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R Ramirez

Publications and source records attributed to R Ramirez.

At least 73 records · Page 4Linked to original sources
PubMed1991

Purification of a procollagenase-activator present in medium of cultured guinea pig carrageenin granuloma.

Activation of procollagenase constitutes a crucial event in collagenolytic activity regulation. In this study we have purified by DEAE-cellulose, Ultrogel AcA-44, and zinc chelate sepharose chromatographies, a procollagenase-activator from the culture medium of the guinea pig carrageenin granuloma model. On SDS-PAGE, the activator migrates as a principal band of Mr approximately 44,000. The molecule activates procollagenase from human lung fibroblasts in a concentration dependent manner and an enhancement of collagenase activity of trypsin-treated crude culture medium was observed. A loss of about 50% of its activity occurs after heating. In addition, this activator degrades gelatin and casein. All these data suggest that this procollagenase-activator might be stromelysin. The activator was found in both phases of the granuloma, at 7 days when collagen is actively deposited and an important proportion of the collagenolytic activity remains in latent form; and at 14 days, when this enzymatic activity is fully expressed.

Animals↗
PubMed1990

Analysis of the mechanisms involved in NK resistance induced by a new tumor factor NK-RIF.

The mechanisms involved in susceptibility or resistance of neoplasic cells to lysis by NK cells are not well known. We have recently described a 12-kDa factor (NK-RIF), produced and released by different tumor cell lines, making K562 resistant to NK lysis without affecting the cytotoxic function of NK effector cells. In this paper we further study the mechanism involved in NK resistance of K562 mediated by NK-RIF and its biological implications. The results show that NK-RIF does not affect the binding capacity of target and effector cells nor the levels of HLA class I antigen expression on the target cells, as a proof that resistance to NK-mediated lysis is not always associated with a defect in target effector binding or with an increased MHC class I antigen expression. However NK-RIF-treated K562 loses its capacity to induce NK cell activation and the subsequent capacity to release NKCF and makes K562 resistant to lysis by NKCF. Therefore our results show that induction of resistance to NK cytotoxicity can be the result of the modulation of target structures responsible for inducing effector cell activation without affecting target/effector binding molecules. This indicates that the structures involved in adherence and activation of NK cells have a different nature and that molecules other than HLA participate in NK resistance.

Biological Factors↗
PubMed1990

Natural killer susceptibility is independent of HLA class I antigen expression on cell lines obtained from human solid tumors.

The susceptibility to natural killer (NK) cell-mediated cytotoxicity of 20 cell lines obtained from human solid tumors and their class I histocompatibility antigen (HLA) levels were studied in an attempt to determine whether major histocompatibility complex (MHC) products expressed on cells derived from human solid tumors influence NK susceptibility. The effect of interferon-gamma (IFN-gamma) treatment on these elements was also analyzed. The MHC class I (HLA-ABC, HLA-A and HLA-B) antigen levels and degree of NK lysis were very heterogeneous and no correlation was found on comparison. After treatment with IFN-gamma a marked decrease in NK susceptibility was observed in all the cell lines, including the control line K-562. However, the level of HLA class I expression was not modified in any of the lines with the exception of the K-562, which increased. In some cell lines the expression of HLA class I-like antigens. CDla, b and c, was also measured before and after IFN treatment; however, no correlation was found between CD1 levels and NK susceptibility. Consequently, from our results it is possible to conclude that HLA class I antigens do not play a decisive role in NK susceptibility of cell lines derived from human solid tumors and to suggest that molecules which are not HLA class I antigens but IFN-gamma inducible may confer NK resistance to these lines.

Antigens, CD1↗
PubMed1990

Non-enzymatic protein glycosylation: back-titration assay.

