Biomedical subjects

J LeBlanc

Publications and source records attributed to J LeBlanc.

At least 55 records · Page 3Linked to original sources

PubMed1989

Effects of aluminum and other cations on the structure of brain and liver chromatin.

The reactivity of aluminum and several other divalent and trivalent metallic cations toward chromatin from rat brain and liver has been investigated. Two criteria are used to determine the relative reactivity of these cations toward chromatin. The first involves the ability of the ions to compact the chromatin fibers to the point where chromatin precipitates. The second criterion measures the ability of cations to interfere with the accessibility of exogenous structural probes (nucleases) to chromatin. Of the divalent cations tested, nickel, cobalt, zinc, cadmium, and mercury were the most reactive toward chromatin, on the basis of their ability to induce precipitation of chromatin in the micromolar concentration range. The divalent cations magnesium, calcium, copper, strontium, and barium were much less effective, although all cations precipitate chromatin if their concentration is increased. Of the trivalent cations tested, aluminum, indium, and gallium were very effective precipitants, whereas iron and scandium were without effect at the concentrations tested. Of all the cations tested, aluminum was the most reactive. Aluminum's ability to alter the structure of chromatin was investigated further by testing its ability to interfere with nuclease accessibility. This test confirmed that aluminum does induce considerable changes in chromatin structure at micromolar concentrations. Furthermore, chromatin from cortical areas of the brain was much more sensitive to aluminum than chromatin from liver. These results are discussed in light of the known toxicity of these cations, with particular emphasis on the possible role of aluminum in Alzheimer's disease.

Aluminum↗

PubMed1989

Cephalic postprandial thermogenesis in human subjects.

To study the role of food palatability on postprandial thermogenesis, a study was designed in which human subjects ingested palatable food while O2 consumption was measured continuously during 30 minutes before and 60 minutes after the meal. In a first experiment (normal feeding), the subjects ate a portion of sugar pie containing 1672 kJ. A rapid increase in O2 consumption was noted which reached a peak value at about 15 minutes from the beginning of the meal. In a second experiment (sham feeding), the subjects were given the same food and they were asked to chew it and to spit it out. During the first 30 minutes following the meal, sham feeding produced a significantly larger increase in O2 consumption than meal feeding, whereas in the second postprandial period the thermogenic effect of food was larger with meal feeding. The integrated elevation of O2 during one hour was the same with meal feeding as with sham feeding. These results show that sensory stimulations without food being absorbed caused an important increase in O2, and confirms in humans the presence of a cephalic postprandial thermogenesis. In the third experiment (blank feeding), the subjects mimicked the muscular activities associated with feeding such as hands, arms, jaw and throat movements. Blank feeding produced a small and transient increase in O2 consumption. An elevation of plasma norepinephrine was observed during the cephalic phase and this effect was significantly larger with sham than with meal feeding. Subjective ratings for palatability, hunger reduction and degree of fullness were higher with meal than with sham feeding.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1989

Influence of echocardiography in pre-operative cardiac catheterization in congenital heart disease.

The influence of echocardiography on pre-operative cardiac catheterization was assessed in a retrospective analysis comparing two 12-month periods. Of 245 operations in 1983, 200 (82%) had pre-operative cardiac catheterization when two-dimensional echocardiography only was used in the pre-operative assessment compared to 162 of 238 (68%) operations in July 1985-June 1986 when pulsed Doppler echocardiography also was used (P less than 0.001). Significant reductions in pre-operative cardiac catheterization were present in both open (87/87 vs 89/102, P less than 0.001) and closed (113/158 vs 73/136, P less than 0.005) heart procedures. The group with the most significant reduction in pre-operative cardiac catheterization before open heart surgery were children with atrial septal defects; of the closed heart surgical groups, the greatest reductions were in patent ductus arteriosus, coarctation of the aorta and tetralogy of Fallot. Echocardiogram diagnostic errors occurred in 22/245 (9%) in 1983 compared to 9/238 (4%) in 1985/86 (P less than 0.05). Echocardiography has resulted in a significant reduction in pre-operative cardiac catheterization and has become more accurate in diagnosis.

Cardiac Catheterization↗

PubMed1988

Shivering and nonshivering thermogenesis in exercised cold-deacclimated rats.

