Clinical presentation and management of patients with primary hyperparathyroidism in Italy.

PURPOSE: Evaluation of the phenotype of primary hyperparathyroidism (PHPT), adherence to International Guidelines for parathyroidectomy (PTx), and rate of surgical cure. METHOD: From January 2014-January 2016, we performed a prospective, multicenter study in patients with newly diagnosed PHPT. Biochemical and instrumental data were collected at baseline and during 1-year follow-up. RESULTS: Over the first year we enrolled 604 patients (age 61 ± 14 years), mostly women (83%), referred for further evaluation and treatment advice. Five hundred sixty-six patients had sporadic PHPT (93.7%, age 63 ± 13  years), the remaining 38 (6.3%, age 41 ± 17  years) had familial PHPT. The majority of patients (59%) were asymptomatic. Surgery was advised in 281 (46.5%). Follow-up data were available in 345 patients. Eighty-seven of 158 (55.1%) symptomatic patients underwent PTx. Sixty-five (53.7%) of 121 asymptomatic patients with at least one criterion for surgery underwent PTx and 56 (46.3%) were followed without surgery. Negative parathyroid imaging studies predicted a conservative approach [symptomatic PHPT: OR 18.0 (95% CI 4.2-81.0) P < 0.001; asymptomatic PHPT: OR 10.8, (95% CI 3.1-37.15) P < 0.001). PTx was also performed in 16 of 66 (25.7%) asymptomatic patients without surgical criteria. Young age, serum calcium concentration, 24 h urinary calcium, positive parathyroid imaging (either ultrasound or MIBI scan positive in 75% vs. 16.7%, P = 0.001) were predictors of parathyroid surgery. Almost all (94%) of patients were cured by PTx. CONCLUSIONS: Italian endocrinologists do not follow guidelines for the management of PHPT. Negative parathyroid imaging studies are strong predictors of a non-surgical approach. PTx is successful in almost all patients.

Essential oils: effects of application rate and modality on potential for combating northern fowl mite infestations.

The northern fowl mite (NFM), Ornithonyssus sylviarum (Mesostigmata: Macronyssidae), is the primary blood-feeding ectoparasite found on poultry in the U.S.A. Three experiments were conducted in vitro to test the acaricidal properties of cade, garlic, lavender, lemongrass, pine and thyme essential oils against NFM, and to evaluate whether these effects are altered by adjusting oil application rates and application modality (direct vs. vapour contact). Applied at the rate of 0.21 mg/cm2 , the essential oils of cade, thyme, lemongrass and garlic resulted in higher NFM mortality at 24 h post-application than lavender and pine oils, and the untreated and ethanol-treated controls. Cade and thyme were the most consistent and fast-acting of the essential oils in terms of toxicity to NFM. Cade applied at 0.21 mg/cm2 and 0.11 mg/cm2 and thyme applied at 0.21 mg/cm2 were effective in eliminating NFM within 2 h through direct contact. The modality of application did not affect the efficacy of cade and thyme essential oils. The results suggest that essential oils may be utilized as alternatives to chemical pesticides and could be used as fumigants for the control of NFM.

Cooled perch effects on performance and well-being traits in caged White Leghorn hens.

We assessed the effects of chilled water cooling perches on hen performance and physiological and behavioral parameters under "natural" high temperatures during the 2013 summer with a 4-hour acute heating episode. White Leghorns at 16 wk of age (N = 162) were randomly assigned to 18 cages (n = 9) arranged into 3 units. Each unit was assigned to one of the 3 treatments through 32 wk of age: 1) cooled perches, 2) air perches, and 3) no perches. Chilled water (10°C) was circulated through the cooled perches when cage ambient temperature exceeded 25°C. At the age of 27.6 wk, hens were subjected to a 4-hour acute heating episode of 33.3°C and plasma corticosterone was determined within 2 hours. Egg production was recorded daily. Feed intake and egg and shell quality were measured at 5-week intervals. Feather condition, foot health, adrenal and liver weights, plasma corticosterone, and heat shock protein 70 mRNA were determined at the end of the study at 32 wk of age. The proportion of hens per cage perching, feeding, drinking, panting, and wing spreading was evaluated over one d every 5 wks and on the d of acute heat stress. There were no treatment effects on the measured physiological and production traits except for nail length. Nails were shorter for cooled perch hens than control (P = 0.002) but not air perch hens. Panting and wing spread were observed only on the day of acute heat stress. The onset of both behaviors was delayed for cooled perch hens, and they perched more than air perch hens following acute heat stress (P = 0.001) and at the age 21.4 wk (P = 0.023). Cooled perch hens drank less than control (P = 0.019) but not air perch hens at the age 21.4 wk. These results indicate that thermally cooled perches reduced thermoregulatory behaviors during acute heat stress, but did not affect their performance and physiological parameters under the ambient temperature imposed during this study.

