Effects of ethanol on energy balance of rats and the inappropriateness of intraperitoneal injection.

Energy balance of female rats that were either injected daily with ethanol or received the alcohol by gavage was determined and the results compared with saline animals. Food intake, feces elimination, and body weight were recorded daily. After a 20-day period of treatment the animals were sacrificed and the energy content of the carcasses and feces was determined by bomb calorimetry. The results indicated that ethanol-injected animals underwent an impairment in the energy balance, with losses in body weight and body energy. Also, there was a decrease in metabolized energy intake. The results of a group of saline rats pair-fed to alcohol-injected rats showed that the impairment of the energy balance was not only a consequence of the decreased energy intake, because the ethanol-fed animals had an energy balance that was worse than the one of the pair-fed rats, even though both had eaten the same amount of food. Nevertheless, when alcohol was given by gavage, no alteration in the energy balance parameters was detected. Macroscopic observation of the abdominal cavity showed adherences in the gut of the alcohol-injected animals. It is concluded that the ethanol by itself does not alter the energy balance; however, depending on the route of administration it could indirectly impair the energy balance.

Thermogenic mechanisms in cold-acclimated animals.

1. This paper reviews the mechanisms of thermogenesis after cold-acclimation. 2. Upon exposure to cold, the oxygen consumption of animals increases by means of shivering and non-shivering thermogenesis. As cold exposure progresses, shivering decreases while non-shivering thermogenesis increases, so that the cold-acclimated animal produces heat mostly by non-shivering thermogenesis. 3. Brown adipose tissue in several species, including man, is an essentially thermogenic organ that produces heat by uncoupling mechanisms in mitochondria. 4. The activity of brown adipose tissue can be assessed by physiological and biochemical methods. 5. After cold acclimation, the activity and mass of brown adipose tissue are higher than in control animals. Brown adipose tissue is considered the main factor responsible for non-shivering thermogenesis.

Energy balance of pregnant rats.

Energy balance of pregnant and non-pregnant female rats was determined after 20 days of gestation. Energy contents of male and female pups and placentae were also determined. The metabolizable energy intake of pregnant rats was 33% higher than that of non-pregnant controls. Body weight gain was 9.4-fold that of non-pregnant rats. Gains in energy and body weight in pregnant rats exceeded those of pups and placentae. This implies that the excess energy was stored, probably for later use in an energy-requiring process such as lactation. Food was processed as expected in pregnant rats, since although gross food efficiency (gain in body energy divided by metabolizable energy intake) was greater in pregnant than in non-pregnant rats (5.4% vs 17.5%), only 53.7% of the extra energy intake was deposited in the dams.

Effect of food intake on oxygen consumption in cold-acclimated rats.

The objective of the present study was to determine the relative importance of thermoregulatory and energy conservation mechanisms in cold-exposed, food-restricted rats at thermoneutrality. Oxygen consumption was measured at 25 degrees C and 10 degrees C in rats acclimated at 30 degrees C and fed ad libitum and in animals acclimated at 10 degrees C and either fed ad libitum or subjected to food restriction. Rectal temperature was taken before and after each oxygen consumption measurement. Rats from all three groups showed a similar oxygen consumption measured at 10 degrees C. At 25 degrees C, the cold-acclimated rats on ad libitum intake displayed a higher oxygen consumption than did non-acclimated animals. The food-restricted rats at thermoneutrality showed an oxygen consumption similar to that of non-acclimated animals. Rectal temperature did not change significantly under any type of condition. It is concluded that the energy conservation mechanism in food-restricted rats is present only when the thermoregulatory drive is not too strong.

The effect of fasting and refeeding on oxygen consumption by rats.

