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Biomedical subjects

R Rizzoli

Publications and source records attributed to R Rizzoli.

At least 235 records · Page 13Linked to original sources
PubMed1988

Protection from progressive renal failure and hyperparathyroid bone remodeling by WR-2721.

In chronic renal failure (CRF), secondary hyperparathyroidism (sHPT) plays a major role in skeletal lesions and also probably in the deterioration of renal functions consecutive to nephrocalcinosis. In this study we tested whether WR-2721 [S-,2-(3-aminopropylamino)-ethylphosphorothioic acid], an inhibitor of parathyroid hormone (PTH) secretion, could prevent the deleterious effects of sHPT at both the bone and kidney level in an animal model of CRF. Rats were either subtotally nephrectomized (NX) or sham-operated (SHAM). They were then pairfed a high phosphorus (1.4%), middle Ca (0.6%) diet. This regimen accelerated the deterioration of renal function in NX rats which displayed signs of severe sHPT in bone (three- to fourfold increase in osteoclast number and resorption surfaces) and kidney (sixfold increase in Ca content) after four weeks. Chronic administration of WR-2721 (20 mg = 0.093 mmol/kg s.c. twice daily) during four weeks completely prevented the progressive elevation of both plasma urea and inorganic phosphate, and the fall of plasma Ca. It also prevented kidney Ca accumulation to the same extent as parathyroidectomy. However, WR-2721 given at this dose only partially prevented the histomorphometric indices of increased bone resorption and formation. This discrepant response suggests that WR-2721 could exert an additional protective effect at the kidney level that might be related to its property of acting as a free radical scavenger. In conclusion, this study suggests that WR-2721 might be a useful compound in CRF, not only because it inhibits PTH secretion, but also because it could protect against the deleterious effect of secondary hyperparathyroidism on kidney functions.

Amifostine↗
PubMed1988

Influence of the disaccharide lactitol on intestinal absorption and body retention of calcium in rats.

Various sugars are known to stimulate intestinal calcium absorption by a mechanism that is still poorly understood. One of those, the disaccharide 4-gal-actosyl-sorbitol (lactitol), is only metabolized in the large intestine, where it is converted into acidic residues. We investigated the effect of this compound on net intestinal absorption and body retention of calcium in rats. Because dietary calcium is in a poorly absorbable form when it reaches the large intestine, attempts were made to modify the absorption of calcium present in the large intestine contents by administering lactitol. Net intestinal absorption and body retention of calcium were significantly increased by 2.5 g lactitol/(kg b.w.d) given by a gavage over a 7-d period. This was associated with a lower pH and a better availability to absorptive systems of calcium present in the large intestine contents. The results indicate that in rats lactitol given chronically increases net intestinal absorption of calcium with a subsequently more positive calcium balance.

Animals↗
PubMed1988

Effect of synthetic tumoral PTH-related peptide on cAMP production and Na-dependent Pi transport.

Malignant hypercalcemia can be associated with a biochemical syndrome very similar to that encountered in primary hyperparathyroidism. The putative tumoral factor responsible for this syndrome has been isolated very recently from conditioned medium of a cultured lung squamous cell carcinoma (BEN), cDNA clones characterized, and an amino-terminal fragment synthesized. We investigated and compared the effect of this synthetic amino-terminal fragment of parathyroid hormone-related peptide [PTHrP-(1-34)], to purified PTHrP-(1-141) isolated from the same lung squamous cell carcinoma, and to bovine parathyroid hormone [bPTH-(1-34)] on adenosine 3',5'-cyclic monophosphate (cAMP) production and sodium-dependent phosphate transport (NaPiT) in opossum kidney (OK) epithelial cells. PTHrP-(1-34) and bPTH-(1-34) were equipotent in eliciting a 30-fold increase of cAMP production. NaPiT, as assessed by measuring the initial rate of Pi uptake, was inhibited in a concentration-dependent manner by either synthetic peptide. Half-maximal inhibition was observed with approximately 0.03-0.1 nmol/l of either bPTH-(1-34) or PTHrP-(1-34). At 10 nmol/l, either peptide produced an inhibition of 55 +/- 4 and 53 +/- 6%, respectively. This effect was specific for Pi, since the Na-dependent transport of glucose or alanine was not altered by either peptide. In OK cells dose-dependent stimulation of cAMP production and inhibition of NaPiT were also observed with purified native PTHrP-(1-141). In LLC-PK1 cells, which are devoid of PTH receptors, none of the peptides affected NaPiT. These results demonstrate a direct and specific effect of tumoral PTHrP on cAMP production and NaPiT in cultured renal epithelial cells in a way similar to bPTH.(ABSTRACT TRUNCATED AT 250 WORDS)

Alanine↗
PubMed1988

Chromatin structural transitions following histone H1 displacement by phosphatidylserine vesicles and low pH treatment. A multiparametric analysis involving flow cytometry, electron microscopy, and nuclease digestion.

