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Effects of wheel running on food intake and weight gain of male and female rats
Physiology & Behavior, Vol. 28, pp. 899-903. Pergamon Press and Brain Research Publ., 1982. Printed in the U.S.A.
Effects of Wheel Running on Food Intake and Weight Gain of Male and Female Rats KUMPEI TOKUYAMA,* MASAYUKI SAITOt AND HIROMICHI OKUDA*
*Second Department of Medical Biochemistry and tFirst Department of Medical Biochemistry, School of Medicine, Ehime University Shigenobu, Onsen-gun, Ehime 791--02, Japan Received 28 September 1981 TOKUYAMA, K., M. SAITO AND H. OKUDA. Effects of wheel running on food intake and weight gain of male and female rats. PHYSIOL. BEHAV. 28(5) 899-903, 1982.--Adult male and female rats were housed in a sedentary condition or given free access to a running wheel for 50 days. Running wheel activity of female rats was higher than that of males throughout the experiment. Food intake, of both male and female rats that could take exercise increased, and the rate of increase of females was greater than that of males. In both males and females there was a positive correlation between food intake and running wheel activity. These findings suggest that the sex difference in the rate of increase in food intake elicited by wheel running is at least partly explained by the sex difference in running wheel activity. Although food intake increased as a function of running wheel activity, the weight gains of both sexes were slower than those of sedentary rats. In both sexes this slower weight gain was mainly due to less accumulation of fat.
Exercise
Food intake
Body composition
Sex differences
PHYSICAL training results in decrease in body weight in rats [4, 5, 7, 11, 13, 17, 19] and humans [2, 3, 12, 14, 18]. The effect of exercise in reducing weight gain has been studied by many groups by investigating the effect of exercise on food intake, because change in food intake plays an important role in regulation of body weight. Although there are slight discrepancies between reported results, several groups have suggested sex differences in the effect of spontaneous exercise on food intake in rats. When rats had free access to a running wheel, females ate significantly more than their sedentary controls whereas males did not [10,15]. Since females took consistently more exercise than males in these experiments, the absence of hyperphagia in males could be due to their low activity. In the present study we tested this possibility by examining the relation between activity on a running wheel and food intake of male and female rats. We also examined the effect of wheel running on the body composition. METHOD
Animals Wistar King rats were purchased from Kitayama Labes Co., Kyoto. Littermates were obtained in the animal laboratory of our school and maintained in an air conditioned room at 24_+0.5°C (relative humidity, 60_+15%). The room was illuminated for 12 hr from 10 a.m. each day. Water and commercial powdered chow (M. Oriental Yeast Co., Tokyo) were available at all times.
Procedure In Experiment 1, 10 male and 10 female rats were used.
Rats of 40 days old (10 days before the beginning of the experiment) in each litter were weight matched and separated into sedentary and exercising groups. All rats were kept in individual wire bottomed cages (15 x 25 x 15 cm) with a locked running wheel (circumference I m, KC-8000, Tokushima Medical Instrument Mfg. Co., Tokushima). The running wheel of the exercising group was unlocked when the rats were 50 days old (the day of the beginning of the experiment), and the rats were allowed free access to it for 50 days. The running wheel of the sedentary group was kept locked throughout the experiment. Running wheel activity was recorded with a microswitch and an electromagnetic counter as revolutions per day (RPD). The powdered chow was placed in circular glass containers with tightly fitting covers that had a 4.5 cm diameter opening. A perforated steel disk was placed in the containers on top of the food to prevent the animals from scattering the food. The food container was weighed every day and the amount of food consumed was calculated from its change in weight. The amount of spilt food was neglected, because it amounted to less than 2% of the total intake. Body weight was measured every fifth day. When the rats were 100 days old (50 days after the beginning of the experiment), they were anesthetized with ether and exsanguinated from the jugular vein. Then the liver, heart, kidneys, perigonadal, retroperitoneal and perirenal adipose tissues, and soleus and gastrocnemius muscles were removed and, weighed, and put back into the carcass. Because it was difficult to separate retroperitoneal and perirenal adipose tissues, their combined weight was measured. The whole body was kept frozen at -20°C until the body composition was analyzed. The procedures were the same in Experiments 2 and 3 unless otherwise stated. In Experiments 2 and 3, rats in the
Copyright © 1982 Brain Research Publications Inc.--0031-9384/82/080899-05503.00/0
TOKUYAMA. SAIT() AND ()KUDA
90o •
A 15000,
Female
Sedentary
o Female
Exercising
• Male ~] M a l e
Sedentary Exercising
07
/
•~ 10000-
o~
5000-
(N=5)
o
25'
c
20"
"o o
,o 15-
i~ ' i
(N=9) i
v
~
1
(N=9) v
500-
v
400-
Z.m 300-
g 200' •
-;0
6
lb
2b
3'o 4b
Day of Experiment
sb
-~'0
6
EXERCISE
lb
2b
(N=9)
3'o go
1
go
Day of Experiment
FIG. I. Changes in mean values of running wheel activity, food intake and body weight. Rats in the exercising group were allowed to run when they were 50 days old (day 0 of the
experiment). Numbers of animals per group are given in parentheses. Asterisks indicate significant differences from values for the sedentary group (p<0.05).