Oxygen consumption is usually measured on fasted animals to avoid the thermal effect of feeding. However, fasting itself may decrease oxygen consumption as a way of conserving energy. The present study was undertaken to determine how long the fasting period should be to avoid the thermal effect of feeding without promoting a further decrease in oxygen consumption by the activation of energy-conservation mechanisms. Oxygen consumption was also measured to evaluate the effect of refeeding after different fasting periods. There was a 16% decrease in oxygen consumption from 0 to 12 h fasting related to the thermal effect of feeding, followed by a less intense (12%) decrease from 12 to 48 h fasting resulting from the energy conservation mechanism. During refeeding, oxygen consumption was higher during the first 30-min period than during the last 30-min period of the 1-h measurement, indicating the probable presence of a cephalic phase of postprandial thermogenesis. We conclude that 12-h fasting is the most appropriate period to avoid the thermal effect of feeding without significantly stimulating the energy conservation mechanism.

Effects of temperature acclimation on rabbit metabolic rate and rectal temperature.

The metabolic rates and rectal temperatures of cold-(10 degrees C), warm-(20 degrees C) and heat-(30 degrees C) acclimated rabbits were measured at 10, 20 and 30 degrees C. When the logarithm of metabolic rate was plotted against the logarithm of body weight, no differences could be demonstrated between the slopes of the lines obtained for each of the nine experimental groups. Metabolic rate, expressed as kcal h-1 kg-1, kcal h-1 kg-3/4 and kcal h-1 kg-2/3, was mass-independent for most of the experimental conditions. The rabbits were able to maintain constant rectal temperature during cold or heat exposure only when previously acclimated to these temperature extremes. The increase in metabolic rate of cold-acclimated rabbits observed during cold exposure seemed to be too low to explain the maintenance of rectal temperature. The lower metabolic rate of heat-acclimated rabbits exposed to heat probably played an important role in preventing increased rectal temperatures.

Energy balance of rats subjected to continuous and intermittent food restriction.

Data from our laboratory have demonstrated that food restriction leads to alterations in energy balance such as reduced energy expenditure as an energy conservation mechanism. Food restriction may be imposed on the animals in different ways. The most common is to give equal daily amounts of restricted food. Alternatively, food may be given once every two or three days so that the food intake is not constant with the animal tending to eat more on the first day and be very restricted during the subsequent days of the period. The former model may elicit habituation to the low food intake while the latter may decrease the habituation stimulus since the food intake is not constant. Energy balance was determined in 3 groups of female rats weighing 206.7 +/- 2.0 g (N = 6 each): control (C), which received food ad libitum; continuously food restricted (CR), which received 8 g of food daily, and intermittently food restricted (IR), which received 24 g of food every 3 days. On the 21st day of treatment, the animals from both food-restricted groups showed a similar reduction of body weight (-47.9 +/- 5.1 and -55.8 +/- 4.0 g for CR and IR, respectively) and body energy (-501.0 +/- 65.5 and -427.0 +/- 82.1 for CR and IR, respectively), and they had similar energy expenditure (2643 +/- 72 and 2518 +/- 97 for CR and IR, respectively) which was different from ad libitum controls (4.6 +/- 2.9 body weight gain, 277.3 +/- 42.5 body energy gain and 4574 +/- 290 energy expenditure). Body weight decreased continuously in the CR group while in the IR group it followed the pattern of food intake with up-and-down shifts. We conclude that the energy balance pattern presented by food-restricted animals is the same regardless of the form of food restriction imposed.

Oxygen consumption of rats with broad intestinal resection.

The study was performed to investigate possible alterations in oxygen consumption in an animal model with broad intestinal resection. Oxygen consumption and the thermal effect of a short meal were measured in rats subjected to short bowel syndrome. Four groups of rats were used. Group I was the control group, group II was sham operated, group III was submitted to 80% jejunum-ileum resection, and group IV was submitted to 80% jejunum-ileum resection with colon interposition. Ninety days after surgery, oxygen consumption was measured over a period of 6 h with the animals fasted overnight. The thermal effect of feeding was determined in another session of oxygen consumption measurement in animals fasted for 12 h. A 12-kcal meal was then introduced into the animal chamber and oxygen consumption was measured for a further 4 h. No differences in fasting oxygen consumption or in the thermal effect of the meal were detected among the groups studied. It is concluded that short bowel syndrome does not affect the overall energy expenditure of rats.