We describe several morphological and functional modifications in isolated rat liver nuclei incubated in the presence of phosphatidylserine (PS) multilamellar vesicles (MLV). These effects, which occur through the release of histone H1, induce chromatin decondensation, as shown by electron microscopy and nuclease digestion. Flow cytometry was employed to monitor these changes in chromatin structure in isolated nuclei by means of perpendicular light scatter (PLS) and fluorescence signals. Chromatin decondensation induced by PS or by low pH treatment was accompanied by an increase in perpendicular light scatter and by less efficient binding of ethidium bromide. These flow cytometric findings are peculiar to chromatin decondensation induced by displacement of histone H1. Conversely, chromatin decondensation caused by lowering of the divalent ion concentration, without displacement of histone H1, is characterized only by an increase in perpendicular light scatter.

Animals↗
PubMed1987

Effect of a single injection of two new bisphosphonates on the hypercalcemia and hypercalciuria induced by Walker carcinosarcoma 256/B in thyroparathyroidectomized rats.

The effect of one single injection of two new bisphosphonates, 4-amino-1-hydroxybutylidene-1,1-bisphosphonate and 2-(2-pyridyl)ethylidene-1,1-bisphosphonate, and of dichloromethylenebisphosphonate on the hypercalcemia and hypercalciuria induced by the Walker carcinosarcoma 256/B in the thyroparathyroidectomized rat was evaluated. When given either before or after the development of hypercalcemia and hypercalciuria, 16.1 mumol/kg 4-amino-1-hydroxybutylidene-1,1-bisphosphonate or 2-(2-pyridyl)ethylidene-1,1-bisphosphonate totally inhibited hypercalciuria, whereas hypercalcemia was only partially reduced over the 14 days of the experiment. At 10 and 100 times lower doses, the effect was strongest the first days, but still partially present 14 days later. The difference of activity on calcemia and calciuria appears to be due to the fact that the tumor increased both bone resorption and renal reabsorption of calcium. Only the former was altered by the bisphosphonates. The two new compounds appeared to be of similar potency and more active than dichloromethylenebisphosphonate. These compounds could be promising for the treatment of malignant hypercalcemia and other conditions with increased bone resorption in humans, even when given only over short periods of time.

Alendronate↗
PubMed1987

Use of poligonal windows for physical discrimination among mononuclear subpopulations in flow cytometry.

Peripheral blood mononuclear cells from ten healthy normal donors were analyzed by means of monoclonal antibodies and flow cytometry (FACS IV). In order to apply optimal gating for the identification and exclusion of monocytes from lymphocyte populations, mononuclear cells were analyzed on the scattergram using rectangular or poligonal computer-generated windows. Two main windows on lymphoid population were used which mainly differed for the up-right corner, in the border area between lymphocytes and monocytes. While the number of lymphocytes contained either in the regular or in the poligonal windows was the same, the number of contaminating monocytes decreased by two-fold in the poligonal one. Besides, the use of tight lymphocyte gating, in order to reach lower monocyte contamination, leads to a loss of lymphoid cells which does not appear to be random, but seems to affect mainly the Leu11c+ population with natural killer activity. These cells produce forward and perpendicular scatter signals higher than other lymphocyte subsets, and, therefore, are mainly located in the area of the scattergram which divides lymphocytes from monocytes. These data are in accordance with the large granular morphology of natural killer cells. The use of the poligonal windows seems to be useful to reduce monocyte contamination with no selective loss of natural killer lymphocytes, and may be particularly helpful in the analysis of pathological samples.

Antibodies, Monoclonal↗
PubMed1987

Effect of dexamethasone on parathyroid hormone stimulation of cyclic AMP in an opossum kidney cell line.

The influence of the glucocorticoid dexamethasone on the cAMP response to parathyroid hormone (PTH) and various agonists was studied in epithelial monolayers of opossum kidney (OK) cells. The incubation with dexamethasone for 72 hours led to a dose-dependent higher cAMP response to PTH or forskolin in intact cells as well as in digitonin-permeabilized cells. This effect did not appear to result from changes in phosphodiesterase (PDE) activity nor from alterations in cAMP efflux from the cells. Moreover, dexamethasone increased the formation of domes by OK cell epithelium. Thus, dexamethasone seems to promote a more differentiated renal epithelial phenotype as suggested by enhanced hormonal response.

