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J C Meunier

Publications and source records attributed to J C Meunier.

At least 127 records · Page 7Linked to original sources
PubMed1981

Plasma and urinary cortisol levels after dexamethasone in affective disorders.

The validity of the dexamethasone suppression test was evaluated for the differential diagnosis of primary and secondary depressions. Forty hospitalized psychiatric patients (14 primary depressed, 15 secondary depressed and 11 non-depressed controls) were studied. The Research Diagnostic Criteria of Spitzer et al. (1978) were used to classify these patients. Eight out of the 14 primary depressed patients had an abnormally high plasma cortisol at 4 p.m. after dexamethasone. Only 2 out of the 15 secondary depressed patients and none of the 11 controls had an abnormal response to dexamethasone. Based on these results, the dexamethasone suppression test has a sensitivity of 57%, a specificity of 87% and a predictive value of 80%. The determination of urinary free cortisol excretion does not improve the performance of the test.

Adult↗
PubMed1981

On the activation of fructose-1,6-bisphosphatase of spinach chloroplasts and the regulation of the Calvin cycle.

Activation by light of spinach fructose-1,6-bisphosphatase is mimicked by dithiothreitol. This process of activation by dithiothreitol implies the specific reduction of two disulfide bridges and a conformation change of the enzyme that makes eight sulfhydryl groups available. The activated enzyme has an apparent allosteric kinetic behavior with respect to both fructose 1,6-bisphosphate and magnesium.

Binding Sites↗
PubMed1981

Substrate-binding isotherms of spinach chloroplastic fructose-1,6-bisphosphatase and the photoregulation of the Calvin cycle.

Fluorescence titration experiments of chloroplastic fructose-1,6-bisphosphatase by fructose bisphosphate and magnesium have been effected using the inactive dimeric, the inactive tetrameric and the active tetrameric enzyme forms. Magnesium binding to the inactive dimeric enzyme exhibits a positive cooperativity whereas fructose 1,6-bisphosphate exhibits no cooperativity at all. The binding of either magnesium or fructose bisphosphate to the inactive oxidized tetramer exhibits a succession of negative and positive cooperativities (mixed cooperativity). Upon reduction of the inactive tetramer by dithiothreitol and activation, the ligand binding properties of the enzyme are changed. Magnesium and fructose bisphosphate are bound to the active enzyme with a positive cooperativity. Non-linear least-square fitting allows one to estimate thea binding constants, and therefore the free energy of binding of either magnesium or fructose bisphosphate to the various forms of the enzyme. Whatever the state of fructose-1,6-bisphosphatase, one ligand is bound per subunit. The affinity constants of magnesium for the active or inactive enzyme forms are much greater than those of fructose bisphosphate. This suggests that the metal ion gives to the enzyme the right conformation to bind the sugar phosphate.

Binding Sites↗
PubMed1980

Opiate receptor sites in the rabbit cerebellum: autoradiographic distribution.

The distribution of the [3H] diprenorphine binding sites in the rabbit cerebellum has been analyzed after specific labelling of tissue slices in vitro followed by autoradiographic processing. High, moderate and very low silver grain densities were observed over the molecular, granular and white layers, respectively. Within each layer, the distribution of the autoradiographic grain exhibited no evident patterning. Therefore, further work using complementary techniques is needed to determine the precise location of the opiate receptor sites in the rabbit cerebellum.

Animals↗
PubMed1979

Cerebellar opiate receptors in lagomorphs. Demonstration, characterization and regional distribution.

The cerebellum of lagomorphs (pika, rabbit, hare) binds 100--200 femtomoles of [3H]etorphine per milligram of protein. This is very high in comparison with the 10--15 fmol/mg found in the cerebellum of rodents (mouse, hamster, rat). In the rabbit cerebellum, the etorphine sites have binding properties indistinguishable from those of genuine opiate receptor sites in brain. They exhibit a high affinity for [3H]etorphine (KD = 1 X 10(-10) M), [3H]naloxone (KD = 9 X 10(-10) M), morphine and levorphanol but not for dextrophan. Moreover, sodium ions enhance binding of naloxone (antagonist response) and diminish binding of etorphine, morphine and levorphanol (agonist response) to cerebellum homogenates. The regional distribution of [3H]etorphine binding sites in the rabbit cerebellum points toward concentrations higher in the neocerebellum (hemispheres) than in the archecerebellum (lingula and flocculonodular lobe). Finally, the specific concentration of opiate receptor sites in the isolated molecular layer is at least two times that in the isolated granular layer and ten times that in white matter.

Animals↗
PubMed1979

The natural tolerance of the afghan pika (Ochotona rufescens) to morphine.