sedentary group were kept in individual simple wire meshed cages (38×25× 17 cm) while the rats in the exercising group were kept in individual wire bottomed cages with running wheels as in Experiment 1. In Experiment 2, 8 male and 8 female rats were used. Revolution of the running wheel was measured for 10 days from day 30 to 40 of the experiment. In Experiment 3, 14 male and 14 female rats were used. Revolution of the running wheel and food intake were measured for 10 days from day 30 to 40 of the experiment. The body weight, tissue weight, and body composition were not measured.
weight of the dry residue. The weight of non-fat solid was calculated by subtracting the weight of body water and body fat from the body weight.
Statistical Analysis Data are shown as means_+S.E.M. The significance of difference between sedentary and exercising groups were determined by the t-test for paired littermates weight matched 10 days before the beginning of the experiment. Analysis of covariance was used to compare regression lines for male and females.
Analysis of Body Composition The whole body was blended with water (50 ml/100 g) in a Waring blender. A portion of the homogenate (100 g) was freeze-dried and the water content was calculated from its change in weight. The dried homogenate was extracted with 300 ml of chloroform-methanol (2:1, v/v) in a Waring blender and filtered. The residue was reextracted twice with 300 ml of chloroform-methanol. These filtrates were combined and evaporated, and the fat content was calculated from the
RESULTS AS described in the Method section we used two conditions for sedentary groups. In Experiment 1 rats of the sedentary group were kept in wire bottomed cages with a locked running wheel while in Experiments 2 and 3 rats of the sedentary groups were kept in simple wire meshed cages. There was no significant difference in the food intakes or weight gains of the sedentary groups of Experiments 1-3 (see
FOOD I N T A K E A N D G R O W T H A F T E R E X E R C I S E
901
q) O
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10 days, but then became higher than the latter reaching a plateau within 20 days. The exercising group gained significantly less weight than the sedentary group.
~E
Relationship Between Running WheelActivity and Food Intake
c-
~ ~2o x ® I.~'0
m / ~f _ _
B E ] ~
A positive correlation between activity on the running wheel and food intake was observed in both males and females in the 10 day period from 30 to 40 after the beginning of wheel running (Fig. 2).
r = 0. 767
B B
p
¢~ . IOC "(3 0
~
6
Y=O.O018X* 95 r =0.744 p
Tissue Weight
,0b00
2o~oo
Running Wheel Activity (RPD) FIG. 2. Relation between running wheel activity and food intake of exercising rats. Food intake is shown as a percentage of that of sedentary littermates, weight matched on 10 days before the beginning of the experiment. O; Female rats in Experiment 1. O; Female rats in Experiment 2 or 3. n; Male rats in Experiment 1. lq; Male rats in Experiment 2 or 3.
also Fig. 2). Therefore, data obtained in these experiments were combined.
In both males and females, the weight of adipose tissue was significantly lower in exercising groups than in sedentary groups. The weight of the soleus was higher in exercising males and females than in sedentary animals. The weight of the heart of exercising females was also more than that of sedentary females (Table 1).
