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Biomedical subjects

J LeBlanc

Publications and source records attributed to J LeBlanc.

At least 91 records · Page 5Linked to original sources
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↗
PubMed1981

Glycogen and nonspecific adaptation to cold.

Exposure to moderate cold for a few weeks causes adaptation through the development of nonshivering thermogenesis primarily in the brown adipose tissue. Exposure to severe cold by repeated short exposures also causes adaptation but by mechanisms that seem to be different. These latter results were confirmed in mice. It was also found that this type of adaptation is nonspecific because it can be produced by other stresses such as swimming or fasting. Simultaneous determinations of glycogen in the liver and soleus and tibialis muscles indicated a possible role for this substrate in cold resistance. Repeated cold exposure (8 times at -15 degrees C for 10 min), swimming for 3 h, or fasting for 48 h--all reduced the glycogen stores when measured immediately after the stress. However, the levels of glycogen were significantly increased above the initial values (P less than 0.01) when the determinations were made 24 h later. Cold tolerance measured by resistance to hypothermia at -5 degrees C was improved only when the test was done 24 h after the stress had taken place. Thus, cold resistance, as described in this study, is nonspecific and our results suggest that glycogen stores could serve as a rate-limiting substrate.

Acclimatization↗
PubMed1981

Morphologic aspects of adhesion and spreading behavior of amphibian blastula and gastrula cells.

By means of SEM we have examined spreading and adhesive behavior of cells isolated from superficial and deep regions of germ layers from blastula to late gastrula in Rana pipiens embryos. Each of the cell populations sampled show adhesive and spreading characteristics distinctive for each region and stage which we interpret as demonstrating the following: (1) From blastula through late gastrula, cells from each region have already acquired the ability to express surface morphologic and adhesive features independently of their association with their neighbors, i.e. autonomously. (2) The distinctive spreading and adhesive characteristics for each tissue sub-population suggest kinetic properties seemingly related to their in vivo morphogenetic movements, epiboly or invagination. (3) The appearance within germ layers of two subpopulations between blastula to mid-gastrula, suggests early intratissue inductive interactions. (4) The outermost, superficial cells from each germ layer show proximal and distal surface differences which may reflect adhesive differentials as postulated by Steinberg (1970) for presumptive ectoderm cells. (5) With the exception of superficial cell proximal and distal differentiation, freshly disaggregated cells do not show morphologic characteristics seen in corresponding cells spreading for one hour.

Animals↗
PubMed1981

Calcium and spreading behaviour of amphibian blastula and gastrula cells.

Cell locomotion involves several structural-functional activities: membrane extensibility, microfilament regulation and adhesive interactions. There is evidence for Ca2+ requirement in all of these. Our data may clarify the role of Ca2+ in locomotion and adhesion. Morphologic and spreading responses of isolated blastula--late gastrula Rana pipiens germ layer cells to varying molar concentrations of Ca2+; 0-Ca2+, Standard Ca2+ (Barth's X solution), 1.5 x and 2.0 x Std Ca2+ were viewed by S.E.M. after 1 h in culture. Ionic strength and pH were constant. All cells showed quantitative relationships between Ca2+ concentration and surface extensibility, projection formation and presumably adhesion, but with tissue- and stage-specific variations. Cells in Ca2+-free medium fail to adhere (50%), flatten or form surface projections. Cells in media with increasing Ca2+ generally formed more numerous and extensive surface projections, spread and adhered to a greater extent. In some cases there were no quantitative differences in response between 1.5x and 2.0x standard Ca2+. Cells in suspension for 1 h in standard solution remained spherical, forming no projections. We infer from these results that both Ca2+ and contact with a physical substratum, cell--cell of cell--glass are required for mobilization of the various systems involved in locomotion and adhesion. In addition, components of these systems are quantitatively activated by increased availability of Ca2+.

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↗
PubMed1979

Effects of physical training and adiposity on glucose metabolism and 125I-insulin binding.

