The effect of 110mAg on ceruloplasmin oxidase activity in rats

The effect of single i.v. injection of 110mAgNO3 (0.183 mg Ag+ X kg-1 b.wt.) in rats on the ceruloplasmin oxidase activity (Cp) and copper serum concentration was studied. It was found that Cp activity in the serum decreased to 70% of the control value and simultaneously serum copper concentration decrease to 30% of the control level. In both cases the decrease was independent on the time elapsed after silver administration. Comparing these results with those reported recently in mice Cu deficit in the rat serum was approximately twice higher. This fact is considered to be an inter-species difference. The concentration of copper in the hepatic supernatant significantly decreased (to eight times from control value) after silver injection. Only less than 10% of the total amount of Ag found in whole liver was taken up to hepatic supernatant. GPC analysis of the supernatant (Sephadex G-75) revealed that no Ag-metallothionein fraction is present. On the basis of the results obtained it was concluded that the mechanism of silver inhibition of Cp oxidase activity remains still in question.     

The effect of CdCl2 on the respiration of rat small intestine mucosa

Process of oxygen consumption of rat small intestine have already been studied at the level of whole intestinal wall or mucosa only by means of manometric or polarographic methods. The influence of cadmium on mucosal respiration of three sections of rat small intestine was determined because of its toxicological importance. Oxygen consumption was measured polarographically with Clark electrode at 38 degrees C in Krebs Ringer phosphate medium with 0.011 mol/l glucose. Control as well as cadmium affected respiration values were measured one after the other on the same mucosa. High cadmium concentration (applied as CdCl2) that is 2.2 and 1.4 . 10(-2) mol/l significantly inhibited the respiration in duodenum, jejunum and ileum. Observed inhibition of 80 and 50% on the average approximately for these two concentrations was related (similarly as following effects) to 100% value of control respiration. Concentrations 7.8 and 4.5. 10(-3) mol/l caused mostly lower inhibition of oxygen consumption (with the exception of significant 53% inhibition of jejunal respiration for 7.8. 10(-3) mol/l CdCl2). Low concentrations 10(-4) - 10(-6) mol/l CdCl2 had either no effect or stimulated oxygen uptake in intestinal mucosa. In older rats (weight 300-350 g) the respiration of duodenal and jejunal mucosa was inhibited with cadmium chloride concentration of 10(-6) mol/l.     

Biliary excretion of 110mAg and its kinetics in the isolated perfused liver in rats

The biliary excretion of 110mAg in rats after i.v. administration of an aqueous solution of 110mAgNO3 (4.57 micrograms; 16kBq per rat) was studied for a period of 24 hours. The maximum rate of excretion was reached in 30th minute after the metal administration and over 70% of the silver dosed was excreted during 24 hours. Using the method of isolated perfused liver it was observed that 110mAg is rapidly taken up in the liver. During the five minutes period of the perfusion less than 50% of silver administered was found in the perfusion medium. In following minutes the level of the metal in the medium remained approximately constant. It was suggested that the rate of excretion of silver and its high uptake in the liver tissue is in connection with an unusual binding of it in the bile.     

The effect of thyroidectomy on the subcellular Mg distribution in rat liver

The subcellular distribution of Mg²⁺ in livers of normal and thyroparathyroidectomized rats has been studied. Significant increases in Mg²⁺ are found in the mitochondrial fractions of thyroparathyroidectomized rats accompanied by a decrease in the Ca²⁺ content. In the microsomal fractions no significant modifications of both ions were detected. Propylthiouracil administration reproduced the ionic alterations found after surgical thyroidectomy and a triiodothyronine replacement therapy to thyroidectomized rats resulted in a reversion of the Mg²⁺ content back to normal levels. The possible participation of the parathyroid in the above mentioned phenomena could be excluded in the present work.     

A study of 110mAg in aquatic and terrestrial ecosystems

Experiments on a simulated terrestrial agricultural ecosystem were carried out using the pot culture approach. The most representative plants in local vegetable gardens were selected to investigate the root uptake of (110m)Ag. The results show that carrot, kale and flowering cabbage have the largest transfer factor values among the vegetables. Flowering cabbage, as the most popular leafy vegetable in Hong Kong and the South China area, can be used as a biomonitor for radioisotope contamination in vegetables. Soil column and adsorption tests were also carried out to study the leaching ability of the silver isotope in soil and (110m)Ag was mainly adsorbed in the top 1 cm of soil regardless of the pH value. Experiments on a simulated aquatic ecosystem for freshwater fish and marine organisms were carried out in glass aquaria. The freshwater fish Cyprinus carpio, the marine fish Cuvier and some local abundant seashore molluscs were selected to investigate the kinetic metabolism of (110m)Ag in the compartmental system. The results show that molluscs absorb (110m)Ag much more than fish. Clibanarius infraspinatus has the largest concentration factor among the marine organisms selected. Fish liver, although representing a minor portion of the total body mass, shows the highest (110m)Ag concentration factor, whereas muscle, although representing a major portion of the total body mass, is characterized by an absence of (110m)Ag.     