Norepinephrine (NE)-induced increase in oxygen consumption (VO2) and colonic temperature (Tc) was greater in cold-acclimated rats housed at 4 degrees C for 4 weeks (CA) than warm-acclimated controls housed at 24 degrees C for 4 weeks (WA). On the other hand, shivering activity measured at 4 degrees C was less in CA than in WA, while propranolol administration eliminated the difference between these two groups by enhancing shivering in CA. Wet weight and protein content of interscapular brown adipose tissue (IBAT) were greater in CA than in WA. Following cold acclimation, CA were deacclimated at 24 degrees C for 5 weeks. During deacclimation, half of this latter group were forced to run (15 m.min-1 for 1 h) every day (CD-T) while the remaining rats remained sedentary (CD-S). Shivering activity assessed at 4 degrees C 4 weeks after commencing cold deacclimation was significantly less in CD-T than in CD-S and the difference disappeared following propranolol injection. VO2 and Tc responses to NE injection measured 1, 2 and 5 weeks after commencing cold deacclimation did not differ between CD-S and CD-T. Although IBAT weight was lighter in CD-T than in CD-S, its total protein content was not different between the latter two groups of rats. These results suggest that a greater degree of NE-independent nonshivering thermogenesis (NST) is retained in rats that are exercised during the process of deacclimation as compared with animals that are sedentary. This difference in NST would not seem to be directly related to BAT thermogenic capacity.

Acclimatization↗

PubMed1988

Interaction between exercise training and cold acclimation in rats.

Five groups of 10 rats were used. Group A included sedentary rats kept at 24 degrees C, group B exercised-trained rats and group C rats exposed at -15 degrees C for 2 h every day and kept at 24 degrees C for the remaining time. These 3 groups were kept on this regimen for 10 weeks. In addition group D was acclimated to cold (2 h.d-1 at -15 degrees C) for 6 weeks and subsequently deacclimated at 24 degrees C for 4 weeks. Group E was also acclimated to cold for 6 weeks and during the deacclimation, at 24 degrees C period which lasted 4 weeks, the animals were exercised 2 h per day. Following the 10 week experimental period all animals were sacrificed and DNA and protein content of the IBAT as well as its total mass were measured. The results show significant increases in the cold adapted group. Exercise training which had no effect on brown adipose tissue IBAT at room temperature, caused an accelerated reduction in weight, DNA and protein content of the BAT in rats previously acclimated to cold. In spite of this, the thermogenic response to noradrenaline was significantly enhanced in the group which exercised during the deacclimation period. It is suggested that tissues other than IBAT may explain this enhanced heat production capacity.

Acclimatization↗

PubMed1988

Left ventricular systolic and diastolic function after two-stage anatomic correction of transposition of the great arteries.

Anatomic repair of transposition of the great arteries (TGA) has been developed because of concerns about right ventricular function after atrial repair by the Mustard or the Senning technique. This study assessed left ventricular systolic and diastolic function in three patients after two-stage anatomic repair. Two patients had a ventricular septal defect (one with coarctation), and the third patient had right ventricular dysfunction precluding atrial repair. All had pulmonary artery banding. The mean ages at the time of repair and catheterization were 2.75 and 4.9 years, respectively. The control group included 10 patients with insignificant or no cardiac disease. At cardiac catheterization the group with TGA had a higher mean end-diastolic volume index (110.9 +/- 4.74 ml/m2) compared to normal subjects (79.1 +/- 14.55; p less than 0.001), mean end-systolic volume index (37.3 +/- 3.69 vs 22.7 +/- 4.42; p less than 0.001), mass index (101.0 +/- 16.9 vs 68.2 +/- 12.34; p = 0.038), and stroke volume index (73.6 +/- 3.52 vs 56.5 +/- 12.1; p = 0.0027). The ejection fractions, end-diastolic and peak systolic pressures, and stresses were not different. There was no difference in the relationship between the mean rate-corrected velocity of circumferential fiber shortening and end-systolic stress for the group with TGA, but myocardial stiffness was markedly elevated (29.5 +/- 1.84 vs 10.8 +/- 2.20; p less than 0.001). Thus, this study found abnormalities of left ventricular size after two-stage anatomic repair of TGA in this group of patients with TGA.(ABSTRACT TRUNCATED AT 250 WORDS)

Cardiac Catheterization↗

PubMed1988

A role for insulin in cephalic phase of postprandial thermogenesis in dogs.

