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Biomedical subjects

A Felipe

Publications and source records attributed to A Felipe.

At least 19 recordsLinked to original sources
PubMed1992

Amino acid deprivation leads to the emergence of System A activity and the synthesis of a specific membrane glycoprotein in the bovine renal epithelial cell line NBL-1.

1. Amino acid deprivation of confluent monolayers of the bovine renal epithelial cell line NBL-1 causes a stimulation of Na(+)-dependent alanine transport. 2. This stimulation is mediated by a protein-synthesis-dependent induction of 2-(methylamino)isobutyric acid (methyl-AIB)-sensitive alanine transport activity (System A), which was not previously present in these cells. 3. Induction was prevented by the addition of methyl-AIB, alanine or glutamine. 4. Tunicamycin prevented the induction of alanine transport activity. 5. Induction of System A activity was accompanied by incorporation of [3H]mannose into a single membrane protein band of molecular mass 113-140 kDa. 6. These results are consistent with the possibility that induced System A activity in confluent NBL-1 cells is mediated by the synthesis of a 113-140 kDa membrane glycoprotein.

Alanine↗
PubMed1992

Uridine transport in basolateral plasma membrane vesicles from rat liver.

The characteristics of uridine transport were studied in basolateral plasma membrane vesicles isolated from rat liver. Uridine was not metabolized under transport measurements conditions and was taken up into an osmotically active space with no significant binding of uridine to the membrane vesicles. Uridine uptake was sodium dependent, showing no significant stimulation by other monovalent cations. Kinetic analysis of the sodium-dependent component showed a single system with Michaelis-Menten kinetics. Parameter values were KM 8.9 microM and Vmax 0.57 pmol/mg prot/sec. Uridine transport proved to be electrogenic, since, firstly, the Hill plot of the kinetic data suggested a 1 uridine: 1 Na+ stoichiometry, secondly, valinomycin enhanced basal uridine uptake rats and, thirdly, the permeant nature of the Na+ counterions determined uridine, transport rates (SCN- greater than NO3- greater than Cl- greater than SO4(2-)). Other purines and pyrimidines cis-inhibited and trans-stimulated uridine uptake.

Animals↗
PubMed1992

Changes in alanine and glutamine transport during rat red blood cell maturation.

Alanine and glutamine transport have been studied during red blood cell maturation in the rat. Kinetic parameters of Na(+)-dependent L-alanine transport were: Km 0.43 and 1.88 mM and Vmax 158 and 45 nmoles/ml ICW/min for reticulocytes and erythrocytes, respectively. During red cell maturation in the rat there is a loss of capacity and affinity of the system ASC for L-alanine transport. The values for Na(+)-dependent L-glutamine transport in reticulocytes were Km 0.51 mM and Vmax 157 nmoles/ml ICW/min. On the other hand, a total loss of L-glutamine transport mediated by both N and ASC systems is demonstrated in mature red cells. This seems to indicate that during rat red cell maturation the system N disappears. Furthermore, the system ASC specificity in mature cells changes, and glutamine enters the red cell by non-mediated diffusion processes.

Alanine↗
PubMed1992

Control of neck nodes in squamous cell carcinoma of the head and neck by radiotherapy: prognostic factors.

313 patients with cervical metastases from a squamous carcinoma of the head and neck treated with radiotherapy, were studied by means of a multivariant analysis in order to determine the prognostic factors for cure. These were: lymph node response to irradiation (P = 0.0000), size of node (P = 0.0000), radiotherapy dose (P = 0.0037), condition of the primary (controlled vs non-controlled) (P = 0.0015), recurrent cervical metastases post-surgery (P = 0.0286).

Adolescent↗
PubMed1991

Amino acid uptake by liver of genetically obese Zucker rats.

Alanine and glutamine uptake by the liver of 50-52-day-old genetically obese Zucker rats and their lean littermates has been studied. The net uptake in vivo of L-alanine is 2-fold higher in the obese animals. No significant change in L-glutamine net balance was found. We also studied the Na(+)-dependent uptake of L-alanine and L-glutamine into plasma-membrane vesicles isolated from either obese- or lean-rat livers. Vmax. values of both L-alanine and L-glutamine transport were 2-fold higher in those preparations from obese rats. No change in Km was observed. As suggested by inhibition studies, this seemed to be mediated by an enhancement of the activities of systems A, ASC and N. We conclude that the liver of the obese Zucker rat is extremely efficient in taking up neutral amino acids from the afferent blood, which results in an enhanced net uptake of L-alanine in vivo. The changes in transport activities at the plasma-membrane level might contribute to increase amino acid disposal by liver, probably for lipogenic purposes, as recently reported by Terrettaz & Jeanrenaud [Biochem. J. (1990) 270, 803-807].

Alanine↗
PubMed1991

L-lactate uptake by rat liver. Effect of food deprivation and substrate availability.

