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Biomedical subjects

D Richard

Publications and source records attributed to D Richard.

At least 181 records · Page 10Linked to original sources
PubMed1983

Pancreatic insulin response in relation to exercise training.

The present study was undertaken to measure the effects of exercise training on pancreatic insulin secretion in response to glucose and nonglucose stimuli. Wistar female rats with an initial body weight of approximately 180 g were divided into trained and sedentary groups. After a period of 10 weeks of training, glucose-, tolbutamide-, and arginine-tolerance tests were performed in vivo in both trained and untrained animals. The tests were done in nonanesthetized animals 40 h after the last exercise bout. It was found that exercise training leads to a diminution of plasma insulin levels after either glucose, tolbutamide, or arginine administration. These results present direct evidence that exercise training reduces plasma insulin response not only to glucose but also to nonglucidic secretagogues.

Animals↗
PubMed1982

Variations in plasma glucose, insulin, growth hormone and catecholamines in response to insulin in trained and non-trained subjects.

Previous studies have shown a reduced insulin secretion in trained subjects challenged by a glucose load. In the present study the response to insulin of 8 athletes was compared to that of 8 non-trained subjects. The disappearance of plasma insulin was not different between the two groups, but the level of hypoglycemia was greater in the trained subjects. The injection of insulin increased the plasma levels of epinephrine (E) and norepinephrine (NE) in both groups of subjects, but the raise in E was greater in the trained subjects. Similarly, the increase of growth hormone (GH) was greater in the trained subjects. These findings substantiate previous results showing a decreased insulinic index and an increased insulin binding to monocytes in trained subjects. It is also suggested that the enhanced E and GH secretion found in trained subjects injected with insulin, is possibly related to the greater fall in plasma glucose in the trained subjects compared to the non-trained subjects.

Adult↗
PubMed1982

Role of exercise-training in the prevention of hyperinsulinemia caused by high energy diet.

The present study was undertaken to determine whether exercise-training done in combination with feeding a high energy diet could modulate carbohydrate metabolism. Male rats were divided into exercise-trained or sedentary groups that received either a palatable high energy diet or merely standard laboratory diet. After 10 weeks of training, the animals were subjected to an intravenous glucose tolerance test. Body weight, epididymal fat pads, and adipocyte volume were reduced following training. The results also showed that exercise-training protects against deterioration of glucose tolerance produced by high energy diet. Training prevented the elevation of basal as well as glucose challenged insulin levels induced by the high energy diet in spite of a high fat as well as high overall energy intake. A highly significant coefficient of correlation (r = 0.78, P less than 0.01) was observed between the size of adipocytes and the insulin response to glucose load and suggests that the prevention of hyperinsulinemia in rats fed high energy foods while training could be associated with the ability to prevent obesity.

Adipose Tissue↗
PubMed1982

Catecholamines and triiodothyronine variations and the calorigenic response to norepinephrine in cold-adapted and exercise-trained rats.

A comparison was made of the thermogenic response to norepinephrine (NE) in cold-adapted (2 h per day at -15 degrees C for 5 weeks) and in exercise-trained rats (2 h swimming per day for 5 weeks). The oxygen consumption and the plasma catecholamine elevation were comparable for both conditions. Similarly plasma corticosterone determinations indicated comparable elevations in acute stress exposure and reduced responses in both exercise-trained and cold-adapted rats. The marked increase in colonic temperature which was observed in cold-adapted animals injected with NE (30 micrograms/100 g s.c.) was not found in exercise-trained rats. Similarly the brown adipose tissue was double in size in the cold-adapted rats but remained unchanged with exercise training. An important elevation of triiodothyronine (T3) was found in cold-exposed rats, either adapted or not. However, exercise was found to decrease plasma T3 in trained and nontrained rats. The results indicate that swimming for 2 h and exposure to cold (-15 degrees C) for 2 h produced comparable elevation of plasma corticosterone and catecholamine, and of oxygen consumption. However, only the cold-adapted animals develop a NE-induced thermogenesis. It is suggested that thyroid hormones are necessary as permissive factor, in stress-induced thermogenesis.

