L Picon

French National Centre for Scientific Research, Lutetia Parisorum, Île-de-France, France

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Publications (63)231.61 Total impact

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    ABSTRACT: 1. In oxidative (soleus) and glycolytic (extensor digitorum longus) muscles of obese Zucker rats, a significant decrease in the percentage of relative area occupied by glycolytic fibers was observed. 2. The activity of citrate synthase and beta-hydroxy-acyl-CoA-dehydrogenase was significantly higher in muscles of obese than of lean Zucker rats. 3. In rats, 6 weeks after lesion of the ventromedial hypothalamus, no changes were observed. 4. This indicates that neither the proportion of oxidative fibers, nor the oxidative capacities are decreased in skeletal muscles of obese rats suggesting that insulin resistance cannot be ascribed to a higher glycolytic-oxidative fiber ratio.
    Comparative biochemistry and physiology. B, Comparative biochemistry 11/1993; 106(2):269-72. · 2.07 Impact Factor
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    ABSTRACT: The present study was carried out to determine whether genetically obese Zucker rats present changes in brain glucose utilization and/or insulin binding when compared to their lean counterparts. Glucose utilization in the whole brain, determined by measurement of 2-deoxy(1-3H)glucose-6-phosphate, was significantly lower in obese than in lean Zucker rats. In order to precise the structure involved, we then used quantitative autoradiography methods after either (1-14C) 2-deoxyglucose injection or 125I-insulin incubation. In obese rats, local cerebral glucose utilization (LCGU) was significantly decreased in the external plexiform layer (-37%, p < 0.05), in the lateral hypothalamus (-23%, p < 0.05), and in the basolateral amygdaloid nucleus (-30%, p < 0.05). In contrast, no difference in specific insulin binding was found between the two genotypes in any of the areas studied. These results are consistent with some data showing a decrease of LCGU in hyperinsulinemic rats. All together, these data show perturbations of glucose utilization, particularly in structures linked to the regulation of body weight and food intake in obese Zucker rats.
    Physiology & Behavior 10/1992; 52(4):713-6. · 3.16 Impact Factor
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    ABSTRACT: Hyperinsulinemia, a main feature of both human and animal obesity, has been demonstrated to be due to both an increased sensitivity to nutrient secretagogues and an impairment of the nervous regulation of insulin secretion. Recent studies have shown that pancreatic islet blood flow increases under conditions associated with an enhanced insulin secretion. The aim of this study was to determine whether or not changes in islet blood flow are present in hyperinsulinemic obese rats. Using the nonradioactive microsphere technique, we were able to show a significantly higher islet blood flow in obese rats either of the Zucker strain or Wistar rats after lesion of the ventromedial hypothalamus than in their respective lean controls. Subdiaphragmatic vagotomy had no significant effect on basal islet blood flow of lean rats, whereas it decreased significantly that of obese Zucker rats. Conversely, clonidine, an alpha 2-adrenergic agonist, induced a higher decrease of islet blood flow in obese than in lean Zucker rats. The injection of an intravenous bolus of glucose (375 mg/kg iv) increased significantly more islet blood flow in obese than in lean Zucker rats. It is concluded that obese rats present an increased pancreatic islet blood flow, which may result, at least in part, from exaggerated parasympathetic activity and lower than normal sympathetic activity. This could participate in the hyperinsulinemia observed in these rats.