The glycosylation of albumin in vitro, as judged from the incorporation of D-[U-14C]glucose into trichloroacetic acid (TCA)-precipitable material represents a time-, temperature- and concentration-related process. It is markedly increased by NaCNBH3. A close correlation is observed between the radioactive data and the percentage of glycosylated albumin, as measured by affinity chromatography. The latter method, however, does not give information on the precise stoichiometry of the protein glycosylation. The relative extent of protein glycosylation can also be estimated by a back-titration procedure, the condensation of labelled D-glucose with the protein being inversely related to its prior degree of glycosylation. The back-titration assay was applied to plasma samples from normal and diabetic rats or human subjects and used to compare the glycosylation of albumin by distinct hexoses and hexose-phosphates. L-Glucose was found as efficient as D-glucose in causing albumin glycosylation and, hence, could conceivably be used to investigate in vivo changes in the intrinsic properties of extracellular proteins secondary to their glycosylation.

Animals↗
PubMed1990

Blood gas transport properties in endurance-trained athletes living at different altitudes.

Hemoglobin oxygen binding properties and acid-base status were investigated in Colombian athletes (A) and controls (C) from Cali (C-1000 m) and Bogotá (B-2600 m). [Hb] and Hct values were not influenced by altitude, but Hct was lower in the blood of athletes (in Cali 2.6%, in Bogotá 1.4%). Both training and altitude produced a right-shift of the standard oxygen dissociation curve (P50 in CC 28.5 +/- 0.9 mmHg, AC 31.0 +/- 1.4 mmHg, CB 29.6 +/- 1.5 mmHg) leading to highest P50 in blood of altitude athletes (32.3 +/- 1.1 mmHg). Opposite to the position of the ODC the slope "n" was only increased by altitude influence (delta "n" in controls 0.07, in athletes 0.28). The BCCO2 was increased in AC over the whole saturation range, whereas BCLac was neither significantly influenced by training nor by altitude. All altitude effects can be explained by higher [DPG] (delta[DPG] in controls 5.0 mumol/gHb, in athletes 3.9 mumol/gHb), but the cause for the training effects still remains unclear. The acid base status in altitude residents was characterized by low BE and pCO2, which was most pronounced in altitude athletes, the latter correcting the actual venous pH to normal values. No significant variations of the Hb-O2-binding properties could be detected in athletes one day after leaving high altitude when compared with blood samples of athletes taken at high altitude, whereas BE and venous pCO2 were already increased. It is concluded that high altitude athletes are favoured during aerobic and handicapped during anaerobic exercise after the rapid descent to low altitude.

Acid-Base Equilibrium↗
PubMed1990

Kinetic behaviour of liver glucokinase in diabetes. II. Possible role of non-enzymatic protein glycation.

The phosphorylation of D-glucose, as catalyzed by liver postmicrosomal supernatants, prepared from diabetic rats, under conditions aiming at the characterization of gluco-kinase activity, indicates, in addition to the classical fall in enzyme activity, an altered kinetic behaviour, the affinity for D-glucose and the apparent energy of activation being both lower in diabetic than normal rats. These kinetic anomalies persist after separation of cytosolic proteins from low molecular weight metabolites by gel filtration chromatography. They are simulated, to a limited extent, when liver cytosolic proteins from normal rats are glycated in vitro through prolonged exposure to a high concentration of D-glucose. Diabetes causes an increased non-enzymatic glycation of liver cytosolic proteins, including lactate dehydrogenase, as judged by either the ketoamine test, a back-titration procedure or the separation of glycated proteins by affinity chromatography. These findings suggest that chronic hyperglycemia might alter the intrinsic properties of liver glucokinase through a process of non-enzymatic glycation.

Animals↗
PubMed1990

Kinetic behaviour of liver glucokinase in diabetes. III. Possible role of insulinopenia.

In both starved and diazoxide-treated rats, the rate of D-(U-14C)glucose phosphorylation (10 mM) by liver cytosol, as measured in the presence of D-glucose 6-phosphate, was lower than in fed control rats. Moreover, in these two models of insulinopenia, the sensitivity of glucokinase to a lowering of temperature from 30 degrees C to 10 degrees C and its apparent affinity for D-glucose were both decreased. Such kinetic anomalies could not be attributed to the restricted contribution of N-acetyl-D-glucosamine kinase to the phosphorylation of D-glucose. It is proposed, therefore, that insulin deficiency may lead to a perturbation in either the intrinsic kinetic behaviour of glucokinase or the participation of its regulatory protein, independently of any change in glycemia.