Eighteen young male subjects, aged 18-30 yr, with maximal oxygen intake (VO2max) varying between 36 and 80 ml.kg-1.min-1, were studied. Between 20 and 120 min after injection, tolerance to iv glucose (20 g/m2) was not affected by VO2max but the insulin response was very significantly reduced in the better trained subjects. 125I-insulin binding to monocytes was found to be greater in the best trained subjects. Simple correlation analysis indicates that both VO2max and adiposity are related to plasma glucose and plasma insulin levels as well as to 125I-insulin binding. Because VO2max is negatively correlated to percent of body fat, a partial correlation analysis was made. Results indicate that the differences observed in athletes with regard to glucose and insulin levels and 125I-insulin binding are related to reduced adiposity rather than to enhanced VO2max.

Adipose Tissue↗
PubMed1979

Plasma catecholamines and cardiovascular responses to cold and mental activity.

Plasma epinephrine (E) and norepinephrine (NE) as well as blood pressure and heart rate variations were measured in 12 male subjects before, during, and after a cold hand test (5 degrees C for 2 min), a mental arithmetic test, and a combination of both these tests. Although the cold and mental tests had comparable effects on blood pressure, the heart rate response was greater than the mental test. The mental test produced a greater increase of E than the cold test, but the effect of the cold test was greater on NE than on E. Changes in heart rate were significantly correlated with E variations but not with NE, whereas changes in blood pressure were correlated with NE. Resting NE was correlated with resting blood pressure and resting E with resting heart rate. Finally the levels of basal E were positively correlated with the increase in E during the test. Cardiovascular changes were shown to be differently modified by a mental and a cold test. Evidence was given indicating that these changes are related to differences in E and NE responses in the presence of these tests.

Adrenal Medulla↗
PubMed1979

An economic evaluation of present and proposed methods of compensating hearing loss.

The basis for compensation of industrial hearing loss in the Province of Ontario is described, and contrasted with schemes utilized in other parts of Canada, United Kingdom, Australia, and the United States. Changes are suggested for the method used to derive the percentage of permanent disability related to hearing loss. A randomly selected population of claimants for industrial hearing loss have been used to model the economic effect of such changes, which are discussed.

Audiometry↗
PubMed1978

Effects of age, sex, and physical fitness on responses to local cooling.

The response to local cooling was estimated by the cold hand test (5 degrees C for 2 min) and the cold face test (0 degrees C with 66 km.h-1 wind for 2 min). Heart rate, blood pressure, and skin temperature were measured before, during, and after the tests. The increase in blood pressure (cold hand test) and the fall in Tsk (cold face test) were reduced in trained subjects. Similarly older subjects (53-60 yr of age) responded less to a cold hand test than younger subjects aged 20-40. However, the bradycardia caused by the cold face test was more pronounced in the older subjects. The responses to the cold hand and cold face tests were the same for male and female subjects. During the 2 min after the test, blood pressure and heart rate fell below initial values in the female group but not in the male. It is concluded that, besides adaptation to cold, individual factors such as age, sex, and physical fitness also have a relative importance in the responses to local cooling.

Adult↗
PubMed1977

Metabolic and cardiovascular responses to norepinephrine in trained and nontrained human subjects.

Forty young male adults, aged 18-30 yr, with maximal oxygen intake (VO2 max) varying between 35 and 76 ml-kg-1-min-1 were studied. The fasting subjects were perfused for 15 min with saline and thereafter for 30 min with norepinephrine (0.1 mug/kg per min). Blood variables were determined at the end of slaine perfusion, at 15 and 30 min during norepinephrine perfusion and 15 min after the end of NE perfusion. Trained subjects are characterized by lower basal plasma glucose and insulin concentration. NE perfusion produced a larger increase in plasma glucose in the trained subjects. Levels of insulin in the postperfusion period were smaller in the trained group. Serum free fatty acids (FFA) and glycerol increased less in the trained subjects during NE perfusion and this difference persisted in the post-perfusion period. During NE perfusion, blood lactate increased only in the nontrained subjects. Initial heart rate and blood pressure were lower in trained subjects but, during NE perfusion, elevated levels of blood pressure and decreased levels of heart rate were comparable in both groups. Because of similarities in responses to exercise and to NE in trained subjects, the results of the present study suggest a possible role for NE in exercise training.

