

The relation between the concentration of calcium salts in the urine and renal stone composition in patients with calcium-containing renal stones

1. Diurnal variations in urine calcium oxalate and calcium phosphate activity products were observed in normal men and patients with recurrent calcium oxalate or mixed oxalate—phosphate renal stones.

2. Maximum and minimum calcium oxalate products were higher in the patients than in the controls, the difference being most marked in the patients with calcium oxalate stones.

3. Maximum and minimum calcium phosphate products expressed as octocalcium phosphate [(Ca8H2(PO4)6], brushite or hydroxyapatite, were significantly higher than normal in the patients with mixed stones but not in the patients with calcium oxalate stones.

4. The raised calcium oxalate products in the patients were due mainly to increased concentrations of Ca2+ ions; these, in turn, were due mainly to an increased rate of excretion of calcium. Raised calcium phosphate products were due mainly to hypercalciuria, combined with abnormally high urine pH values.

5. Patients with recurrent calcium stones appear to fall into two types: (1) patients with calcium oxalate stones associated with hypercalciuria, a normal or raised urine oxalate and a normal urine pH; (2) patients with mixed oxalate—phosphate stones associated with hypercalciuria, a normal or raised urine oxalate and a raised urine pH.

6. The implications of these findings in regard to treatment are discussed.

Relationships between calcium and oxalic acid intake in the diet and their excretion in the urine of normal and renal-stone-forming subjects

1. The short-term effects of different intakes of calcium and oxalic acid on the urinary excretion of these substances was studied in eight normal men and eight men with a history of calcium-containing renal stones.

2. The effect of dietary oxalate on urine oxalate depended partly upon the calcium intake. Thus, on a normal calcium intake an increase in oxalate intake caused an increase in oxalate excretion that corresponded to 3·6% of the additional dietary oxalate; on a low calcium diet, however, the increase corresponded to 8·1%.

3. A decrease in daily calcium intake from 1000 to 250 mg caused a fall in calcium excretion averaging 150 mg/day in the patients and 60 mg/day in the controls but this was accompanied by average rises of 10 and 7 mg/day respectively in oxalate excretion, with the result that the calcium oxalate activity products remained almost unchanged.

4. A decrease in oxalate as well as calcium intake resulted in a fall in calcium excretion that was not accompanied by a rise in oxalate excretion, and there was a statistically significant fall in the calcium oxalate activity product in both the patients and normal subjects.

A combined qualitative and quantitative procedure for the chemical analysis of urinary calculi

A better understanding of the physico-chemical principles underlying the formation of calculus has led to a need for more precise information on the chemical composition of stones. A combined qualitative and quantitative procedure for the chemical analysis of urinary calculi which is suitable for routine use is presented. The procedure involves five simple qualitative tests followed by the quantitative determination of calcium, magnesium, inorganic phosphate, and oxalate. These data are used to calculate the composition of the stone in terms of calcium oxalate, apatite, and magnesium ammonium phosphate. Analytical results and derived values for five representative types of calculi are presented.

Determination of Oxalic Acid in Biological Material

The properties of oxalic acid are reviewed, together with the use that may be made of these in various methods of oxalate analysis, which are critically compared. Information is given on the oxalate content of biological fluids, urinary calculi, tissues, and foods.

Urinary excretion of calcium and creatinine in relation to age and body weight in normal subjects and patients with renal calculus

1. Variations with age in body weight, urine volume and calcium and creatinine excretion were determined in 246 normal subjects and 305 patients with calcium-containing renal stones.

2. Body weight, urine volume and creatinine excretion increased with age to a maximum in the third decade in both male and female controls and stone-formers. Thereafter body weight and urine volume did not change appreciably but creatinine excretion decreased.

3. In normal subjects the daily excretion of calcium and calcium concentration increased in the first two decades and remained relatively constant thereafter until the eighth decade when they decreased. The calcium/creatinine ratio was high in the first decade and fell during the second and third decades. Thereafter it remained relatively constant in men until the eighth decade when it fell. In women, however, there was a second rise in the fifth and sixth decades. The calcium/body weight ratio remained relatively constant with age until the eighth decade, when it fell.

4. Patients with renal calculus showed similar variations in calcium excretion with age. The mean values, however they were expressed, were higher than those in normal subjects of the same age and sex.

5. The daily excretion of calcium was higher in men than women, whether normal subjects or stone-formers. This difference was abolished when calcium excretion was related to body weight and reversed when excretion was related to creatinine.

6. Comparison of the present data with previous data from the same population indicated that the mean daily excretion of calcium by both normal subjects and patients with renal calculi has increased during the last decade.

7. The significance of these observations in relation to calcium homeostasis and renal calculus formation is discussed.

Plasma oxalic acid and calcium levels in oxalate poisoning

Observations are reported on five cases of suicide or attempted suicide by poisoning with oxalic acid or ethylene glycol. Elevated oxalic acid levels were observed in the plasma, stomach contents, and a number of tissues. Raised oxalic acid levels in plasma were associated with reduced total and ultrafilterable calcium levels. It is suggested that the reduction in plasma total calcium level is due mainly to the deposition of calcium oxalate in the soft tissues, but inhibition of the parathyroid glands may be a contributory factor. Microscopic examination of various tissues indicated that oxalic acid is deposited in the tissues in two forms: (1) crystalline calcium oxalate dihydrate in the kidney and (2) a non-crystalline complex of calcium oxalate and lipid in liver and other tissues.