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G Ronca

Publications and source records attributed to G Ronca.

At least 19 recordsLinked to original sources
PubMed1992

Energy metabolism in myocardial stunning.

We investigated the effect of reversible ischemia, leading to persistent contractile dysfunction (stunning), on myocardial energy metabolism. The balance of energy metabolism is expressed by the phosphorylation state of cytosolic nucleotides. This variable cannot be measured directly because of nucleotide compartmentation, but in the isolated heart it can be estimated by the release of purine catabolites. We have previously shown that increased energy consumption or impaired energy production cause purine release to increase, while primary reduction in energy consumption has the opposite effect. Isolated working rat hearts were reperfused after 10 min of global ischemia, measuring hemodynamic variables, tissue high energy phosphate compounds and purine release. In post-ischemic recovery, aortic flow and minute work decreased to 82 +/- 3% and 77 +/- 4% of control, adenine nucleotide pool was reduced by 4.6 mumol/g dry wt, phosphocreatine to creatine ratio increased significantly and purine release decreased to 42 +/- 6% (P < 0.01). The rate of purine salvage, as evaluated by the incorporation of exogenous 3H-adenosine and 14C-hypoxanthine into tissue nucleotides, was much lower than net purine release, and was unchanged after ischemia and reperfusion. The adenine nucleotide pool could be depleted to the same extent as in the stunned myocardium by prolonged (60 min) aerobic perfusion. In this group the hemodynamic variables were unchanged and purine release averaged 87 +/- 9% of control (P = NS). In other experiments prolonged perfusion was combined with preload reduction in order to decrease energy demand. This protocol reproduced the effects of ischemia-reperfusion: aortic flow and minute work averaged 79 +/- 4% and 73 +/- 9% of control, adenine nucleotide depletion was 4.4 mumol/g dry wt and purine release decreased to 38 +/- 5% (P < 0.01). Our findings support the view that stunning is not due to adenine nucleotide depletion or to impairment in energy production, which would cause purine release to increase, but rather to primary reduction in energy utilization.

Animals↗
PubMed1992

Cardiac A2 adenosine receptors--influence of ischaemia.

OBJECTIVE: The aim was to detect cardiac A2 adenosine receptors through radioligand binding, and to assess the effect of ischaemia on these receptors. METHODS: Isolated working rat hearts were subjected either to aerobic perfusion or to global ischaemia. A membrane fraction was prepared from ventricular tissue, and 3H-5'-N-ethylcarboxamide adenosine (NECA) binding was determined in the presence of N6-cyclopentyl adenosine (CPA). A2 binding was calculated as the fraction of NECA binding displaced by 100 microM CPA but not displaced by 50 nM CPA. RESULTS: Analysis of A2 NECA binding according to single binding site model yielded Kd = 22.0 nM, Bmax = 34.0 fmol.mg-1 in control hearts; Kd = 49.7 nM, Bmax = 44.3 fmol.mg-1 in hearts subjected to 30 min ischaemia (p < 0.05 for difference in Kd). In the control group a two site model provided a significantly (p < 0.05) better fit (Kd = 5.6 and 183.7 nM, Bmax = 9.5 and 64.4 fmol.mg-1 for the high and low affinity sites respectively). The high affinity component of A2 NECA binding disappeared in the presence of the GTP analogue guanyl-5'-yl imidodiphosphate, suggesting the existence of multiple coupling states of the receptor. In the ischaemic group no significant improvement in data fitting was obtained with the two site model. CONCLUSIONS: The results provide evidence of the existence of cardiac A2 adenosine receptors. Ischaemia modifies receptor properties and appears to affect chiefly the high affinity component of A2 binding, possibly by preventing receptor interaction with membrane G proteins.

Adenosine↗
PubMed1992

Effect of gallopamil on cardiac sarcoplasmic reticulum.

