Search PubMed⌕ Search

Biomedical subjects

A Linares

Publications and source records attributed to A Linares.

At least 73 records · Page 4Linked to original sources
PubMed1984

Squalene, lanosterol and cholesterol synthesis from acetate in neonatal chick tissues.

Acetate incorporation into squalene, lanosterol and cholesterol by liver and kidney slices and intestinal mucosa scrapes from neonatal chick was studied. Contrary to what is observed when using mevalonate as substrate, cholesterol was the main nonsaponifiable synthesized from acetate in all the conditions assayed. Low percentages of squalene and lanosterol were synthesized by liver and kidney slices, while in intestinal mucosa squalene was practically undetectable. The highest percentage of radioactivity in cholesterol was found in liver, followed by intestinal mucosa and kidney. Relative percentages of squalene, lanosterol and cholesterol were practically similar in each tissue at any incubation time and acetate concentration considered. Only in kidney these percentages, especially in the case of squalene, seemed to decrease at higher acetate concentrations (8-12 mM).

Acetates↗
PubMed1983

Relationship between changes in free cholesterol and pyrophosphomevalonate decarboxylase activity during myelination.

The patterns of cholesterol content in chick brain and liver were studied during embryonic development and compared with the variations in the specific activities of mevalonate-activating enzymes during the same period. Total cholesterol content in both embryonic chick brain and liver increased during incubation. The relative percentage of free cholesterol was always maintained over 85% in brain, while in liver this percentage decreased to less than 10% during the later days of incubation. A straight parallelism was observed between free cholesterol and pyrophosphomevalonate decarboxylase activity in the embryonic brain. On the other hand, the hepatic decarboxylase exhibited a lower specific activity than in brain and did not show significant variations throughout the same period of incubation. Changes in brain pyrophosphomevalonate decarboxylase activity were more pronounced than those observed in both mevalonate kinase and phosphomevalonate kinase activities, in spite of that the specific activity of decarboxylase was the lowest of the three mevalonate-activating enzymes, suggesting that this reaction is one rate-limiting step for cholesterogenesis during myelination.

Animals↗
PubMed1983

3-hydroxy-3-methylglutaryl-CoA reductase from neonatal chick.

The optimal conditions for identification of mevalonic acid as the product of 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) reductase are described, as well as the effect of different buffer constituents on the enzyme activity. Under the chosen assay conditions, reductase activity from neonatal chick liver increased with the incubation time up to 60 min and was proportional to the amounts of protein added in a range of 0.1-0.5 mg. The specific activity was maximal in brain and liver and lower in intestine of 6-day-old chicks. Thermostability of hepatic reductase was studied. When microsomal preparations were maintained at 4 degrees C, reductase activity remained unchanged for 6 hr and decreased afterwards. Addition of 50 mM KF to the homogenization medium had no effect on the reductase activity. Similarly, preincubation of microsomal preparations with 105,000 g supernatants in the presence or absence of KF did not significantly increase the reductase activity. These results suggest that HMG-CoA reductase was isolated from neonatal chick in the fully activated form.

Animals↗
PubMed1983

Studies of the in vivo metabolism of mevalonic acid in the neonatal chick.

After 4 hr of the intraperitoneal injection of different doses of (R)-[5-14C]mevalonic acid (MVA), its incorporation into nonsaponifiable and saponifiable lipids was maximal in neonatal chick kidneys and liver, and minimal in brain, spinal cord and skin. Using 14CO2 production from [5-14C]MVA as an index of the shunt pathway not leading to sterols, we have demonstrated for the first time that about 11% of MVA was in vivo metabolized by this pathway in nonmammalian species. Kidneys presented the maximal ability to incorporate MVA into nonsaponifiable and saponifiable lipids at any time considered (15-750 min). The percentage of radioactivity recovered as saponifiable lipids in liver and kidney decreased after 12 hr the injection of MVA. Although the absolute amounts of 14C incorporated in both derivatives were much less in brain, spinal cord and skin than in liver and kidneys, the relative percentages found in the saponifiable fraction were clearly higher in the former tissues, especially in the spinal cord.

Animals↗
PubMed1983

Incorporation of mevalonate into squalene, lanosterol and cholesterol by different neonatal chick tissues.