Adolescent↗
PubMed1976

Effect of adrenaline on insulin secretion in rats treated chronically with adrenaline.

To determine whether rats could adapt to a chronic exogenous supply of adrenaline by a decrease in the well-known inhibitory effect of adrenaline on insulin secretion, plasma glucose and insulin levels were measured in unanesthetized control and adrenaline-treated rats (300 mug/kg twice a day for 28 days) during an adrenaline infusion (0.75 mug kg-1 min-1), after an acute glucose load (0.5 g/kg), and during the simultaneous administration of both agents. Chronic treatment with adrenaline did not modify the initial glucose levels but it greatly diminished the basal insulin values (21.57+/-2.48 vs. 44.69+/-3.3muU/ml, p less than 0.01). In the control rats, despite the elevated glucose concentrations, a significant drop in plasma insulin levels was observed within the first 15 min of adrenaline infusion, followed by a period of recovery. In the adrenaline-treated group, in which plasma glucose levels were lower than in control animals, plasma insulin levels did not drop as in control rats, but a significant increase was found after 30 min of infusion. During the intravenous glucose tolerance test, the plasma glucose and insulin responses showed similar patterns; however, during the concomitant adrenaline infusion, the treated rats showed a better glucose tolerance than their controls. These results indicate that rats chronically treated with adrenaline adapt to the diabetogenic effect of an infusion of adrenaline by have a lower inhibition of insulin release, although the lower basal insulin levels may indicate a greater sensitivity to endogenous insulin.

Animals↗
PubMed1976

Effects of temperature and wind on facial temperature, heart rate, and sensation.

Skin temperature measurements of the face have shown that the cheek cools faster than the nose and the nose faster than the forehead. The cooling effect of wind is maximum at wind speeds between 4.5 and 6.7 m/s. Cold winds produce significant bradycardia, which is, however, much more pronounced during the expiratory phase of respiration. A significant correlation was noted between cooling of face and the reflex bradycardia observed. Similarly, a very significant correlation was noted between drop in skin temperature and subjective evaluation of cold discomfort. Consequently, the drop in skin temperature, reflex bradycardia, and subjective evaluation are parameters which are directly affected by cold wind and can be used as adequate indicators of the degree of discomfort. When comparing the present results with the windchill index, it was found that in the zone described as "dangerously cold" the index fits well with the physiological measurements. In the zone described as "bitterly cold," the index by comparison with actual skin temperature measurements and subjective evaluation underestimates the cooling effects of combined temperature and wind by approximately 10 degrees C.

Adult↗
PubMed1975

Effects of adrenaline on the dynamics of carbohydrate metabolism in rats treated chronically with adrenaline.

Following a subcutaneous injection of adrenaline (300 mug/kg), blood-glucose levels were lower in rats treated chronically with adrenaline (300 mug/kg twice a day for 28 days) than in control rats during at least 2.5 h after the injection. To explain this difference of response, the turnover rate of glucose was measured in control and adrenaline-treated rats during adrenaline infusion (0.75 mug/kg- minus 1 min- minus 1), with [U- minus 14C]glucose as tracer. It was found that the rate of appearance of glucose was greater in the control than in the adrenaline-treated group after a 120-min infusion of adrenaline. The rate of disappearance of glucose in the treated rats increased during the first 60 min of infusion and stayed at this elevated level for a subsequent 2 h, whereas in the control rats, it remained unchanged at the beginning of adrenaline infusion and significantly increased only during the second and third hours of infusion. In addition, the metabolic- clearance rate of glucose was not modified by adrenaline in the treated group, but in the control group, the initial clearance rate was significantly less than in the treated group, and decreased during the first hour of adrenaline infusion even though blood glucose reached values of 244 mg/100 ml. ,rom these data, it is suggested that rats adapt to a chronic exogenous supply of adrenaline by a reduced increase in glucose production in response to adrenaline infusion and a better glucose utilization, which possibly indicates a decrease in the inhibitory effect of adrenaline on insulin secretion.

