Mineral and electrolyte metabolism最新文献

Aims: To study the distribution of vitamin D receptor (VDR) gene alleles in hypercalciuric and nonhypercalciuric nephrolithiasis patients, hypothesizing that distinct biochemical parameters would be associated with different VDR genotypes.

Methods: 12 hypercalciuric, 15 normocalciuric nephrolithiasis patients, and 150 healthy subjects were recruited. The individual genetic pattern for VDR was evaluated by DNA extraction followed by polymerase chain reaction amplification of the VDR gene and digestion with the restriction enzyme BsmI.

Results: In the hypercalciuric group, Bb patients represented 50% (6/12); bb patients 33% (4/12), and BB cases were 16% (2/12). The VDR frequency distribution was not statistically different in hypercalciuric patients and controls (Bb 72%; bb 16%; BB 12%). In the nonhypercalciuric group, the prevalence of the bb genotype (7/15; 47%) was thrice the percentage of control subjects, while the percentage of BB patients was similar to that of the control group (2/15; 13%). Patients with the bb haplotype exhibited a higher daily urinary calcium excretion. Among hypercalciuric patients, after a calcium-restricted diet, bb patients showed a 39% reduction in daily urinary calcium excretion in comparison with a nonsignificant 13% reduction observed in BB subjects (p = 0.004).

Conclusions: The effects of VDR gene polymorphism on calcium metabolism contribute to the understanding of the pathogenesis of urinary calculi.

Animals fed a low calcium diet develop hypocalcemia and osteoporotic bone. Earlier we conjectured that a low calcium environment might be one of the factors causing abnormalities in hard tissues. Osteoblastic MC3T3-E1 cells (E1 cells) undergo a process of proliferation and differentiation and then produce small mineralized nodules. In this study, we examined the effects of a low calcium environment on osteoblast-like cells cultured with 10% fetal bovine serum and ascorbic acid. Under the culture condition, nodules with characteristics of normal bone appeared by day 30 regardless of the calcium conditions. However, the low calcium environment enhanced the mRNA expressions of c-fos, c-jun and osteocalcin, a specific marker of the osteoblast phenotype. And the exposure to the low calcium medium inhibited the formation of bone nodules. We further studied the differential expressions of c-fos and c-jun in relation to their responses to serum as a function of phenotypic development in the low calcium environment. Both c-fos and c-jun expressions were highly activated by treatment with epidermal growth factor (EGF), but the magnitude of activation was significantly larger under the low calcium condition than the normal condition at each stage. In addition, DNA-binding activities of activating protein-1 (AP-1), Fos/Jun family dimers, were also accelerated by EGF treatment in the low calcium environment. Our findings suggested that osteocalcin, a bone formation marker, c-fos and c-jun genes, and family protein products (AP-1) interacted to restore the normal cell function which deteriorated in the low calcium environment.

Cholinergic agents increase the activity of the renal Na-HCO(3) cotransporter and have been shown to stimulate the production of nitric oxide (NO) in other cells. To study the role of NO in mediating the effect of carbachol on Na-HCO(3) cotransporter, we measured the activity of the cotransporter in rabbit proximal tubule cells treated with carbachol (10(-4 )M) or the NO inhibitor, L-NAME (10(-3) M), or carbachol+L-NAME. The activity of NaHCO(3) cotransporter was measured by recovery of intracellular pH (pH(i)) in cells loaded with pH-sensitive dye, BCECF. In control cells, carbachol significantly increased Na-HCO(3) cotransporter activity while L-NAME did not affect the activity of the cotransporter but completely blocked the enhancement induced by carbachol. Carbachol increased NO production by proximal tubule cells. We also studied the effect of the NO donor, SNAP (10(-3) M), on the cotransporter incubated for 1 h in cultured proximal tubule cells. SNAP caused a similar enhancement in the activity of the cotransporter suggesting that a different NO donor is capable of enhancing the activity of the cotransporter to the same extent as that observed with carbachol. Because the effect of NO is thought to involve cGMP, we examined the effect of 8-Br-cGMP (10(-3 )M) on the cotransporter. 8-Br-cGMP caused stimulation of the Na-HCO(3) cotransporter activity although to a lesser degree than carbachol. We have previously shown that carbachol increases cytosolic calcium but the role of intracellular calcium (Ca(i)) per se on the cotransporter has not been studied. We therefore studied the role of Ca(i) on the activity of Na-HCO(3) cotransporter in rabbit proximal tubule cells by utilizing the calcium ionophore, ionomycin, the microsomal Ca-ATPase inhibitor, thapsigargin, and the calcium chelator, BAPTA. Ionomycin, 5 microM, caused a significant stimulation of Na-HCO(3) cotransporter which was prevented by BAPTA. The microsomal Ca-ATPase inhibitor, thapsigargin, also increased the cotransporter activity. As expected both ionomycin and thapsigargin caused a significant increase in Ca(i). Calyculin A, an inhibitor of protein phosphatase 2A prevented the stimulation of the cotransporter by calcium (in pH units/min: control 1.8+/-0.13; Ca 2.22+/-0.07; p<0.05; Ca+calyculin A 1.9+/-0.09, p<0.025) suggesting that calcium acting through kinases/phosphatases, plays a role in the phosphorylation of the cotransporter. These results demonstrate that NO and Ca(i) modulate the activity of the cotransporter.

