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Lack of anorexia following prolonged intragastric feeding in rats
Physiology and Behavior, Voi. 14, pp. 673--675. Brain Research Publications Inc., 1975. Printed in the U.S.A.
BRIEF COMMUNICATION Lack of Anorexia Following Prolonged Intragastric Feeding in Rats I SIDNEY NELSON AND CHARLES KSIR
Department o f Psychology, University o f Wyoming, Laramie, ICY
(Received 20 August 1974)
NELSON, S. AND C. KSIR. Lack of anorexia following prolonged intragastric feeding in rats. PHYSIOL. BEHAV. 14(5) 673-675, 1975. - Adult rats starved for 5 days ate less than normal when food was reintroduced, whereas rats fed a non-nutritive diet by gastric intubation for 6 days and rats fed a complete diet by gastric intubation for fourteen days showed no such anorexia. The lack of eating experience did not interfere with normal eating upon reintroduction of food, indicating that poststarvation anorexia may be a result of gastrointestinal changes caused by a lack of dietary bulk. Starvation
Anorexia
Intragastric feeding
Rats
Eight of the rats began receiving 3 injections of nonnutritive liquid per day. The non-nutritive substance was made by mixing 20 g methylcellulose and 9 g NaC1 in 1 liter distilled water, heating to 70°C, cooling to 5°C, and then allowing to stand at room temperature before adding 60 ml Kaopectate. Each of these rats was etherized, a tube was passed into the stomach, and 5 ml of non-nutritive liquid was forced into the stomach at 10 a.m., 1 p.m., and 8 p.m. (approximate times). Body weight and water consumption measures were obtained for all rats prior to the morning feeding. The 8 rats which were not fed were starved for 5 days, and the tube-fed rats were intubated for 6 days so that the two groups would have approximately the same mean body weights when refeeding occurred. On the next morning, powdered Lab Chow was replaced on each cage. Body weight and food and water consumption measures were taken daily for the next 3 days.
HAMILTON [1] has reported that rats starved for 6 - 1 0 days eat less than normal when food is reintroduced. It was suggested that this "post-starvation anorexia" may have been due to the lack of ingestlonal experience during the starvation period. It was not clear whether the act of ingestion was important or whether the effect of food on maintenance of the gastrointestinal tract was the major factor in maintaining normal food intake. The current study was an attempt to determine if rats which were not allowed to eat and were fed by intragastric intubation would be anorectic upon reintroduction of food. EXPERIMENT
1
The first experiment compared 5 days of starvation with 6 days of tube feeding with a non-nutritive hquid bulk diet.
Method Animals. Sixteen female Holtzman-derived albino rats were used. At the beginning of the experiment each rat was 9 0 - 1 2 0 days of age. Each rat was housed in an individual metabolism cage, with water freely available throughout the experiment. Procedure. Daily measures of body weight and consumption of ground dry Purina Lab Chow and water were obtained from each rat for 2 days prior to the beginning of the experiment. Food was then removed from all the cages.
Results Two of the rats fed the non-nutritive liquid died following an intubation. Two more of these rats and 3 of the unfed rats died during the first day after food was reintroduced. Thus, only data from 4 fed and 5 unfed rats were analyzed. Figure 1 gives daily group mean body weight and water
~Send reprint requests to. Charles Ksir, Department of Psychology, Box 3415, University of Wyoming, Laramie, WY 82071. 673
674
NELSON AND KSIR
240-
PRE
STARVATION
was similar throughout the experiment, except that the tube-fed group consumed an average of 14.3 and 19 ml on the last 2 days of tube-feeding, while the starved group consumed an aveiage of 9.6 and 8.0 ml on the last two days of starvation.
POST
20-
~
EXPERIMENT
200-
,eo 140
Method
180-
Antmals. Eight female Holtzman-derived albino rats of the same approximate ages as in Experiment 1 were used. They were housed in individual metabolism cages. Procedure. Daily measures of body weight and consumption of ground dry Purina Lab Chow and water were obtained from each rat for two days prior to the beginning of the experiment. Food was then removed from the cages and water was removed from the cages of 4 of the rats. For the next 14 days, each rat received 3 mtubations of a complete liquid diet per day. The liquid diet was prepared according to the formula given by Teitelbaum and Epstein [2]. Intubation times and procedures were as in Experiment 1, except that the volume intubated was varied to maintain each rat's body weight ( 1 0 - 1 4 ml/intubatlon). Body weight and daily water consumption measures were taken before the morning feeding. After 14 days of intragastrlc feeding, dry Lab Chow was replaced on the cages. Body weight, food consumption, and water intake measures were obtained from each rat for the next 3 days.