    The American journal of physiology 06/1992; 262(5 Pt 1):E736-40. · 3.28 Impact Factor
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    ABSTRACT: The objective of our study was to investigate the effect of hyperinsulinemia associated with either euglycemia, hypoglycemia, or hyperglycemia on the short-term mitotic activity of arterial smooth muscle cells (SMCs) after aortic injury. The proliferative reaction of arterial SMCs was provoked by the passage of an embolectomy catheter with a tightly inflated balloon. DNA synthesis was measured as DNA specific activity after incubation of the aorta in a medium containing 3[H]thymidine. Unrestrained rats were rendered hyperinsulinemic (4-7 nM versus 0.3 nM in controls) immediately after aortic injury by insulin infusion (10 units/day) and either euglycemic (about 5.6 mM), hyperglycemic (14-17 mM), or hypoglycemic (about 2.8 mM) by adjusting the flow rate of hypertonic glucose (30% wt/vol) that was infused simultaneously. The infusion was performed via a catheter inserted into the jugular vein and lasted 2 or 4 days after the aortic injury. After the injury, SMC mitotic activity was dramatically increased on day 2 in control rats with deendothelialized aortas and declined between days 2 and 4. In euglycemic-hyperinsulinemic and hyperglycemic-hyperinsulinemic rats, SMC proliferation showed the same pattern as in controls. At no time was a significant difference observed among the three groups of rats. In hypoglycemic-hyperinsulinemic rats, SMC mitotic activity increased to a lesser extent than in controls on day 2 after deendothelialization. These data indicate that hyperinsulinemia with or without hyperglycemia does not stimulate the early stages of arterial SMC proliferation in the rat although a long-lasting effect of hyperinsulinemia cannot be excluded.(ABSTRACT TRUNCATED AT 250 WORDS)
    Arteriosclerosis and thrombosis: a journal of vascular biology / American Heart Association 06/1992; 12(5):633-8.
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    ABSTRACT: Early after lesion of the ventromedial hypothalamus nuclei (VMH), insulin-induced glucose utilization is increased in white adipose tissue (WAT), whereas oxidative and glycolytic muscles are, respectively, normoresponsive or resistant to insulin. Five weeks later, all of the muscles are resistant, whereas WAT returns to normal responsiveness. The aim of this study was to characterize the insulin receptor kinase activity in WAT and muscles 1 and 6 wk after lesion. The number and affinity of insulin receptors were not modified in any of the tissues studied. Autophosphorylation and phosphorylation of an exogenous substrate were similar in oxidative and glycolytic muscles of VMH and control rats both 1 and 6 wk after the lesion. Insulin receptors from WAT of 1-wk VMH rats exhibited a 2.5-fold increase in insulin-stimulated autophosphorylation and phosphorylation. Six weeks after the lesion, both autophosphorylation and phosphorylation returned to normal values. This suggests that insulin receptor tyrosine kinase activity does not play a significant role in the insulin resistance of skeletal muscles but has a crucial role in mediating the variations of insulin action on WAT observed during the development of VMH obesity.
    The American journal of physiology 03/1992; 262(2 Pt 1):E161-6. · 3.28 Impact Factor
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    ABSTRACT: We investigated the effects of intrauterine mild hyperglycemia during late fetal life on glucose regulation and insulin secretion in adult rats. Unrestrained pregnant rats were continuously infused with glucose during the last week of pregnancy to induce mild hyperglycemia (6.5-8 mM). Control rats were infused with a glucose-free solution. The offspring were studied, as adults, from 1 to 20 mo by performing glucose tolerance and insulin secretion tests. Young-adult rats from hyperglycemic dams showed mild glucose intolerance and impairment of glucose-induced insulin secretion. This situation gradually evolved to basal hyperglycemia and severe impairment of glucose tolerance and insulin secretion. Insulin secretion was also studied in vitro in 20-mo-old rats with the isolated perfused-pancreas technique. Insulin release in response to glucose stimulation from pancreases of hyperglycemic dams was similar to that of controls, and the response to arginine was increased but not significantly. The possible involvement of enhanced sympathetic nervous system activity in the impairment of insulin secretion in adult rats from hyperglycemic mothers was then investigated by performing glucose tolerance and insulin secretion tests in the presence of the alpha 2-blocker idazoxan in 8-mo-old rats. Under these conditions, rats from hyperglycemic dams recovered almost normal glucose tolerance, and glucose-induced insulin secretion was greatly improved. These data show that mild hyperglycemia induced in the fetus during late pregnancy leads to persistent impairment of glucose regulation and insulin secretion. They suggest that the impairment of insulin secretion in vivo results from a perturbation of the neuroregulation of insulin secretion rather than an intrinsic pancreatic beta-cell defect.