1-Methyl-3-isobutylxanthine↗
PubMed1987

The Walker 256/B carcinosarcoma in thyroparathyroidectomized rats: a model to evaluate inhibitors of bone resorption.

The Walker 256/B mammary carcinosarcoma implanted in male Fischer rats was used to evaluate bone resorption inhibitors. The model was improved by thyroparathyroidectomizing the animals to avoid counter-regulation by parathyroid hormone or calcitonin, by pair-feeding them, and by using 2 hour fasting calciuria as a resorption index to minimize the influence of differences in growth or in intestinal calcium absorption. Over a 10 day period, the control animals displayed a progressive increase of plasma calcium (Ca) and fasting urinary Ca excretion, a decrease of plasma phosphate, and an increase of urinary phosphate excretion. Osteocalcin did not change. The daily administration of dichloromethylene bisphosphonate (Cl2MBP) totally prevented the increase of fasting urinary Ca excretion, whereas plasma Ca remained at a higher level than thyroparathyroidectomized (TPTX) control rats. Osteocalcin decreased. Two new aminobisphosphonates, 4-amino-1-hydroxybutylidene-1,1-bisphosphonate (AHBuBP), and 6-amino-1-hydroxyhexylidene-1,1-bisphosphonate (AHHexBP) had a similar effect. The order of potency shown by the three bisphosphonates was similar to that reported using the metaphyseal bone density evaluation method in growing rats: AHBuBP greater than AHHexBP greater than Cl2MBP, the difference each time being one order of magnitude. The analysis of the relationship between urinary and plasma values in tumor-bearing animals suggested an increased renal tubular reabsorption of Ca and a decreased reabsorption of phosphate (Pi). Therefore, in this model of malignant osteolysis, urinary Ca excretion is the best marker for bone resorption.

Animals↗
PubMed1987

Interleukin-1 decreases renal sodium reabsorption: possible mechanism of endotoxin-induced natriuresis.

Administration of pyrogen or endotoxins such as Escherichia coli lipopolysaccharide can elicit a marked increase in urinary sodium excretion. This response occurs without any elevation in the filtered load of sodium and it does not appear to be prostaglandin mediated. The various effects produced by endotoxins appear to have interleukin-1 as a common mediator. In the present work, we have studied whether human recombinant interleukin-1 beta (hrIL-1) could affect the renal handling of sodium and thus, could be implicated in natriuretic response to pyrogens or endotoxins. We observed that hrIL-1 intravenously injected into conscious rats provokes a marked increase in sodium excretion. This natriuretic response was not associated with any increase in glomerular filtration rate (clearance of [3H]inulin), nor was it accompanied by significant changes in the urinary excretion of potassium, calcium, or inorganic phosphate. The only concomitant alteration was a decrease in urinary pH. Pretreatment with indomethacin abolished the effect of hrIL-1 on urinary pH but did not modify the natriuretic response. In conclusion, hrIL-1 elicits a selective decrease in tubular sodium reabsorption, which does not appear to involve a change in prostaglandin synthesis. This observation strongly suggests that interleukin-1 could be a key mediator in endotoxin-induced natriuresis.

Absorption↗
PubMed1987

Management of hypercalcemia in relation to pathophysiology.

Hypercalcemia results from an imbalance between the fluxes of calcium (Ca) entering and leaving the extracellular space. The two most important influxes are the net intestinal Ca absorption and the net skeletal Ca resorption, whereas the renal excretion represents the main route of elimination. When produced in excess, various factors, particularly calciotropic hormones and cytokines, can disturb the Ca fluxes at intestinal, skeletal and renal tubular sites. If the excessive production of these substances cannot be controlled by surgical or pharmacological means, the next most rational therapeutic strategy should be aimed at correcting those Ca fluxes which are abnormally increased. In hypercalcemia of malignancy (HM), an augmentation in net bone resorption (BR) is observed in most patients. However, a sustained stimulation in tubular Ca reabsorption (TRCa), despite correction of volume depletion by saline infusions, may not only contribute to the hypercalcemia, but in some cases it appears to be the prevailing disturbance. In these patients the effects of the antiresorbing agent clodronate (500 mg/8 h iv in one single infusion) is incomplete, despite the normalisation of BR. Thus, administration of an antiresorbing agent, such as clodronate, is the treatment of choice in HM with elevated BR and normal TRCa. It should be given with other therapeutic agents when a sustained increase in TRCa is the prevailing mechanism for hypercalcemia. In this regard, experimental studies suggest that the agent WR-2721, which specifically inhibits TRCa could be an effective drug for rapidly lowering plasma Ca in HM with high TRCa.