Regulation of Ca2+ fluxes in rat liver mitochondria by Ca2+. Effects on Ca2+ distribution

Rat liver mitochondria are able to temporarily lower the steady-state concentration of external Ca²⁺ after having accumulated a pulse of added Ca²⁺. This has been attributed to inhibition of a putative -modulated efflux pathway [Bernardi, P. (1984)Biochim. Biophys. Acta 766, 277–282]. On the other hand, the rebounding could be due to stimulation of the uniporter by Ca²⁺ [Kröner, H. (1987)Biol. Chem. Hoppe-Seyler 369, 149–155]. By measuring unidirectional Ca²⁺ fluxes, it was found that the uniporter was stimulated during the rebounding peak both under Bernardi's and Kröner's conditions, while no effects on the efflux could be demonstrated. The rate of unidirectional efflux of Ca²⁺ was not affected by inhibition of the uniporter. It appears likely that the rebounding is due to stimulation of the uniporter rather than inhibition of efflux.     

The effect of ferric iron complex on Ca2+ transport in isolated rat liver mitochondria

The in vitro effects of iron (III)-gluconate complex on the production of malondialdehyde and on the Ca2+ transport in isolated rat liver mitochondria were studied. A correlation between the concentration of iron added and the formation of malondialdehyde was found. The enhancement by iron of lipid peroxidative process in the mitochondrial membrane brought about the induction of Ca2+ release from mitochondria. Experimental evidence based on the membrane potential pattern of mitochondria pre-loaded with a low pulse of Ca2+ suggested that Ca2+ efflux was not due to a nonspecific increase in the inner membrane permeability, i.e. to a collapse of membrane potential, but rather to the activation of an apparently selective pathway for Ca2+ release.     

Effect of pentoxifylline on CdCl2-induced nephrotoxicity in the rat

We developed a rat model of cadmium (Cd)-induced nephrotoxicity and tried to prevent renal damage by treating the animals with pentoxifylline (PTX). Sprague-Dawley (SD) rats given CdCl₂ 3.0 mg/kg sc, daily for 2 wk showed evidences of renal proximal tubular damage, including significant increases in urine volume, urinary excretion ofN-acetyl-β-D-glucosaminidase (NAG), alanine aminopeptidase (AAP), and fractional excretion of sodium (FENa), and a decrease in the percentage of tubular reabsorption of phosphate (%TRP). PTX significantly improved the urinary excretion of NAG and %TRP. Urine volume was increased threefold in the CdCl₂-treated rats and fivefold in the Cd+PTX-treated rats, respectively, as compared with saline-treated control. Total protein, AAP, and creatinine clearance, showed no change after PTX administration. Concentration of Cd in the renal cortex was three times higher than that in the renal medulla, but there were no differences in concentration between the Cd-treated rats and the Cd+PTX-treated rats. Our animal model was useful in studying the renal tubular damage produced by cadmium. PTX appears useful for improving the nephrotoxicity of Cd.     

The effect of Ca2+ on the oxidation of exogenous NADH by rat liver mitochondria.

The respiratory rate of rat liver mitochondria in the presence of NADH as exogenous substrate is enhanced by the addition of CaCl₂ (> 50 μM) when inorganic phosphate is present in the medium. The Ca-induced oxidation of NADH is inhibited by rotenone but is not affected by uncoupling agents. EDTA, which does not reverse the swelling of mitochondria which occurs in the presence of Ca²⁺ and phosphate, is able to inhibit reversibly the Ca-stimulated NADH oxidation. A stimulation of the rate of oxidation of NADH by Ca²⁺ is also observed in mitochondria partially swollen in a hypotonic medium.     

The effects of Mg2+ on rat liver microsomal Ca2+ sequestration

The effects of Mg2+ on the hepatic microsomal Ca2(+)-sequestering system was tested. Ca2(+)-ATPase activity and Ca2+ uptake were both dependent on the concentration of free Mg2+, reaching maximum levels at 2 mM. The effects of Mg-ATP were also influenced by the concentration of free Mg2+, being maximally effective at a ratio of 1:1. The results suggest that Mg2+ influences Ca2+ sequestration at various steps, namely in addition to forming the substrate of the Ca2(+)-ATPase reaction, Mg-ATP, Mg2+ stimulates the reaction at an additional step, as indicated by its stimulatory effect on the Ca2(+)-ATPase reaction and on Ca2+ uptake, even at optimal Mg-ATP levels. The stimulatory effect of Mg2+ was evident at various pH levels tested, and it was nucleotide specific. The stimulatory effect of Mg2+ might be exerted at the dephosphorylation step of the enzymatic reaction or at an other, yet undefined, site. The results demonstrate a plural effect of Mg2+ on the hepatic microsomal sequestration system. This indicates that, depending on its magnitude, changes in Mg2+ distribution might influence cytosolic Ca2+ levels.     

