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Biomedical subjects

D Robin

Publications and source records attributed to D Robin.

At least 37 records · Page 2Linked to original sources
PubMed1994

Stimulation of phosphoenolpyruvate carboxykinase gene expression by fatty acids.

We used the 3T3-F442A adipocytes and the FAO hepatoma cells to analyze the effect of oleate on phosphoenolpyruvate carboxykinase (PEPCK) gene expression. In serum-deprived, glucose-free medium, 1 mM oleate, bound to albumin in a 6:1 ratio, specifically stimulated PEPCK mRNA. In 3T3-F442A adipocytes, the maximum 5-fold increase occurred in 4 hours then rapidly declined to reach the basal level 20 hours later. This increase was cycloheximide-independent and actinomycin D-dependent, suggesting a direct, transcriptional effect of oleate. FAO cells also responded to oleate with a transient induction of PEPCK mRNA, although the extent of stimulation was lower. Thus, the PEPCK gene provides a useful molecular tool for studying the mechanisms by which fatty acids stimulate gene expression.

3T3 Cells↗
PubMed1994

Glucocorticoids antagonize retinoic acid stimulation of PEPCK gene transcription in 3T3-F442A adipocytes.

Cytosolic phosphoenolpyruvate carboxykinase (GTP) (PEPCK) is a key glyceroneogenic enzyme in adipose tissue. The regulation of PEPCK gene expression by retinoic acid (RA) and dexamethasone (DEX) was studied in 3T3-F442A adipocytes maintained in a serum-free medium. RA induced whereas DEX reduced PEPCK mRNA steady-state level. RA stimulation was about 4-fold and DEX repression was of 80% in 4 hrs. In addition to reducing basal mRNA level, DEX was able to counteract RA induction in a dominant manner. The use of the glucocorticoid antagonist RU 38486 indicated that the DEX effect was mediated by the glucocorticoid receptor. Stable transfectants bearing the region of the PEPCK promoter from -2100 to +69 fused to the chloramphenicol acetyltransferase (CAT) gene (pPL1-CAT) were used to study PEPCK gene regulation in differentiated adipocytes. In such cells, RA stimulated CAT expression 3 to 5.5 fold. DEX had no effect on basal CAT activity whereas it inhibited the stimulation induced by RA. Thus, in adipocytes, the PEPCK gene regulatory region between -2100 and +69 bp mediates both stimulation by RA and repression by DEX of RA action.

3T3 Cells↗
PubMed1993

A top-down control analysis in isolated rat liver mitochondria: can the 3-hydroxy-3-methylglutaryl-CoA pathway be rate-controlling for ketogenesis?

We incubated isolated liver mitochondria with palmitoyl-CoA, 2,4-dinitrophenol and malonate. Under these conditions all the flux of carbon from palmitoyl-CoA was directed towards acetoacetate synthesis. We measured the rate of acetyl-CoA formation from palmitoyl-CoA (by measuring the rate of oxygen consumption) and the rate of acetoacetate production from acetyl-CoA at three different acetyl-CoA/CoA ratios. Using the top-down approach of metabolic control analysis we calculated the control over ketogenesis exerted by (a) the conversion of extramitochondrial palmitoyl-CoA to intramitochondrial acetyl-CoA and by (b) the conversion of acetyl-CoA to acetoacetate (the 'HMG-CoA pathway'). The overall flux control coefficients of the groups of enzymes involved in (a) and (b) over ketogenesis were 0.28 and 0.72, respectively. Our results show that it is possible for significant control to be exerted over ketogenesis by the enzymes of the HMG-CoA pathway.

Acetoacetates↗
PubMed1993

Glucose and pyruvate metabolism in preimplantation blastocysts from normal and diabetic rats.

