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Biomedical subjects

G Colombo

Publications and source records attributed to G Colombo.

At least 217 records · Page 12Linked to original sources
PubMed1980

[Iatrogenic risks. Medicolegal and organizational problems concerning the performance of radiographic examinations with intravenous administration of contrast media].

The forensic medicine and organizational aspects of doing X-rays with i.v. contrast medium are discussed. Special attention is paid to the pathogenetic and clinicotherapeutic aspects of X-ray and contrast medium induced accidents together with the organizational problems posed by these problems in small hospitals without anaesthesia and resuscitation departments.

Contrast Media↗
PubMed1980

Increase of T.G lymphocytes in human one-way mixed lymphocyte culture.

Human one-way mixed lymphocyte culture induces a significant increase of EA(7S) rosette-forming cells. Using fractionation procedures, an increased number of Fc receptor-bearing cells in the T high-enriched populations was found from alloactivated lymphocytes compared with similar fractions obtained after autologous control cultures. Additional experiments showed a parallel increase of E-rosette-forming cells in the Fc receptor-enriched alloactivated fractions. The results indicate that an increase of T.G lymphocytes occurs during in vitro alloactivation in man.

Cell Count↗
PubMed1979

A renal abnormality as a possible cause of "essential" hypertension.

The renal abnormality which causes hypertension in the Milan hypertensive strain of rats disappears as hypertension develops. Because of the many analogies between the condition in these rats and "essential" hypertension in man, the same pattern of change may occur if a renal abnormality is the cause of essential hypertension in man. This hypothesis was tested in two groups of young normotensive subjects matched for age, sex, and body-surface area; in the first group both parents were hypertensive, and in the second group both parents were normotensive. Renal plasma-flow, glomerular filtration-rate, plasma-volume, plasma-renin activity, plasma-concentrations of Na+, K+, and catecholamines, 24 h urinary excretion of Na+, K+, and aldosterone, and the cardiac index were measured so that renal function and the role of factors affecting blood-pressure regulation could be assessed. Renal plasma-flow was significantly higher (p less than 0.01) in the first group, whereas results of tests for all the other factors were almost the same in both groups. The hypothesis that a primary kidney abnormality causes hypertension in a proportion of patients with essential hypertension is proposed.

Adult↗
PubMed1979

T cell defect in essential mixed cryoglobulinaemia.

Peripheral blood lymphocytes from untreated patients with essential cryoglobulinaemia were studied for their surface markers and for their in vitro mitogenic reactivity. No differences in lymphocyte subpopulations were observed between cryoglobulinaemic patients and normal controls. Cultures of separated lymphocytes were stimulated with different concentrations of phytohaemagglutinin, Con-A and pokeweed mitogen. Incorporation of [3H]-thymidine in patients' cultures was compared with that of normal controls. Significantly decreased reactivity to phytohaemagglutinin and Con-A, but not to pokeweed mitogen, was found in all patients studied. The depressed mitogenic reactivity to phytohaemagglutinin and Con-A might be referred to a qualitative T cell defect.

Adult↗
PubMed1978

A vicinal dithiol containing an essential cysteine in phosphoenolpyruvate carboxykinase (guanosine triphosphate) from cytosol of rat liver.

The highly purified form of phosphoenolpyruvate carboxykinase (PEPCK) contained 13 thiols (all in the reduced state) per 72 000 daltons. Modification of the enzyme with equimolar 5,5'-dithiobis(2-nitrobenzoate) (Nbs2) caused rapid formation of a cystine disulfide bridge and an even more rapid loss of enzymatic activity. Formation of the cystine bridge proceeded about 25 times faster than formation of the analogous intramolecular disulfide of dithiothreitol induced by Nbs2. o-Iodosobenzoate, Cd2+, and the 2,3-dimercapto-1-propanol complex of arsenite were potent, time-dependent, irreversible inhibitors of PEPCK. The inactivation by arsenite-2,3-dimercapto-1-propanol and o-iodosobenzoate was first order with respect to both time and inhibitor concentration. The sum of these data indicates the existence in PEPCK of a critical cysteine that is in a vicinal dithiol grouping with a second cysteine. PEP protected against cystine bridge formation induced by equimolar Nbs2 but not against the extent of inactivation. In the presence of PEP, the modification by Nbs2 of one cysteine/mol of enzyme (k = 1.2 X 10(6) M-1 min-1 at pH 7.2) caused nearly complete inactivation. Replacing the bulky 5-thio-2-nitrobenzoate moiety with cyanide did not result in any reactivation. This critical, cyanylated cysteine was determined to be 44% of the distance from the amino terminus.

