Urinary Citrate, Bone Resorption and Intestinal Alkali Absorption in Stone Formers with Fasting Hypercalciuria

Reduced citrate in urine and increased fasting excretion of calcium are abnormalities frequently reported in stone forming (SF) patients. Increased dietary acid (or reduced alkali) introduction or absorption may be a potential cause of both these pathological findings. To test this hypothesis, we studied 64 SF patients {32 with fasting hypercalciuria (FH) and 32 without FH (NFH)}. After a basal evaluation for nephrolithiasis, while on a 500 mg calcium diet, they were evaluated for: (1) daily intestinal alkali absorption (IAA), by urinary electrolyte excretion; (2) basal concentrations of PTH, calcitonin (CT) and 1,25(OH)2-VitD; (3) oral calcium load for evaluation of changes in calcium and hydroxyproline urinary excretions; (4) intestinal calcium absorption (18 patients), with double curve analysis (stable Sr as tracer); and (S) changes in citrate excretion after an alkali load (50 mEq of a mixture of calcium gluconate, lactate and carbonate) in 10 patients. The results demonstrated: (1) FH stone formers had reduced citrate excretion and lower mean IAA levels than NFH stone formers; (2) FH stone formers also had higher bone resorption levels with lower PTH and higher CT levels; (3) IAA levels were related to both citrate excretion and bone turnover indices; and (4) the increases in citrate excretion after oral alkali load were strictly related to basal IAA values (index of alkali absorption and/or generation after oral load), demonstrating that a different absorptive capacity of alkali rather than a different dietary content may underlie these metabolic abnormalities

Impact of the method of calculation on assessment of the PTH-calcium set point

Background. Although the methodology for calculating the PTH secretory parameters is well established, a consensus on a common methodology for calculation of the set point value has not yet been achieved. This is probably one of the major reasons for the conflicting results obtained for this secretory parameter. The aim of the present study was to analyse the influence of the different methods of calculation on the values of set point obtained in clinical nephrology practice. Methods. We analysed 68 PTH-calcium sigmoidal curves, obtained by infusion of 37 mg/kg Na-2-EDTA i.v. in 2 h and 8 mg/kg Ca gluconate based on the calcium element i.v. in 2 h on two separate days. The set point was calculated according to three different methods: method A, the originally described method, based on the classical four-parameter model, which considers the set point as the calcium concentration corresponding to the PTH value intermediate between the maximal and minimal values (the midrange value method); method B (set point = calcium concentration corresponding to 50% of maximal PTH), and method C (set point=calcium concentration corresponding to 50% inhibition of basal PTH value). The three different sets of set point values were entered into the formula of the sigmoidal curve to test the best fitting of the PTH experimentally observed values. Results. The set point values calculated with the classical midrange value method were lower than the corresponding values calculated by the other two methods; method C gave the highest values. Furthermore the best fitting of the experimentally observed PTH levels was obtained by method A, the worst by method C, while method B gave intermediate results. The difference between method A and method B was analysed in order to see if this difference is constant over the whole range of PTH secretory conditions and calcium concentrations. The higher the basal serum calcium concentrations and the lower the suppressibility of PTH, the greater was the overestimation of set point values by method B compared to the midrange value method. Conclusions. Method A, the midrange value method, gives the set point values closest to the original concept of the four parameter model. Although method B (50% of maximal PTH) is well correlated with the original method, it overestimates the set point values and most importantly, this overestimation is not constant, but largely affected by calcium concentration and by the secretory conditions of parathyroid glands

Neurological manifestations of Tick-borne encephalitis in North-Eastern Italy

Tick-borne encephalitis (TBE) is an infectious zoonotic disease, moving from Central Europe to other countries and still rare in Italy. The disease, produced by the European subtype virus, typically takes a biphasic course with neurological disorders of different severity during its second phase. We report the first three TBE cases in Friuli Venezia Giulia (FVG), characterised by extremely variable clinical features. Knowledge of these different presentations will assist physicians in increasing their level of attention to TBE also in this region, where no cases of TBE had been reported in the past, despite the fact that it borders countries with high prevalence of the infection

