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J Viña

Publications and source records attributed to J Viña.

At least 73 records · Page 4Linked to original sources
PubMed1985

Gamma-glutamyl-amino acids as signals for the hormonal regulation of amino acid uptake by the mammary gland of the lactating rat.

The mammary gland is a good model to study the hormonal regulation of amino acid uptake. Danazol, which decreases gonadotrophin release, causes a fall in gamma-glutamyltranspeptidase (GGT) and in amino acid uptake by the gland. Treatment of the rats with estrogens and progesterone partially reverts this effect. Treatment with gonadotrophins completely reverts it. gamma-Glutamyl-amino acids (GAA) increase the uptake of amino acids by the mammary gland in rats previously treated with bromocriptine. We suggest that GAA may act as signals to stimulate amino acid uptake and that the role of GGT may be to generate that signal.

Amino Acids↗
PubMed1985

[Quantification of concealed conduction in the atrioventricular node].

Twenty-eight anaesthetized open-chest mongrel dogs were used. Programmed atrial pacing was used and Hisian electrograms recorded through endocavitary electro-catheters to study and quantify the concealed conduction of non-transmitted atrial impulses in the A-V node. An exponential model was used in three situations to quantify the nodal conduction during incremental atrial pacing: a) during 1:1 conduction, b) during 2:1 nodal block, and c) during pacing, coupling an atrial impulse delivered at fixed intervals and blocked in the A-V node to each transmitted impulse. The relation between intranodal conduction times was analyzed both with and without the presence of blocked impulses, and the quotient between the obtained functions in situations b, c and situation a was determined. In a subgroup of 13 dogs the study was repeated following pharmacological block of the autonomic nervous system. In dogs with autonomic block, this relation always tended to decrease when the atrial pacing rate increased. The variations in the group of dogs with intact autonomic nervous systems were not homogeneous. During pacing with coupled block impulses, the progressive removal of conduction curves obtained for each coupling interval with respect to those obtained during 1:1 transmission, expresses the interval with respect ot those obtained during 1:1 transmission, expresses the lesser influence of the blocked impulses on decreasing their coupling interval.

Animals↗
PubMed1983

Effect of starvation and refeeding on amino acid uptake by mammary gland of the lactating rat. Role of ketone bodies.

Arteriovenous differences of amino acids across the mammary glands of lactating rats are diminished when the rats are starved for 24 h. When 24 h-starved rats were refed for 2 1/2 h, the arteriovenous differences of amino acids returned to values similar to those found in well-fed rats. In order to find a possible explanation for these rapid changes, we tested the effect of ketone bodies on amino acid uptake by the gland. At 5 min after injection of acetoacetate to fed rats, when the total concentration of ketone bodies in blood was similar to that found in starvation, the uptake of amino acids by the mammary gland was similar to that found after starvation, i.e. lower than in fed rats. However, 30 min after administration of acetoacetate, when the arterial concentration of ketone bodies had returned to values similar to those in fed rats, the arteriovenous differences of amino acids were similar to those found in fed rats. We conclude that the changes in blood ketone bodies may be responsible, at least in part, for the changes in amino acid uptake that occur in starvation and in the starvation--refeeding transition.

Acetoacetates↗
PubMed1983

Effect of specific inhibition of gamma-glutamyl transpeptidase on amino acid uptake by mammary gland of the lactating rat.

We showed [Biochem. J. (1981) 194, 99-102] that inhibition of gamma-glutamyl transpeptidase in vivo with serine-borate decreases amino acid uptake by mammary gland. However, doubts arose about the validity of this inhibitor in metabolic studies because it must be used in very large amounts. New inhibitors have been isolated, like anthglutin and acivicin, which are effective at low concentrations in vivo. Here, we show that treatment of lactating rats with these substances decreases the transpeptidase activity and the amino acid uptake by the gland. These results support the hypothesis that the gamma-glutamyl cycle functions as an amino acid transport system in mammary gland.

Amino Acids↗
PubMed1983

The effect of cysteine oxidation on isolated hepatocytes.

Isolated hepatocytes incubated with 4mM-cysteine lose reduced glutathione, adenine nucleotides and intracellular enzymes, thus showing extensive membrane damage. The toxic effects of cysteine are enhanced by NH4Cl. Lactate, ethanol and unsaturated fatty acids afford significant protection against cysteine-induced cytoxicity. Addition of catalase to the incubation medium also protected against cysteine toxicity, indicating that H2O2 formed during the oxidation of cysteine is involved in the toxic effects observed. Under anaerobic conditions cysteine did not cause leakage of lactate dehydrogenase from cells, confirming that rapid autoxidation is an essential condition for development of the toxic effects of cysteine.

Adenosine Triphosphate↗
PubMed1983

Effects of cysteine and N-acetyl cysteine on GSH content of brain of adult rats.

Intraperitoneal injections of cysteine or N-acetyl cysteine induce a depletion of reduced glutathione (GSH) in rat brain. The doses required to promote GSH depletion are lower than those reported to cause a disseminate neurodegenerative syndrome. Since physiological GSH concentrations are required to maintain cell membranes, we suggest that consideration of the cysteine-induced GSH depletion is important in attempts to understand the mechanism of cysteine-induced cytotoxicity in brain.

Acetylcysteine↗
PubMed1983

Isocitrate oxidation in dog heart mitochondria under anoxic conditions.