Body Composition The body fat contents of exercising rats of both sexes were significantly lower than those of sedentary animals, but no significant difference was observed in the body water and non-fat solid contents of sedentary and exercising groups (Table 2).
Running Wheel activity, Food Intake, Body Weight
DISCUSSION
Figure 1 shows changes in the mean values for activity on the running wheel (revolutions of the running wheel), food intake and body weight during the experiment. Female rats. Running wheel activity increased rapidly in the first 10 days to a plateau (about 11,000 RPD). F o o d intake of the sedentary group was essentially constant throughout the experiment; that of the exercising group was lower than that of the sedentary group for the first 5 days, but then became higher than the latter attaining a plateau within 15 days. The exercising group gained significantly less weight than the sedentary group. Male rats. Running wheel activity increased in the first 10 days to a plateau (about 4,000 RPD). Throughout the experiment, male rats used the running wheel consistently less than females. F o o d intake of the sedentary group was essentially constant throughout the experiment; that of the exercising group was lower than that of the sedentary group in the first
In this work, we observed changes in the mean values of running wheel activity, food intake and body weight of male and female rats as a function of time after the beginning of wheel running. Running wheel activity of females was several times higher than that of males throughout the experiment, as already reported [10,15]. F o o d intake of both males and females in the exercising group increased after a transient decrease. The finding that food intake and running wheel activity attained plateaus within 20 days after the beginning of wheel running suggests that both males and females adapt to wheel running within 20 days. Although food intake of both males and females increased after adaptation to wheel running, the rate of increase was higher in females. One possible explanation of this sex difference is that the difference in the rates of increase in food intake elicited by wheel running merely reflects the sex difference in running wheel activity. If this is
TABLE I TISSUE WEIGHT Female
Adipose tissue (g) Perigonadal Perirenal + Retroperitoneal Liver (g) Heart (g) Soleus (g) Gastrocnemius (g)
Male
Sedentary
Exercising
Sedentary
Exercising
6.1 _+ 1.0 7.8 _+ 1.0
2.8 _+ 0.6* 3.2 _+ 0.7*
6.5 _+ 0.6 10.2 _+ 1.1
4.6 _+ 0.5* 5.2 _+ 1.0"
17.1 -+ 0.8 1.30 -- 0.04 0.38 _ 0.1 6.0 _+ 0.2
16.1 -+ 0.8 1.32 _+ 0.03 0.41 _+ 0.01* 5.6 -+ 0.2
9.9 0.86 0.25 3.9
__ 0.4 __ 0.02 x 0.01 _+ 0.1
10.4 0.97 0.30 3.6
_+ 0.3 _+ 0.02* _+ 0.02* _+ 0.1
Groups of 9 rats were used. Asterisks indicate significant differences from values for the sedentary group (/7<0.05).
902
T O K U Y A M A , SAI'IO ,~ND O K U I ) A TABLE 2 BODY COMPOSITION Female
Body Weight (g) Fat(g) Water(g) Non-fat Solid (g)
Male
Sedentary
Exercising
Sedentary
Exercising
285 _+ 8
263 _+ 5*
472 _+ 13
428 _+ 12"
47_+ 8 170_+ 5 68_+ 2
31 _+ 3* 165_+ 4 67 + 1
70_+ 5 287_+ 8 114+ 3
49_+ 6* 272_+_ 5 107_+ 3
Body weights measured after exsanguination from the jugular vein. Body weights of female sedentary, female exercising, male sedentary and male exercising rats measured before exsanguination were 292 _+ 8, 271 _+ 5, 482 _+ 13 and 438 _+ 12 g, respectively. Groups of 9 animals were used. Asterisks indicate significant differences from values for the sedentary group (/)<0.05).
the case, there should be a positive correlation between running wheel activity and rate of increase in food intake in males and females, and in fact we found good correlations in both sexes. There was no significant difference in the slopes of regression lines for males and females. These findings suggest that the sex difference in running wheel activity contributes at least in part to the sex difference in the rate of increase in food intake elicited by wheel running. Rolls and Rowe [15] also found a sex difference in the effect of wheel running on food intake. In their experiment food intake of males in the exercising group decreased while that of females increased 10 weeks after the beginning of wheel running. But recently, Mondon et al. [8] reported that food intake of males in their exercising group increased 7 weeks after the beginning of wheel running. Mondon et al.