We investigated the effect of gallopamil on cardiac sarcoplasmic reticulum (SR) function. Heavy SR was prepared from bovine ventricular muscle. Oxalate-supported calcium uptake was stimulated by gallopamil at concentrations ranging from 10 to 300 nM, whereas higher concentrations were ineffective. Peak stimulation averaged 25-30% of control calcium uptake and was observed at free calcium concentrations ranging from 1 to 6 microM. Calcium uptake is actually the difference between active calcium transport by SR calcium-adenosine triphosphate (calcium-ATPase), and passive efflux through SR calcium-release channels. In the presence of 300 microM of ryanodine, a blocker of SR channels, calcium uptake increased by 43% under control conditions, but not further stimulation was produced by gallopamil. SR calcium-ATPase was not affected by gallopamil. Similar results were obtained when oxalate-supported calcium uptake was determined with use of unfractionated homogenate obtained from rat hearts. We conclude that gallopamil acts on SR calcium-release channels and reduces the probability of channel opening and/or channel conductivity. The dose-response curve is bell shaped, and the maximum effect, which corresponds to 65% of the maximum effect of ryanodine, is achieved at therapeutic concentrations. Such action might contribute to the beneficial effect of gallopamil in the treatment of myocardial ischemia.

Animals↗
PubMed1992

[Variations in the purine metabolism of the reperfused heart].

Isolated hearts were subjected to 30 min of aerobic perfusion followed by 10 min of global normothermic ischemia and 40 min of reperfusion. We determined the release of purine catabolites (adenosine, inosine, hypoxanthine, xanthine, uric acid) and the incorporation of exogenous 3H-adenosine and 14C-hypoxanthine into cellular nucleotides. Ischemia-reperfusion produced remarkable reduction in the release of purine catabolites, with no significant variation in the incorporation of adenosine and hypoxanthine.

Analysis of Variance↗
PubMed1992

L-carnitine and coenzyme Q10 protective action against ischaemia and reperfusion of working rat heart.

The protective effect of L-carnitine, coenzyme Q10 and their combination on haemodynamic and metabolic variables has been investigated in isolated perfused working rat hearts after 10 min of global normothermic ischaemia followed by 60 min of reperfusion. In untreated rats or in rats treated only with L-carnitine or with coenzyme Q10, this experimental condition did not induce any irreversible myocardial injury as measured by leakage of cardiac enzymes; however, it decreased some haemodynamic parameters such as cardiac output and minute work, as well as the ATP concentration and the total adenine nucleotide pool. No variations in haemodynamic and metabolic parameters were observed in the rats treated with L-carnitine plus coenzyme Q10. In the perfusate of the hearts of the rats treated with both compounds, a lower purine release (a good index of myocardial energy balance) was also obtained. Although the molecular mechanisms remain to be defined, it appears that the association of L-carnitine and coenzyme Q10 is more effective than using these compounds separately. The complementary and synergic actions of L-carnitine and coenzyme Q10 on metabolism and against peroxidation by oxygen reaction species may explain the efficacy of their association.

Animals↗
PubMed1992

Protection of isolated perfused working rat heart from oxidative stress by exogenous L-propionyl carnitine.

The effect of exogenous L-propionyl carnitine on peroxidative injury was investigated on isolated working rat hearts. The addition of 190 microM hydrogen peroxide to the perfusion buffer caused a marked decrease in aortic flow, minute work and peak aortic pressure, and a release of intracellular enzymes. In the presence of L-propionyl carnitine the haemodynamic damage was significantly lower and enzyme leakage remarkably decreased. The protection was concentration-dependent and the whole structure of the molecule was required, since carnitine alone was found less effective and propionate had no effect. In the absence of hydrogen peroxide L-propionyl carnitine increased heart performance. The effect of L-propionyl carnitine on oxidative stress could account for the beneficial effect of this substance in different models of ischaemic injury. L-propionyl carnitine increases the cardiac performance and protects the rat heart from peroxidation through metabolic and antiperoxidative mechanisms.

Animals↗
PubMed1992

[Effects of oxygen free radicals on the function of the cardiac sarcoplasmic reticulum].