We have studied the role of substrate availability on net L-lactate uptake by liver of anaesthetized fed and 24 h-fasted rats. L-Lactate was infused through a mesenteric vein at infusion rates equivalent to 0, 0.125, 0.25 and 0.5 times the basal turnover rate (Rt). By these means we were able to increase L-lactate portal concentrations up to 5.5 mM, without significant changes in portal pH. In the basal state (0 Rt), a net L-lactate uptake by liver was found in 24 h-fasted animals. No net balance was observed in fed rats. Infusion of L-lactate in fed animals failed to induce a net hepatic uptake, except when L-lactate levels in portal vein were raised above 5 mM. In fasted animals, net L-lactate uptake by liver increased linearly (r = 0.99) as a function of L-lactate concentration in the portal vein, even beyond the saturation of its specific carrier. It is concluded that, first, the L-lactate carrier does not limit net L-lactate uptake, and second, that substrate availability is an important factor modulating net L-lactate uptake by liver.

Animals↗
PubMed1991

Differences in L-alanine uptake by livers of Wistar and lean Zucker rats.

The L-alanine uptake by livers of Wistar and lean Zucker rats has been studied. The hepatic uptake and fractional extraction rates of alanine were estimated in 50-55 day old rats. No significant differences in amino acid concentrations and blood flows in afferent and efferent liver vessels were seen in lean Zucker rats when compared with Wistar rats. However, the hepatic uptake (1.6 +/- 0.1 and 0.7 +/- 0.1 mumol/min/100 g bw, p less than 0.01) and the fractional extraction (26.8 +/- 2.1 and 15.2 +/- 3.1%, p less than 0.05) were much lower in Zucker than in Wistar rats. The hepatic active transport of L-alanine was determined in vitro using isolated plasma membrane vesicles. Vesicles isolated from livers of lean Zucker rats showed similar values of Km (2.5 +/- 0.7 vs. 2.0 +/- 0.5 mM for Wistar and Zucker respectively, N.S.), but lower values of Vmax when compared with Wistar rats (1.1 +/- 0.1 vs 0.6 +/- 0.005 nmol/mg prot 5 s, p less than 0.01, for Wistar and lean Zucker rats respectively). These results indicate that, the liver of lean Zucker rats concentrates alanine less efficiently than the liver of Wistar rats. This fact correlates well with a lower capacity of the Na(+)-dependent L-alanine transport in liver plasma membrane vesicles from lean Zucker rats.

Alanine↗
PubMed1991

Pharmacology of the potent new non-steroidal anti-inflammatory agent aceclofenac.

Aceclofenac (2-[(2,6-dichlorophenyl) amine]phenylacetoxyacetic acid; CAS 89796-99-6) is a new orally effective non-steroidal anti-inflammatory agent of the phenylacetic acid group which showed remarkable anti-inflammatory, analgesic, and antipyretic properties. Hence, aceclofenac possesses a potent inhibitory activity in several models of acute and chronic inflammation in rodents, and resembles indometacin and diclofenac in its pharmacodynamic profile, being superior to naproxen and phenylbutazone. In addition, aceclofenac was found to be highly active against sodium urate-induced synovitis in dogs and adjuvant-induced polyarthritis in rats, both prophylactically and therapeutically. The analgesic effect of aceclofenac on the pain elicited by chemical and mechanical stimuli was nearly equal to or slightly better than that of indometacin and diclofenac. Fever induced by brewer's yeast injection in rats was also markedly suppressed by aceclofenac. In contrast, the acute gastric ulcerogenic activity of aceclofenac was about 2, 4 and 7-fold lesser than that of naproxen, diclofenac, or indometacin, respectively. As a consequence of its high anti-inflammatory activity and lower potential for gastric damage aceclofenac exhibited the most favourable therapeutic ratio in comparison with indometacin, diclofenac, naproxen, and phenylbutazone. These data indicate that aceclofenac could be a potent anti-inflammatory and analgesic agent with a wide margin of safety in clinical practice.

Animals↗
PubMed1990

Bicarbonate stimulation of Na+ transport in liver basolateral plasma membrane vesicles requires the presence of a transmembrane pH gradient.

The effect of bicarbonate on the uptake of 22Na+ into liver basolateral plasma membrane vesicles was studied under conditions where the pH of the medium was controlled by the use of high buffer concentrations. Bicarbonate stimulated the rate of Na+ uptake only in the presence of a pH gradient (acid inside). The stimulation by bicarbonate was inhibited by both amiloride and DIDS. No evidence for electrogenic Na+/HCO3- symport was found. These results are in part consistent with electroneutral Na+/HCO3- symport, but other explanations cannot be excluded.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed1990

Changes in glycine and leucine transport during red cell maturation in the rat.

Both glycine and leucine transport in rat red blood cells have been studied. The glycine uptake showed two different components, one sodium-dependent and another diffusion-like process. In contrast, leucine uptake was sodium independent. Both, Na(+)-dependent glycine and the overall leucine uptake in red blood cells showed a saturable pattern. Kinetic parameters in reticulocytes were: i) glycine: apparent Km 0.16 mM; Vmax 100.2 nmol/ml ICW/min; ii) leucine: apparent Km 2.11 mM; Vmax 3.88 mumol/ml ICW/min. The erythrocytes kinetic parameters were: i) glycine: apparent Km 0.17 mM; Vmax 9.47 nmol/ml ICW/min; leucine; apparent Km 4.77 mM; Vmax 7.42 mumol/ml ICW/min. The Kd values (sodium independent glycine uptake) were similar in both kind of cells, but the importance of this component in total glycine uptake in erythrocytes was much higher than in reticulocytes. Our results confirm that rat red blood cells have both saturable leucine and Na(+)-dependent glycine uptake, but some important changes occur during cell maturation.