The roles of NAD- Specific Isocitrate Dehydrogenase (NAD- IDH) (EC 1.1.1.4), NADP- Specific Isocitrate Dehydrogenase (NADP- IDH) (EC 1.1.1.42) and Piridin Nucleotide Transhydrogenase (Transhydrogenase) (EC 1.6.1.1) in the mitochondrial oxidation of isocitrate through the respiratory chain in conditions of normal and increased energy requirements have been studied in submitochondrial particles isolated from healthy and ischemic dog hearts. The activities of both, NAD- IDH and NADP- IDH were increased in conditions of anoxia, while Transhydrogenase remained unchanged. The results obtained showed that the mitochondrial oxidation of isocitrate in dog myocardium occurs mainly through the NAD- IDH pathway in normoxic and anoxic conditions.

Animals↗
PubMed1981

Effect of premature weaning on amino acid uptake by the mammary gland of lactating rats.

1. Arteriovenous differences of amino acids across the lactating mammary gland were measured in normal rats and weaned for 4, 5 and 24h. 2. Uptake of amino acids by mammary glands of rats weaned for 5h or more was significantly lower than that of controls. This was not reversed by injection of prolactin. 3. By using 'unilaterally weaned' rats we showed that milk accumulation plays an important role in amino acid uptake by mammary gland. 4. gamma-Glutamyltransferase activity was significantly lower in 'weaned' glands than in 'normal' glands. This provides further support for the hypothesis of the function of the gamma-glutamyl cycle in the mammary gland in vivo.

Amino Acids↗
PubMed1981

Involvement of gamma-glutamyltransferase in amino-acid uptake by the lactating mammary gland of the rat.

1. Arteriovenous differences of amino acids across the lactating mammary gland have been measured in normal rats and in rats injected with serine--borate (an inhibitor of gamma-glutamyltransferase). 2. Comparison of the arteriovenous differences show that gamma-glutamyltransferase is involved in amino-acid uptake by the gland. 3. Reduced-glutathione content of isolated acini incubated with high concentrations of amino acids was lower than that of the controls. 4. High concentrations of amino acids had no effect on reduced-glutathione content of isolated acini when serine--borate was added to the incubation medium. 5. The findings provide evidence for the functioning of the gamma-glutamyl cycle in the lactating mammary gland in vivo.

Amino Acids↗
PubMed1980

Effect of ethanol on glutathione concentration in isolated hepatocytes.

1. Ethanol induces a decrease in GSH (reduced glutathione) concentration is isolated hepatocytes. Maximal effects appear at 20 mM-ethanol. The concentration-dependence of this decrease is paralleled by the concentration-dependence of the activity of alcohol dehydrogenase. 2. Pyrazole, a specific inhibitor of alcohol dehydrogenase, prevents the ethanol-induced GSH depletion. 3. Acetaldehyde, above 0.05 mM, also promotes a decrease in GSH concentration in hepatocytes. 4. Disulfiram (0.05 mM), an inhibitor of aldehyde dehydrogenase, potentiates the fall in GSH concentration caused by acetaldehyde. 5. The findings support the hypothesis that acetaldehyde is responsible for the depletion of GSH induced by ethanol. 6. Methionine prevents the effect of alcohol or acetaldehyde on GSH concentration in hepatocytes.

Acetaldehyde↗
PubMed1979

[Effect of alloxan in pancreatectomized rats (author's transl)].

Sensitivty to alloxan of pancreatectomized rats is studied injecting on the seventh day after surgical resection with different dose of monohydrated alloxan. Totally pancreatectomized rats develop a strong diabetes just the same as the control group, but the former present higher glycemias and longer survival.

Alloxan↗
PubMed1978

Maintenance of glutathione content is isolated hepatocyctes.

1. During the standard procedure for the preparation of rat hepatocytes, about half of the cellular GSH (reduced glutathione) is lost. 2. This loss is prevented by the addition of 0.1 mM-EGTA (but no EDTA) to the perfusion medium. 3. On incubation with and without EGTA, isolated hepatocytes prepared in the presence of EGTA lose GSH. This loss is prevented by near-physiological concentrations of methionine or homocysteine, but not of cysteine. 4. Cysteine, at concentrations above 0.2 mM, causes a loss of GSH probably by non-enzymic formation of a mixed disulphide. 5. Serine together with methionine or homocystein increases GSH above the value in cells from starved rats in vivo. This is taken to suggest that cystathionine may be a cysteine donor in the synthesis of gamma-glutamylcysteine, the precursor of GSH.

Animals↗
PubMed1978

[Effect of insulin on germination and ionic exchange in Raphanus sativus (author's transl)].

Hypoglycemic sulfamide BZ-55 activates or inhibits germination of Raphanus sativus, depending upon the dosis. Since this drug acts upon the glycemia by increasing the secretion and action of insulin, the influence of this hormone on germination and ionic changes (Na+-K+) between seeds and culture medium, were studied. Seeds were incubated during 72 h with different concentrations of insulin in 10 ml deionized water or in 10 ml 18 mM K+ (KCl) solutions at 37 degrees C in vapor saturated atmosphere. A solution of 0.125 IU insulin/ml in water increases the germination to 110% whereas 0.175 IU insulin/ml inhibits it to 40% against controls. Further increases in insulin concentration always inhibit germination. Similar results have been obtained with K+ containing media. Germination rate changes in a small concentration range suggest that insulin might affect an enzymatic activity in the seed.

Blood Glucose↗