Peroxidative stress, exerted by oxygen free radicals, seems to be an important mechanism of the ischemia-reperfusion myocardial damage. In the present study we evaluated the modifications of sarcoplasmic reticulum function subjected to peroxidation by ferric ions. A subcellular fraction enriched in sarcoplasmic reticulum was obtained from rabbit hearts by homogenization and differential centrifugations. Sarcoplasmic reticulum vesicles were peroxidated through incubation for 5 min at 37 degrees C in presence of ferric cloride (FeCl3) ranging in concentration between 0.3 and 0.9 mM. Peroxidation of sarcoplasmic reticulum vesicles determined a dose-dependent reduction of Ca-uptake (39.2 +/- 10.3, 36.5 +/- 9.9, 28.9 +/- 8.4 and 18.8 +/- 8.2 nmol/min/mg in presence of 0, 0.3, 0.6 e 0.9 mM FeCl3; NS, p less than 0.05 and less than 0.01, respectively) which was paralleled by an increase in the production of malondialdehyde, an index of lipid peroxidation (1.0 +/- 1.0, 7.0 +/- 3.2, 14.1 +/- 3.9 and 27.0 +/- 4.7 nmol/mg in presence of 0, 0.3, 0.6 e 0.9 mM FeCl3; p less than 0.05, less than 0.01 and less than 0.01, respectively). Depression of Ca-uptake was not accounted for by modifications of Ca-ATPase activity or membrane aspecific permeability to Ca++ ions, since these parameters were not affected by exposure to 0.3-0.9 mM FeCl3. On the contrary, the responsiveness of Ca-release channels to the specific inhibitor ryanodine was greatly altered, even at lower FeCl3 concentrations.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

Effects of verapamil, gallopamil, diltiazem and nifedipine on sarcoplasmic reticulum function in rat heart.

We investigated the effect of the calcium antagonists verapamil, gallopamil, diltiazem and nifedipine on cardiac sarcoplasmic reticulum function. In a cell-free homogenate from rat hearts, oxalate-supported Ca uptake was stimulated by verapamil, gallopamil and diltiazem at concentrations in the order of 10 nM to 100 nM, while higher concentrations were ineffective. Nifedipine was also ineffective. Peak stimulation of Ca uptake averaged 15-20% of control. Ca uptake is the difference between active Ca transport by Ca-ATPase and passive efflux through sarcoplasmic reticulum channels. In the presence of 300 microM ryanodine, which blocks sarcoplasmic reticulum channels, Ca uptake increased by 50%, but no further stimulation was produced by the addition of any calcium antagonist, at concentrations ranging from 1 nM to 100 microM. In a fraction enriched in sarcoplasmic reticulum, no drug affected the activity of Ca-ATPase at concentrations able to stimulate Ca uptake. We conclude that low concentrations of verapamil, gallopamil and diltiazem reduce Ca efflux through the Ca channels of the sarcoplasmic reticulum. Such an action might contribute to the clinical effect of these drugs.

Animals↗
PubMed1992

Recent findings on the regulatory functions of CoA and the normalizing activity on plasma lipids of exogenous CoA.

In recent years many studies have shown that coenzyme A (CoA) is not only an acyl carrier coenzyme but it also has an important role in the regulation of metabolic functions and cell activities such as transport from the Golgi cisternae. This regulatory role is carried out by CoA, its precursor, catabolites and acylated derivatives. The acylation (myristylation and palmitylation) process of peptides and proteins dependent on CoA seems to be an important regulatory mechanism of cell activities. Furthermore exogenous CoA has been shown to decrease the triacylglycerols, cholesterol and Apo B of plasma lipoproteins in man. This regulatory mechanism acts either on VLDL synthesis and secretion or on their plasma clearance. CoA also protects cell-membrane and plasma lipoproteins against the peroxidative action of oxygen free-radicals.

Animals↗
PubMed1979

Affinity labeling of histidine and lysine residue in the adenosine deaminase substrate binding site.

1. Adenosine deaminase was inactivated by 9-(4-bromoacetamidobenzyl)-adenine (I) and 9-(2-bromoacetamidobenzyl)adenine (II), two affinity labels. 2. The stoichiometry of the reaction with reagent II is reported: 1 mol reagent is bound per mol inactive enzyme. Amino acid analysis of the 6 N HCl hydrolyzate of the inactive enzyme identified CM-histidine as the main alkylation product. This is the first evidence of the presence of a histidine in the active site region. 3. The alkylation rate and involved amino acid residues were studied for both reagents I and II, at pH 8 and 5.5. The particular reactivity of a lysine near or in the active site is discussed.

Adenine↗
PubMed1977

Blood lymphocytes in chronic lymphocytic leukaemia and Hodgkin's disease: Immunological features and enzymes of nucleoside metabolism.