Balance of non-metabolizable base in continuous peritoneal dialysis patients

Acid generation and elimination processes compared to titratable non-metabolizable base (NaOH equivalents, NB) turnover in end-stage renal disease patients are examined in the light of the Law of electroneutrality. The application over 2 days of the whole-body NB balance technique to 18 patients undergoing continuous ambulatory peritoneal dialysis is evaluated. The results show that the mean rate of NB loss with peritoneal effluent (as bicarbonate and organic acid anions) exceeded the mean rate of NB gain with the dialysis fluid (as salts of lactic acid) by 24 (27), m (SD), mmol per 2 days. In spite of this, the bicarbonate and pH of the plasma remained stable and within normal limits. The concurrent mean rate of the intestinal NB absorption was about 61 (27) mmol per 2 days, as calculated from the whole body balances of the several electrolytes in the metabolic steady-state. This intestinal absorption was more than sufficient to restore the body base consumed in neutralizing endogenous acid generation: 37 (14), 2H2SO4 mmol per 2 days, the remaining NB being eliminated as bicarbonate and organic acid anions. The ample spectrum of plasma acid-base (A B) values appears to some extent influenced by patient-related factors, such as the rate of drinking water intake and the set point deviation for organic acid turnover

Acid production and base balance in patients on chronic hemodialysis

Acid generation and elimination processes were compared with total base (bicarbonate plus metabolizable anions) turnover in 18 anuric patients undergoing post-dilutional haemofiltration. The study was conducted during the second haemodialysis session of the week by means of a whole-body base balance technique. The results showed that the mean rates of base loss and base gain during dialysis did not differ (i.e. the dialysis base balance approximated to zero). The concurrent mean rate of intestinal base absorption was 66+/-26 mmol/2 days, as calculated from the whole-body balance of the various inorganic cation and anion differences in a metabolic steady state. This level of intestinal base absorption would be capable of neutralizing the 59+/-21 mmol of H(+) ions/2 days that is contributed by sulphuric acid, which is the most important endogenous acid produced in anuric patients. In spite of the fact that intestinal base supply was adequate to neutralize endogenous acid production completely, our patients presented with pre-dialysis non-carbonic acidosis. The depression of plasma bicarbonate levels could not, however, be explained by increased concentrations of the anion gap and organic acids, which were within normal limits both before and after dialysis. We suggest as an alternative hypothesis that this pre-dialysis acidosis may represent an isotonic dilution acidosis that is induced by the ingestion of base-free tap water in order for plasma tonicity to be protected from the accumulation of impermeant dietary solutes, which takes place during the interdialysis period in anuric patients

Different dietary calcium intake and relative supersaturation of calcium oxalate in the urine of patients forming renal stones.

1. Dietary calcium restriction, an efficient practice in reducing urinary calcium excretion, has been reported to induce either an increase or no change in oxalate excretion, questioning its use in hypercalciuric stone-forming patients. In addition, calcium restriction has been previously demonstrated to induce other urinary changes which might influence the relative supersaturation of calcium oxalate. So the overall effect of calcium deprivation on the relative supersaturation of calcium oxalate is unpredictable. 2. The aim of the study was to evaluate the effect of dietary calcium restriction on the relative supersaturation of calcium oxalate in the urine of stone-forming patients utilizing a computer methodology which takes into account the main soluble complex species of oxalate. 3. We studied 34 stone-forming patients on both a free-choice diet, whose Ca and oxalate content (24 and 1.2 mmol respectively) was assessed by dietary inquiry, and after 30 days on a prescribed low-calcium and normal oxalate diet (11 and 1.1 mmol respectively). Under both conditions, the excretion of the main urinary parameters related to dietary composition, electrolytes, oxalate and daily citrate urinary excretion, were measured. The relative supersaturation of calcium oxalate was calculated by means of an iterative computer method which takes into account the main soluble complex species on which the solubility of calcium oxalate is dependent. In addition, intact parathyroid hormone and 1,25-dihydroxyvitamin D blood levels were also evaluated. In 13 of the patients intestinal calcium absorption was evaluated during both a free- and a low-calcium diet, utilizing kinetics methodology. 4. The low-calcium diet induced, together with an expected reduction of calcium excretion, a marked increase in oxalate urinary output. This finding was independent of the presence or otherwise of hypercalciuria and of the serum levels of parathyroid hormone and vitamin D. Intestinal calcium absorption was also stimulated by calcium deprivation and its levels were well correlated with oxalate excretion. Minor changes in magnesium and citrate excretion were also observed. The overall effect on the relative supersaturation of calcium oxalate consisted in a substantial increase in this parameter during the low-calcium diet. 5. In conclusion, our data reinforce the concept that dietary calcium restriction has potentially deleterious effects on lithogenesis, by increasing the relative supersaturation of calcium oxalate