Amifostine↗
PubMed1986

Increase of adenylate cyclase catalytic-unit activity by dexamethasone in rat osteoblast-like cells.

Glucocorticoids are known to increase the cyclic AMP response to parathyroid hormone (PTH) in cultured bone organs or bone cells. Using the osteoblast-like cell line ROS 17/2.8, which possesses receptors for both PTH and glucocorticoids, we investigated which component of the complex hormone receptor-guanine nucleotide regulatory unit--adenylate cyclase was affected by dexamethasone treatment. In response to PTH, isoproterenol or forskolin, a compound that is supposed to act directly on the catalytic unit, cyclic AMP production by intact cells and adenylate cyclase activity in purified plasma membrane were markedly increased by dexamethasone. Whereas NaF, guanosine 5'-[beta gamma-imido]triphosphate and Mn/ stimulated adenylate cyclase activity were similarly enhanced in membranes isolated from glucocorticoid-treated cells, the activity of the stimulatory guanine nucleotide regulatory unit, as assessed by reconstitution into membranes from the CYC- clone, which is genetically devoid of this component, was not altered. Thus in osteoblast-like cells dexamethasone appears to increase cyclic AMP synthesis by influencing the catalytic unit. Moreover, since it has been reported that glucocorticoids may produce changes in cell calcium metabolism, we evaluated cytoplasmic free Ca2+ concentration ([Ca2+]i) and intracellular Ca2+ stores mobilizable by the bivalent-cationophore ionomycin, by using the intracellular fluorescent indicator Quin-2. The results indicated that dexamethasone treatment did not influence [Ca2+]i but markedly decreased ionomycin-releasable Ca2+ stores.

Adenylyl Cyclases↗
PubMed1986

Heterologous desensitization by 1,25-dihydroxyvitamin D-3 of cyclic AMP response to parathyroid hormone in osteoblast-like cells and the role of the stimulatory guanine nucleotide regulatory protein.

The influence of 1,25-dihydroxyvitamin D-3 on the cAMP response to parathyroid hormone was studied in the osteoblast-like rat osteosarcoma cells ROS 17/2.8. The stimulation by parathyroid hormone of cAMP production in intact cells and of adenylate cyclase activity in isolated plasma membranes was attenuated by 1,25-dihydroxyvitamin D-3 treatment. This was associated with a reduction of the stimulatory guanine nucleotide regulatory protein, as demonstrated by a lower response to NaF and guanosine 5'-[beta, gamma-imido]triphosphate, and by a lower activity of solubilized plasma membrane extracts in the reconstitution assay. 1,25-dihydroxyvitamin D-3 blunted also the cAMP response to parathyroid hormone in cells incubated with the glucocorticoid dexamethasone, where a higher activity of the adenylate cyclase catalytic unit was observed. Thus, the two steroids appear to affect distinct levels of the adenylate cyclase system. Furthermore, the two hormones also showed an antagonistic effect upon the production of osteocalcin, an osteoblast-specific extracellular matrix protein. The release of this non-collagenous matrix protein by ROS 17/2.8 cells was increased by 1,25-dihydroxyvitamin D-3 and decreased by dexamethasone.

Adenylyl Cyclases↗
PubMed1986

Sodium-dependent phosphate transport inhibited by parathyroid hormone and cyclic AMP stimulation in an opossum kidney cell line.