    Diabetes 01/1992; 40 Suppl 2:109-14. · 7.90 Impact Factor
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    ABSTRACT: The insulin secretion rate in response to different secretagogues and neurotransmittors was studied in perifused pancreas of 5-day-old lean (Fa/Fa) and preobese (fa/fa) Zucker rats. Glucose (16.6 mM) alone or in combination with 20 mM arginine or 5 mM theophylline induced a net stimulation of insulin secretion. This effect was similar in the two groups. By contrast, the stimulatory effect of acetylcholine on glucose-induced insulin secretion was significantly higher in preobese pups than in lean rats. There was also a tendency toward a higher inhibitory effect of norepinephrine on insulin secretion in preobese than in lean rats, but this difference did not reach statistical significance. Together these results demonstrate a normal insulin secretion in response to nutrient secretagogues in preobese fa/fa rats but an enhanced effect of acetylcholine. This latter effect may be related to the changes in the autonomic nervous system activity, which is usually described in obese fa/fa rats.
    Endocrinology 11/1991; 129(4):2219-24. · 4.72 Impact Factor
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    ABSTRACT: Previous experiments have shown that insulin-induced glucose utilization is increased in white adipose tissue of young obese Zucker rats. We have investigated the possible role of over-expression of the muscle/fat glucose transporter (Glut 4) and key lipogenic enzymes in this increased insulin-responsiveness. The amount or activity and the mRNA concentrations of Glut 4, fatty acid synthase (FAS) and acetyl-CoA carboxylase (ACC) were measured before and after weaning in white adipose tissue of obese and lean Zucker rats. Comparison of the levels of Glut 4 and lipogenic-enzyme expression in 15-day-old suckling and 30-day-old weaned rats on a high-carbohydrate diet shows a marked increase in the latter group. The increase was, in lean and obese rats respectively, 6- and 7-fold for the amount of Glut 4 and 2- and 3-fold for its mRNA concentrations, 40- and 100-fold for the activity of lipogenic enzymes (FAS and ACC) and 30- and 10-fold for their mRNA concentrations. Furthermore, all these parameters, except the amount of Glut 4, were 2-5-fold higher in obese rats, both before and after weaning. Changes at weaning were largely blunted when rats were weaned on to a high-fat diet, although the differences between lean and obese rats persisted, and even became significant for the amount of Glut 4. Whatever the experimental conditions, plasma insulin levels were significantly higher in obese than in lean rats. These results indicate the existence of an enhanced expression of Glut 4, FAS and ACC in white adipose tissue of young obese fa/fa rats which could be related to the increased plasma insulin levels.
    Biochemical Journal 11/1991; 279 ( Pt 1):303-8. · 4.65 Impact Factor
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    ABSTRACT: 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.
    Metabolism 09/1991; 40(8):873-6. · 3.10 Impact Factor
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    ABSTRACT: This study was undertaken to determine the changes which could occur in glucose homeostatis during the suckling-weaning transition in the genetically obese Zucker (fa/fa) rat. Glucose kinetics and glucose utilization in individual tissues were determined in 15-day-old suckling and 30-day-old weaned obese Zucker rats either in the post-absorptive state or during a glucose infusion. During suckling, glucose turnover rates in the basal state as well as glucose production and utilization during the glucose infusion were identical in lean and obese rats. Furthermore, individual tissue glucose utilizations were similar in the two groups of rats, except in brown adipose tissue where utilization was lower in obese than in lean rats during the glucose challenge. After weaning, glucose turnover rates and glucose utilization in individual tissues were identical in the two genotypes in the basal state. During the glucose infusion, hepatic glucose production was less suppressed in the obese. Furthermore, glucose utilization was significantly lower in muscles (extensor digitorum longus, tibialis anterior, diaphragm) and higher in white adipose tissue of obese rats. These data show that, before weaning, pre-obese Zucker rats present a perturbation only in the uptake of glucose in brown adipose tissue. Major defects in the regulation of glucose homeostatis occur after weaning.