The effect of thyroid hormone on the high affinity Ca2+-ATPase in rat liver plasma membrane

The effect of thyroid hormone on the high affinity Ca2+-ATPase activity in rat liver plasma membrane was studied. The high affinity Ca2+-ATPase activity in plasma membrane was activated by 10(-7)-10(-5) M of Ca2+ and was inhibited by 70 microM trifluoperazine. Thyroidectomy of rats was associated with an increase in the activity of high affinity Ca2+-ATPase. The increased enzyme activity was normalized by T4 administration to the animals. On the other hand, Na+-K+-ATPase activity in the membrane was decreased by thyroidectomy and the decreased enzyme activity was normalized by T4 administration. The results suggest that thyroid hormone inhibits the Ca2+ extrusion system by inhibiting calmodulin-independent high affinity Ca2+-ATPase in liver plasma membrane.     

Overlapping distribution of the 130- and 110-kDa myosin I isoforms on rat liver membranes

The biochemical and mechanochemical properties and localization of myosin I suggest the involvement of these small members of the myosin superfamily in some aspects of intracellular motility in higher cells. We have determined by quantitative immunoblotting with isoform-specific antibodies that the 130-kDa myosin I (myr 1 gene product) and 110-kDa myosin I (myr 2 gene product) account for 0.5 and 0.4%, respectively, of total rat liver protein. Immunoblot analyses reveal that the 130- and 110-kDa myosins I are found in several purified subcellular fractions from rat liver. The membrane-associated 130-kDa myosin I is found at the highest concentration in the plasma membrane (28 ng/microg plasma membrane protein) followed by the endoplasmic reticulum-like mitochondria-associated membrane fraction (MAM; 10 ng/microg MAM protein), whereas the 110-kDa myosin I is found at the highest concentration in Golgi (50 ng/?g Golgi protein) followed by plasma membrane (20 ng/microg) and MAM (7 ng/microg). Our analyses indicate that myosin I is peripherally associated with Golgi and MAM and its presence in these fractions is not a consequence of myosin I bound to contaminating actin filaments. Although found in relatively low concentrations in microsomes, because of the abundance of microsomes, in liver most of the membrane-associated myosin I is associated with microsomes. Neither myosin I isoform is detected in purified mitochondria. This is the first quantitative analysis addressing the cellular distribution of these mammalian class I myosins.     

The distribution pattern of NADP+-dependent isocitrate dehydrogenase in rat liver

Activities of the NADP+-dependent isocitrate dehydrogenase were measured along the entire sinusoidal path (1) between small portal tracts and central veins and (2) between regions of adjoining septal branches and central veins in the liver of male Wistar rats using a Lowry technique. The measured activities show a slight increase from the periportal to the perivenous end, whereas no such septal-) perivenous gradient could be established. These profiles of enzyme activity give further support to previous studies, suggesting functional heterogeneity of liver sinusoids and their abutting hepatocytes related to morphological differences of the sinusoidal bed.     

The effect of chronic diazepam administration on lipid peroxidation and Ca2+ -ATPase activity in rat liver

Chronic administration of diazepam (DZP) caused an increase in malondialdehyde (MDA) levels and a decrease in glutathione (GSH) content. DZP also markedly lowered Ca2+ATPase activity. Treatment with Se plus vitamin E reduced MDA levels and increased GSH content. Our results suggest that, increased lipid peroxidation together with alteration in Ca2+ -ATPase activity may play a role in DZP induced hepatic injury and Se plus vitamin E treatment may contribute to the attenuation of DZP induced hepatotoxicity.     

Effect of polyaspartic acid on CdCl2-induced nephrotoxicity in the rat

We produced an animal model of CdCl₂ nephrotoxicity in rats, and treated them with polyaspartic acid (PAA) to prevent renal damage. Male Sprague-Dawley (SD) rats (190–200 g) were used to induce proximal renal tubular damage by daily injection of CdCl₂ 3.0 mg/1,000 g body wt for 2 wk. CdCl₂-exposed SD rats exhibited significant increases in urine volume, urinary excretion ofN-acetyl-β-D-glucosaminidase (NAG), alanine aminopeptidase (AAP), and fractional excretion of sodium (FENa) and a decrease in the percentage of tubular reabsorption of phosphate (%TRP). Of these indicators of proximal tubular function, AAP and %TRP are more sensitive than NAG or FENa. No glycosuria or aminoaciduria, however, were observed. PAA markedly improved these indicators of proximal tubular function. Daily urinary protein excretion and creatinine clearance, on the other hand, did not change after administration of PAA. Cd concentrations in the cortex were 3 times higher than in the medulla, however, there were no differences between Cd-treated rats and PAA-treated rats. Our animal model is an excellent one for determining the effect of cadmium on renal proximal tubule damage. PAA appears to be useful in the treatment of CdCl₂ nephrotoxicity.