Ventilatory responses during electrically induced muscular work in anesthetized dogs, after both deafferentation and cross circulation of hindlimbs.

1. The role of the neural afferent component from moving limbs during exercise hyperpnea has been studied in dogs. The influence of neural and humoral effects was evaluated by dorsal root section and limb cross-circulation. 2. Respiratory minute volume (Ve), frequency (f), tidal volume (VT) and oxygen consumption (VO2) were measured in anesthetized dogs submitted to light electrically-induced exercise (ventral root stimulation of L6 or L7), both before and after deafferentation. 3. In control experiments the increase of respiratory minute volume (Ve) was directly proportional to VO2, and primarily due to changes in frequency. After dorsal root section (L1 to S1), VO2 increased, but no significant changes were observed in the other respiratory parameters. 4. In contrast to the deafferentation experiments, no changes were detected either in Ve or in f during exercise in the cross-circulation experiments. 5. It is concluded that during light exercise reflexes generated by moving limbs are important for triggering the exercise tachypneic response.

Potassium-induced ventilatory reflexes originating from the dog hindlimb during rest and passive exercise.

1. It has been previously shown that Ketalar-anesthetized dogs do not exhibit alterations either in ventilation or in oxygen uptake during passive motion. In the present study, the same model was used to study the effects induced by increasing extracellular K+ to the concentration achieved during active exercise. 2. The isolated hindlimbs of twelve dogs anesthetized with ketamine hydrochloride i.v., after induction with sodium pentobarbital, were perfused with control (2.8 mM KCl) and experimental (8 mM KCl) physiological solutions under resting conditions, and in passive motion. 3. Respiratory minute volume (VE), respiratory rate (f) and tidal volume (VT) were determined by collecting the expired air in a Tissot gasometer. 4. During the control perfusion, the values of VE, f and VT for passive exercise did not differ significantly from those obtained under resting conditions. However, during perfusion with 8 mM KCl, a significant increase in VE was observed, possibly due to an increase of VT under resting conditions and to an increase of f during passive exercise. 5. The results suggest that passive exercise can induce a significant increase in ventilation only when accompanied by local chemical changes such as an increase in extracellular K+.

The participation of shivering and nonshivering thermogenesis in warm and cold-acclimated rats.

1. Both shivering and nonshivering thermogenesis are ways of increasing oxygen consumption in the rat. The participation of nonshivering thermogenesis after cold acclimation is well established, but there is little evidence of the relative importance of each kind of thermogenesis in acclimated and nonacclimated rats. 2. Oxygen consumption and rectal temperature were measured in warm and cold-acclimated rats exposed both to cold (10 degrees C) and warm (30 degree C) environments. 3. Shivering was blocked by mephenesin (10 mg/100 g body wt) and nonshivering thermogenesis was blocked by propranolol (0.5 mg/100 g body wt). 4. Control animals were injected with saline (0.5 ml/100 g body wt). 5. The results showed that shivering is not effective in maintaining a constant rectal temperature and that nonshivering thermogenesis does not contribute to the increase in oxygen consumption of warm-acclimated rats exposed to cold.

Food restriction and refeeding in growing rats.

1. The interrelationship between food intake, body weight and oxygen consumption was analysed at 25 degrees C in growing rats. 3. The experiment was divided into two phases lasting four weeks each. During the first phase the animals were subjected to energy restriction and during the second phase they were allowed ad lib energy intake. Four groups of rats were studied: Control with ad lib food intake and three restricted groups R4, R5, and R6 which received during the first phase 4, 5, and 6 g per day of stock diet in a single meal. 3. The results showed a decrease in body weight and oxygen consumption during the restriction period and a recovering of the latter during the refeeding period, without body weight recovering. 4. It is concluded that an energy conservation mechanism is present during food restriction and for some time after refeeding.