Acclimatization↗
PubMed1982

Effect of diet and exercise on norepinephrine-induced thermogenesis in male and female rats.

Male and female rats were fed standard laboratory chow or a highly palatable diet (cafeteria diet) for 10 wk. The cafeteria diet caused an increase in caloric intake and in body weight, and it induced thermogenesis that was associated with elevated plasma triiodothyronine (T3) levels, increased brown adipose tissue size, and enhanced metabolic response to norepinephrine. For a comparable caloric intake, body-weight gain was significantly greater in female than in male rats possibly because of difference in thermogenesis as suggested by the response to norepinephrine. Exercise training (swimming 2 h/day for 10 wk) reduced food intake and body-weight gain and failed to increase norepinephrine-induced thermogenesis in rats fed laboratory chow. In animals fed the cafeteria diet, food intake and body-weight gain were also reduced by exercise training, which at the same time diminished the diet-induced thermogenesis as evidenced by the diminution of 1) brown fat hypertrophy, 2) the elevation of plasma T3, and 3) the hyperthermic response to injected norepinephrine. It is suggested that the thyroid hormone and catecholamines through their actions on the brown adipose tissue are the important regulatory of thermogenesis. Exercise training would reduce the diet-induced thermogenesis by preventing increased T3 production. Enhanced thermogenesis may be considered an adaptive reaction as it serves to reduce fat deposition in animals fed cafeteria diet and to promote nonshivering heat production in the cold. On the other hand, exercise training reduces thermogenesis and thus prevents energy wasting.

Adipose Tissue↗
PubMed1982

Interactions between dietary obesity and exercise-training on carbohydrate metabolism.

The present study addressed the important question of whether exercise-training could reduce insulin levels in exercise-trained rats made obese by a diet composed of palatable foods. Female rats were divided in exercise-trained or in sedentary groups which receive either a palatable high-energy diet or merely a standard laboratory chow. The high-energy diet was composed of supermarket foods including chocolate chips cookies, pop-corn, bologna, etc. Exercise-training program consisted of forced swimming, 6 d per week, 2 h per d, in water maintained at 36 degrees C. At the end of both fattening and exercise-training program, the animals were subjected to an intravenous glucose tolerance test. The results showed that high-energy diet and exercise-training had opposite effects on both glucose tolerance and insulin secretion: the former impaired glucose tolerance and increased insulin levels, whereas the latter leads to opposite adaptations. In addition, some abnormalities in insulin metabolism persisted in rats simultaneously assigned to exercise-training and high-energy diet. Thus, the present results also suggested that physical training alone could not reduce plasma insulin under control levels, and that a change in energy balance is possibly necessary to achieve this purpose.

Adipose Tissue↗
PubMed1982

[Electrophysiological and anatomical data on the interneurons involved in the visual orientation of the cricket (Gryllus bimaculatus)].

103 interneurones in the neck connective of the cricket were recorded, and two of them were anatomically identified by ionophoretic injection of cobalt. These neurones, when stimulated with repetitive flashes of light, show low pass filter properties. The stained neurones have their cell-body located in the protocerebron, and axonic arborisations extend towards the motoneurones of the thoracic ganglia.

Animals↗
PubMed1981

Studies on the sparing effect of exercise on insulin requirements in human subjects.

The reduced insulin response of trained subjects in the presence of normal glucose tolerance has been confirmed. It was also found that this beneficial effect of exercise is greatly reduced if trained subjects are inactive for 3 days while eating ad libidum. During that period excessive food intake (3291 cal/day) was noted. However, when the subjects were on a restricted diet (2076 cal/day) the reduced insulin response to a glucose load was retained. The ratio of food intake with regard to caloric utilization is possibly the important modulator of the action of exercise on insulin requirements. The effect of exercise on insulin secretion was also found to be acquired rapidly since it was observed 18 hr after 1 hr of physical activity at 70% of V02 max in non-trained subjects. For all these studies a correlation (p less than 0.01) was found between the secretion of insulin in response to glucose challenge and both basal plasma glucose and insulin.

Adolescent↗
PubMed1980

Influence of the visual cortex upon receptive field organization of lateral geniculate cells in rabbits.