Animals↗
PubMed1976

Specific modification of an effector binding site of phosphofructokinase by pyridoxal phasphate.

Conditions are described for the covalent modification of rabbit skeletal muscle phosphofructokinase by pyridoxal phosphate plus sodium borohydride to produce an enzyme that appears by a number of criteria to be modified at the citrate binding site. Evidence that modification occurs at this site is as follows. (1) Protection against activity loss due to modification is provided by the combination of MgATP and citrate, whereas neither low concentrations of citrate nor MgATP alone is effective. This is consistent with the increased affinity for citrate that is observed in the presence of MgATP. (2) The extensive changes in activity and equilibrium binding result from the incorporation of only 1 mol of pyridoxal phosphate per mol of protomer. (3) Modification greatly increases sensitivity to MgATP inhibition, an effect consistent with the known synergism between MgATP and citrate. (4) The affinity of the enzyme for both MgATP and MgIPT at the catalytic site is increased by the modification. (5) The sensitivity of the enzyme to citrate inhibition is greatly diminished following covalent modification. (6) Modification abolishes the equilibrium binding of citrate. (7) Enhanced binding of MgATP is observed following modification, a result consistent with the enhancement of MgATP binding by citrate. Phosphofructokinase protected by citrate plus MgATP can also be modified by the incorporation of 1 or more mol of pyridoxal phosphate, but the enzyme so produced is capable of interacting with citrate and shows none of the properties herein described for the enzyme modified in the absence of citrate.

Adenosine Triphosphate↗
PubMed1975

Interaction of inhibitors with muscle phosphofructokinase.

The interaction of several inhibitors with muscle phosphofructokinase has been studied by both equilibrium binding measurements and kinetic analysis. At low concentrations of citrate a maximum of 1 mol is bound per mol of enzyme protomer. Tight binding requires MgATP and very weak binding is observed in the absence of either magnesium ion or ATP. ITP at low concentrations cannot replace ATP. In the presence of MgATP and at pH 7.0, the dissociation constant for the enzyme-citrate complex is 20 muM. At 50 muM citrate and excess magnesium ion, the concentration of ATP required to give half-maximal binding of citrate is approximately 3 muM . Both P-enolpyruvate and 3-P-glycerate compete for the binding of citrate and the estimated Ki values are 480 and 52 muM, respectively. Creatine-P, another inhibitor of muscle phosphofructokinase, does not compete with the binding of citrate. Measurement of the equilibrium binding of ATP shows that citrate, 3-P-glycerate, P-enolpyruvate, and creatine-P all increase the affinity of enzyme for MgATP with the concentration required to give an effect increasing in the order given. In kinetic studies, citrate, 3-P-glycerate and P-enolpyruvate each act synergistically with ATP to inhibit the phosphofructokinase reaction. This is indicated by the observation that the three metabolites do not inhibit the enzyme with ITP as the phosphoryl donor and that they inhibit at ATP concentrations that are not themselves inhibitory. Furthermore, the sensitivity to the inhibitors increases with increasing ATP concentrations. Striking differences in the extent of inhibition can be seen by varying the order of addition of assay components. Preincubation of the enzyme with ATP and citrate, 3-P-glycerate, or P-enolpyruvate results in greater inhibition than when the inhibitor is added after the reaction is started with fructose-6-P. Furthermore, the inhibition is reversed partially 10 to 15 min after the addition of fructose-6-P. This phenomenon is particularly striking with creatine-P as the inhibitor. Very high concentrations of this inhibitor are required to show any effect if the inhibitor is added after fructose-6-P. These effects are interpreted as reflecting slow conformational changes between an active form with high affinity for fructose-6-P and an inactive, or less active, conformation that binds the inhibitors. Citrate, 3-P-glycerate, P-enolpyruvate, and creatine-P increase the rate of the phosphofructokinase at subsaturating concentrations of MgITP. The results indicate a common binding site on the enzyme for citrate, 3-P-glycerate, and P-enolpyruvate that is distinct from the ATP inhibitory site. An additional site (or sites) for creatine-P is indicated. All four inhibitors act synergistically with ATP by increasing the affinity of the enzyme for MgATP at an inhibitory site. The inhibitors appear also to increase the affinity of the catalytic nucleoside triphosphate site for substrate.

Adenosine Triphosphate↗