In the present study we investigated the characteristics of the transport of inorganic phosphate (Pi) in an opossum kidney cell line endowed with parathyroid hormone (PTH) receptors. In confluent epithelial cell culture, a Na-dependent Pi transport (NaPiT) was identified. Preincubation for 1 h with bovine (b)PTH(1-34) at 10(-7) M inhibited the NaPiT from 2.76 +/- 0.11 to 1.08 +/- 0.10 nmol/mg protein X 2 min-1 (p less than 0.001). This inhibition was already expressed 5 min after exposure to 10(-7) M bPTH. It was associated with a 4-fold increase in cellular cyclic AMP. The NaPiT was significantly inhibited at 10(-9) M bPTH, a hormonal concentration which stimulated the cellular cyclic AMP by only 30%. Kinetic analysis of the NaPiT inhibition by 10(-7) M bPTH revealed a decrease in Vmax (from 4.14 +/- 0.32 to 2.41 +/- 0.14 nmol/mg protein X 2 min-1) with no change in Km (0.093 +/- 0.016 versus 0.094 +/- 0.012 mM). The effect of bPTH on NaPiT was not associated with a change in the Na-dependent glucose methylglucopyranoside transport also present in the opossum kidney cell line. The inhibitory influence of bPTH on NaPiT was not affected by blockage of new protein synthesis by cycloheximide. Stimulation of cyclic AMP production by 10(-5) M forskolin, 10 micrograms/ml cholera toxin, 10(-5) M prostaglandin E2 or addition of 10(-5) M dibutyryl cyclic AMP mimicked the PTH-induced reduction in NaPiT. In conclusion, the present study indicates that the opossum epithelial cell line is endowed with a Na-dependent Pi transport system which is selectively inhibited by PTH and agents which increase cyclic AMP production.

1-Methyl-3-isobutylxanthine↗
PubMed1986

Electron microscopy microsampling of isolated nuclei sorted by flow cytometry.

This paper describes an efficient method to concentrate for electron microscopic examination minute quantities of subcellular particles obtained by cytofluorimetric sorting. The advantages of this micromethod, based on diafiltration on Millipore filters under constant positive nitrogen pressure, are discussed.

Animals↗
PubMed1986

Calcium absorption in the rat colon measured in vivo.

Calcium absorption in the large intestine was studied under physiological conditions in the rat. When 45Ca was administered directly into the caecum, the isotope was significantly absorbed. This absorption was modulated by dietary Ca and Pi as well as by the 1,25(OH) D3 status. On the other hand, calcium coming from the food, either as 45Ca or as 40Ca, was not absorbed to a significant amount. When the absorption of 45Ca from the caecal content was assessed in duodenal loops, less 45Ca was absorbed when the isotope was administered orally than when it was added to the caecal content. Thus, the fact that oral Ca is not absorbed in the colon despite the efficient Ca transport system of this part of the intestine may be due to the transformation in the digestive tract of Ca from an absorbable into a non-absorbable form.

Administration, Oral↗
PubMed1986

Nuclear thyroid hormone receptors in cultured bone cells.

Thyroid hormones influence bone metabolism, but a direct interaction of triiodothyronine with nuclear T3 receptors in bone cells has not yet been reported. We investigated 125I-T3 binding to nuclei isolated from the cloned osteoblastlike rat osteosarcoma cells ROS 17/2.8. At 37 degrees C, saturable 125I-T3 binding to isolated nuclei reached equilibrium by 30 minutes and was completely displaced upon the addition of 500 nmol/L unlabeled T3. Nonsaturable binding represented about 0.5% of the radioactivity added (20% of the total binding). Thyroxine and 3,3',5'triiodothyronine competed with 125I-T3 with a 20-fold and 400-fold lower affinity than T3, respectively. Analysis of equilibrium competition experiments revealed the presence of a single class of homogeneous binding sites with an association constant of 5.0 +/- 0.3 X 10(9) mol/L-1 and a maximum nuclear binding capacity of 0.13 +/- 0.02 ng/mg DNA. A twofold increase of bone Gla protein (BGP) secretion was observed with T3 treatment suggesting that these T3 nuclear receptors are coupled with a biological response.

Animals↗
PubMed1986

Calcium absorption in rat large intestine in vivo: availability of dietary calcium.

Calcium absorption in the large intestine of the rat was investigated in vivo. After a single injection of 45CaCl2 into the cecum, 26.0 +/- 2.5% (mean +/- SE, n = 9) of the 45CaCl2 injected disappeared. This absorption was modulated by 1,25-dihydroxyvitamin D3, increased to 64.0 +/- 4.2% under a low-Ca diet, and increased under low-Pi diet. In contrast, when the difference of nonradioactive Ca in the cecal content and the feces was measured, only 4.1 +/- 4.6% (not significant) was absorbed. Secretion of intravenously injected 45Ca into the lumen was small and not altered by any of the conditions tested. When cecum contents were placed into duodenal tied loops, 14 +/- 6.2% were absorbed in situ when 45Ca was given orally, whereas when 45Ca was directly added to the content 35.6 +/- 4.6% were absorbed (P less than 0.02). These results indicate that the large intestine has an important vitamin D-dependent Ca absorptive system detectable if 45Ca is injected into the cecum. However, it is not effective in vivo because the Ca arriving in the large intestine appears to be no longer in an absorbable form.

Animals↗