28 24 2O
d 0
0 I1
16
12 60 40
(5 "1-
2
Although the tube-fed rats in Experiment 1 ate more on refeeding than the starved rats, it is possible that a longer period without ingestional experience might produce anorexia even in tube-fed rats. Experiment 2 examined the effect on food consumption of fourteen days of feeding rats a complete liquid diet by gastric mtubatlon.
20
Results !
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DAYS FIG. l. Dady group mean body weights, food consumption, and water consumptmn before, dunng, and after either starvation or feeding with a non-nutritive substance. Open circles represent starved rats, f'dled circles are for rats fed the non-nutritivesubstance.
consumption measures for the enttre experiment and daffy food consumption measures before and after the starvation period. Although the tube-fed rats had initially higher body weights than the unfed rats, they lost weight at approximately the same rate and, due to the extra day without nutrition actually reached similar weights before refeeding. On the first refeeding day, the tube-fed rats consumed an average of 21.8 g of food and gained an average of 27.2 g in body weight. The unfed rats consumed only 12.6 g and gained only 13.0 g in body weight. While the difference in intake was not quite significant (t(7) = 1.6, p<0.10), the weight gain difference was significant (t(7) = 2.1, p<0.05). Food intake and body weight gains after the first day were similar for the two groups. Water intake for the two groups
One of the rats which had water available died during the gastric feeding period and those data have been eliminated from the analysis. Figure 2 gives group mean body weight data before, during and after the tube-feeding period. In addition food consumption measures before and after the tube feeding period are shown, and water consumption measures before and after the tube-feeding period for the group which did not have water available during that period, and water consumption measures throughout the experiment for the group which had water available during the tube-feeding period. It is evident that the feeding regimen was sufficient to maintain a stable body weight, and that the lack of ingestlonal experience had no effect on food consumption on the day followmg the tube-feeding period. Lack of waterdrinking behavior dunng the tube-feeding period also did not prevent normal refeeding. DISCUSSION
Experiment 1 showed that five days of starvation produced a relative anorexia, whereas rats ate normally after 6 days of gastric intubation with a non-nutritive substance. This rules out weight loss and lack of nutrition as causative factors, in agreement with data presented by
EATING A F T E R GASTRIC FEEDING
210 "* PRE
675
GASTRIC FEEDING
1
,oJ\ 50-
"E o
25-
.1-
0DAYS FIG. 2. Group mean body weights, food consumption, and water consumption before, during, and after gastric intubation with a complete liqmd diet. Open circles are for the group which had access to water during the gastric intubation period, filled circles represent the rats which had no water dunng this period. Hamilton [1]. It also indicates that lack of ingestional experience for a period of 6 days does not produce anorexia. Experiment 2 shows that fourteen days without ingestional behavior, even when drinking behavior was also prevented, did not produce anorexia. It appears that the presence of bulk in the digestive tract is sufficient to m a i n t a i n n o r m a l f e e d i n g behavior when food is reintroduced. One possible alternative exists, however. Unpublished
data from this laboratory indicate that rats of the age and strain we used, starved for 6 or more days, reach a point of c o m p l e t e adipsia. Unfortunately, most of these rats eventually die even when force-fed. It may be that starvat i o n p r o d u c e s adipsia, subsequent dehydration, and secondary dehydration anorexia. Since both of the diets used in this study contained some water, it may have been the hydration which prevented anorexia from developing.
REFERENCES Hamilton, C. L. Problems of refeeding after starvation in the rat.Ann. N. Y. acad. $cL 157: 1004-1017, 1969.
2.
Teitelbaum, P. and A. N. Epstein. The lateral hypothalamic syndrome: Recovery of feeding and drinking after lateral hypothalamic lesions. Psychol. Rev. 69: 74-90, 1962.