[8] selected rats that ran more than 2 milesMay on days l i after the beginning of wheel running and measured their food intake. Thus the discrepancy between the results of Rolls and Rowe [15] and Mondon et al. 18] can be partly explained by the difference in the running wheel activities of the rats in their experiments. The decrease in food intake of males in the exercising group of Roils and Rowe could not be explained by our regression line for running wheel activity and food intake. In our experiment, wheel running was started after a preliminary 10-day period. During this period, we confirmed that there was no significant difference in the food intakes or body weights of sedentary and exercising groups. Rolls and Rowe began their experiment by transferring rats of the exercising group to cages with a running wheel. Therefore, in their experiment the rats in the exercising group may have been affected not only by wheel running itself but also by transfer to the new cage. We did not detect any effect of transfer to a new cage on food intake or body weight gain, but Routtenberg et al. [16] reported that food intake decreased significantly when rats were transferred to cages with a locked running wheel. Although food intake increased as a ['unction of the amount of wheel running, the increase in food intake was not sufficient to compensate for the increase in energy expenditure elicited by wheel running. Thus both males and females in the exercising group gained weight slower than sedentary rats. These findings suggest that wheel running not only increased energy expenditure but also decreased the set-point of energy balance that regulates the amount of food intake 11, 6, 9, 2O]. In both males and females the body fat contents of exercising rats were significantly lower than those of sedentary rats, but there was no significant difference in the body water or non-fat solid contents of the two groups. Consistent with this finding, the adipose tissue weights of exercising rats were significantly lower than those of sedentary rats. Further study is necessary to elucidate the effect of wheel running on lipid metabolism.
REFERENCES 1. Armstrong, S., G. Coleman and G. Singer. Food and water 7. Mayer, J., N. B. Marshall, J. J. Vitale, J. H. Christensen, M. B. deprivation: Changes in rat feeding, drinking, activity and body Mashayekhi and F. J. Stare. Exercise, food intake and body weight. Neurosci. Biobehav. Rev. 4: 377-402, 1980. weight in normal rats and genetically obese adult mice. Am. J. 2. Bj6mtorp, P., P. Berchtold, G. Grimby, B. Lindholm, H. Physiol. 177: 544-548, 1955. Sanne, G. Tibblin and L. Wilhelmsen. Effects of physical train8. Mondon, C. E., C. B. Dolkas and G. M. Reaven. Site of ening on glucose tolerance, plasma insulin and lipids and on body hanced insulin senstivity in exercise-trained rats at rest. Am..I. composition in man after myocardial infarction. Acta. reed. Phsyiol. 239: E169-EI77, 1980. stand. 192: 439-443, 1972. 9. Mrosovsly, N. and T. L. Powley. Setpoints for body weight and 3. Bjfrntorp, P., M. Fahlrn, G. Grimby, A. Gustafson, J. Holm, P. fat. Behav. Biol. 20: 205-223, 1977. Renstrfm and T. Scherstrn. Carbohydrate and lipid metabolism 10. Nikoletseas, M. M. Obesity in exercising, hyperphagic rats in middle-aged, physically trained men. Metabolism 21: 1037treated with monosodium glutamate. Physiol. Behav. 19: 7671044, 1972. 773, 1977. 4. Crews, E. L., III, K. W. Fugem, L. B. Oscai, J. O. Holloszy 11. Oscai, L. B. and J. O. Holloszy. Effects of weight changes and R. E. Shank. Weight, food intake, and body composition: produced by exercise, food restriction, or overeating on body effects of exercise and of protein deficiency. Am. J. Phsyiol. composition. J. clin. Invest. 48: 2124-2128, 1969. 216: 359-363, 1969. 12. Parizkova, J. Impact of age, diet and exercise on man's body 5. Holloszy, J. O. Biochemical adaptations in muscle. Effects of composition. Ann. N. Y. Acad. Sci. 110: 661-674, 1963. exercise on mitochondrial oxygen uptake and respiratory 13. Pitts, G. C. and L. S. Bull. Exercise, dietary obesity and growth enzyme activity in skeletal muscle. J. biol. Chem. 242: 2278in the rat. Am. J. Physiol. 232: R38-R44, 1977. 2282, 1976. 14. Pollock, M. L., H. S. Miller, Jr., R. Janeway, A. C. Linnerud, 6. Keesey, R. E., P. C. Boyle, J. W. Kemnitz and J. S. Mitchel. B. Robertson and R. Valentino. Effects of walking on body The role of the lateral hypothalamus in determining the body composition and cardiovascular function of middle-aged men..I. weight set point. In: Hunger: Basic Mechanisms and Clinical appl. Physiol. 30: 126-130, 1971. Implications, edited by D. Novin, W. Wyrwicka and G. Bray. New York: Raven Press, 1976, pp. 243-255.
