Elevated cytosolic calcium of adipocytes in chronic renal failure

AN OVERVIEW OF NURSES' MANAGEMENT OF SECONDARY HYPERPARATHYROIDISM: HOW IS EUROPE DOING?

BACKGROUND

Nurses have an important role to play in the management of secondary hyperparathyroidism (SHPT). An online survey conducted by the European Dialysis and Transplant Nurses Association/European Renal Care Association (EDTNA/ERCA) in conjunction with Amgen (Europe) GmbH surveyed nephrology nurses' knowledge of secondary hyperparathyroidism, treatment targets, current treatments, patient adherence and nephrology nurse training education needs. The survey's aim was to establish common practices being used by nurses in the management of secondary hyperparathyroidism and to identify nephrology nurses' training and educational needs in order to improve patient care.

METHODS

DESIGN

Descriptive study.

MEASUREMENTS

An online survey of multiple choice and closed questions.

PARTICIPANTS

A sample of nephrology nurses from Spain, Italy, France and the Netherlands.

RESULTS

A total of 111 nurses completed the questionnaire (98% response rate, 82% of which were fully completed). Collected data revealed that there were specific aspects of SHPT patient management where nurses lacked confidence, despite the majority of respondents having 15 years nephrology nursing experience. These aspects included explaining the disorder and therapies to patients, managing side effects of drugs and appreciating the significance of controlling biochemical targets. Over 40% of the respondents felt they did not have sufficient training to support patients who were non-compliant.

CONCLUSION

Nursing skills are integral to SHPT patient management as part of the multidisciplinary approach. The nurse's role is particularly important in patient assessment and monitoring, and in the provision of patient education and support, particularly with treatment adherence. Nephrology nurses who are better informed about SHPT and who receive training on practical patient care may improve the care of patients.

Intracellular free calcium in the neutrophils of maintenance haemodialysis patients

Chronic renal failure has on occasion been referred to as a state of calcium toxicity. The aim of this study was to investigate the status of intracellular free Ca2+ in the neutrophils of chronic renal failure patients on maintenance haemodialysis treatment. Factors previously suggested to influence intracellular free Ca2+ were investigated including PTH levels, oxidative stress and recombinant human erythropoietin administration. The study involved 14 chronic renal failure patients on the haemodialysis programme of the Pretoria Academic hospital. Intracellular free Ca2+ and transmembrane Ca2+ fluxes were investigated by fluorescence spectrophotometry. Increases above control values were found in intracellular free Ca2+ (P-value 0.0242) and in the transmembrane Ca2+ flux upon fMLP stimulation (P-value 0.0002). The results showed significant differences in intracellular free Ca2+ between patients on rHuEPO and patients not on rHuEPO. The apparently rHuEPO-induced increase in intracellular free Ca2+ persisted in the presence of calcium channel blockers. No overt indications of oxidative stress could be detected by the antioxidant vitamin levels. It is concluded that factors other than those associated with uraemia, such as rHuEPO administration, might contribute to the often reported increase in intracellular free Ca2+ in these patients. Further studies to investigate the relationship between intracellular free Ca2+, rHuEPO and calcium channel blockers are suggested.

Antagonistic effects of vitamin D and parathyroid hormone on lipoprotein lipase in cultured adipocytes

The effects of 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) (calcitriol) and parathyroid hormone (PTH) on synthesis and secretion of lipoprotein lipase (LPL) were studied in 3T3-L1 adipocytes. Expression of the vitamin D receptor was demonstrated by saturation kinetics with radiolabeled calcitriol. Incubation with calcitriol (10(-8) M) for up to 4 d resulted in a time-dependent significant increase in heparin-releasable LPL activity (LPLa) accompanied by a significant increase in LPL mRNA. In contrast, incubation with intact (1-84) PTH (10(-6) to 10(-9) M) produced a time- and dose-dependent significant decrease in LPLa, but no change in LPL mRNA. The effect of PTH (24-h incubation, 10(-8) M) could be prevented by the calcium channel blocker verapamil. Coincubation with both calcitriol and PTH at equimolar concentration (10(-8) M) resulted in an increase in LPLa and LPL mRNA. These data indicate an antagonistic role for calcitriol and PTH in the regulation of LPL, possibly mediated by intracellular calcium, which may contribute to the alterations in lipoprotein metabolism occurring in uremia.

Effects of excess PTH on nonclassical target organs

The classical target organs for parathyroid hormone (PTH) are the bone and kidneys. In uremia, however, numerous studies have shown that PTH may also affect the function of a number of nonclassical organs and tissues besides the bone and kidney, including the brain, heart, smooth muscles, lungs, erythrocytes, lymphocytes, pancreas, adrenal glands, and testes. Most of these effects do not apply to the generally accepted actions or normal regulatory mechanisms of PTH. Thus, the potential role of PTH as one of the possibly many toxins in uremia is of current interest. The molecular basis for the actions of elevated PTH levels on various nonrenal and nonskeletal organs or tissues might be mediated via the widespread distribution of the classical PTH/PTH-related peptide (PTHrP) receptors and via the novel PTH2 receptors. The present survey deals with an evaluation of the nonrenal and nonskeletal effects of excess PTH in uremia, taking into consideration the presently available information on the organ-specific expression of the classical and novel PTH receptors, and of the expression and function of PTHrP.