BRIEF COMMUNICATION Lack of Anorexia Following Prolonged Intragastric Feeding in Rats I SIDNEY NELSON AND CHARLES KSIR
Department o f Psychology, University o f Wyoming, Laramie, ICY
(Received 20 August 1974)
NELSON, S. AND C. KSIR. Lack of anorexia following prolonged intragastric feeding in rats. PHYSIOL. BEHAV. 14(5) 673-675, 1975. - Adult rats starved for 5 days ate less than normal when food was reintroduced, whereas rats fed a non-nutritive diet by gastric intubation for 6 days and rats fed a complete diet by gastric intubation for fourteen days showed no such anorexia. The lack of eating experience did not interfere with normal eating upon reintroduction of food, indicating that poststarvation anorexia may be a result of gastrointestinal changes caused by a lack of dietary bulk. Starvation
Anorexia
Intragastric feeding
Rats
Eight of the rats began receiving 3 injections of nonnutritive liquid per day. The non-nutritive substance was made by mixing 20 g methylcellulose and 9 g NaC1 in 1 liter distilled water, heating to 70°C, cooling to 5°C, and then allowing to stand at room temperature before adding 60 ml Kaopectate. Each of these rats was etherized, a tube was passed into the stomach, and 5 ml of non-nutritive liquid was forced into the stomach at 10 a.m., 1 p.m., and 8 p.m. (approximate times). Body weight and water consumption measures were obtained for all rats prior to the morning feeding. The 8 rats which were not fed were starved for 5 days, and the tube-fed rats were intubated for 6 days so that the two groups would have approximately the same mean body weights when refeeding occurred. On the next morning, powdered Lab Chow was replaced on each cage. Body weight and food and water consumption measures were taken daily for the next 3 days.
HAMILTON [1] has reported that rats starved for 6 - 1 0 days eat less than normal when food is reintroduced. It was suggested that this "post-starvation anorexia" may have been due to the lack of ingestlonal experience during the starvation period. It was not clear whether the act of ingestion was important or whether the effect of food on maintenance of the gastrointestinal tract was the major factor in maintaining normal food intake. The current study was an attempt to determine if rats which were not allowed to eat and were fed by intragastric intubation would be anorectic upon reintroduction of food. EXPERIMENT
1
The first experiment compared 5 days of starvation with 6 days of tube feeding with a non-nutritive hquid bulk diet.
Method Animals. Sixteen female Holtzman-derived albino rats were used. At the beginning of the experiment each rat was 9 0 - 1 2 0 days of age. Each rat was housed in an individual metabolism cage, with water freely available throughout the experiment. Procedure. Daily measures of body weight and consumption of ground dry Purina Lab Chow and water were obtained from each rat for 2 days prior to the beginning of the experiment. Food was then removed from all the cages.
Results Two of the rats fed the non-nutritive liquid died following an intubation. Two more of these rats and 3 of the unfed rats died during the first day after food was reintroduced. Thus, only data from 4 fed and 5 unfed rats were analyzed. Figure 1 gives daily group mean body weight and water
~Send reprint requests to. Charles Ksir, Department of Psychology, Box 3415, University of Wyoming, Laramie, WY 82071. 673
674
NELSON AND KSIR
240-
PRE
STARVATION
was similar throughout the experiment, except that the tube-fed group consumed an average of 14.3 and 19 ml on the last 2 days of tube-feeding, while the starved group consumed an aveiage of 9.6 and 8.0 ml on the last two days of starvation.
POST
20-
~
EXPERIMENT
200-
,eo 140
Method
180-
Antmals. Eight female Holtzman-derived albino rats of the same approximate ages as in Experiment 1 were used. They were housed in individual metabolism cages. Procedure. Daily measures of body weight and consumption of ground dry Purina Lab Chow and water were obtained from each rat for two days prior to the beginning of the experiment. Food was then removed from the cages and water was removed from the cages of 4 of the rats. For the next 14 days, each rat received 3 mtubations of a complete liquid diet per day. The liquid diet was prepared according to the formula given by Teitelbaum and Epstein [2]. Intubation times and procedures were as in Experiment 1, except that the volume intubated was varied to maintain each rat's body weight ( 1 0 - 1 4 ml/intubatlon). Body weight and daily water consumption measures were taken before the morning feeding. After 14 days of intragastrlc feeding, dry Lab Chow was replaced on the cages. Body weight, food consumption, and water intake measures were obtained from each rat for the next 3 days.