Glucose metabolism was analysed in day-5 rat blastocysts incubated in the presence of [5-3H]-, [6-14C]- or [U-14C]glucose. Glycolysis, quantified by 3H2O recovery rate, was the main pathway of glucose utilization by fresh (11.5 +/- 0.36 pmol per embryo h-1) or cultured (24 h) blastocysts (20.4 +/- 0.6 pmol per embryo h-1). Glucose consumption rate was almost saturated at a medium glucose concentration of 0.28 mmol l-1 (Km: 0.17 mmol l-1; Vmax: 23 pmol per embryo h-1). A further 10% increase in glucose utilization was obtained with a tenfold higher glucose concentration (3 mmol l-1). Phloretin completely abolished the rapid component of glucose utilization kinetics, suggesting the existence of a Na(+)-independent glucose transport system. Less than 1% of [6-14C]glucose consumed by cultured blastocysts was oxidized through the Krebs cycle. [1-14C]pyruvate, however, was oxidized at a rate of 2 pmol per embryo h-1 by fresh blastocysts. The pentose-phosphate pathway accounted for about 2% of glucose utilization. One to two per cent of the total glucose metabolized in 24 h was retained in macromolecules. Insulin had no effect on glucose uptake, utilization, incorporation and turnover, or on pyruvate oxidation. Blastocysts from diabetic mothers utilized glucose at a rate similar to that of normal blastocysts. These results show that glucose is actively taken up by rat blastocysts and utilized mainly through the Embden-Meyerhof pathway, which is rapidly saturated at low glucose concentrations. Retention of glucose-derived products in macromolecules, although relatively small, may modulate the effect of high glucose concentrations on embryo growth.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

Maternal insulin treatment improves pre-implantation embryo development in diabetic rats.

Pre-implantation embryos were recovered from control, diabetic and insulin-treated diabetic rats on day 5 of pregnancy. Compared to control animals, diabetic rats had a 20% reduction in the number of embryos per rat and blastocysts recovered from diabetic rats showed a 19% decrease in total cell number. The cellular decrease observed in blastocysts was mainly at the expense of the inner cell mass. Insulin replacement therapy was started on day 1 of pregnancy and normalized the glycaemia of diabetic rats but failed to raise the number of embryos per rat toward the control value. Insulin treatment, however, fully restored the normal cell number in both the inner cell mass and trophectoderm of blastocysts. The dead cell index, which was significantly elevated in the inner cell mass of blastocysts from diabetic rats, also returned to the control value following insulin treatment. Our data suggest that diabetes-induced impairment of pre-implantation development can be partly prevented by insulin treatment started shortly after conception.

Animals↗
PubMed1991

Control of hepatic mitochondrial 3-hydroxy-3-methylglutaryl-CoA synthase during the foetal/neonatal transition, suckling and weaning in the rat.

(1) We assayed active and total (i.e. active plus succinylated) 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) synthase in mitochondria isolated from foetal, neonatal, suckling or weaned rats. (2) HMG-CoA synthase was substantially succinylated and inactivated in mitochondria isolated from term-foetal, (1-h-old, 6-h-old, 1-day-old) neonatal, suckling and high carbohydrate/low-fat (hc)-weaned rats. Succinylation of HMG-CoA synthase was very low in mitochondria isolated from the livers of foetal, 30-min-old neonatal and high-fat/carbohydrate-free (hf)-weaned rats. (3) There was a negative correlation between active HMG-CoA synthase and succinyl-CoA content in mitochondria isolated from term-foetal, suckling and hc-weaned rats. (4) Differences in active enzyme could not be entirely accounted for by differences in succinylation and inactivation of the synthase. Immunoassay confirmed that the absolute amounts of mitochondrial HMG-CoA synthase increased during the foetal/neonatal transition and decreased with hc weaning. The levels remained elevated with hf weaning. (5) From these data we propose that mitochondrial HMG-CoA synthase is controlled by two different mechanisms in young rats. Regulation by succinylation provides a mechanism for rapid modification of existing enzyme in response to changing metabolic states. Changes in the absolute amounts of HMG-CoA synthase provide a more long-term control in response to nutritional changes.

Acyl Coenzyme A↗
PubMed1991

Effect of insulin on the properties of liver carnitine palmitoyltransferase in the starved rat: assessment by the euglycemic hyperinsulinemic clamp.

The effect of insulin on the properties of liver carnitine palmitoyltransferase I (CPT I) was assessed in conscious starved rats with the euglycemic hyperinsulinemic clamp. A 24-hour clamp was necessary to fully reverse the effect of starvation on liver malonyl-CoA concentration, CPT I maximal activity, and apparent km and Ki for malonyl-CoA. Since glucagon was not decreased during the clamp, insulin is the major factor involved in the regulation of CPT I.

Animals↗
PubMed1991

Stimulatory and inhibitory effects of glucose and insulin on rat blastocyst development in vitro.