Distribution of energy between food-restricted dams and offspring.

Pregnant and nonpregnant rats were subjected to one of four food intake schedules: ad libitum, 20, 40 and 60% of food restriction, during 20 days, with the objective of studying the distribution of energy between food-restricted mothers and offspring. The animals were anesthetized and the conceptuses were removed and separated into male, female, and placental tissues. The rats were then killed and all carcasses were prepared for energy balance determination. A baseline group of weight-matched rats were killed in the first day of the experiment to evaluate the initial body energy. The results obtained showed that the energy balance of pregnant rats was impaired as a consequence of the food restriction imposed. The offspring from restricted mothers had lower body weight and energy content and were less in number than the ones from the control dams. It is also suggested that food restriction causes the mother to transfer similar percent energy to the offspring as in control animals which will deplete the mother energy stores more than in ad libitum fed rats.

Effect of long term differences in energy intake on metabolic rate and thyroid hormones.

Long term effects of differences in energy intake on thyroid hormone metabolism and the rate of oxygen consumption were studied in two groups of young pigs. The pigs were kept at 25 degrees C and fed either a high (H) or low (L) energy intake such that H = 2L for six weeks. The rate of oxygen consumption, the plasma levels of thyroxine (T4) and 3,5,3'-triiodothyronine (T3) and the fractional rate of disappearance of T4 and T3 were measured each week. The metabolic rate at thermal neutrality was lowest in the animals on the L intake and the critical temperature was lowest in the pigs on the H intake. These differences tended to increase with time. The fractional disappearance rate (K) for T4 began by being greater in the animals on the H intake, but after four weeks the difference reversed. The catabolic rate of T4 in nmol.kg-1h-1 showed similar changes. The k values for T3 were not significantly different between treatments. It is tentatively suggested that the different energy intakes lead to a change in the tissue sensitivity to thyroid hormone.

Effects of aging on the energy balance of pregnant rats.

In pregnant and non-pregnant female rats at various ages the energy balance was determined to study the age-induced alterations in the mother and conceptus. The animals were anesthetized and the conceptus removed and separated into male, female, and placental tissues. The animals were then killed and the carcasses prepared for energy balance determination. The results obtained showed that the older animals gained less energy in the body and had lower gross food efficiency than the younger animals. The number, energy and weight of the offspring were not affected by the mother's age. Nevertheless, due to its constant growth during life, the rat is not the best model to study age-related processes.

The effect of benzodiazepine on the increase of oxygen consumption in cold exposed rats.

1. Oxygen consumption and rectal temperature of warm and cold acclimated rats were measured after chronic and acute injections of saline or benzodiazepine (diazepam). 2. Benzodiazepine has blocked the increase in oxygen consumption of warm acclimated rats on exposure to cold. 3. After cold acclimation, the benzodiazepine did not affect the increase in oxygen consumption. 4. Benzodiazepine caused a slight hypothermia when injected chronically, but did not affect rectal temperature over a short period of time.

Impact of maternal food restriction on cold-induced thermogenesis in the offspring.

Food restriction imposed during pregnancy usually leads to many alterations in the development of the conceptus. Some of these alterations can be reverted after birth by adequate nutritional rehabilitation, while there are others which are permanent. The aim of this article is to study the influence of maternal food restriction on offspring thermoregulation. Offspring of dams with food restriction during pregnancy (50%) were fed ad libitum after weaning. Rectal temperature was measured every 15 days from weaning to the 90th day of life. From the 60th to the 90th day the animals were either acclimated at 25 or 5 degrees C. On the 90th day the animals were killed and their carcasses were processed for energy balance analysis and body composition determination. The results showed that animals from food-restricted mothers were not able to maintain body temperature for a longer period of time than the pups from control dams. Energy balance parameters and body composition did not show significant differences between rats from control and food-restriction mothers at the same environmental temperature. Thus, the results suggest that intrauterine food restriction may delay the development of the hypothalamus-thyroid axis which, in turn, may affect brown adipose tissue development leading to inefficient thermoregulation during neonatal life.

