Tube-fed Rats Research Articles

Metabolic and sympathetic nerve activities of brown adipose tissue in tube-fed rats

To investigate possible contribution of oropharyngeal factors to thermogenesis in brown adipose tissue (BAT), rats were given a liquid diet orally or through a gastric tube for 4-12 days. Tube-fed rats weighed more and had heavier white adipose tissue than orally fed rats, although they were given the same amount of the diet. Triglyceride content of the interscapular BAT was higher in tube-fed rats, but the rate of fatty acid synthesis was lower than those in orally fed rats. Uptake of 2-deoxyglucose (2DG), an index of glucose utilization, in BAT was also lower in tube-fed rats. Surgical sympathetic denervation of BAT reduced both lipogenic activity and 2DG uptake to abolish the differences in these metabolic activities between tube-fed and orally fed rats. Sympathetic nerve activity in the BAT assessed from the turnover rate of norepinephrine in the tissue was lower in tube-fed rats. The results suggest that there is a sympathetically mediated mechanism dependent on afferent input from oropharyngeal receptors to regulate BAT thermogenesis and that greater fattening seen after tube feeding may be attributable to a decreased BAT thermogenesis because of the absence of food-induced sensory stimulation.

Energy Balance, Thermogenesis and Brown Adipose Tissue Activity in Tube-Fed Rats

Young adult male rats were given a portion (42%) of their normal daily food intake by stomach tube (tube-fed), but they were also allowed free access to the same powdered diet. Total metabolizable energy intake was identical to that of controls, but tube-fed rats gained 25% weight and 50% more body energy than controls over 15 days. Total energy expenditure and resting oxygen consumption, measured during the latter part of the day, were reduced in tube-fed rats. Intubated animals showed a lower thermogenic response to noradrenaline and depressed activity of the mitochondrial proton conductance pathway in brown adipose tissue (assessed from GDP-binding), but brown fat mass, protein content, the density of β-adreno-receptors in brown fat cell membranes and plasma triiodothyronine (T3) levels did not differ between groups. These data indicate that the enhanced energetic efficiency and fat deposition of tube-fed rats is due to a lower energy expenditure, resulting, at least in part, from lower levels of thermogenesis in brown adipose tissue.

Dietary obesity in golden hamsters: Reversibility and effects of sex and photoperiod

Golden hamsters fed a high-fat diet do not overeat, but they become obese because of decreases in energy expenditure. This decrease in actual energy expenditure is accompanied by increases in thermogenic capacity and brown adipose tissue mass, protein content, and DNA content. Three experiments examined this phenomenon in more detail. Experiment 1 demonstrated that this form of dietary obesity is largely reversible simply by returning the animals to a high-carbohydrate chow diet. However, the obesity which develops solely because of decreased energy expenditure is reversed primarily by decreased energy intake. In this respect fat-fed hamsters resemble tube-fed rats. Experiment 2 revealed that the effects of high-fat diet are at least as robust in female hamsters as in males. Experiment 3 examined the interactions between diet and photoperiod. Short days (10 hr light per 24 hr) had almost no effect on male hamsters fed Purina chow. However, nearly all of the effects of the high-fat diet (i.e., increases in body weight gain, feed efficiency, carcass energy content, percent ingested energy stored in the carcass, carcass lipid content, brown adipose tissue protein, and brown adipose tissue DNA) were exaggerated in hamsters housed in short days. High-fat-diet-induced increases in metabolic efficiency and thermogenic capacity may be of value in readying hamsters for winter. Furthermore, as winter approaches, decreasing day length might synergize with changes in diet quality to promote these beneficial changes in energy metabolism. Finally, fat-fed hamsters could be a useful animal model of some kinds of human obesity.

Effect of Antibiotics on Growth of the Immature Rat

The purpose of this study was to quantify the growth promoting effect of a mixture of antibiotics for rats eating diets deficient in protein or an essential amino acid. Male albino weanling rats (70 to 80 g weight, 4 weeks old) were fed (a) a control diet containing all other required nutrients and varying amounts of casein (0 to 27%), or (b) a purified amino acid diet containing all other required nutrients and varying amounts of valine (0 to 70 mumoles/g diet), threonine (0 to 69 mumoles/g diet) or tryptophan (0 to 8.6 mumoles/g diet), with and without an oral antibiotic supplement consisting of neomycin sulfate (10 mg/100 g body weight/day), bacitracin (500 units/100 g body weight/day), and polymyxin B sulfate (1 mg/100 g body weight/day). At suboptimal intake of casein, valine, tryptophan or threonine, rats eating antibiotic-enriched diet showed up to 3 times greater daily body weight gain (deltaBW) than rats eating a similar diet without antibiotics. The growth-promoting effect of antibiotics can be expressed as percent sparing of specified nutrient (casein or individual amino acid), defined as below: (see journal) where nutrient intakeO ab or nutrient intakeab represents that intake of casein or of a particular amino acid which is required to produce a specific deltaBW in antibiotic-free or antibiotic-supplemented group, respectively. The percent sparing was inversely proportional to the dietary content of casein or limiting amino acid. For diets containing 10% to 25%, 25% to 50%, 50% to 75%, and 75% to 100% of the daily requirement of the limiting nitrogenous nutrient, sparing on the average was greater than 80%, 60%, 20%, and less than 10%, respectively. Data on daily food intake of ad libitum fed rats, and data from an experiment with tube-fed rats, showed that the growth-enhancing effect of antibiotics was independent of changes in food intake.

Effect of feeding pattern on the energy metabolism of rats given low-protein diets.