A lagomorph, the afghan pika, Ochotona rufescens showed no effect whatever following the subcutaneous injection of morphine in doses up to 50 mg per 100 g of body weight, i.e. 250 times the ED50 for the rat. Higher doses were toxic and induced convulsions. However, the pika is responsive to synthetic opiates such as etorphine, pentazocine and phenoperidine. Interestingly enough, morphine antagonized the opiate response elicited by those narcotics to which the animal is sensitive. Pharmacokinetic analysis demonstrated that morphine enters the pika's brain as readily as it does the rat's. In addition, opiate receptor sites, which are present in normal amounts in pika brain retained their high affinity for 3H-etorphine (KD = 0.3 nM), 3H-naloxone (KD = 1.2 nM) and morphine. Moreover, binding of morphine to pika brain homogenates was inhibited in the presence of sodium ions (agonist response). Therefore, the antagonism of phenoperidine action by morphine appeared not to occur at the opiate receptor site; the mechanism of the pika's natural tolerance to morphine may reside in molecular events that normally preceed (metabolism?) or follow (enzyme activation?) the interaction between the drug and its specific recognition sites.

Animals↗
PubMed1979

Enzyme memory. Effect of glucose 6-phosphate and temperature on the molecular transition of wheat-germ hexokinase LI.

A theory is presented that associates burst (orlag) kinetics with the respective concentrations of enzyme initial states X1 and X6 and with the cooperation of a mnemonical enzyme. The theory predicts that for an enzyme with a negative cooperation, decreasing the initial concentration of X1 (or increasing that of X6) tends to increase the induction time. This increase may correspond to a reversal of a burst in a lag. Similarly, if the enzyme has a positive cooperation, decreasing the initial concentration of X6 (or increasing that of X1) increases the induction time. The first case above is expected to apply to wheat germ hexokinase LI, X1 being the form that binds glucose preferentially, and X6 the one that binds glucose 6-phosphate. By changing solely the respective concentrations of the two initial forms, one may expect to modify the pre-steady-state phase but not the steady-state kinetics of the reaction. By jumping the temperature of the enzyme solution from 4 degrees C to 30 degrees C and letting the transconformation ewuilibrium relax for various periods of time before mixing enzyme with the substrates, one can analyse the effect of the relative concentrations of X1 and X6 on the induction time. One can estimate in that way one of the rate constants of the transconformation between the two free enzyme forms. The shorter the incubation time at 30 degrees C then the smaller is the negative induction time (in absolute values). Another possibility of controlling the ratio between the two initial concentrations of the enzyme, is to pre-mix hexokinase with glucose 6-phosphate and to arrange that glucose-6-phosphate concentration, after mixing enzyme and substrates, is held constant whatever the pre-mixing conditions. When wheat germ hexokinase LI is pre-mixed 30 min at 30 degrees C with glucose 6-phosphate before the reaction starts, the burst does not disappear. If, on the other hand, pre-mixing is effected at 4 degrees C the burst is reversed into lag. This result is taken to mean that the equilibrium constant between the two free enzyme forms (the 'circle' and the 'rhombus') is strongly dependent on temperature. A direct study of the effect of glucose 6-phosphate on the conformational equilibrium of wheat germ hexokinase, gives support to this interpretation. If hexokinase is mixed at 4 degrees C with glucose 6-phosphate a slow increase in fluorescence of tryptophanyl residues is observed, which indicates that the 'rhombus' conformation accumulates under these conditions. On the other hand, at 30 degrees C, glucose 6-phosphate does not produce any significant change in the fluorescence of the protein. As expected, these results imply that the equilibrium between the two free enzymes species is freely reversible a 4 degrees C and nearly irreversible at 30 degrees C. The equations derived from the mnemonical model allow fitting or simulation of the experimental results.

Enzyme Induction↗
PubMed1979

The usefulness of a rapid method for total fast hemoglobins determination in screening for diabetes control.

We have used a simple and rapid method for the determination of total fast hemoglobins (HbA1a+b+c) in 102 diabetics and 36 normal controls. The method was described by Kynoch and marketed by Isolab. It proved to be useful in screening for patients with inadequate metabolic control in whom as a rule, total fast Hb values were higher than 8.5%. Mean Hb A1a+b+c value was significantly higher in the group of diabetics in comparison with normals (9.9 +/- 0.2 versus 6.9 +/- 0.8%). The diabetic patients were separated into four groups according to predetermined criteria of recent metabolic control. Even the patients considered to have a very good diabetes control during the past eight weeks, had supranormal total fast Hb values (7.7 +/- 0.2%). In the patients with good, poor and bad diabetes control, mean total fast Hb levels were respectively 9.3 +/- 0.3, 10.1 +/- 0.3 and 12.5 +/- 0.4%. In normals, there was a positive correlation between individual fasting blood glucose and total fast Hb values and in diabetics, mean blood glucose values correlated with total fast Hb levels. Hb A1a+b+c determinations also correlated with triglyceride values. We could find no significant association between high total fast Hb levels (greater than 8.5%) and the prevalence of retinopathy.

Blood Glucose↗