Animals↗
PubMed1990

Cationic and anionic amino acid transport studies in rat red blood cells.

The transport of L-proline, L-lysine and L-glutamate in rat red blood cells has been studied. L-proline and L-lysine uptake were Na(+)-independent. When the concentration dependence was studied both showed a non-saturable uptake assimilable to a difussion-like process, with high Kd values (0.718 and 0.191 min-1 for L-proline and L-lysine respectively). Rat red blood cells showed high impermeability to L-glutamate. No sodium dependence was observed and the Kd value was low (0.067 min-1). Our results show firstly, that rat red blood cells do not have amino acid transport systems for anionic and cationic amino acids and secondly that erythrocytes show no sodium-dependent L-proline transport, and that these cells are very permeable to this amino acid.

Alanine↗
PubMed1990

Circadian changes in glycogen content in rat interscapular brown adipose tissue: effect of cold exposure and food deprivation.

The effects of food deprivation and cold exposure on brown adipose tissue (BAT) glycogen and lipid levels during the circadian cycle were studied. BAT glycogen levels in control animals followed a definite circadian cycle, showing an increase during the light period. In cold-exposed animals the pattern was different, with minimal values at the beginning of the dark period. Food deprivation caused a decrease in BAT glycogen concentration only after 48-hours. In contrast to the control animals, where BAT and liver showed a different glycogen pattern, in the cold exposed group the observed changes were similar. During cold exposure, lipid stores in BAT were decreased. The results obtained in this work highlight with the important role of glycogen and lipid stores in BAT thermogenesis.

Adipose Tissue, Brown↗
PubMed1990

Pharmaco-toxicological effects of acetaminophen in rodents. Battery of tests to screen potential analgesic acetaminophen derivatives.

The pharmacological effects of acute oral administration of acetaminophen have been extensively evaluated in rodents. Using this drug as reference compound we have also standardized several pharmaco-toxociological tests in order to select new analgesic-antipyretic acetaminophen derivatives. According to the results obtained in this work, the following battery of assays is proposed to screen these compounds: a) pharmacological: antipyretic activity against Brewer's yeast-induced pyresis in rats; analgesic activity against chemical-induced writhings in mice and paw pressure test in rats; b) toxicological: oral acute toxicity in mice with and without phenobarbital pretreatment; determination of SGOT and SGPT activities as well as total bilirubin in mice. The usefulness of this procedure in the evaluation of drug effects is also considered.

Acetaminophen↗
PubMed1989

Na+-dependent alanine transport in plasma membrane vesicles from late-pregnant rat livers.

Liver plasma membrane vesicles retaining Na+-dependent L-alanine transport were purified from either virgin or 21-d pregnant rats. Kinetic analysis of L-alanine uptake data revealed that vesicles from pregnant rats show a slight increase in Vmax without significantly affecting Km. Plasma membrane marker recoveries were used to calculate alanine utilization indexes. These data showed that the overall liver capacity to take up alanine was increased 2-fold in late pregnant rats. When considering utilization indexes in the physiologic range of L-alanine concentrations in blood (0.1-2 mM), we found a highly significant enhancement of the liver capacity to take up this amino acid. It is concluded that, at late pregnancy, when amino acid requirements by the fetus are high, amino acid disposal by the maternal liver is not limited by a low transport capacity; thus, other mechanisms should be contributing to the nitrogen sparing at late pregnancy.

Alanine↗
PubMed1988

Glutamine as a major nitrogen carrier to the liver in suckling rat pups.

We measured the amino acid concentrations in the afferent and efferent vessels of the liver in anaesthetized fed adult rats and in fed suckling rat pups. A much higher content of glutamine in the portal vein and the aorta than in hepatic veins suggests that this amino acid is actively taken up by the liver of fed suckling rat pups, conversely to what is found in adult rats. In an attempt to characterize further the mechanism(s) contributing to this enhanced glutamine uptake, we monitored the time course of 1 mM-glutamine transport into plasma-membrane vesicles purified from the livers of either adult or suckling rats. The concentrative Na+-dependent uptake of glutamine was lower in those vesicles obtained from pups than in those obtained from adult rats. Glutaminase and glutamine synthetase activities in livers from both experimental groups were also measured. Glutaminase and glutamine synthetase activities in suckling rats were about 3-fold higher and 2-fold lower respectively than those in adult rats. It is concluded that glutamine is a main nitrogen carrier to the liver in fed suckling rats. A high availability of this amino acid and an enzyme imbalance between glutamine-synthesizing and -degrading activities may account for the net uptake found in vivo.

Amino Acids↗