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Biomedical subjects

J Le Magnen

Publications and source records attributed to J Le Magnen.

At least 55 records · Page 3Linked to original sources
PubMed1984

[Mechanisms of regulation of energy balance].

To establish energy balance, the three distinct terms of the balance must be precisely defined and measured. These terms are: the energy input by food intake, energy expenditure as heat and the body energy content in the form of lean and fat masses. The constancy of this fat store, generally associated with that of body weight, is an indication of the balance between energy intake and the sum of expenditure and non-lipidic energy retention. This balance is only carried out at medium or long-term. It results from the initiation of mechanisms regulating strongly positive or negative short-term balances between gains and losses. Four possible models of this regulation are presented and discussed using experimental data. A number of works is reported, demonstrating the role played by two complementary mechanisms of regulation. The first one is neuroendocrine mechanism controlling food intake and adjusting it to the input and output of glucose in the blood compartment. The second one is an autonomous mechanism regulating the body fat mass. It corrects, at medium and long-term, the filling and depletion of the adipose compartment which result from imbalances in the overall energy balance. This mechanism indirectly affects food intake in a regulatory sense. It is neurally controlled by the sympathetic and parasympathetic nervous system and governed by the medioventral nuclei of the hypothalamus.

Adipose Tissue↗
PubMed1983

Fast-induced changes in plasma glucose, insulin and free fatty acid concentration compared in rats during the night and day.

Changes in PG, PI and PFFA were examined and compared in fed rats or after 0 to 12 hours of fasting, during the night or during the day. At night, a progressive decrease in PG and PI and an increase in PFFA were induced by 0 to 12 hours of food deprivation. During the light period a decrease in PG occurred only from the 6th hour of fasting. A slight, progressive increase in PFFA levels was induced from 0 to 12 hours of fasting, while no significant variation of PI levels was observed. The results are discussed in terms of relationships between blood glucose, PFFA levels, and food intake in control rats over the circadian cycle.

Animals↗
PubMed1983

Reflex insulin response associated to food intake in human subjects.

The occurrence of a reflex insulin discharge at the beginning of a meal, and its possible influence on intake were studied in 7 normal weight humans. Each subject was tested twice under three standard meal conditions. The evolutions of insulinemia and glycemia were recorded over an 84 min observation period, starting 2 min before food presentation. Blood was drawn continuously from an antecubital vein, and collected in 1-min samples for the first 30 min, and then in 3-min samples. The average glycemia curve was stable until some 18-20 min after meal onset. By contrast, a significant rise in plasma insulin appeared as early as the 4th min after meal onset and it is hypothesized to be preabsorptive, of cephalic and/or gastric origin. However, inter-test variations were large even in the same person. Schematically, three types of early insulin responses were observed: high and/or sustained rise, moderate and/or short increase, moderate decrease in plasma insulin. The shape of the early insulin response was not related to any meal characteristic. The potential biological and behavioral significance of the early insulin release is discussed.

Adult↗
PubMed1983

Effects of a daytime infusion of exogenous insulin on subsequent nocturnal food intake and body weight in rats.

Normal rats with chronic cardiac catheters were infused with regular insulin at various doses (0.1 to 0.6 IU/hr). The insulin infusion was limited to the 12 light hours and repeated for 4 consecutive days. Daytime insulin infusion increased the 12 hr cumulative food intake in a dose-dependent fashion. This increase was associated with a compensatory decrease in the subsequent nocturnal intake, so that the 24 hr food intake remained unchanged. Results are discussed in relation to mechanisms involved in the normal circadian rhythms of feeding.

Animals↗
PubMed1983

Decrease in ethanol consumption by naloxone in naive and dependent rats.

Acute effects of the opiate antagonist, naloxone, on alcohol intake have been examined and compared in naive and behaviorally dependent rats. In naive rats the aversion to an 8% alcohol solution exhibited in a 30 min presentation was selectively augmented by an IP administration of naloxone (1 mg/kg) 30 min before a morning drinking session. In other rats, behavioral dependence was established by 15 days of IG administration of intoxicating doses of alcohol. This dependence was exhibited by a sustained preference for ethanol for 6 days. Naloxone (1 mg/kg) abolishes the acquired preference for ethanol tested during an 8 hour day time presentation. These effects of naloxone on alcohol intake in ethanol naive and dependent rats are interpreted in relation to a general non-specific action of naloxone on preferred or aversive flavoured solutions.