The effect of glucose and insulin on the in vitro development of the rat preimplantation embryo was studied by incubating rat blastocysts recovered on days 5 or 6 of pregnancy in the absence or presence of increasing levels of glucose and/or insulin for 24 or 48 h. A differential cell-staining method allowed the separate counting of inner cell mass (ICM) and trophectoderm (TE) cells at the end of the incubation period. In a high-glucose medium (17 mM), ICM and, to a lesser extent, TE developments were significantly and irreversibly inhibited. Low insulin concentrations (3 pM) stimulated ICM and TE development in the presence of 1.1 or 6 mM glucose. Higher insulin levels (30-600 pM) in a 6-mM glucose medium, resulted in a dose-dependent inhibition of ICM and, to a lesser extent, TE development after both 24 and 48 h. This insulin-induced inhibition was reversible if insulin was removed from the medium after 24 h. In the absence of glucose in the medium, insulin was neither stimulatory nor inhibitory on ICM growth. Dead-cell occurrence in ICM after a 48-h incubation increased with increasing glucose concentration in the medium. Insulin alone did not increase dead-cell number but enhanced the effect of glucose. These results show that, in the presence of glucose, insulin might be stimulatory (at low concentrations) or inhibitory (at higher concentrations) on ICM development. A high glucose level was also inhibitory and increased dead-cell occurrence. The data suggest that insulin and glucose might interact and modulate blastocyst development as a function of their respective concentrations.

Animals↗
PubMed1990

[An overview of psychogenic sterility].

The authors remind of the difficulty in defining psychogenic sterilities and evaluating their exact frequency. Then, they attempt to offer a classification based on clinical examples. Secondary sterilities of psychogenic origin are only seen in women who have lost a child in the pre, per or post-partum period. This is even a characteristic example of non organic sterility. Primary sterilities may be psychological in origin, especially by absence of maturation of the child planning project (case of sterilities cured after adoption). They are seen more infrequently: in adult anorexia nervosa, psychological sexual differentiation disorders, masculine women. These difficulties are not easy to approach as much as psychological and organic factors may be entangled. In addition, one question is raised: who should take care of it? The psychiatrist or the gynecologist? Overall, the latter is preferable under the condition that he/she is properly trained. Anyway, it is ultimately the woman's choice.

Adult↗
PubMed1988

Intramitochondrial factors controlling hepatic fatty acid oxidation at weaning in the rat.

Fatty acid oxidation was studied in isolated liver mitochondria of rats during the suckling-weaning transition. The oxidation rate of oleyl-CoA and palmitoylcarnitine was reduced 2.5-fold in rats weaned on a high-carbohydrate diet compared to suckling rats, when acetyl-CoA produced by beta-oxidation was directed towards ketone-body synthesis. Weaning on a high-fat diet minimized this change. Channeling of acetyl-CoA towards citrate synthesis doubled the oxidation rate of both substrates in HC-weaned rats. Thus, in addition to changes in carnitine palmitoyltransferase I activity, the beta-hydroxymethylglutaryl-CoA synthase pathway is also involved in the decreased fatty acid oxidation at weaning. This was confirmed by measurement of beta-hydroxymethylglutaryl-CoA synthase pathway activity.

Acetyl Coenzyme A↗
PubMed1988

Decreased hepatic fatty acid oxidation at weaning in the rat is not linked to a variation of malonyl-CoA concentration.

In rats weaned on a high-carbohydrate diet, hepatic fatty acid oxidation capacity is decreased when compared to suckling rats. Previous studies (Benito et al., 1979) suggested that a malonyl-CoA-dependent mechanism could be at the origin of this decrease. Studies on isolated hepatocytes show that despite, respectively, a low and a high lipogenic rate in suckling and weaned rats, malonyl-CoA concentrations are similar in the two groups. This might be due to the lower ratio fatty acid synthetase/acetyl-CoA carboxylase (EC 6.4.1.2) activities during suckling than after weaning. Different rates of hepatic fatty acid oxidation despite similar malonyl-CoA concentrations can be explained by the 2.5-fold higher carnitine palmitoyltransferase I (EC 2.3.1.21) activity in suckling rats together with a 7-fold higher Ki for malonyl-CoA. This precludes a tight control of fatty acid oxidation by [malonyl-CoA] in suckling rats. Weaning on a high-fat carbohydrate-free diet abolishes the changes previously described for the kinetic characteristics of carnitine palmitoyltransferase I suggesting that nutritional modifications rather than a developmental stage are involved. Thus, during the suckling-weaning transition, a variation of [malonyl-CoA] is not responsible for the decrease in hepatic fatty acid oxidation. It involves, in addition, a decrease in carnitine palmitoyltransferase I activity and an increase of the sensitivity of this enzyme to malonyl-CoA.