28 24 2O
d 0
0 I1
16
12 60 40
(5 "1-
2
Although the tube-fed rats in Experiment 1 ate more on refeeding than the starved rats, it is possible that a longer period without ingestional experience might produce anorexia even in tube-fed rats. Experiment 2 examined the effect on food consumption of fourteen days of feeding rats a complete liquid diet by gastric mtubatlon.
20
Results !
i
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2
;
I
I
I
I
2
3
4
5
I
;
I
2
3
DAYS FIG. l. Dady group mean body weights, food consumption, and water consumptmn before, dunng, and after either starvation or feeding with a non-nutritive substance. Open circles represent starved rats, f'dled circles are for rats fed the non-nutritivesubstance.
consumption measures for the enttre experiment and daffy food consumption measures before and after the starvation period. Although the tube-fed rats had initially higher body weights than the unfed rats, they lost weight at approximately the same rate and, due to the extra day without nutrition actually reached similar weights before refeeding. On the first refeeding day, the tube-fed rats consumed an average of 21.8 g of food and gained an average of 27.2 g in body weight. The unfed rats consumed only 12.6 g and gained only 13.0 g in body weight. While the difference in intake was not quite significant (t(7) = 1.6, p<0.10), the weight gain difference was significant (t(7) = 2.1, p<0.05). Food intake and body weight gains after the first day were similar for the two groups. Water intake for the two groups
One of the rats which had water available died during the gastric feeding period and those data have been eliminated from the analysis. Figure 2 gives group mean body weight data before, during and after the tube-feeding period. In addition food consumption measures before and after the tube feeding period are shown, and water consumption measures before and after the tube-feeding period for the group which did not have water available during that period, and water consumption measures throughout the experiment for the group which had water available during the tube-feeding period. It is evident that the feeding regimen was sufficient to maintain a stable body weight, and that the lack of ingestlonal experience had no effect on food consumption on the day followmg the tube-feeding period. Lack of waterdrinking behavior dunng the tube-feeding period also did not prevent normal refeeding. DISCUSSION
Experiment 1 showed that five days of starvation produced a relative anorexia, whereas rats ate normally after 6 days of gastric intubation with a non-nutritive substance. This rules out weight loss and lack of nutrition as causative factors, in agreement with data presented by
EATING A F T E R GASTRIC FEEDING
210 "* PRE
675
GASTRIC FEEDING
1
,oJ\ 50-
"E o
25-
.1-
0DAYS FIG. 2. Group mean body weights, food consumption, and water consumption before, during, and after gastric intubation with a complete liqmd diet. Open circles are for the group which had access to water during the gastric intubation period, filled circles represent the rats which had no water dunng this period. Hamilton [1]. It also indicates that lack of ingestional experience for a period of 6 days does not produce anorexia. Experiment 2 shows that fourteen days without ingestional behavior, even when drinking behavior was also prevented, did not produce anorexia. It appears that the presence of bulk in the digestive tract is sufficient to m a i n t a i n n o r m a l f e e d i n g behavior when food is reintroduced. One possible alternative exists, however. Unpublished
data from this laboratory indicate that rats of the age and strain we used, starved for 6 or more days, reach a point of c o m p l e t e adipsia. Unfortunately, most of these rats eventually die even when force-fed. It may be that starvat i o n p r o d u c e s adipsia, subsequent dehydration, and secondary dehydration anorexia. Since both of the diets used in this study contained some water, it may have been the hydration which prevented anorexia from developing.
REFERENCES Hamilton, C. L. Problems of refeeding after starvation in the rat.Ann. N. Y. acad. $cL 157: 1004-1017, 1969.
2.
Teitelbaum, P. and A. N. Epstein. The lateral hypothalamic syndrome: Recovery of feeding and drinking after lateral hypothalamic lesions. Psychol. Rev. 69: 74-90, 1962.