Dietary style and acid load in an Italian population of calcium kidney stone formers.

BACKGROUND AND AIMS: Animal protein intake may cause an acid load that predisposes individuals to stones by influencing calcium and citrate excretion. These associations were not confirmed in recent studies. Therefore the present study was aimed to compare acid load of diet in stone formers and controls. METHODS AND RESULTS: Participants to the study were 157 consecutive calcium stone formers and 144 controls. Diet was analyzed in these subjects using a software that evaluated nutrient intake from a three-day food intake diary. This software also estimated the potential renal acid load (PRAL, mEq/day). Twenty-four-hour urine excretion of ions and citrate was measured in stone formers. Stone former diet had lower intake of glucose, fructose, potassium and fiber and higher PRAL in comparison with controls. The multinomial logistic regression analysis showed that stone risk decreased in association with the middle and the highest tertiles of fiber intake and increased in association with the highest tertile of PRAL. The linear multiple regression analysis showed that calcium excretion was associated with the sodium excretion and that citrate excretion was associated with the PRAL and animal protein intake in stone formers. CONCLUSION: Our findings suggest that stone formers may undergo a greater dietary acid load sustained by a low vegetable intake and base provision. Dietary acid load does not appear as the main determinant of calcium excretion, but may promote stone risk by decreasing citrate excretion. Sodium intake may predispose to stones by stimulating calcium excretion.

Calcium sensing receptor and renal mineral ion transport.

Calcium sensing receptor (CaSR) is a component of the C family of the G protein-coupled receptors. It is ubiquitously expressed in human and mammal cells but is more expressed in parathyroid glands and kidney cells. It is located on the cell plasma membrane and senses the changes of extracellular calcium concentrations. Thus, it may modify cell functions according to serum calcium levels. CaSR has a key role in calcium homeostasis because it allows parathyroid glands and kidney to regulate PTH secretion and calcium reabsorption in order to keep serum calcium concentration within the normal range. CaSR appears as an important player in the regulation of renal calcium handling and body calcium metabolism. Thus, CaSR may protect human tissues against calcium excess. In kidneys, its protective effect includes the stimulation of diuresis and phosphate retention, along with the potential prevention of calcium precipitation and deposition in kidney tubules and interstitium.

Renal osteodystrophy and vascular calcification.

Chronic kidney disease (CKD) is characterized by phosphate retention and reduced synthesis of 1.25(OH)2-vitamin D stimulating parathyroid hyperplasia. These changes cause a complex osteopathy, defined as renal osteodystrophy, and vascular calcification. Renal osteodystrophy increases the risk of fracture and causes deformities and disability. Vascular calcification occurs in a large proportion of hemodialysis patients and is a marker of arteriopathy. Calcifying arteriopathy induces arterial stiffness and contributes to the high cardiovascular mortality and morbidity among CKD patients. Vascular calcification results from a process of local bone formation induced by osteoblast-like cells developing in the vascular wall from resident cells. Osteoblast differentiation of resident vascular cells may be mediated by metabolic factors and may be induced by high concentrations of phosphate. Therefore, phosphate retention appears as the most detrimental factor affecting arteries in CKD patients. There is no specific therapy to revert soft tissue calcification, but calcification must be prevented in the early stages of CKD.