Purified lymphocytes from venous blood of sixteen healthy adult subjects, eight patients with chronic lymphocytic leukaemia (CLL) and ten with Hodgkin's disease (HD), were examined for adenosine deaminase (ADA), cytidine deaminase (CDA), purine nucleoside phosphorylase (PNPase) and adenosine monophosphate deaminese (AMPA), after thawing and homogenization. The same cells were examined for the capacity to form E rosettes and to respond to phytohaemagglutinin (PHA) stimulation. In CLL a significant reduction (P less than 0-001) of AMPA, PNPase and ADA activities was observed without variation of CDA. In contrast in HD PNPase, AMPA and CDA were increased (P less than 0-01) while ADA was in the normal range. The E-rosette forming cells were significantly reduced in both diseases and the capacity to respond to PHA-stimulation was strongly impaired in CLL. By this experimental approach it seems possible to demonstrate different states of functional activity of the lymphocytic cells in two diseases characterized by reduced T-cell-mediated immunity.

AMP Deaminase↗
PubMed1977

[Biochemical evaluation of damage due to lead: importance and significance of erythrocyte zinc-protoporhyrin IX and urinary amino acid determination].

The early detection of lead intoxitation needs practical, simple, reproducible and diagnostically valid screening test. The determination of ALA-D (delta-amino-levulinic acid-dehydratase) in erythrocytes is one of the most reliable test for the evaluation of the occupational exposure to lead. However this test is difficult to standardize, sensible to lead contamination of laboratory glassware and the activity of enzyme decreases rapidly if stored. The determination of erythrocytes ZPP (zinco-protoporphyrin IX) was proposed as useful, alternative test. The protoporphyrin IX is a metabolic intermediate in heme biosynthesis; in erythrocytes is present as free form and zinc-boundend compound. The ZPP give high values only in lead intoxication and sideropenic anemia. The ALA-D and ZPP in erythrocytes were measured and compared in a group of workers exposed to lead. We have shown a good correlation between these two biochemical parameters. Aminoacid excretion in urine from workers exposed to lead was measured and compared with other biochemical parameters of intoxication. All lead workers examined had excessive urinary CP (coproporphyrin) and ALA (delta-amino-levulinic acid) excretion. An abnormal excretion of glycine was present in eight workers (32%), whereas in other four (15%) the glycinuria was at limit of normal values. An abnormal excretion of lysine was present in six workers (21%). The last data appear very interesting because the action of lead in lysine metabolism was not known.

Aminolevulinic Acid↗
PubMed1975

The nature of inactivation of rat muscle 5'-adenylate aminohydrolase by fluorodinitrobenzene.

1. The inactivation of rat skeletal muscle AMP deaminase by Dnp-F (1-fluoro-2,4-dinitrobenzene) is accompanied by the arylation of thiol, amino and phenolic hydroxyl groups. 2. The number of thiol groups that react with Dnp-F is about 12; this is the number that reacts with Nbs2 [5,5'-dithiobis-(2-nitrobenzoic acid)] and N-ethylmaleimide without loss of enzyme activity, and it appears to be the same thiol groups that all three reagents attack. 3. Dinitrophenylation of these reactive SH groups is not the cause of inactivation, since active N-ethylmaleimide-substituted enzyme is also inactivated by Dnp-F.4. Complete inactivation of the N-ethylmaleimide-treated AMP deaminase occurs when about six tyrosine and two lysine residues are dinitrophenylated. 5. Since the treatment of Dnp-enzyme with 2-mercaptoethanol restores much of the enzyme activity, inactivation of AMP deaminase by Dnp-F is probably largely due to modification of tyrosine residues. 6. The kinetic properties of the Dnp-enzyme indicate that a marked decrease in V occurs only after extensive enzyme modification. The decreased activity after slight inactivation results from modification of Km.

AMP Deaminase↗
PubMed1975

A general method of purification of adenosine deaminase by affinity chromatography.

Affinity chromatography has been used to purify adenosine deaminase from various sources: calf spleen, calf intestinal mucosa, chicken duodena and human erythrocytes. For this purpose a specific inhibitor, 9-(p-aminobenzyl) adenine, was synthesized and covalently joined to agarose. Adenosine deaminase is selectively retained by such an inhibitor-resin when highly impure solutions are chromatographed through it. After elution from the resin with guanylurea, a competitive inhibitor, the enzyme is homogeneous and can be recovered in yields of 80 percent or more and the same number of multiple forms of the enzyme is present in the purified preparation and in the crude extract.

Adenine↗