FOOD INTAKE AND GROWTH AFTER EXERCISE 15. Rolls, B. J. and E. A. Rowe. Exercise and the development and persistence of dietary obesity in male and female rats. Physiol. Behav. 23: 241-247, 1979. 16. Routtenberg, A. "Self-starvation" of rats living in activity wheels: Adaptation effects. J. comp. Psychol. 66: 234--238, 1968. 17. Sclafani, A. and D. Springer. Dietary obesity in adult rats: Similarities to hypothalamic and human obesity syndromes. Physiol. Behav. 17: 461-471, 1976.
903 18. Skinner, J., J. O. Holloszy and T. Cureton. Effects of a program of endurance exercise on physical work capacity and anthropometric measurements of fifteen middle-aged men. Am. J. Cardiol. 14: 747-752, 1964. 19. Stevenson, J. A. F., B. M. Box, V. Feleki and J. R. Beaton. Bouts of exercise and food intake in the rat. J. appl. Physiol. 21: 118-122, 1966. 20. Woods, S. C. and S. Porte. Insulin and the set-point regulation of body weight. In: Hunger: Basic Mechanisms and Clinical Implications, edited by D. Novin, W. Wyrwicka and G. Bray. New York: Raven Press, 1976, pp. 273-280.
Effects of Wheel Running on Food Intake and Weight Gain of Male and Female Rats KUMPEI TOKUYAMA,* MASAYUKI SAITOt AND HIROMICHI OKUDA*
*Second Department of Medical Biochemistry and tFirst Department of Medical Biochemistry, School of Medicine, Ehime University Shigenobu, Onsen-gun, Ehime 791--02, Japan Received 28 September 1981 TOKUYAMA, K., M. SAITO AND H. OKUDA. Effects of wheel running on food intake and weight gain of male and female rats. PHYSIOL. BEHAV. 28(5) 899-903, 1982.--Adult male and female rats were housed in a sedentary condition or given free access to a running wheel for 50 days. Running wheel activity of female rats was higher than that of males throughout the experiment. Food intake, of both male and female rats that could take exercise increased, and the rate of increase of females was greater than that of males. In both males and females there was a positive correlation between food intake and running wheel activity. These findings suggest that the sex difference in the rate of increase in food intake elicited by wheel running is at least partly explained by the sex difference in running wheel activity. Although food intake increased as a function of running wheel activity, the weight gains of both sexes were slower than those of sedentary rats. In both sexes this slower weight gain was mainly due to less accumulation of fat.
Exercise
Food intake
Body composition
Sex differences
PHYSICAL training results in decrease in body weight in rats [4, 5, 7, 11, 13, 17, 19] and humans [2, 3, 12, 14, 18]. The effect of exercise in reducing weight gain has been studied by many groups by investigating the effect of exercise on food intake, because change in food intake plays an important role in regulation of body weight. Although there are slight discrepancies between reported results, several groups have suggested sex differences in the effect of spontaneous exercise on food intake in rats. When rats had free access to a running wheel, females ate significantly more than their sedentary controls whereas males did not [10,15]. Since females took consistently more exercise than males in these experiments, the absence of hyperphagia in males could be due to their low activity. In the present study we tested this possibility by examining the relation between activity on a running wheel and food intake of male and female rats. We also examined the effect of wheel running on the body composition. METHOD
Animals Wistar King rats were purchased from Kitayama Labes Co., Kyoto. Littermates were obtained in the animal laboratory of our school and maintained in an air conditioned room at 24_+0.5°C (relative humidity, 60_+15%). The room was illuminated for 12 hr from 10 a.m. each day. Water and commercial powdered chow (M. Oriental Yeast Co., Tokyo) were available at all times.