[What do we know after ten years of genetic research into calcium kidney stones?]. / Quali insegnamenti dopo dieci anni di ricerca genetica sulla calcolosi renale di calcio?

Genetic studies of calcium kidney stones have so far assessed single candidate genes by testing linkage disequilibrium or association between a locus and stone disease. They showed the possible involvement of the calciumsensing receptor gene, vitamin D receptor gene, and bicarbonate-sensitive adenylate cyclase gene. In addition to research in humans, the study of different strains of knock-out mice let us include the gene of phosphate reabsorption carrier NPT2, caveolin-1, protein NHERF-1 modulating calcium and urate reabsorption, osteopontin and Tamm-Horsfall protein among the possible determinants. However, the interactions between genes and also between environmental factors and genes are generally considered fundamental in calcium stone formation. Thus, the genetic studies carried out to date have not led to a significant growth of the knowledge about the causes of calcium kidney stones, even though they have allowed us to assess the size of the problem and define criteria to address it. Further knowledge of the causes of calcium stones may be obtained using the instruments that modern biotechnology and bioinformatics have made available to researchers.

R990G polymorphism of calcium-sensing receptor does produce a gain-of-function and predispose to primary hypercalciuria.

An association between the R990G polymorphism of the CaSR gene, coding for calcium-sensing receptor, and primary hypercalciuria was found in kidney stone formers. To confirm this relationship, we investigated hypercalciuric women without stones and studied the effect of CaSR gene in human embryonic kidney cells (HEK-293). We genotyped for CaSR A986S, R990G, and Q1011E polymorphisms, 119 normocalciuric and 124 hypercalciuric women with negative history of kidney stones. Homozygous (n=2) or heterozygous (n=21) women for the 990G allele considered as one group had an increased risk to be hypercalciuric (odds ratio=5.2; P=0.001) and higher calcium excretion (P=0.005) in comparison with homozygous women for the 990R allele (n=220). HEK-293 cells were transfected with the variant allele at the three CaSR gene polymorphisms and with the most common allele with no variants. The transient increment of intracellular calcium caused by the stepwise increase of extracellular calcium was evaluated in stable transfected cells loaded with fura-2 AM. The extracellular calcium concentration producing the half-maximal intracellular calcium response was lower in HEK-293 cells transfected with the 990G allele than in those transfected with the wild-type allele (P=0.0001). Our findings indicate that R990G polymorphism results in a gain-of-function of the calcium-sensing receptor and increased susceptibility to primary hypercalciuria.

[Calcium kidney stones. Diagnostic and preventive prospects]. / La calcolosi renale di calcio. Prospettive diagnostiche e preventive.

Kidney stone disease is one of the main causes of hospitalization in Italy. Its prevalence increased in the last century and is probably still increasing. The pathogenesis of the disease is not known, although two main theories have been elaborated. The first hypothesizes that hydroxyapatite deposition in the interstitium of the renal papillae (Randall's plaque) precedes urinary calcium oxalate precipitation on the ulcered surface of the papilla to form a stone. The second presumes the tubular lumen of Bellini's duct to be the site where calcium-oxalate salts precipitate to form the nucleus for stone formation within the urinary tract. These pathogenetic processes may be favored by different dietary and genetic factors. The genes involved are not known, although many studies have been performed. Polymorphisms of genes coding for the vitamin D receptor, calcium-sensing receptor, interleukin-1 receptor antagonist, and urokinase were found to be associated with kidney stones, but these results have not been replicated. Different nutrients are suspected to predispose patients to calcium kidney stone disease. A high intake of animal proteins, sodium, vitamin C and oxalate has been implicated in stone formation, whereas calcium, alkalis and phytate may have a protective effect. The prevention of calcium stone formation is based on the recognition of risk factors like those already mentioned here. Furthermore, a family history of kidney stones may be useful in identifying subjects predisposed to become calcium stone formers. However, the expectations of the scientific community are turned to the advances in genetics and to the findings of genetic studies, which may provide diagnostic tools and criteria to define the risk profile of the single individual.