Acetylglucosamine↗
PubMed1990

Effects of high-carbohydrate or high-fat diet on carbohydrate metabolism and insulin secretion in the normal rat.

The effects of changes in the content of dietary carbohydrate, protein and fat on glucose metabolism and insulin secretion were examined in normal male rats. The animals were fed for 10 days with three types of diet: (a) standard diet, (b) glucose diet and (c) high fat/protein diet. The weight of the rats fed with the glucose diet decreased when compared to the standard diet fed rats. The glucose diet decreased insulin secretion in response to glucose in vivo and in vitro and slightly improved glucose tolerance. The hepatic glycogen content was approximately three times higher in animals fed with the glucose diet than in the control group. When compared to the standard diet, the high fat/protein diet induced an increase of the weight gain. This type of diet caused an increase of the fasting plasma glucose, a decrease of hepatic glycogen and a marked glucose intolerance to an intravenous load as demonstrated by lower rates of glucose disappearance. Plasma insulin levels were increased both in basal and glucose stimulated states. These results indicate that the glucose diet leads to an enhanced insulin sensitivity of the target tissues. By contrast, the high fat/protein diet induces an obesity-like state and an in vivo insulin resistance.

Animals↗
PubMed1989

Anomeric specificity of D-glucose phosphorylation by rat liver glucose-6-phosphatase.

The anomeric specificity of D-glucose phosphorylation by hepatic glucose-6-phosphatase was examined in rat liver microsomes incubated in the presence of carbamoyl phosphate. At 10 degrees C, the Km for the equilibrated hexose and phosphate donor was close to 56 mM and 11 mM, respectively. The enzymic activity, which was increased in diabetic rats, was about 40% lower in untreated than in sonicated microsomes. No anomeric difference in affinity was found in sonicated microsomes. In untreated microsomes, however, the Km for beta-D-glucose was slightly lower than that for alpha-D-glucose. The maximal velocity was higher with beta- than alpha-D-glucose in both untreated and sonicated microsomes. These data indicate that the phosphotransferase activity of glucose-6-phosphatase cannot account for the higher rate of glycolysis and glycogen synthesis found in hepatocytes exposed to alpha- rather than beta-D-glucose.

Animals↗
PubMed1986

Excretory urography with iohexol: evaluation in children.

A multicenter clinical study was conducted using iohexol, a second-generation nonionic contrast medium, for excretory urography performed in 130 children. Doses of iohexol (300 mg iodine/ml) ranged between 150 and 660 mgI/kg (0.5 and 2.2 ml/kg). Iohexol was tolerated well, and no significant adverse reactions occurred. Sixty-five iohexol urograms were evaluated to determine the minimum dose for adequate visualization of the kidneys and collecting systems. A dose greater than 300 mgI/kg (1.0 ml/kg) always resulted in a urogram of diagnostic quality, while visualization was insufficient for diagnosis in 10% of studies done with doses of 150-300 mgI/kg (0.5-1.0 ml/kg). Another 65 iohexol urograms were compared in a blinded manner with a similar number of studies performed using iothalamate meglumine at comparable iodine concentration and dose. Visualization of calyces and pelvoinfundibular structures achieved with iohexol was rated better with statistical significance, but there was no difference in visualization of the renal parenchyma or ureters. Use of iohexol in excretory urography may be advantageous in children who are at greatest risk for an adverse reaction to contrast media or in those most likely to benefit from use of a low osmolality contrast agent.

Adolescent↗
PubMed1984

Marginal malnutrition in school-aged Colombian boys: efficiency of treadmill walking in submaximal exercise.

Measurements of oxygen consumption (VO2) were made during submaximal treadmill exercise (3.5 mph) in 658 boys 6 to 16 yr of age classified as nutritionally normal, low weight for age, and low weight for height. Gross efficiency (at 15% grade) increased with age and was significantly lower in low weight for age and height boys than in normal children but delta efficiency showed no statistically significant differences between nutritional groups. It is concluded that marginal malnutrition has no effect on the efficiency of submaximal work during treadmill walking.

Adolescent↗