ATP Citrate (pro-S)-Lyase↗
PubMed1986

Evidence that the development of hepatic fatty acid oxidation at birth in the rat is concomitant with an increased intramitochondrial CoA concentration.

The development of hepatic fatty acid oxidation during the perinatal period in the rat was studied using isolated mitochondria. Ketone body synthesis from substrates entering at different levels of beta-oxidation was 2-3 times lower in mitochondria isolated from term-fetal liver than in 16-h-old newborn or adult liver mitochondria. The low rate of palmitoyl-L-carnitine oxidation in term-fetal mitochondria was linked neither to the low capacity of the respiratory chain nor to the removal of acetyl-CoA in the hydroxymethylglutaryl-CoA synthase pathway. The 2.5-times lower concentration of CoA found in term-fetal liver mitochondria when compared to 16-h-old or adult liver mitochondria might be the factor responsible for the low rate of fatty acid oxidation in term-fetal liver mitochondria.

2,4-Dinitrophenol↗
PubMed1981

Quantitative and qualitative circadian variations of amino acid intestinal efflux in mixed-fed and in protein-meal-fed rats.

The magnitude and composition of amino acid intestinal efflux was followed over a light-dark cycle in rats ingesting the same daily amount of protein administered either in a mixed diet (12% casein) or as a separate meal (70% casein concentrate) fed 2 hours after the onset of the light period with a protein-free diet available at all times. Intestinal efflux was determined by an instant porto-aortic difference measured on pooled samples from six rats at time-points spaced every 3 hours over a light-dark cycle. During protein digestion (dark for the mixed-fed rats) and (light for the separately-fed ones), essential amino acid composition of intestinal output fell into line with that of the protein ingested (casein) while non-essential amino acid composition did not. The discrepancy bore on alanine and glycine which were released in excess and on aspartic and glutamic acids, glutamine and serine which were released in deficit from their content in casein. From the follow-up of individual amino acid release and uptake, we concluded that intestinal efflux reflects the composition of the dietary protein only with respect to the amino acids, mostly essential, that are not metabolized by the intestinal wall.

Amino Acids↗
PubMed1981

Circadian variations of liver free amino acid content in mixed-fed and protein-meal-fed rats.

Hepatic amino acid contents were determined at time-points regularly spaced over a light-dark cycle in rats fed either a 12% casein diet or a single daily meal given 2 hours after the onset of the light phase with a protein-free diet and libitum. In mixed-fed rats, non-essential amino acid hepatic content remained stable over 24 hours while that of essential amino acids rose during the early part of the night in connection with the onset of prandial activity, but long before portal levels increased. The possibility of factors related to food intake (insulin, glucagon, gastrointestinal hormones) or to its chronology (corticoids) stimulating active transport is discussed. In separately-fed rats, amino acid pools increased in the 30 minutes following protein administration in connection with rising portal levels. During the rest of the light phase, a general depletion of non-essential amino acids occurred. It was most rapid for glutamine, alanine and aspartic acid and was followed by accumulation during the night phase, a pattern fitting well with gluconeogenesis and ureogenesis stimulation following protein ingestion. Essential amino acid decrease was linear and spanned over both the light and dark phases in correlation with decreasing portal levels.

Amino Acids↗
PubMed1979

A physiological profile of Canadian Greco-Roman wrestlers.

The sport of Greco-Roman wrestling is relatively new in North America. However, this is the national sport of seven European countries and a great deal of research literature is available. The purpose of the present investigation was to establish baseline data for Canadian Greco-Roman wrestlers for a data bank which can be used to compare with World Class wrestlers. The results indicate that the Canadian National Team is made up of athletes with only average values for the physiological measures taken. However, the correlation between wrestling success and the physiological parameters measured is 0.91.

Adult↗