A longitudinal study on the effect of nifedipine therapy and its discontinuation on [Ca2+]i and proliferation of B lymphocytes of dialysis patients

The abnormalities in cytosolic calcium ([Ca2+]i) and proliferation of B cells in uremic patients are significantly improved by treatment with nifedipine. The rapidity with which this agent induces its beneficial effect and whether these derangements reemerge after cessation of therapy are not known. We studied six hemodialysis patients before, during, and after treatment with nifedipine. Before treatment, [Ca2+]i of B cells was markedly elevated (125 +/- 4.3 nmol/L) and their proliferation markedly reduced (5.2 +/- 0.36 x 10(3) cpm). After 1 month of therapy, [Ca2+]i fell significantly (P < 0.01) to 95 +/- 1.7 nmol/L and to a normal value of 84 +/- 1.6 after 2 months. The levels of [Ca2+]i rose significantly (P < 0.01) to 95 +/- 2.3 nmol/L after 1 month of cessation of therapy and were 115 +/- 2.8 nmol/L by 2 months. Proliferation of B cells improved significantly (P < 0.01) after 1 month of therapy (9.4 +/- 1.1 x 10(3) cpm) with further improvement during the subsequent month, reaching a normal value (12.2 +/- 1.1 x 10(3) cpm) by the end of the 2 months. Proliferation of B cells decreased after cessation of therapy and was 5.2 +/- 0.17 x 10(3) cpm after 2 months, a value similar to the pretreatment level. The blunted inhibitory effect of PTH-(1-84) on B cell proliferation was reversed by nifedipine treatment and reappeared after discontinuation of therapy. Also, serum globulin levels increased after administration of nifedipine and decreased again after cessation of treatment. The results show that nifedipine rapidly reversed the elevation in [Ca2+]i of B cells, the impairment in their proliferation, and the blunted inhibitory effect of PTH on B cell proliferation, and was associated with increased serum globulin levels. These derangements reemerged after cessation of therapy. These data indicate that nifedipine therapy is effective in the management of the abnormalities in B cell metabolism and function in hemodialysis patients. The treatment with this drug must be maintained to sustain its beneficial effects. Other calcium channel blockers may also be effective, but their effects were not examined in the current study.

Benefits of calcitriol therapy and serum phosphorus control in dogs and cats with chronic renal failure. Both are essential to prevent of suppress toxic hyperparathyroidism

Daily oral calcitriol at low doses is safe and effective in the control of renal secondary hyperparathyroidism in dogs and cats. Low doses of calcitriol are most effective when started early in uremia before the advanced stages of renal secondary hyperparathyroidism. At early stages calcitriol both diminishes PTH synthesis in the parathyroid cells present and prevents the hyperplasia that, if unchecked, results in the most extensive an difficult-to-control hyperparathyroidism. The salutary effects on the dog's or cat's sense of well being, appetite, activity, strength, and lifespan as reported by the veterinarians of our survey are attributed primarily to keeping PTH levels below a toxic threshold. Additionally, some of the benefits achieved by calcitriol are likely a direct consequence of calcitriol interacting with the vitamin D receptor in a wide variety of tissues throughout the body. Phosphorus restriction through a combination of diet and intestinal phosphate binders is important to allow calcitriol therapy to successfully lower PTH levels, but it likely has no direct effects that are independent of interactions involving calcitriol. Phosphorus restriction is also important to minimize chances for adverse tissue mineralization. Calcitriol therapy can be considered for treatment of chronic renal failure after serum phosphorus has been decreased to less than 6.0 mg/dL in patients in whom it was initially elevated. Calcitriol supplementation to dogs and cats with chronic renal failure makes good endocrinologic sense. Calcitriol deficits cause increased PTH and, as these two hormones are designed to maintain calcium and phosphorus homeostasis, the PTH increase is initially adaptive. One of the important effects of PTH is to stimulate additional calcitriol formation as a powerful means to raise blood calcium through increased calcium absorption from the diet. With too great an increase in PTH, however, its effects become harmful to many tissues due to the widespread distribution of the PTH receptor in many cell types that are likely normally responsive only to the paracrine PTH-related peptide that shares the PTH receptor. Exogenous supplemental calcitriol administration allows concentrations of calcitriol in the bloodstream to remain normal without the toxic consequences of excessive PTH secretion that would otherwise be provoked. Studies involving young dogs with subtotal nephrectomy may not parallel those on older dogs and cats with spontaneous chronic renal failure. In particular, higher doses are needed to effect PTH change in these young dogs than we have found necessary for older dogs and cats. Because survey participants agreed most strongly with the idea that their calcitriol-treated dogs and cats were living longer than comparably uremic animals they had treated previously, further studies to evaluate the ability of calcitriol to retard the progression of renal lesions and loss of excretory renal function seem warranted. Additional studies to document the beneficial effects of calcitriol on the many organs adversely affected by excess PTH during uremia are also needed because findings thoroughly documented and proven in humans and rats may not always extrapolate to dogs and cats.