    International Journal of Obesity 09/1991; 15(8):505-11. · 5.22 Impact Factor
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    ABSTRACT: To explore the interplay between the mitotic activity of arterial smooth muscle cells and the variations of plasma glucose and insulin concentrations, we have studied over 14 days the response of thoracic aorta to injury with a balloon catheter in rats submitted to fasting and refeeding. Animals were fasted from the day before until the third day after injury. The proliferative reaction of intima-media was assessed 2, 3.5, 4, 6, 8, and 14 days after injury, comparing freely fed with fasted-refed rats. Fasting decreased plasma glucose and insulin concentrations and DNA synthesis by intima-media, whereas refeeding increased these three variables transiently. The DNA content of intima-media at any time during the response to injury and the intimal thickening on day 14 were not influenced by the sequence of fasting and refeeding, which suggests that the early decrease in DNA synthesis induced by fasting had been compensated for by the later increase in DNA synthesis induced by refeeding. In conclusion, besides hormonal influences (such as insulin), metabolic influences (such as the availability of energetic fuels) are likely to act on the proliferative response of arteries to injury.
    The American journal of physiology 08/1991; 261(1 Pt 2):H190-5. · 3.28 Impact Factor
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    ABSTRACT: The purpose of this study was to investigate the effects of a 48-h glucose (30% wt/vol) infusion in unrestrained catheterized healthy rats (HG) on subsequent in vivo and in vitro insulin response to glucose. High hyperglycemia (400-450 mg/dl) and resulting hyperinsulinemia (1.2 +/- 0.1 mU/ml vs. 0.15 +/- 0.03 mU/ml in controls) were maintained throughout the infusion period. Glucose-induced insulin secretion was examined in vivo 3 h after the end of infusion by performing either a glucose tolerance test or a hyperglycemic clamp (225 mg/dl for 60 min). In addition, in vivo insulin secretion was studied on day 1, 3, 5, and 7 after the end of glucose infusion by performing glucose tolerance tests. Insulin secretion was also investigated in vitro, using the isolated perfused pancreas technique, 3 h and 1 day post glucose infusion. During glucose tolerance tests and hyperglycemic clamps performed at 3 h, insulin secretion was much greater in HG rats than in controls, and remained increased until day 5. By contrast, when studied in vitro 3 h after the end of the infusion, glucose-induced insulin release from isolated perfused pancreases was impaired in HG rats as compared with controls, and the insulin response to arginine was dramatically increased. However, insulin secretion in vitro returned partially to normal after day 1. These data indicate that prolonged hyperglycemia has quite different effects on the subsequent insulin secretion in vivo or in vitro. It impairs, but reversibly, glucose-induced insulin secretion in vitro, whereas it increases it durably in vivo. This suggests that humoral and/or nervous interferences can counterbalance the possible perturbing effects of prolonged hyperglycemia on the normal B cell responsiveness to glucose.
    Endocrinology 06/1991; 128(5):2526-33. · 4.72 Impact Factor
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    ABSTRACT: We have investigated the respective roles of insulin and glucagon in the initiation of hepatic glycogen degradation during the early postnatal period in rats, with special regard on the inhibitory effect of insulin on this process. Pregnant rats were rendered either slightly (8.5 mM) or highly hyperglycemic (22 mM) by infusing glucose during the last week of pregnancy. Fasted, newborn rats were studied from delivery to 16 h postpartum. At birth, newborns from slightly hyperglycemic rats showed higher glycemia and insulinemia and lower plasma glucagonemia compared with controls. Newborns from highly hyperglycemic rats were still more hyperglycemic and exhibited low plasma glucagon concentrations, but they were not hyperinsulinemic. In control newborns, hepatic glycogen breakdown was triggered by 2 h after delivery. By contrast, hyperglycemic-hyperinsulinemic newborns (newborns from slightly hyperglycemic rats) were unable to mobilize liver glycogen before 8-10 h after delivery. In hyperglycemic-normoinsulinemic newborns (newborns from highly hyperglycemic rats), hepatic glycogen concentration significantly started to decline 2 h after delivery and was no longer different from controls at 8 h. Anti-insulin serum injection at delivery promoted a prompt decrease in liver glycogen stores in controls as well as in newborns from slightly hyperglycemic rats. Phosphorylase a/synthase a ratio rose rapidly after delivery in controls and in newborns from highly hyperglycemic rats (maximum 4 h), whereas in newborns from slightly hyperglycemic rats, it rose much more slowly than in the two other groups (maximum 16 h). These data suggest that, in newborns from hyperglycemic mothers, hyperinsulinemia during late fetal and early neonatal life is the main factor preventing postnatal hepatic glycogenolysis.