Alcohol Drinking↗
PubMed1983

Ethanol preference following hypothalamic stimulation: relation to stimulation parameters and energy balance.

Rats were given 5, 10, 20 and 30 min daily sessions of lateral hypothalamic stimulation. Approximately half of the rats showed a large and highly significant increase in their total intake of and preference for 10% v/v ethanol which was continuously available in their home cages. In terms of latency, total consumption and preference for ethanol, 10 min of daily stimulation produced a much greater enhancement than did 30 min. The ethanol drinking rats used more energy per unit of body weight which suggests that the stimulation and/or the ethanol itself may have increased energy expenditure. Simply changing the diet from powdered chow to identical composition pellets produced a large reduction in both total ethanol intake and preference. Reinstating the powdered diet produced a rapid reinstatement of ethanol drinking. These data are discussed in terms of ethanol's role in modulating stimulation induced changes in energy balance.

Alcohol Drinking↗
PubMed1983

The effect of naloxone on intragastric ethanol self-administration.

The acute effect of 1.25 and 2.50 mg/kg naloxone was tested in a group of male Wistar rats readily self-administering 10% w/v ethanol intragastrically following 12 days of forced ethanol intoxication. Compared to saline pretreatment, naloxone did not alter 24 hr intakes of food, water or ethanol. However, both does strongly and significantly inhibited lever pressing for ethanol during 2 hr following pretreatment. The results indicate that naloxones's inhibition of ethanol intake does have a transient postabsorptive component, although this component is unlikely to be specific to ethanol.

Alcohol Drinking↗
PubMed1983

Vagotomy abolishes the differential palatability of food.

The magnitude of preabsorptive insulin release varies as a function of palatability. This suggests that the palatability-dependent rise in plasma insulin could accentuate the systemic stimulus to eat, which in turn could modulate the size of the meal. The present experiment was designed to test this hypothesis by investigating the ingestive responses of vagotomized rats, which no longer exhibit preabsorptive insulin release, when they are offered nutritionally identical diets differing only in their sensory characteristics. The presented foods were three forms of the rat's regular diet: unaltered, sweetened with sodium cyclamate or adulterated with quinine hydrochloride. It was shown that vagotomized rats ate exactly the same amount of the three diets in three different test-meals: without cephalic insulin release, meal size no longer seems to be modulated by oral cues.

Animals↗
PubMed1983

Endocrine basis for weight gain after fasting or VMH lesion in rats.

To study some hormonal and metabolic factors contributing to the regulation of body fat mass, food intake, and the circadian lipogenesis-lipolysis pattern, insulin and glucose responses to intravenous glucose loads were measured in both phases of the light-dark cycle in two groups of rats considered to be below their level of body fat mass regulation [rats with lesion of the ventromedial hypothalamus nuclei (VMH) in the "dynamic" phase of obesity and food-restricted rats during the refeeding phase] compared with the responses of two other groups at this level (VMH-lesioned rats in "static" phase and normal rats). Glucose tolerance and insulin release were greater during the dynamic phase and to a lesser degree during refeeding than during the static phase and normal feeding. The differences between night and day found in normal rats disappeared in dynamic and refed animals and reappeared at the level of static phase. Thus the normal circadian hormonal metabolic patterns responsible for increased lipogenesis and relative hyperphagia during the night and lipolysis with hypophagia during the day were lost in rats below their level of body fat mass regulation and were reinstated in animals on returning to this level.

Animals↗
PubMed1983

[Cephalic phase of insulin secretion and the variety of the food in rat feed].

Immunologically reactive insulin levels were determined in freely-moving normal rats offered three different test-meals. In test I, they were offered their normal diet for 4.5 min. In test II, they first ate the same diet for the same amount of time, then a cookie for 6 min, and finally they had free access to lard. In test III, the normal diet was followed by a synthetic sweetener and then by vaseline. It was shown that in a varied meal (tests II and III), the ingestion of each new food was immediately followed by a peak of insulin secretion superimposed on normal postprandial hyperinsulinemia. This resulted in an overall increase in insulinemia over the 15-min period measured. It is well known that in a varied meal more food is consumed. Thus, it may be that when a varied meal is offered, final satiety is postponed. This could be due to sensorially-triggered peaks of insulin secretion which would explain why the "cafeteria diet" induces hyperphagia and obesity.

Animal Feed↗
PubMed1982

Meal related effects of IV glucose, glucagon and insulin on blood glucose level: role in glucoregulation exhibited by self-injecting rats.