R990G polymorphism of the calcium-sensing receptor and renal calcium excretion in patients with primary hyperparathyroidism.

CONTEXT: Primary hyperparathyroidism (PHPT) shows a great variability in clinical course and severity. Data concerning the association between polymorphic variants of the gene encoding the calcium-sensing receptor (CaSR) and clinical characteristics of PHPT are not conclusive. OBJECTIVE: To evaluate the frequency of three polymorphisms; A986S, R990G, and Q1011E of CaSR in patients with PHPT and to correlate the genotypes with clinical and biochemical parameters. PATIENTS AND METHODS: The study included 94 consecutive unrelated patients referred to our Departments for PHPT diagnosis and management between 2000 and 2005 and 137 age and sex-matched healthy subjects. Patients and controls were genotyped according to standard procedures. Due to the rarity of 990G allele, homozygous and heterozygous subjects were grouped in R/G+G/G set. All PHPT patients were studied for calcium metabolism parameters and renal and bone complications. RESULTS: The proportion of CaSRvariants was similar in PHPT patients and controls. In PHPT patients, only R990G polymorphism was associated with disease parameters; in comparison with R/R, R/G+G/G patients showed lower mean serum parathyroid hormone (PTH) and phosphate levels (139.9 +/- 62.2 vs 199.9 +/- 136.3 pg/ml, P < 0.05 and 0.69 +/- 0.12 vs 0.81 +/- 0.18 mmol/l, P = 0.031 respectively), higher mean 24-h urine calcium concentration and calcium excretion (9.05 +/- 2.05 vs 6.77 +/- 4.31 mmol/24 h, P = 0.012 and 67 +/- 20 vs 51 +/- 26 mumol/l GF, P = 0.039), and increased prevalence of nephrolithiasis (90.0 vs 44.2%, P = 0.007). CONCLUSIONS: The study showed that patients with PHPT, bearing the 990G allele, had lower serum PTH levels and higher urinary calcium excretion in comparison with the other genotype, suggesting an increased sensitivityof the variant receptor to extracellular calcium. Since this variant was associated with increased occurrence of nephrolithiasis, analysis of this polymorphism might help to predict renal complication of the disease.

Erythrocyte calcium influx is related to severity of ventricular arrhythmias in uraemic patients.

BACKGROUND: Myocardial disorders are a remarkable cause of morbidity and mortality in chronic haemodialysed patients (HD). They could be favoured by alteration of cell Ca(2+) handling. In previous studies we characterized an erythrocyte Ca(2+) influx, sensitive to membrane potential and inhibited by Ca(2+) antagonists. Since its maximal influx rate was decreased in HD patients, this study investigates if Ca(2+) influx alterations are related to myocardial disorders in HD patients. METHODS: Voltage-sensitive erythrocyte Ca(2+) influx was measured in 30 healthy controls and in 53 patients (47 HD patients and six patients with left ventricular hypertrophy and normal kidney function), using fura 2. In 29 HD patients and in six healthy subjects Ca(2+) influx was also determined in the presence of parathyroid hormone (PTH) in vitro. Patients were classified according to Lown's ventricular arrhythmias classification after 24-h Holter electrocardiograph (ECG) monitoring. Forty-six patients underwent echocardiography. RESULTS: Voltage-sensitive erythrocyte Ca(2+) influx was significantly reduced in HD patients. Maximal influx rate was significantly higher in HD patients of Lown's classes 3 and 4 (0.789 +/- 0.156 nmol/s, n = 8; P < 0.01) than in patients of classes 1 and 2 (0.499 +/- 0.055 nmol/s, n=15), or without ventricular arrhythmias (0.400 +/- 0.041 nmol/s, n = 24). Maximal influx rate was directly correlated to left ventricular mass index (LVM) (r = 0.353, P < 0.05). Subjects with left ventricular hypertrophy and normal kidney function displayed erythrocyte Ca(2+) influx similar to that of normal subjects. Multiple regression indicates that LVM and Ca(2+) influx were independently related to severity of arrhythmias. When added to the influx assay, PTH increased the maximal influx rate only in patients with ventricular arrhythmias. CONCLUSION: Myocardial dysfunction and altered ventricular excitability could be related in uraemic HD patients to alterations of calcium transport, as found in the erythrocyte model. Reduced resistance to PTH could contribute to this phenomenon.