The influence of insulin in the cephalic phase of postprandial thermogenesis was investigated in dogs. O2 consumption (VO2) and respiratory quotient (RQ) were continuously monitored 1 h before and 2 h after a 1,015-kcal meal during a control, an atropine, or a pancreatic-denervation experiment. A first phase (cephalic phase) in VO2 increase, lasting at least 50 min, followed by a second phase (digestive phase) were found in the control experiment. During both the atropine and pancreatic-denervation experiment, the first phase of VO2 was inhibited by 52%. The second phase was completely abolished with atropine, whereas it remained comparable to the control in the case of pancreatic denervation. A peak increase for insulin (70 microU/ml over 0 time) was observed 2 min after the onset of feeding in control. It was followed after 25 min by a second increase related to changes in glycemia. Maximal rises of norepinephrine (NE) and epinephrine corresponded to 215 and 120 pg/ml above basal values at 2 min in control experiment. During both atropine and pancreatic denervation the cephalic phase of insulin release was suppressed and the NE increase was inhibited by congruent to 65%. During the digestive phase pancreatic denervation caused an increase in plasma insulin comparable to that of the control, whereas atropine produced no such effect. It is suggested that the cephalic phase of postprandial thermogenesis is mediated through a causal relationship between insulin and NE release.

Animals↗

PubMed1988

Aortic valve insufficiency and coronary artery narrowing in a child with polyarticular juvenile rheumatoid arthritis.

Involvement of the cardiac valves in juvenile rheumatoid arthritis (JRA) is a rare but life threatening complication. We report a 9 1/2-year-old girl with rheumatoid factor positive polyarticular JRA who developed aortic insufficiency that required valve replacement. Six months later she developed angina due to narrowing of the left coronary artery, probably secondary to aortitis.

Aortic Valve↗

PubMed1987

Metabolic and hormonal responses to long-distance swimming in cold water.

The acute effects of long-distance swimming in cold water on selected hormonal and metabolic variables were evaluated on 22 long-distance swimmers (16 males and 6 females) during a 32-km swimming competition (La Traversée Internationale du Lac St-Jean). The water temperature was 18.5 degrees C and the mean performance times were 8 h and 32 min for men (M) and 9 h and 1 min for women (F). The blood samples were withdrawn in the fasting state during the week preceding the event and within 30 min after completion of the race. A positive correlation was obtained, for both groups, between percent body fat and rectal temperature measured at the end of the competition. After the competition, an increase in plasma epinephrine, norepinephrine, cortisol, thyroxine, free fatty acids, lactate, a decrease in glucose and insulin and no change in growth hormone, triiodothyronine, triglycerides, and cholesterol concentrations were observed in both groups. The increase in plasma thyroxine was more pronounced in the slower swimmers while the change in blood cortisol concentrations was higher in the subjects having the most acute decrease in body temperature. Male and female swimmers have a similar metabolic and hormonal response to a long-distance swimming competition in cold water.

Adolescent↗

PubMed1987

Role of autonomic nervous system in postprandial thermogenesis in dogs.

Two phases in postprandial thermogenesis have been recently identified in dogs; an initial cephalic phase lasting 45 min and a subsequent digestive phase occurring after 45 min. The objective of this study was to determine the role of the autonomic nervous system during these two phases in dogs. O2 uptake (VO2) as well as respiratory quotient (RQ) were monitored at least 1 h before and 2 h after a meal of 1,034 kcal under the following infusion conditions: saline, propranolol, atropine, propranolol plus atropine, phenoxybenzamine, and propranolol plus phenoxybenzamine. The initial peak value for VO2 increase was 100% in the cephalic phase and 40% in the digestive phase during the saline infusion. The VO2 response during the initial phase was 58 and 56% less with propranolol and atropine, respectively, compared with the control experiment. A 36% decrease in the VO2 response was found during the digestive phase with propranolol, whereas it was abolished by atropine. Propranolol and atropine given together decreased the VO2 response during the cephalic phase by 27% and abolished it completely in the digestive phase. Phenoxybenzamine did not affect the VO2 or RQ responses during the whole period and when given in combination with propranolol the same result as propranolol alone was found. These findings indicate that both the parasympathetic and sympathetic nervous system participate in the control of postprandial thermogenesis during both the cephalic and digestive phases.

Animals↗

PubMed1987

Hormonal control of postprandial thermogenesis in dogs.

The role of catecholamines, insulin, and thyroid hormones on postprandial thermogenesis was determined in dogs. O2 consumption (VO2) and respiratory quotient (RQ) were continuously monitored 1 h before and 2 h after a 1,016-kcal meal under the three following experimental conditions corresponding to 1) normal feeding, 2) sham feeding (with food deflected into an esophageal pouch), and 3) tube feeding intragastrically. A first phase (cephalic phase), lasting at least 45 min, was observed during both normal and sham feeding, whereas a second phase (digestive phase), occurred in both normal and tube feeding. Increases of 260% for norepinephrine (NE) were found during the cephalic phase in both normal and sham feeding. Epinephrine (E) increased by 425 and 600% during this early phase in normal and sham feeding, respectively. No change in plasma catecholamines was found in the tube-feeding experiment. Large increases of 75 and 39 microU/ml of insulin occurred early after the meal in both normal and sham feeding, whereas insulin increased only after 30 min in tube feeding. Thyroxine and triiodothyronine were not changed with any feeding experiment. Insulin change was positively correlated with NE and E changes rather than with glucose change during the cephalic phase after feeding. The results suggest an important role of catecholamines in the increased postprandial thermogenesis during the cephalic phase with a possible modulating effect of insulin.