Procedure In Experiment 1, 10 male and 10 female rats were used.
Rats of 40 days old (10 days before the beginning of the experiment) in each litter were weight matched and separated into sedentary and exercising groups. All rats were kept in individual wire bottomed cages (15 x 25 x 15 cm) with a locked running wheel (circumference I m, KC-8000, Tokushima Medical Instrument Mfg. Co., Tokushima). The running wheel of the exercising group was unlocked when the rats were 50 days old (the day of the beginning of the experiment), and the rats were allowed free access to it for 50 days. The running wheel of the sedentary group was kept locked throughout the experiment. Running wheel activity was recorded with a microswitch and an electromagnetic counter as revolutions per day (RPD). The powdered chow was placed in circular glass containers with tightly fitting covers that had a 4.5 cm diameter opening. A perforated steel disk was placed in the containers on top of the food to prevent the animals from scattering the food. The food container was weighed every day and the amount of food consumed was calculated from its change in weight. The amount of spilt food was neglected, because it amounted to less than 2% of the total intake. Body weight was measured every fifth day. When the rats were 100 days old (50 days after the beginning of the experiment), they were anesthetized with ether and exsanguinated from the jugular vein. Then the liver, heart, kidneys, perigonadal, retroperitoneal and perirenal adipose tissues, and soleus and gastrocnemius muscles were removed and, weighed, and put back into the carcass. Because it was difficult to separate retroperitoneal and perirenal adipose tissues, their combined weight was measured. The whole body was kept frozen at -20°C until the body composition was analyzed. The procedures were the same in Experiments 2 and 3 unless otherwise stated. In Experiments 2 and 3, rats in the
Copyright © 1982 Brain Research Publications Inc.--0031-9384/82/080899-05503.00/0
TOKUYAMA. SAIT() AND ()KUDA
90o •
A 15000,
Female
Sedentary
o Female
Exercising
• Male ~] M a l e
Sedentary Exercising
07
/
•~ 10000-
o~
5000-
(N=5)
o
25'
c
20"
"o o
,o 15-
i~ ' i
(N=9) i
v
~
1
(N=9) v
500-
v
400-
Z.m 300-
g 200' •
-;0
6
lb
2b
3'o 4b
Day of Experiment
sb
-~'0
6
EXERCISE
lb
2b
(N=9)
3'o go
1
go
Day of Experiment
FIG. I. Changes in mean values of running wheel activity, food intake and body weight. Rats in the exercising group were allowed to run when they were 50 days old (day 0 of the
experiment). Numbers of animals per group are given in parentheses. Asterisks indicate significant differences from values for the sedentary group (p<0.05).
sedentary group were kept in individual simple wire meshed cages (38×25× 17 cm) while the rats in the exercising group were kept in individual wire bottomed cages with running wheels as in Experiment 1. In Experiment 2, 8 male and 8 female rats were used. Revolution of the running wheel was measured for 10 days from day 30 to 40 of the experiment. In Experiment 3, 14 male and 14 female rats were used. Revolution of the running wheel and food intake were measured for 10 days from day 30 to 40 of the experiment. The body weight, tissue weight, and body composition were not measured.
weight of the dry residue. The weight of non-fat solid was calculated by subtracting the weight of body water and body fat from the body weight.
Statistical Analysis Data are shown as means_+S.E.M. The significance of difference between sedentary and exercising groups were determined by the t-test for paired littermates weight matched 10 days before the beginning of the experiment. Analysis of covariance was used to compare regression lines for male and females.