Choroidal calcifications in patients with Gitelman's syndrome.

Gitelman's syndrome is a renal tubular disorder characterized by a sodium and chloride reabsorption defect in distal tubular cells that determines hypokalemia, metabolic alkalosis, hypomagnesemia, and low calcium excretion. The presence of choroidal calcifications was sought in five patients with Gitelman's syndrome by ophthalmic examination, fluorescein angiography, indocyanine green angiography, and ocular ultrasonography. Calcifications observed in the choroid of two patients were shown by ultrasonography in both patients. Ophthalmic and fluorangiographic examinations detected this alteration in one of the two subjects. Chondrocalcinosis was found in one patient with choroidal calcifications. These findings suggest that precipitation of calcium salts can occur in the choroidal tissue of patients with Gitelman's syndrome. Deposits appeared to be well seen by ultrasonography because of their depth in ocular tissues. Sclerochoroidal calcifications may be favored by the low calcium excretion, which is associated with normal intestinal calcium absorption in patients with Gitelman's syndrome.

Plasma phospholipid arachidonic acid content and calcium metabolism in idiopathic calcium nephrolithiasis.

BACKGROUND: Reports of an increase in plasma and erythrocyte phospholipid arachidonic acid content and in urinary prostaglandin E2 (PGE2) excretion in patients with idiopathic calcium nephrolithiasis suggested their crucial role in the pathogenesis of hypercalciuria, a well-known risk factor for lithogenesis. METHODS: To confirm this hypothesis, 15 healthy subjects and 20 nephrolithiasis patients were evaluated for plasma phospholipid polyunsaturated fatty acid content and PGE2 concentration, serum parathyroid hormone, 25 hydroxyvitamin D3, 1, 25-dihydroxyvitamin D3, and bone-specific alkaline phosphatase levels, as well as urinary excretion of calcium, biochemical markers of bone resorption (hydroxyproline and crossLaps), and intestinal calcium absorption. Furthermore, the effect of a 30-day fish-oil diet supplementation on the previously mentioned parameters was investigated in the patients. RESULTS: At baseline, patients compared with controls showed higher levels of plasma phospholipid arachidonic acid content (P = 0.002), PGE2 (P = 0.0004), serum 25-vitamin D3 (P = 0.001), and 1,25-vitamin D3 (P = 0.001), urinary excretion of calcium (P = 0.001), hydroxyproline (P = 0.007), and crossLaps (P = 0.019), as well as intestinal calcium absorption (P = 0.03 at 60 min). Fish oil supplementation induced a reduction in the plasma phospholipid arachidonic acid level (P < 0.0001), and except for serum concentrations of 25-vitamin D3, normalized baseline blood and urinary parameters, including intestinal calcium absorption. A close correlation between plasma PGE2 and serum 1,25-vitamin D3 (P = 0.004) and between phospholipid arachidonic acid and intestinal calcium absorption (P = 0.0002) and calciuria (P = 0.007) was observed, as well as between urine excretion of crossLaps and hydroxyproline (P < 0.0001), crossLaps and calcium (P < 0.0001), and hydroxyproline and calcium (P < 0.0001). CONCLUSIONS: These findings indicate that the phospholipid arachidonic acid content anomaly could represent the primary event responsible for the mosaic of metabolic and clinical alterations that are distinctive features of renal stone formers, and suggest that a common pathogenetic mechanism might account for the several forms of hypercalciuria detected in idiopathic calcium nephrolithiasis.

Chloride fluxes activated by parathyroid hormone in human erythrocytes.