The role of neonatal chick liver and kidneys in the incorporation of mevalonic acid into squalene, lanosterol and cholesterol was studied. Differences between the synthesizing ability of these and other tissues and the influence of the in vivo or in vitro conditions were also examined. In the in vivo experiments, distribution of radioactivity among the nonsaponifiable lipids was not dependent of the doses of mevalonic acid injected. About 80-95% of radioactivity was recovered as cholesterol in liver and brain, whereas in kidneys this percentage was only about 35%. Squalene and lanosterol were formed by kidneys in a high percentage, higher than in liver and other tissues. 12 hr after mevalonate injection, the percentage of cholesterol formed by kidneys increased until more than 50%. In the in vitro experiments carried out in the presence of 0.045-4.0 mM mevalonate, cholesterol was also the main nonsaponifiable identified, but in a lesser percentage than in vivo. In the same conditions, the incorporation of mevalonic acid by kidneys was maximal into squalene. After in vitro incubations for 2 hr, the percentage of cholesterol in kidneys also increased.

Animals↗
PubMed1983

[Differences between fatty acids of the linoleic series (n-6) and linolenic (n-3) in erythrocyte phospholipids in newborn and premature infants].

Percentage of fatty acids in phospholipids of red cell membranes from cord blood of 13 full-term and 11 premature infants is studied. Percentage of 22:5n6, final metabolite of n6 series, was significantly diminished in premature infants, whereas the percentage of arachidonic acid was significantly increased in the same group. The possibility that an enzymatic abnormality be present in desaturation from 22:4n6 to 22:5n6 is speculated, as well as of its physiologic implications.

Arachidonic Acids↗
PubMed1982

The in vitro metabolism of mevalonate by sterol and nonsterol pathways in neonatal chick.

1. Incorporation of mevalonate into nonsaponifiable lipids by neonatal chick liver and kidney slices was studied as a function of weight of tissue and incubation time. In the same conditions, more nonsaponifiable lipids were produced in kidney than in liver. 2. CO2 production from mevalonate increased with the weight of tissue and with the incubation time. Over 80% of CO2 produced from mevalonate resulted from the shunt pathway in kidney, while in liver this route was quantitatively insignificant. 3. 2-14C from mevalonate was also incorporated into saponifiable (acidic) fraction by kidney slices. 4. Incorporation into nonsaponifiable lipids and total CO2 increased with the concentration of mevalonate. This increase was more pronounced in kidney than in liver especially at low mevalonate concentrations. In the presence of 0.1-8.0 mM mevalonate over 80% of the CO2 produced from this substrate resulted from the shunt pathway, while liver was practically ineffective whatever be the concentration of mevalonate. 5. The percentage of mevalonate metabolized in the kidney by shunt pathway increased with the incubation time and reached over 15% in the presence of 0.1-8.0 mM mevalonate.

Animals↗
PubMed1982

A comparative study of cholesterogenic activities from acetate of neonatal chick liver, kidney and intestinal mucosa.

1. Acetate incorporation into nonsaponifiable lipids by liver and kidney slices and intestinal mucosa scrapes from neonatal chick was linear up to 100-150 mg of tissue. CO2 production from [1-14C]acetate was also studied as a function of weight of tissues. 2. Rate of acetate incorporation by the three mentioned tissues was essentially linear with respect to the incubation time assayed (0-120 min), CO2 production was also linear up to 60 min in kidney and 120 min in liver and intestinal mucosa. 3. In the conditions assayed the formation of nonsaponifiable lipids by liver slices reached constant values at acetate concentration of approximately 6 mM, while acetate incorporation by kidney and intestinal mucosa in the same conditions increased in nearly linear relationship to the concentration of available substrate. 4. Using the optimal assay conditions, acetate incorporation into nonsaponifiable lipids was maximal in neonatal chick liver, whereas kidney and intestinal mucosa only showed about 10% of the hepatic cholesterogenic activity. The percentage of acetate utilization for cholesterogenesis was also maximal in neonatal liver (about 10%). In the intestinal mucosa this percentage was also important (2-3%) being minimal in kidney slices (0.3%).

Acetates↗
PubMed1982

Partial purification and properties of mevalonate kinase from neonatal chick liver.

Mevalonate kinase from neonatal chick liver has been partially purified by ammonium sulphate precipitation and Sephadex G100 and DEAE-cellulose fractionation. The kinetic characteristics agreed with the sequential mechanism suggested for the enzyme and provided apparent Km values of 0.01 mM for mevalonic acid and 0.25 mM for ATP. Partially purified mevalonate kinase from neonatal chick liver showed an absolute specificity for ATP. Mn2+ was a better activator than Mg2+ at low concentrations (0.1-1.0 mM). Higher Mn2+ concentrations produced a clear inhibition of mevalonate kinase. Likewise, addition of EDTA, with or without metal ions, clearly inhibited the enzymatic reaction.