Animals↗

PubMed1987

Results of surgery for hypertrophic obstructive cardiomyopathy.

Between 1971 and March 1986, 61 patients underwent surgery for hypertrophic obstructive cardiomyopathy. Age at operation varied from 3.5 to 76 years (mean 38). The standard approach was a generous transaortic myectomy. One-quarter of the patients underwent concomitant repair of associated lesions. There was one operative and two late deaths, for an actuarial 5 years survival 93% (+/- 8%). Average follow-up is 3 years per patient. Sixty-four percent of these patients are asymptomatic and another 30% were in New York Heart Association class II. Persistent symptoms were usually related to arrhythmias. Early atrioventricular block did not occur, but two patients were paced for complex arrhythmias 3 and 4 years after surgery. Hemodynamic studies (n = 22), two-dimensional echocardiographic (n = 47), and Doppler assessments (n = 23) demonstrated a left ventricular outflow tract pressure gradient of 70 and 14 mm Hg before and after surgery, respectively, left ventricular diastolic pressure of 18 and 14 mm Hg, percent of patients with mitral regurgitation of 70% and 30%, percent of patients with systolic anterior motion of 100% and 35%, and percent of patients with aortic insufficiency of 9% and 49%. Eight-six percent of the patients catheterized had no resting obstruction. Subaortic myectomy produces symptomatic improvement by reducing the left ventricular outflow tract pressure gradient, mitral regurgitation, and left ventricular end-diastolic pressure, and probably improves longevity.

Adolescent↗

PubMed1986

Exercise suppression of thermoregulatory thermogenesis in warm- and cold-acclimated rats.

An evaluation was made of the effects of an acute exercise bout on nonshivering thermogenesis (NST) in cold-acclimated rats (4 degrees C for 6 weeks) and shivering thermogenesis in 24 degrees C-acclimated rats (24 degrees C for 6 weeks). Assessment techniques included indirect calorimetry during treadmill running and brown adipose tissue (BAT) mitochondrial guanosine diphosphate (GDP) binding immediately following a treadmill run. Calorimetric results for 24 degrees C-acclimated rats running at 4 degrees C indicated total substitution of shivering thermogenesis by exercise-derived heat. No difference in GDP-binding, an index of BAT nonshivering thermogenic activity, was observed between exercised and nonexercised 24 degrees C-acclimated rats. Calorimetric results for cold-acclimated rats running at 4 degrees C indicated a total suppression in the energy cost associated with NST, exercise-derived heat replacing or substituting for NST. Examining BAT properties in the exercised cold-acclimated rats revealed a significant 40% decrease in BAT mitochondrial GDP-binding. These results suggest that during running, metabolic heat due to the exercise totally replaces shivering in 24 degrees C-acclimated rats and totally replaces BAT nonshivering thermogenesis in cold-acclimated rats.

Acclimatization↗

PubMed1986

Thermogenesis in response to various intakes of palatable food.

Complete energy balance studies were made on groups of overfed (A) and underfed (B) Wistar rats. In experiment A one group was fed cafeteria diet ad libitum (the intake was 29% larger than the control), two other groups were fed the same diet but in restricted quantities (18 and 9% above control), and a fourth group, fed a stock diet, served as control. In experiment B, caloric intake was restricted by 12 and 31% in two groups fed cafeteria diet, and by 21 and 34% in two other groups fed stock diet. The experiments lasted 41 days and during that period the protein gain was comparable between the control and the cafeteria-29% group (643.4 +/- 33.3 vs. 578.1 +/- 25.0) but the fat gain was significantly different between the two groups (863.2 +/- 81.6 vs. 1663.2 +/- 99.8 kJ). When energy expenditure (EE) (metabolizable energy less storage added to the cost of storage) is expressed as a percentage of metabolizable energy (ME) intake no significant difference was found among the groups. The average value was congruent to 75%. This finding would not support the presence of dietary-induced thermogenesis in animals overfed on the cafeteria diet. However, since the obligatory cost associated with storing energy would not explain the higher EE of the overfed groups, it is suggested that the level of ME intake exerts continuous proportional regulatory action on EE and, as a result, energy is spared by underfeeding and it is wasted by overfeeding.(ABSTRACT TRUNCATED AT 250 WORDS)

Adipose Tissue, Brown↗

PubMed1986

Effect of meal size and frequency on postprandial thermogenesis in dogs.