The involvement of the sympathetic nervous system in meal-induced thermogenesis in mice.

The acute effect of food intake on the activity of the sympathetic nervous system (SNS) in both heart and brown adipose tissue (BAT) was investigated in mice. Upon delivery to the laboratory mice were housed singly and divided into two groups. Half the mice were accustomed to eat their daily food ration in two meals whereas the other half were given continuous access to food. SNS activity in both heart and BAT was estimated by measuring the accumulation of dopamine (DA) after having blocked the transformation of dopamine into noradrenaline (NA) with 1-cyclohexyl-2-mercapto-imidazole (CHMI). CHMI inhibits the enzyme dopamine beta-hydroxylase. On the day SNS activity was assessed, continuously fed (CF) or meal-fed (MF) mice were injected with either saline or CHMI one hour before being killed. In order to assess the anticipatory effects of being fed, a group of mice already accustomed to the meal-feeding schedule were not allowed to eat after the injections. Additional CF and MF mice were killed without being injected in order to determine the basal levels of both DA and NA. The results show that the accumulation of DA in both heart and BAT was higher in MF than CF mice regardless of whether MF mice were or were not fed after the injection of CHMI. It therefore appears that the intake of food may increase SNS activity in various tissues in mice, and that such a response may be largely of cephalic origin.

Effects of fasting and food restriction on sympathetic activity in brown adipose tissue in mice.

The activity of the sympathetic nervous system in mice that were either fed ad libitum, food restricted or fasted was estimated by measuring the accumulation of dopamine following the inhibition of dopamine beta-hydroxylase activity. Mice in each group were injected with the dopamine beta-hydroxylase inhibitor 1-cyclohexyl-2-mercaptoimidazole and were exposed to either 30 degrees C (warm) or 4 degrees C (cold). Mice were killed 1 h after the injection. Both heart and brown adipose tissue were then quickly removed and homogenized in ice-cold perchloric acid. Dopamine and noradrenaline were determined using high performance liquid chromatography. Regardless of whether mice were warm or cold exposed, both content and concentration of brown adipose tissue and dopamine were predictably higher in 1-cyclohexyl-2-mercaptoimidazole-injected mice than in non-injected animals. In mice fed ad libitum, post-injection content and concentration of dopamine in both brown adipose tissue and heart were higher in cold-exposed mice than in warm-exposed animals. In food-restricted and fasted mice, post-injection concentrations of dopamine in brown adipose tissue were higher in cold-exposed mice than in warm-exposed animals. In food-restricted and fasted mice there was no difference between warm- and cold-exposed animals with respect to post-injection contents and concentrations of dopamine in heart tissue. In fasted mice there was no difference between warm- and cold-exposed animals in post-injection content of dopamine in brown adipose tissue. This study provides further evidence that fasting, in contrast to food restriction, may blunt the tissue sympathetic nervous system response in brown adipose tissue of cold-exposed mice.

Energy expenditure of rats subjected to long-term food restriction.

Food restriction, even when expressed per unit of metabolic mass, leads to energy conservation as seen by decreased oxygen consumption. The objective of the present study was to verify whether the energy conservation mechanism reduces energy expenditure for as long as food restriction lasts or whether a return to basal level may occur without realimentation, mainly in mildly food-restricted rats. Wistar rats were brought to the laboratory on weaning. They were then assigned to control group that received ad libitum food intake, R10 and R20 groups that received 90 and 80%, respectively, of the food eaten by control group and RM group that received an amount of food enough only to keep body weight. The food restriction period lasted for 3 months and was followed by another month during which all groups received ad libitum food intake. The results showed that even in animals subjected to mild food restriction (10%) there was a sustained decrease in oxygen consumption that lasted until refeeding of the animals. The results led to the conclusion that the energy conservation mechanism is active from little food restriction until more stronger levels of restriction, in a proportional manner, and the decreased energy expenditure is maintained during the whole food restriction period.