In anesthetized rabbits, the receptive fields of lateral geniculate cells were mapped prior to and following the interruption of the corticogeniculate feed-back. Visual cortex (V.C.) was depressed by a focal application of 3 M KCl. The responsiveness of the V.C. was verified by monitoring the visually evoked potentials. In off- and on-center cells, the surround excitatory responses were remarkably reduced and even fully abolished in most units. In contrast, the center excitation remained unmodified. These effects were reversible. In some on-center units the center response had also decreased, and was replaced by an evoked inhibitory response. Relay cells and interneurons which yielded on and off responses over the entire area of the receptive field exhibited a loss of only one of the evoked discharges. It is concluded that the V.C. exerts mostly a specific desinhibitory action upon the geniculate network. This action affects either the center or the surround responses differentially. The results are compared with those obtained from cats.

Animals↗
PubMed1980

Reactions of lateral geniculate cells to chemical and electrical excitation of the visual cortex in rabbits.

In anesthetized and paralyzed rabbits unitary discharges of lateral geniculate nucleus (LGN) were studied after cortical excitation by strychnine and following electrical stimulation of the visual cortex (VC). Results showed that local application of strychnine produced a general increase of the spontaneous and evoked activity of geniculate cells. By contrast, cortical depression with KCl led to a differential decrement of one of the evoked responses (on or off). Electrical cortical stimulation paired with on or off stimuli led to a differential increment of on or off responses. The results support the notion that, in rabbits, the corticogeniculate system is center-surround organized. A diagrammatic model is proposed to account for the relationship between the VC and the LGN in rabbits.

Animals↗
PubMed1980

Effects of physical training and food restriction on insulin secretion and glucose tolerance in male and female rats.

The purpose of this study was to assess the respective effects of physical training, adiposity, and total body mass on insulin secretion and glucose tolerance. Male and female rats were used in two separate studies. In a first study male rats were divided into three groups sedentary free-eating control (c), exercise-trained (T), and sedentary pair-weighted. In a second study with female rats, three groups were formed: C, T, and a sedentary food-restricted group. In the two studies, at the end of the training program, the animals were subjected to an intravenous insulin levels without any impairment of glucose tolerance. However, essentially the same results were obtained with both the pair-weighted male rats and the food-restricted female rats. These results suggest that the reduced levels of plasma insulin observed in trained rats challenged or not by a glucose load, could be explained by the reduction of body mass caused by exercise training.

Adipose Tissue↗
PubMed1980

Mechanism of enhanced lipolysis in adipose tissue of exercise-trained rats.

The effects of exercise training and food restriction on the regulation of lipolysis were studied comparatively in adipocytes isolated from male and female rats. Exercise training inhibited cell proliferation in parametrial, but not in epididymal adipose tissue, whereas it significantly reduced adipocyte size in both fat depots. Adipocyte capacity for responding lipolytically to epinephrine (10 microns) or to ACTH (1 micron) was markedly increased by exercise training. Enhanced lipolysis was also observed when cells isolated from exercise-trained animals were stimulated by bypassing with dibutyryl cyclic AMP (5 mM) or theophylline (5 mM) the early metabolic steps associated with hormonal activation of the adenylate cyclase complex. Significantly, binding of (-)-[3H]dihydroalprenolol to cellular receptor sites was not affected by exercise training. It is therefore concluded that exercise training increases adipocyte responsiveness to lipolytic hormones at a metabolic step distal to stimulus recognition by adrenoreceptors, possibly at the level of protein kinases or lipases. Food restriction markedly reduced adipocyte size and partially mimicked the effects of exercise training on adipocyte proliferation and lipolysis.

Adipose Tissue↗
PubMed1978

[Acute inhalation toxicity of ammonia in rabbits].

The aggressivity of ammonia at the pulmonary alveole level (intoxications in controlled ventilation) leads to an acute pulmonary oedema and cardio-vascular disfunctioning. Bradycardia is an early symptome (2,500 X 10(-6) but the real syndrome appears at 5,000 X 10(-6). Arterial pressure variations and blood gases modifications are significant, acidosis is systematic.

Acidosis↗