    Pediatric Research 01/1991; 28(6):646-51. · 2.67 Impact Factor
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    ABSTRACT: The effect of counterregulatory hormones (epinephrine, norepinephrine and glucocorticoids) on insulin-induced glucose utilization in individual tissues of normal rats was investigated in vivo. This was done in normoglycaemic conditions, using the euglycaemic hyperinsulinaemic clamp combined with an injection of 2-[1-3H]-deoxyglucose. The main effect of these hormones was to reduce insulin-induced glucose utilization in skeletal muscles and particularly in the oxidative one. No changes were observed in heart diaphragm and adipose tissues. These results emphazise the role of counterregulatory hormones on glucose utilization and demonstrate that muscles are their major site of action. They support the notion that the increase in plasma concentrations of these hormones could play a role in states of insulin resistance like obesity and diabetes.
    Diabète & métabolisme 01/1991; 17(1):55-60.
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    ABSTRACT: The effect of 4 days of stable hyperglycaemia and resulting hyperinsulinaemia on insulin-induced glucose utilization by individual rat tissues was studied in vivo. The treatment produced a net increase in the glucose utilization index under both basal and insulin-stimulated (euglycaemic/hyperinsulinaemic clamp) conditions in white adipose tissue. On the contrary, glucose utilization was unchanged in aerobic muscles but was decreased in glycolytic skeletal muscles during the clamp.
    Biochemical Journal 12/1990; 272(1):255-7. · 4.65 Impact Factor
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    ABSTRACT: The present study was carried out to characterize the effects of insulin, using the euglycemic hyperinsulinemic clamp, on insulin binding and glucose utilization in specific areas of rat brain, by autoradiographic methods. Binding of [125I]Insulin was significantly higher in the hippocampus CA1, the ventromedial and lateral hypothalamus nuclei of the hyperinsulinemic rats than in control rats. Glucose utilization was slightly but not significantly decreased in the hippocampus CA1, the ventromedial and lateral hypothalamus of hyperinsulinemic rats. These data suggest that insulin, via its specific receptors, may exert its central actions by affecting glucose utilization.
    Neuroscience Letters 08/1990; 115(2-3):279-85. · 2.03 Impact Factor
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    ABSTRACT: Our study investigated whether a deterioration of glucose homeostasis and insulin secretion in adult female rats from hyperglycemic dams could be transmitted to the next generation independent of genetic interferences. Dams (F0) were rendered hyperglycemic by continuous glucose infusion during the last week of pregnancy. Females born of these rats (F1) exhibited glucose intolerance and impaired insulin secretion in vivo at adulthood. When they were 3 mo old, they were matched with males born of control dams. During pregnancy, their glucose tolerance remained impaired compared with that of controls. Consequently, F2 newborns of F1 hyperglycemic dams showed the main features of newborns from diabetic mothers: they were hyperglycemic, hyperinsulinemic, and macrosomic. As adults, they displayed basal hyperglycemia and defective glucose tolerance and insulin secretion. This indicates that the long-range deteriorating effects on glucose homeostasis of gestational hyperglycemia in the F1 generation are transmitted to the F2 generation and suggests that a perturbed fetal metabolic environment contributes to the inheritance of diabetes mellitus.