We used the chloride fluorescent probe, 6-methoxy-N-(3-sulfopropyl)quinolinium (SPQ), to study chloride fluxes in human erythrocytes. The SPQ load was made by hypotonic buffer (150 mOsm, 10 min). Intracellular fluorescence was monitored continuously at 360 nm excitation and 410 nm emission wavelengths. The leakage of SPQ out of cells was <5% h(-1) and the Stern-Volmer constant for quenching of intracellular SPQ by Cl was 0.023 mM(-1). The time course of intracellular [Cl] was measured and the influence of PTH, forskolin, and phorbol 12-myristate 13-acetate (PMA) on erythrocyte Cl transport was examined. The results establish a direct method to measure intracellular [Cl] continuously in erythrocytes and show that PTH induces a Cl efflux inhibited by 4, 4'-diisothiocyanatostilbene-2,2'-disulfonate. This effect was similar to those induced by forskolin, which stimulates cAMP generation, and by PMA, which stimulates protein kinase C.

Erythrocyte voltage-dependent calcium influx is reduced in hemodialyzed patients.

BACKGROUND: Uremia displays increased cytosolic free calcium ([Ca2+]i) in many different cell types, supporting the hypothesis of an altered Ca2+ transport modifying the functional activity of calcium signaling pathway. METHODS: Thirty-five hemodialyzed patients and 20 age-matched subjects were studied. Erythrocyte resting [Ca2+]i and Ca2+ influx were measured by the fluorescent Ca2+-sensitive dye fura-2. RESULTS: We found an increase of resting [Ca2+]i in erythrocytes from uremic hemodialyzed patients compared with matched healthy controls (103 +/- 2.5 nM, N = 20, vs. 90 +/- 4, N = 20, P < 0.01). Moreover, we found an altered voltage-dependent Ca2+ influx showing a reduced transport rate (0.42 +/- 0.03 nM/second vs. 0.74 +/- 0.08, P < 0.01). High levels of plasma parathyroid hormone (PTH) were related to augmented Ca2+ entry (r = 0.511, P < 0.05), contributing to maintain a high level of [Ca2+]i. Hemodialysis had no effect on cell calcium level and Ca2+ influx indices. The therapy with Ca2+ antagonists did not modify the values of resting [Ca2+]i or Ca2+ influx indices, but the correlation between PTH and influx indices was lost. CONCLUSIONS: In conclusion, we found evidence for an alteration of erythrocyte Ca2+ influx caused by uremic toxicity that could be related to some organ disorders in uremia. The chronic increase of cellular calcium may contribute to influx derangement.

Study of calcium metabolism in idiopathic hypercalciuria by strontium oral load test.

Calcium excretion and absorption were evaluated in hypercalciuric calcium stone formers by the study of Sr2+ excretion and absorption after an oral load. Ca2+ stone formers (n = 140) were studied, and the results were compared in the 83 of them who had idiopathic hypercalciuria and in the 57 who had Ca2+ excretion within reference values. Hypercalciuric patients showed increased renal Sr2+ clearance (CRE; 5.26 +/- 0.358 vs 3.29 +/- 0.277 mL/min; P <0.001), whereas Sr2+ absorption [assessed as the area under the serum concentration-time curve (AUC)] was increased at 30 and 60 min (1.53 +/- 0.087 vs 1.21 +/- 0.071 mmol. L-1. min; P <0.05), but not at 240 min after the load. In hypercalciuric patients, the AUCs were positively correlated with urinary Sr2+ fractional excretion (P <0. 001). Conversely, in normocalciuric patients plasma parathyroid hormone (PTH) was negatively correlated with the AUCs (P <0.01) and CRE (P <0.05), whereas 1,25-dihydroxyvitamin D plasma concentrations normalized to PTH were positively correlated with the AUCs (P <0.05). The results of Sr2+ load tests suggest that in the hypercalciuric population, Ca2+ absorption is altered predominantly in the duodenum and that the normal regulation exerted by calciotropic hormones on tubular and enteral Ca2+ handling is lost.

Genotype-phenotype correlations in normotensive patients with primary renal tubular hypokalemic metabolic alkalosis.