The optimal surgical procedure for severe renal secondary hyperparathyroidism (sHPT) is still a point of controversy. Total parathyroidectomy (PTX) without auto-transplantation was abandoned for fear of an adynamic bone condition; however, in the case of autotransplantation recurrent sHPT is frequent and promotes atherosclerosis. We studied 11 hemodialysis patients (age 59+/-12 years) on dialysis for 18 (12-30) years in whom total PTX was performed due to severe sHPT (group I; intact PTH: 1,240+/-230 pg/ml), and 5 patients (age 55+/-10 years) without renal insufficiency who inadvertently received total PTX during thyroid surgery (group II). After total PTX (group I, 26+/-18 [9-59] months; group II, 252+/-188 [22 480] months) both groups showed no measurable intact PTH levels. Calcium homeostasis was maintained by oral substitution with calcium (group I, calcium dialysate of 2.0 mmol/l), vitamin D and calcitriol (serum parameters in groups I and II: calcium 2.4 and 2.2 mmol/l; phosphate 1.8 and 1.1 mmol/l; 25(OH)-vitamin D(3) 21 and 34 ng/ml; 1,25(OH)(2)-vitamin D(3) 32 and 41 pg/ml, respectively). In group I, after total PTX there was a rapid and sustained improvement in bone pain with markedly enhanced physical activity and endurance. High turnover osteopathy markedly improved as indicated by declining levels of native osteocalcin (90+/-17 vs. 26+/-18 ng/ml), bone alkaline phosphatase (74+/-12 vs. 12+/-6 ng/ml), and carboxyterminal cross-linked telopeptide of type-I collagen (65+/-16 vs. 40+/-21 ng/ml) but increasing levels of carboxyterminal propeptide of type-I procollagen (120+/-36 vs. 148+/-41 ng/ml). Recalcification of bone was excellent as demonstrated by X-ray and confirmed by bone histology. Itching extravascular calcific deposits and calcifications of blood vessel and cardiac valves immediately stopped after total PTX. Moreover, 6 sHPT patients suffered from severe atherosclerotic lesions such as thoracic aortic aneurysm (n = 3) or abdominal aortic aneurysm (n = 3) which showed size progression before but not after total PTX when annually controlled by ultrasonography. In group II, even long after total PTX, there was no clinical, radiological, histological or biochemical evidence for low turnover osteopathy. In conclusion, our data indicate that substitution with vitamin D(3) metabolites and calcium can prevent deleterious bone effects of hypoparathyroidism in hemodialysis patients and in patients with normal kidney function and may compensate for the missing PTH action. Over this, a better survival rate is expected as a consequence of the beneficial effect of total PTX on the progression of atherosclerotic lesions. We suggest reconsideration of total PTX without autotransplantation in dialysis patients with severe sHPT who are not eligible for renal transplantation.

Acute hypotension is a frequent hemodialysis complication. This intra-treatment vascular instability is a multifactorial process in which procedure-related and patient-related factors may influence the decrease in plasma volume and the impairment of cardiovascular regulatory mechanisms. Identification of the most susceptible patients and of the various risk factors may contribute to significantly improving cardiovascular stability during dialysis. In some high-risk patients, continuous monitoring of the various parameters can predict the appearance of symptomatic hypotension and help to prevent its onset.

Management of end-stage renal disease (ESRD) has been revolutionized by the advent of erythropoietin replacement. We briefly review its characteristics and clinical use. Also emphasized is the importance of iron deficiency in limiting the clinical response to erythropoietin therapy. Iron-replacement therapy in ESRD patients is briefly discussed.

The powerful effect of psychosocial and acculturating influences on population blood pressure trends seems to be confirmed, through longitudinal observations, in the nuns in a secluded order. After initial observations had been made on culture, body form, blood pressure, diet, and other variables in 144 nuns and 138 lay women, included as a control group, a 30-year follow-up study was undertaken. Most striking were opposite trends noted between the two groups in blood pressure trend. During the follow-up period, blood pressure remained remarkably stable among the nuns. None showed an increase in diastolic blood pressure over 90 mm Hg. By contrast, the control women showed the expected increase in blood pressure with age. This resulted in a gradually greater difference (delta>30/15 mm Hg) in systolic and diastolic blood pressure between the two groups, which was statistically significant. In addition, cardiovascular morbidity and mortality, expressed as the outcome of fatal and nonfatal events, were different in the two groups. They were significantly more common in the lay women than in the nuns. Comparisons between survival curves were statistically significant (p = 0.0043 for fatal events; p = 0.0056 for nonfatal events) between the two groups. In conclusion, it seems reasonable to attribute much of the difference in blood pressure and cardiovascular events, to the different burden in psychosocial factor and to the preserved peaceful lifestyle of the nuns.