    Diabetes 07/1990; 39(6):734-9. · 7.90 Impact Factor
  • C Levacher, L Picon
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    ABSTRACT: In the rat, hyperthyroidism induced from birth has been shown to increase both adipose cell recruitment and de novo lipogenesis at 6 weeks of age. Since preadipose cells are included into the stromavascular fraction (SVF) of adipose tissue, fatty acid synthetizing enzyme activities were estimated separately in adipocytes and SVF cells of adipose tissue of 6 week-old hyperthyroid rats. Fatty acid synthetase (FAS), malic enzyme (ME), glucose-6-phosphate dehydrogenase (G6PD) and 6-phosphogluconate dehydrogenase (6PGD) activities were generally increased in adipocytes and in SVF cells when compared to age-matched controls. Among the enzymes studied, ME activity displayed the highest stimulation in SVF cells and was much more stimulated in these cells than in adipocytes (214% and 73% increase, respectively, above control values, P less than 0.001). These results show that, in vivo, SVF cells and adipocytes can respond differently to an hormonal stimulation and raise the question of the role of ME in the adipose conversion.
    Hormone and Metabolic Research 11/1989; 21(10):537-41. · 2.15 Impact Factor
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    ABSTRACT: Euglycemic-hyperinsulinemic clamps coupled with an injection of [2-3H]deoxyglucose were performed in rats 1 or 6 wk after lesion of the ventromedial hypothalamus (VMH) and their age-matched controls. In the basal state, glucose utilization was not different in controls and VMH rats in all the tissues studied except in white adipose tissue where it was greatly increased after the lesion. When insulinemia was clamped at 850 microU/ml, glucose utilization was less important in glycolytic and normal in oxidative muscles in animals 1 wk after the lesion (VMH1) compared with controls. In animals 6 wk after the lesion (VMH6), all the muscles utilized less glucose than those of controls. In white adipose tissue, glucose utilization was increased twice more in VMH1 and returned to normal in VMH6. These data demonstrate a progressive development of insulin resistance in muscles. Simultaneously, there is a transient insulin hypersensitivity in white adipose tissue. This, together with a hypersecretion of insulin, could contribute to the development of body fat mass by redirecting glucose towards adipose tissue.
    The American journal of physiology 09/1989; 257(2 Pt 1):E255-60. · 3.28 Impact Factor
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    ABSTRACT: This work was designed to study the effects of insulin secretion and action in vivo of moderate hyperglycemia induced by glucose infusion during 4 days in unrestrained rats. The maintenance of a glycemia around 170 mg/dl throughout the infusion time necessitated a gradual increase of glucose infusion rate from 11.5 to 19 g/day. Throughout the infusion period, plasma insulin-to-glucose ratio remained much higher in hyperglycemic rats (HG) than in controls. Glucose tolerance and insulin secretion tests were performed 2 h after the end of the infusion, when glycemia and insulinemia were back to basal values. Incremental plasma glucose values were significantly lower in HG than in control rats without significant changes in incremental plasma insulin concentrations, suggesting an increased insulin efficiency. At the same insulin level, glucose utilization was higher in HG than in control rats during euglycemic-hyperinsulinemic clamps. These data show that short-term hyperglycemia and hyperinsulinemia do not induce a defect in insulin secretion in vivo and do increase tissue sensitivity to insulin.
    The American journal of physiology 09/1989; 257(2 Pt 1):E180-4. · 3.28 Impact Factor

Publication Stats

787 Citations
231.61 Total Impact Points

Institutions

  • 1989–1992
    • French National Centre for Scientific Research
      Lutetia Parisorum, Île-de-France, France
  • 1985
    • Holiste Laboratoire et Développement
      Lyons, Rhône-Alpes, France
  • 1981–1985
    • Université de Vincennes - Paris 8
      Saint-Denis, Île-de-France, France