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Biomedical subjects

M J Nicar

Publications and source records attributed to M J Nicar.

28 records · Page 2Linked to original sources
PubMed1983

A simple technique for assessing the propensity for crystallization of calcium oxalate and brushite in urine from the increment in oxalate or calcium necessary to elicit precipitation.

In an effort to develop a simple and reliable method with which to assess the propensity for spontaneous nucleation of calcium oxalate and brushite in urine, the permissible increment of oxalate and calcium was calculated. This represented the additional amount of oxalate or calcium that could be added to urine in three hours before spontaneous precipitation of calcium oxalate or brushite was initiated. The permissible increment of oxalate inversely correlated (P less than 0.001) with the formation-product ratio-activity-product ratio discriminant score of calcium oxalate, which was previously shown to reflect a quantitative measure of the likelihood for spontaneous nucleation. Similarly, the permissible increment of calcium inversely correlated (P less than 0.001) with the formation-product ratio-activity-product ratio discriminant score of brushite. The permissible increments in oxalate and calcium were significantly lower (P less than 0.001) in patients with renal stones than in control subjects. Moreover, treatment with thiazides, allopurinol, sodium cellulose phosphate, orthophosphate, and diphosphonate significantly raised the permissible increment of oxalate in patients with stones. Thus, the permissible increment was reliable in discriminating "stone-forming" from control urine and in assessing response to treatment.

Calcium↗
PubMed1983

Low urinary citrate excretion in nephrolithiasis.

The urinary citrate excretion was examined in patients with nephrolithiasis who were categorized on the basis of different physiologic or metabolic abnormalities. A wide prevalence of low citrate excretion (hypocitraturia) was observed, with over one half of our patients with stones exhibiting it. Hypocitraturia was found in all patient categories except primary hyperparathyroidism and hyperuricosuric calcium oxalate nephrolithiasis. As expected, hypocitraturia was present in renal tubular acidosis and in enteric hyperoxaluria. However, urinary citrate was also low in absorptive and renal hypercalciurias, and in patients in whom an acid-base disturbance was clearly excluded.

Acidosis, Renal Tubular↗
PubMed1982

Oral magnesium load test for the assessment of intestinal magnesium absorption. Application in control subjects, absorptive hypercalciuria, primary hyperparathyroidism, and hypoparathyroidism.

The intestinal absorption of magnesium (Mg) was estimated from the increment in urinary Mg following oral administration of 25 mmol of Mg. Fasting urinary Mg did not differ between the control group and patient groups (absorptive hypercalciuria, primary hyperparathyroidism, and hypoparathyroidism). As compared to the value in the control group, the increment in urinary Mg above the fasting value was not significantly different in absorptive hypercalciuria. However, it was significantly increased in primary hyperparathyroidism and significantly reduced in hypoparathyroidism. In control subjects, the increment in urinary Mg was much higher during a low than during a high calcium diet. The results suggest that 1,25-(OH)2-vitamin D stimulates Mg absorption, since Mg absorption was elevated in situations associated with stimulated 1,25-(OH)2-vitamin D synthesis (primary hyperparathyroidism and low calcium diet) and reduced in a condition characterized by low 1,25-(OH)2-vitamin D production (hypoparathyroidism). Moreover, the data indicate that 1,25-(OH)2-vitamin D may not be pathogenetically important in absorptive hypercalciuria, since Mg absorption was normal.

Adult↗
PubMed1981

Long-term persistence of metabolic abnormalities in absorptive or renal hypercalciuria.

Seven patients with absorptive hypercalciuria and seven with renal hypercalciuria were re-evaluated 1.67-7.33 years after the original diagnosis. When treatment was temporarily stopped, all showed the same metabolic abnormalities as before: those with absorptive hypercalciuria continued to show increased intestinal absorption of calcium and normal or suppressed parathyroid function, and those with renal hypercalciuria had persistent "renal leak" of calcium and parathyroid stimulation. In view of the persistence of metabolic abnormalities, medical therapy should be regarded as a long-term commitment.

Adult↗
PubMed1981

Jejunal and ileal adaptation to alterations in dietary calcium: changes in calcium and magnesium absorption and pathogenetic role of parathyroid hormone and 1,25-dihydroxyvitamin D.

Previous balance studies have shown that fractional calcium absorption is increased by a low and reduced by a high calcium diet. The present studies were done to determine which segment of the small intestine is most sensitive to alterations in dietary calcium, and to see if dietary calcium intake has an effect on the intestinal absorption of another divalent cation, magnesium. Absorption was measured during constant perfusion of 30-cm segments of jejunum and ileum of normal subjects after 4 or 8 wk of a high (1,900 mg/d) or a low (20 mg/d) calcium diet. We found that calcium absorption rate was higher when subjects had been on a low than when they had been on a high calcium diet; the ileum responded more rapidly and more completely than the jejunum. Similar results were obtained with magnesium, but only the difference in the ileum was statistically significant. Sodium and xylose absorption were not influenced by dietary calcium intake. The serum concentrations of parathyroid hormone and 1,25-dihydroxyvitamin D were higher on the low than on the high calcium diet. We conclude that the ileum is more sensitive than the jejunum to changes in dietary calcium intake, and that ileal adaptation probably plays a major role in protecting the body against a deficiency or excess of body calcium that otherwise would occur when dietary calcium is abnormally low or high. Calcium intake influences ileal magnesium absorption in a similar fashion; it is not known whether or not this serves a protective function. Our data are compatible with the concept that adaptation to dietary calcium intake is mediated by changes in the serum concentrations of parathyroid hormone and 1,25-dihydroxyvitamin D.

Adaptation, Physiological↗
PubMed1981

A lack of unique pathophysiologic background for nephrolithiasis of primary hyperparathyroidism.

The metabolic picture of 32 patients with surgically proven primary hyperparathyroidism presenting with renal stones was compared with that of 37 patients without stones. Between stone-forming and nonstone-forming groups, there was no significant difference in serum 1,25-dihydroxyvitamin D [6.82 +/- 2.62 vs. 6.22 +/- 2.33 ng/dl (mean +/- SD); P greater than 0.05], fractional (intestinal) calcium absorption (0.726 +/- 0.141 vs. 0.690 +/- 0.120), urinary calcium (299 +/- 139 vs. 284 +/- 144 mg/day), serum calcium, phosphorus, and parathyroid hormone, or bone density. Similarly, no differences were found between 29 patients presenting with stones alone and 9 presenting with bone disease alone with respect to the above measures. Moreover, urinary environment was typically supersaturated with respect to stone-forming salts regardless of the presence of stones. The results indicate that there is no unique pathophysiological background for the nephrolithiasis of primary hyperparathyroidism.

Blood Chemical Analysis↗
PubMed1980

Ion binding by small molecular weight substances (1,000-10,000 daltons) in urine.

The reliability of calculated activity products as an index of the urinary saturation of calcium oxalate was tested by comparing the solubility of calcium oxalate in various urine preparations. Urine samples were collected from six control subjects and nine patients with nephrolithiasis. From each sample four urine preparations were prepared: centrifugation at 1400 g. 0.22-mu filtration, ultrafiltration through a 10,000 daltons cutoff filter, and ultrafiltration through a 1000 daltons cutoff filter. Each preparation was incubated with an excess of calcium oxalate to steady-state, and the activity product of calcium oxalate was calculated for the ambient solution. Our findings suggest that most calcium and/or oxalate conplexes in urine that are not recognizable by available computational techniques for activity products probably reside in the fraction of 1000 to 10,000 daltons.

Adult↗
PubMed1978

Talc in drugs.

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Animals↗