Animals↗
PubMed1975

Autonomic nervous system and adaptation to cold in man.

The responses to cold hand test (blood pressure increase and tachycardia) and to a cold face test (blood pressure increase and bradycardia) were used to study the role of the autonomic nevrous system in cold adaptation in humans. The Eskimos (men, women, children) were shown to have a very weak sympathetic response to cold but the vagal response (bradycardia) was identical to that of white people. A group of mailmen from Quebec city living outdoors approximately 30 h/wk throughout the year was also studied. A significant decline in the cold pressor response and an enhanced bradycardia (cold face test) were observed at the end of the winter. Similarly the fall in skin temperature of the cheek was not as pronounced when the measurements were made in May compared to those made in October. A group of soldiers was also studied before and after an Arctic expedition. It was found that the bradycardia of the cold face test was also more pronounced after sojourning in the cold. These results indicate that repeated exposures to severe cold in men activate some adaptive mechanisms characterized by a diminution of the sympathetic response and a concomitant enhancement of the vagal activation normally observed when the extremities and the face are exposed to cold.

Adaptation, Physiological↗
PubMed1975

Ipsilateral acoustic reflex stimulation in normal and sensorineural impaired ears: a preliminary report.

Ipsilateral acoustic reflex thresholds were measured at 1,000 Hz and 2,000 Hz in 38 subjects with normal hearing and in 107 subjects with a symmetrical sensorineural hearing loss. Acoustic reflex thresholds were approximately six dB better for ipsilateral vs. contralateral stimuli for both subject groups. High ipsilateral reflex thresholds were associated with larger static compliance values in the sensorineural hearing impaired subjects. Reversed reflexes (increasing compliance with muscle contraction) were observed for ipsilateral stimulation in five per cent (two) of the normal hearing subjects, and 23 percent (25) of the sensorineural hearing impaired subjects. The number of reversed reflexes was greater for subjects with higher hearing thresholds and higher ipsilateral acoustic reflex thresholds. The results suggest that quantitative use of the ipsilateral acoustic reflex requires additional research. At present it seems prudent to use ipsilateral acoustic reflex measurements as a qualitative rather than a quantitative tool, e.g. in confirming the status of one middle ear when the other has a conductive hearing loss. However, even this limited role has a considerable clinical potential.

Acoustic Stimulation↗
PubMed1975

Studies on protein metabolism during isoproterenol-induced cardiac hypertrophy.

Chronic treatment with isoproterenol (ISO) (30 mug/100 g body wt/day for 21 days) causes a hypertrophy of the heart (approximately 40%). Protein determination made on homogenates of the heart show similar percentages of protein in the control and treated animals. Thus, ISO presumably stimulates protein synthesis in the heart, as its total protein content is increased by chronic treatment. Studies of the stimulation of protein synthesis during a 9-day treatment with ISO have been carried out by following the incorporation of 14C-labeled amino acids in vivo into heart protein. This stimulation attained a maximum after 5 days of treatment and then declined. In other experiments, groups of rats received a single injection of ISO and were killed at various times (from 0 to 48 hr) after the injection. Stimulation of protein synthesis was maximal 3 hr after the injection, and it slowly decreased until the 36th hr. After that time the rate of protein synthesis was equal to that of control animals. Other groups of rats received daily injections of ISO for 9 days and were killed at various times after the ninth injection. Protein synthesis was still stimulated by ISO; however, the stimulation was observed only during the first 12 hr following the injection of the 9th day. There was an apparent inhibition of protein synthesis which lasted from the 30th to the 48th hr following the ninth injection. The rate of protein degradation did not seem to be affected by a chronic treatment with ISO. Thus, the increased rate of protein synthesis seems to be the sole factor responsible for the increase of the total protein content of the heart, even if the stimulation of the incorporation of labeled amino acids decreased after a few days of treatment.

Animals↗