1. The deposition of fat and protein and the utilization of energy by growing rats offered diets ad lib. or in controlled amounts by gastric intubation has been investigated. Diets contained 50, 75, 100 or 200 g protein/kg, mainly as casein. 2. Gain of body-weight and protein increased with increasing dietary protein concentration when animals received the same energy intake, although the reverse was true for fat deposition. However, the differences in live-weight gain were almost entirely due to changes in body water. The dry-matter content of the gain in animals given low-protein diets was 770 g/kg compared to 360 g/kg in those given the control diet. 3. Energy retention was unaffected by dietary protein level in groups given the same energy intake by gastric intubation. In Expt 1 daily heat production increased significantly (P smaller than 0-05) with increasing protein level (50, 75 and 200 g protein/kg diet) when energy intake was constant, but in Expt 2 there was no significant effect of protein level (50, 100 and 200 g protein/kg diet). Problems arose in the selection of a suitable basis for comparison of heat production between groups because of the differences in body-weight and body composition. 4. The energy requirement for zero energy balance was approximately 10 percent lower for the low-protein groups than for those given the diet containing 200 g protein/kg when food intake was just above the maintenance level. When the requirement was expressed per unit metabolic body size (W0-75 KG) dietary protein level had no significant effect. The mean values for Expts 1 and 2 were 452 and 456 kJ respectively. 5. The energy cost of weight gain increased as dietary protein level decreased in pairs of groups gaining at the same rate. The extra energy ingested by the animals given the lower protein level was converted to body tissue with an efficiency of at least 0-70. 6. Striking differences were observed in body composition and energy retention of the two pairs of groups used for the comparison of tube-feeding and ad lib. feeding. With the diet containing 50 g protein/kg, tube-fed rats gained significantly more weight (P smaller than 0-01) and more fat, dry matter and energy (P smaller than 0-001) than their ad lib, counterparts given an isoenergetic intake. 7. The results demonstrate that dietary protein level has little or no effecon the utilization of energy by growing rats when the pattern of intake is controlled by gastric intubation.

Effects of insulin on excretion of nitrogen in normal, depancreatized, and steroid-diabetic rats.

Sexually mature male rats in metabolism cages were adapted to the tube-feeding of a medium carbohydrate diet. In experiment 1, intact rats were fasted for 96 hrs. Injection of glucagon-free insulin caused an increase in urinary NPN. Cortisone caused a greater loss of NPN which was not significantly changed by addition of insulin. In experiment 2, intact tube-fed rats excreted amounts of NPN and glucose increased in proportion to the dose of cortisone. Glycosuria but not nitrogen loss was suppressed by insulin. In experiment 3, the spontaneous glycosuria of partially depancreatized rats was suppressed by insulin and the elevated urinary NPN was also suppressed. When the glycosuria of partially depancreatized rats was induced or aggravated by cortisone it could be suppressed by insulin but the level of urinary NPN remained high.

Temperature response of tube-fed rats.

Colonic temperatures of rats were recorded for periods of 3.5–5 hr after tube feeding at three ambient temperatures. At a neutral temperature (24 C) fall in body temperature was inversely related to calories intubated. In heat (32 C and 38 C) there was a direct relationship between calories intubated and body temperature. At 38 C mortality rate was a direct function of calories.

Growth hormone and carbohydrate tolerance in adrenalectomized rat.

SummaryGrowth hormone in a dose which regularly leads to hyperglycemia and glycosuria in normal tube-fed rats has no such effect in saline or DOCA maintained tube-fed adrenalectomized rats. Treatment with sub-diabetogenic doses of cortisol restores the hyperglycemic response to growth hormone in adrenalectomized rats. These results are compared to previous studies of growth hormone effects in adrenalectomized cats and dogs.

Carbohydrate tolerance of tube-fed rats; main effects and interactions of insulin, growth hormone, and carbutamide.

Carbohydrate tolerance of tube-fed rats; main effects and interactions of insulin, growth hormone, and carbutamide.

Intravenous glucose tolerance test in hypophysectomized rats.

Intravenous glucose tolerance tests were performed on normal and hypophysectomized rats that had been allowed to eat at will or were fed a constant amount by tube. The rates of removal of excess blood glucose ( k) were calculated. The k values for unoperated rats were the same regardless of the means of administration of food. The rate of removal of excess glucose was decreased in ad libitum-fed but not in tube-fed hypophysectomized rats. In the operated animals the value of k was not constant; it increased with time after administration of glucose load. Increasing the duration of fasting of operated tube-fed rats decreased the k; prior oral administration of glucose to hypophysectomized rats fed ad libitum increased the k. The lability of the intravenous glucose tolerance test in hypophysectomized rats is stressed.

The Prevention of Experimental Tooth Decay by Tube-feeding

When intact or desalivated caries-susceptible albino rats were fed adequate amounts of a caries-producing diet by stomach tube they did not develop tooth decay. In contrast, all but one of the intact litter mates and all of the desalivated litter mates which consumed the same diet orally had dental caries. The critical ratios of the differences between the control and experimental groups ranged from 5.7 to 26.6, which indicated that the differences were highly significant. Histologic examination showed that the molar teeth of both groups were surrounded by a great abundance of microorganisms. In the controls, the microorganisms were in direct contact with the tooth surfaces; in tube-fed rats they were separated from the enamel surfaces by a thick organic membrane (possibly remnants of Nasmyth’s membrane) and by foreign matter which was firmly impacted in the fissures. The results of this experiment suggest that, with all other factors being controlled and equal, tooth decay is prevented in caries-susceptible rats when the direct effects of food in the oral cavity are eliminated.