Adenosine Triphosphate↗
PubMed1982

[Effect of sulfhydryl reagents on mevalonate kinase partially purified from chicken liver].

Unlike other vertebrate mevalonate kinase, the enzyme partially purified from neonatal chick liver was not activated by the -SH group protectors reduced glutathione, cysteine, dithiothreitol and beta-mercaptoethanol at any concentrations assayed (0.01-10.00 mM). However, the activity was found to be sensitive to thiol group binding reagents. p-Hydroxymercuribenzoate was the most active inhibitor. At 0.1 mM concentration, p-HMB completely abolished the enzyme activity. N-ethylmaleimide (0.01-1.00 mM) was practically ineffective. Inhibition by p-HMB was temperature dependent, being more potent at 37 degrees C than at 4 degrees C.

Animals↗
PubMed1981

Further studies on mevalonate phosphorylation in neonatal chick brain.

Mevalonate phosphorylation was studied in neonatal chick brain. Formation of phosphorylated derivatives of mevalonic acid increased with the pH in the range assays (5.5-9.5). Phosphomevalonate kinase was completely inactivated after treatment at 50 degree C for 5-10 min, whereas mevalonate kinase was found to retain its activity under the same conditions. Exposure to 65 degree C for 5 min resulted in the inactivation of mevalonate kinase. Both mevalonate-activating enzymes from chick brain were located primarily in the soluble fraction. The amounts of phosphomevalonic acid and pyrophosphomevalonic acid did not show a significant diurnal variation to suggest the presence of a circadian rhythm in either kinase. Cholesterol feeding and fasting had no effect on mevalonate phosphorylation by neonatal chick brain.

Animals↗
PubMed1981

Properties of mevalonate-activating enzymes in developing chick brain.

Phosphorylation of mevalonic acid has been studied in 1-3 day chicks. Addition of Mg2+ or Mn2+ strongly increased the formation of phosphorylated derivatives. Mevalonate phosphorylation showed an absolute nucleotide requirement, being ATP and ITP the most effective phosphate donors. Unlike other vertebrate mevalonate kinases, the enzyme from chick brain did not require thiol group protectors as activators. However, the enzyme was found to be sensitive to thiol binding reagents.

Animals↗
PubMed1980

Postnatal development of mevalonate phosphorylation in the chick brain and kidney.

The quantitative role of the brain and the kidney of the chick the phosphorylation of mevalonic acid was studied in the early steps of development. In both tissues no significant differences were found in the amount of phosphomevalonic acid formed until 4 days, but a sharp decrease between 4 and 6 days was observed. The amount of pyrophosphomevalonic acid formed showed some change with age, but this change was relatively small when compared with the changes in the phosphomevalonic acid formed. According to the function of the brain and the kidney in the sterol and nonsterol pathways in the metabolism of mevalonic acid during neonatal development of chick, an important role for the mevalonate kinase during myelination can be suggested.

Animals↗
PubMed1980

[Neonatal form of Steinert's congenital dystrophia, myotonica. Diagnosis and outcome in eight cases (author's transl)].

Eight infants with neonatal form of dystrophia myotonica, and the outcome in the follow-up of five survivors, are reported. The disease is frequently overlooked in our country, since rare reports are available. Important findings of our series were increased incidence of obstetric complications and severe neonatal affectation with hypotonia and respiratory distress as well as high mortality and psychomotor handicaps in survivors.

Female↗
PubMed1980

[Feto-maternal lipid levels in a case of type V hyperlipoproteinemic mother (author's transl)].

Plasma lipids and lipoproteins, and fatty acids percentage in type V hyperliproteinemic mother and her newborn infant were assessed to better understand the previously unstudied relationships between hypertriglyceridemic maternal situation and the possible fetal repercussions. The difference between total lipid serum levels in the mother (1,580 mg./dl.) and infant (220 mg./dl.) and triglyceride levels in the mother (723 mg./dl.) and infant (71 mg./dl.) are indicative of an impending placental transfer of the maternal hypertriglyceridaemia. Histological placental examination was normal. A significant increase of the prebeta-lipoprotein concentration in cord blood was observed. This might suggest that lipoprotein cord levels should allow, as in type II hyperlipoproteinemia, the neonatal screening of mothers type V infants.

Adult↗