The influence of meal size and frequency on postprandial thermogenesis was studied in nine mongrel dogs (congruent to 18 kg). Oxygen uptake (VO2) and respiratory quotient (R) were continuously monitored by indirect calorimetry during the following experiments. In expt 1, four dogs were fed on alternated days either a large (3.1 MJ) or small meal (0.77 MJ). In expt 2, five different dogs were fed on alternated days either one large meal (3.1 MJ) or four consecutive small meals (0.77 MJ) spaced at 1.5-h intervals. In expt 3, the four dogs of expt 1 after being sham fed 3 times at 1.5-h intervals were given one large meal (3.1 MJ). The VO2 increase during the initial or cephalic phase (congruent to 50 min) was independent of the meal size but it was directly proportional to the amount of food ingested during the digestive phase. The total thermogenic response to four small meals (125 g) fed at 1.5-h intervals was twice as large as that of one large meal (500 g). One large meal (500 g) preceded by three periods of sham feeding was also found to be more thermogenic than a large meal only. For all experiments the changes in R were seen to parallel the postprandial fluctuations in VO2. These findings indicate that the enhanced heat production obtained when meal frequency is increased is caused by the repeated sensory stimulation produced by palatable food.

Absorption↗

PubMed1985

Palatability and postprandial thermogenesis in dogs.

The role of palatability on postprandial thermogenesis was determined in six mongrel dogs of approximately 16 kg. Oxygen uptake (VO2) was continuously monitored by indirect calorimetry for 1 h before and 2 h after a standard meal of 1,390 kcal. In the first experiment each dog was given access to the meal, which was ingested within 5 min. In a second experiment the same meal was sham fed and collected into an esophageal pouch. In a third experiment the dogs were tube fed. In the first experiment a biphasic response was found in the postprandial increase in metabolic rate; a first phase lasting approximately 40 min and the other from 40 to 125 min. In the second experiment the increase in VO2 was comparable with that of the first experiment for the first 40 min but almost abolished for the remaining period; the sight and smell of food alone produced a similar effect. In the third experiment tube feeding caused a small increase in VO2, which was four times smaller than that found in both the first and the second experiment during the initial phase. However, during the second phase the increase in VO2 was comparable with that of experiment 1. An initial phase of feeding lasting approximately 40 min is identified with food palatability, whereas the second phase would correspond to a large extent to specific dynamic action of food.

Animals↗

PubMed1985

Role of palatability on meal-induced thermogenesis in human subjects.

To study the possible participation of food-induced sensory stimulation on meal thermogenesis an experiment was performed with eight female subjects. On alternate days subjects were fed either a highly palatable meal (HPM), containing 710 calories, or a nonpalatable meal (NPM). The NPM was prepared by mixing all the ingredients of the HPM and was presented to the subjects as a desiccated biscuit. The subjects were not informed about the composition of the NPM, which they rated as tasteless and unappetizing. The increase in O2 consumption was approximately 20% during the 90 min following the HPM compared with 12% with the NPM (P less than 0.01). With comparable increases in plasma glucose, plasma insulin level was significantly (P less than 0.01) lower following NPM ingestion than with ingestion of the HPM. At that time a significant increase in plasma norepinephrine was also observed but only following ingestion of the HPM. It would appear that both central sensory stimulation or plasma insulin level, as affected by food palatability, could be considered at this time as possible activators of the increased sympathetic activity observed following ingestion of the HPM. It is suggested that a part of meal thermogenesis is due to food palatability and that the concomitant activation of the sympathetic system may be related to this action.

Adult↗

PubMed1985

Enhanced metabolic response to caffeine in exercise-trained human subjects.

The effect of caffeine on resting metabolic rate (RMR) was investigated in eight trained and eight nontrained young male subjects. The ingestion of 4 mg/kg caffeine produced a greater increase of RMR in trained subjects. This effect was associated with a greater increase in plasma free fatty acids and a larger fall in respiratory quotient, indicating an enhanced lipid oxidation following caffeine in exercise-trained subjects. An initial fall in plasma glucose was observed but only in trained subjects, and caffeine did not change plasma insulin in either group studied. Caffeine caused a significant fall in plasma norepinephrine and an increase in plasma epinephrine in both groups of subjects, but this action was significantly greater in trained subjects. It is suggested that the greater increase in RMR observed in trained subjects following caffeine ingestion is related to an enhanced lipid mobilization, possibly produced by a greater epinephrine secretion and by subsequent increased lipid oxidation.

Adipose Tissue↗