Among the different forms of hereditary renal tubulopathies associated with hypokalemia, metabolic alkalosis and normotension, two main types of disorders have been identified: Gitelman disease, which appears to be a homogeneous post-Henle's loop disorder, and Bartter syndrome, a heterogeneous Henle loop disorder. A specific gene has been found responsible for Gitelman disease, encoding the thiazide-sensitive Na-Cl cotransporter (TSC) of the distal convoluted tubule. From a phenotypic point of view the characteristic findings of this disease are hypocalciuria, hypomagnesemia and tetanic crises appearing during childhood or later. Many subjects are asymptomatic. At least three different genes have been shown to be responsible for Bartter syndrome, characterized by mutations in the proteins encoding respectively the bumetanide-sensitive Na-K-2Cl cotransporter, the inwardly-rectifying renal potassium channel and a renal chloride channel, all protein transports located in the ascending limb of Henle's loop. Mutations in the first two transport proteins have been demonstrated in patients with the hypercalciuric forms of Bartter syndrome associated with nephrocalcinosis (respectively Bartter syndrome type I and II), who were often born after pregnancies complicated by polyhydramnios and premature delivery. Mutations in the gene encoding a renal chloride channel were recently recognized in patients with a Henle tubular defect not associated with nephrocalcinosis (Bartter syndrome type III). Most of the latter group of patients were normo-hypercalciuric and presented dehydration and life-threatening hypotension in the first year of life. However, these three genes do not explain all the patients with Bartter syndrome which unlike Gitelman disease, appears to be a very heterogeneous disorder. Clearance studies, especially if done during furosemide and/or hydrochlorothiazide administration, have been helpful in identifying the site of tubular involvement. Considering both phenotypic and genotypic data, we propose a clinical-pathophysiological and molecular approach to diagnose the different tubulopathies associated with hypokalemic metabolic alkalosis.

Strontium absorption and excretion in normocalciuric subjects: relation to calcium metabolism.

The relationships of Sr intestinal absorption and renal excretion with biohumoral factors regulating Ca metabolism were studied in 47 normocalciuric subjects with Ca kidney stones. Sr concentrations were measured in serum and urine after an oral load of stable Sr (30.2 mumol/kg body wt). Enteral absorption of the ion (9.77 +/- 0.438 mmol.L-1.min, 240 min after Sr administration), expressed as the area under the plasma concentration-time curve (AUC), and renal clearance (CRE) in these subjects during the test (2.80 +/- 0.336 mL/min) were not different from values for 27 controls. CRE was not correlated with AUCs. Plasma concentrations of parathyroid hormone (PTH) negatively correlated with AUCs (P < 0.01) and correlated with CRE after one outlier was excluded (P < 0.05). Plasma concentrations of 1,25-dihydroxyvitamin D correlated positively with AUCs (P < 0.01) when normalized to the plasma concentration of PTH. Multiple stepwise regression showed that PTH and phosphatemia were significantly related to AUC values at 240 min (P < 0.01). These findings suggest that Sr absorption and excretion reflect the regulation of Ca metabolism, but some differences in renal handling of the two ions may exist.

Characterization of voltage-dependent calcium influx in human erythrocytes by fura-2.

Thus far, the methods used to determine erythrocyte Ca2+ influx have not allowed the assessment of the kinetics of ion uptake. To overcome this drawback, we studied a new method, using the fluorescent Ca2+-chelator fura-2, which directly quantifies intracellular Ca2+ changes in human erythrocytes. This method has the advantage over previous techniques that it monitors continuously cellular Ca2+ levels. The Ca2+ influx is modulated by cellular membrane potential in the presence of a transmembrane Ca2+ concentration gradient and exhibits a first slow increase of the intracellular Ca2+ concentration, followed, after the reachment of a threshold value of 125 +/- 13 nM Ca2+, by a faster increase until a plateau is reached. The influx rate is inhibited by dihydropyridines in the micromolar range. These findings support the hypothesis that erythrocyte Ca2+ influx is mediated by a carrier similar to the slow Ca2+ channels and is dependent on membrane depolarization.