In previous works, it was demonstrated that rats self-injected with (IV) glucose, insulin and/or glucagon and that the self-administration pattern was related to the meal. It was suggested that the different preprandial or postprandial blood glucose level (B.G.L) determined the meal and were dependent on it. Previously self-injected amounts of glucose, glucagon and insulin were here injected by an automatic device and their effect on B.G.L. were compared in the post and preprandial conditions. Results indicated that the effects of insulin, glucagon and glucose on B.G.L., which were different during the postprandial hyperglycemia compared to the preprandial normoglycemia, accounted for the different self-injection patterns. Furthermore successive injection of glucose and insulin or glucagon and insulin suggest that rats, by pressing alternatively two levers performed a regulatory correction of variations of their B.G.L. It is concluded that rats may learn to perform a behavioral regulation of their B.G.L. by IV self-injections of glucose and glucoregulatory hormones.

Animals↗
PubMed1982

Effects of short-term nocturnal and diurnal food deprivation on subsequent feeding in intact and VMH lesioned rats: relation to blood glucose level.

Ad lib feeding responses were studied in VMH lesioned rats, following 2 to 6 hours of food deprivation during the dark and the light phases of the diurnal cycle. The correlation between glucose level at the time of restoration of food and these feeding responses was examined. At night, VMH as well as intact rats increased their food intake significantly following 2 to 6 hours of food deprivation. In both groups, the responses were correlated with a decrease in blood glucose which was dependent on the duration of previous food deprivation. During the day, in normal rats, food deprivation did not induce a change either in subsequent food intake or in blood glucose level. On the contrary, VMH lesioned rats increased their food intake following diurnal food deprivation as they did at night. But, surprisingly, this increase was not associated with a fall of blood glucose.

Animals↗
PubMed1982

Daily body energy balance in rats.

The aim of the present study was to examine the balance between caloric intake and expenditures in successive 12 and 24 hour periods, for several consecutive days in rats. The simultaneous and continuous measurements of respiratory exchanges and of the spontaneous feeding pattern were performed in 6 rats during 38 days, in periods of 2 to 4 successive days. At night, caloric intake exceeded caloric expenditures by 32% on the average. In individual rats, the excess was positively correlated to meal size but not to meal number. During the daytime, caloric intake was 24% lower on the average than the concomitant energy expenditures. In individual subjects, these deficits were correlated to meal number but not to meal size. A nocturnal excess and the subsequent daytime deficit, and the diurnal deficit and the excess during the subsequent night were highly positively correlated. In fact, the 24 hour energy balance was either slightly positive (12% excess) or negative (4% deficit). The daily weight gain or loss was highly correlated to the residual excess and/or deficit with a mean caloric cost of 4.8 kcal per g of body weight. The absence of correlation between balances on successive days indicates that the body energy balance is regulated within 24 hr through 12/12 hr compensations and that no compensatory mechanisms are involved beyond 24 hr.

Animals↗
PubMed1982

Parameters of low-dose ethanol intravenous self-administration in the rat.

Male Wistar rats were able to press on an operant lever 24 hr/day for intravenous infusions of saline or ethanol at doses of 0.5, 1.0 or 5.0 mg/kg/infusion. Only the 1.0 mg/kg/infusion group showed a significant increase in responding on the lever as a function of days, whereas the 5.0 mg/kg/infusion group showed a significant decrease in responding as a function of days. The results suggest that the reinforcing value of intravenous ethanol changes from rewarding to neutral or aversive in valence at dose-level below that expected to produce signs of intoxication.

Animals↗
PubMed1982

Induction of high voluntary ethanol intake in dependent rats.

The experimental conditions under which oral high intake may be induced in previously intoxicated rats have been investigated. Seventeen rats were administered intragastrically with 10 g/kg/day of ethanol for 15 days. At cessation of treatment, they were presented a single bottle of alcoholic solution (10% v/v) during 24 hr. For the following 6 days, they received either an ethyl alcohol solution or water in alternation for 8 hours each. Ethanol treated rats exhibited a high oral intake of ethanol equivalent to the previously injected doses. Controls displayed a significantly lower intake of ethanol. It is concluded that the suppression of the withdrawal state by an initial priming oral intake of ethanol in physically dependent rats is a condition for the development of a conditioned taste preference for ethanol as a basis for the behavioral dependence.

Alcohol Drinking↗