Effects of ageing on the energy balance of food-restricted rats.

AIMS: Age can alter energy balance by decreasing the resting metabolic rate. Food restriction can also change energy balance by decreasing energy expenditure as a mechanism of energy conservation. We investigated the influence of food restriction on the energy balance of rats at different ages. METHODS: Wistar EPM-1 female rats were used at ages of 3, 9, 15 and 21 months. At each age, two food intake schedules were provided: control (ad libitum) and food restriction (50%). Animals remained under these schedules for 30 days, and throughout this period body weight, food intake, and stool collection were controlled daily. On the 30th day, animals were killed, blood was collected and the carcasses and faeces were processed for analysis by pump calorimetry. Blood glucose, T(3), T(4) and rT(3) levels were determined. RESULTS: Food restriction reduced energy gain and gross food efficiency of animals at different ages, but more so in older animals. Food-restricted rats also had lower energy expenditure than controls. This reduction was about 40% of the energy expenditure of control animals irrespective of age. Water content increased and fat content decreased in the carcass of food-restricted animals. Serum T(3) and T(4) levels were lower in food-restricted animals pointing out to a major role of thyroid hormones in the mechanism of energy conservation exhibited by food-restricted animals. CONCLUSIONS: The mechanism of energy conservation takes place in all restricted animals and is very important for survival and for species preservation, mainly in aged animals in which food restriction is frequently aggravated by senescence-related organic disorders.

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.

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.

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.

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 percent jejunum-ileum resection, and group IV was submitted to 80 percent 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

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 influence of food restriction during different periods of pregnancy.

Considering that the energy balance can be affected by factors such as pregnancy and food restriction and that the development of foetuses is different during different periods of pregnancy, the aim of this paper was to study the effects on the maternal and offspring energy balance of food restriction imposed at different periods of pregnancy. Pregnant and non-pregnant rats were subjected to four food intake treatments. Control groups received food ad libitum during the 20 days of the experiment. The other three groups were food restricted by receiving 50% of the control group food intake during the first half, the second half, or the whole experimental period. Food restriction imposed during the first half of the experimental period permitted a recuperation of energy intake, but compared to the control group, the rats gained less energy in the body. The offspring parameters studied were not affected by food restriction during the first half of the experimental period. Food restriction during the second half was more deleterious to the dams and to the offspring, which were born with less energy and weight. When food restriction was applied during the whole experimental period, the impairment in energy balance of offspring was similar to the one observed when food restriction occurred during the second half of pregnancy added to a decreased number of offspring. The dams, however, were more deeply affected than when food restriction was applied during the first half of the experimental period.

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.

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.

Energy balance in subcutaneous melanoma-bearing mice

Energy balance of control and melanoma-bearing mice was determined after 15 days of controlled food intake. Body and tumor energy contents were evaluated after preparing the materials for bomb calorimetry. Neither energy intake nor expenditure was different between control and melanoma mice. Body energy gain was lower in melanoma mice, but including tumor energy both groups had similar energy gain during the experimental period. It is concluded that a two-week skin melanoma did not seriously affect the energy balance of mice, and that tumor growth was achieved by utilizing body energy without promoting any increase in energy intake.

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.

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 period. The former model may elicit habituation to the low food intake-while the latter may decrease the habituatiuon stimulus since the food intake is not constant. Energy balance was determined in 3 groups of female rats weighing 206,7 + or - 2.0 g (N=6 each): control (C), which, received food ad libitum; continuosly 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 + or - 5,1 and -55.8 + or - 4.0 g for CR and IR, respectively) and body energy (-501.0 + or - 65.5 and -427.0 + or - 82.1 for CR and IR, respectively), and they had similar energy expenditure (2643 + or - 72 and 2518 + or - 97 for CR and IR, respectively) which was different from ad libitum controls (4.6 + or - 2.9 body weight gain, 277,3 + or - 42.5 body energy gain and 4574 + or - 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 in the same regardless of the form of food restriction imposed

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 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.

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 oxyge 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 conservationn 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

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.

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.

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.

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 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

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.