Analysis of Body Composition The whole body was blended with water (50 ml/100 g) in a Waring blender. A portion of the homogenate (100 g) was freeze-dried and the water content was calculated from its change in weight. The dried homogenate was extracted with 300 ml of chloroform-methanol (2:1, v/v) in a Waring blender and filtered. The residue was reextracted twice with 300 ml of chloroform-methanol. These filtrates were combined and evaporated, and the fat content was calculated from the
RESULTS AS described in the Method section we used two conditions for sedentary groups. In Experiment 1 rats of the sedentary group were kept in wire bottomed cages with a locked running wheel while in Experiments 2 and 3 rats of the sedentary groups were kept in simple wire meshed cages. There was no significant difference in the food intakes or weight gains of the sedentary groups of Experiments 1-3 (see
FOOD I N T A K E A N D G R O W T H A F T E R E X E R C I S E
901
q) O
"•140¢0
10 days, but then became higher than the latter reaching a plateau within 20 days. The exercising group gained significantly less weight than the sedentary group.
~E
Relationship Between Running WheelActivity and Food Intake
c-
~ ~2o x ® I.~'0
m / ~f _ _
B E ] ~
A positive correlation between activity on the running wheel and food intake was observed in both males and females in the 10 day period from 30 to 40 after the beginning of wheel running (Fig. 2).
r = 0. 767
B B
p
¢~ . IOC "(3 0
~
6
Y=O.O018X* 95 r =0.744 p
Tissue Weight
,0b00
2o~oo
Running Wheel Activity (RPD) FIG. 2. Relation between running wheel activity and food intake of exercising rats. Food intake is shown as a percentage of that of sedentary littermates, weight matched on 10 days before the beginning of the experiment. O; Female rats in Experiment 1. O; Female rats in Experiment 2 or 3. n; Male rats in Experiment 1. lq; Male rats in Experiment 2 or 3.
also Fig. 2). Therefore, data obtained in these experiments were combined.
In both males and females, the weight of adipose tissue was significantly lower in exercising groups than in sedentary groups. The weight of the soleus was higher in exercising males and females than in sedentary animals. The weight of the heart of exercising females was also more than that of sedentary females (Table 1).
Body Composition The body fat contents of exercising rats of both sexes were significantly lower than those of sedentary animals, but no significant difference was observed in the body water and non-fat solid contents of sedentary and exercising groups (Table 2).
Running Wheel activity, Food Intake, Body Weight
DISCUSSION
Figure 1 shows changes in the mean values for activity on the running wheel (revolutions of the running wheel), food intake and body weight during the experiment. Female rats. Running wheel activity increased rapidly in the first 10 days to a plateau (about 11,000 RPD). F o o d intake of the sedentary group was essentially constant throughout the experiment; that of the exercising group was lower than that of the sedentary group for the first 5 days, but then became higher than the latter attaining a plateau within 15 days. The exercising group gained significantly less weight than the sedentary group. Male rats. Running wheel activity increased in the first 10 days to a plateau (about 4,000 RPD). Throughout the experiment, male rats used the running wheel consistently less than females. F o o d intake of the sedentary group was essentially constant throughout the experiment; that of the exercising group was lower than that of the sedentary group in the first
In this work, we observed changes in the mean values of running wheel activity, food intake and body weight of male and female rats as a function of time after the beginning of wheel running. Running wheel activity of females was several times higher than that of males throughout the experiment, as already reported [10,15]. F o o d intake of both males and females in the exercising group increased after a transient decrease. The finding that food intake and running wheel activity attained plateaus within 20 days after the beginning of wheel running suggests that both males and females adapt to wheel running within 20 days. Although food intake of both males and females increased after adaptation to wheel running, the rate of increase was higher in females. One possible explanation of this sex difference is that the difference in the rates of increase in food intake elicited by wheel running merely reflects the sex difference in running wheel activity. If this is
TABLE I TISSUE WEIGHT Female
Adipose tissue (g) Perigonadal Perirenal + Retroperitoneal Liver (g) Heart (g) Soleus (g) Gastrocnemius (g)
Male
Sedentary
Exercising
Sedentary
Exercising
6.1 _+ 1.0 7.8 _+ 1.0
2.8 _+ 0.6* 3.2 _+ 0.7*
6.5 _+ 0.6 10.2 _+ 1.1
4.6 _+ 0.5* 5.2 _+ 1.0"
17.1 -+ 0.8 1.30 -- 0.04 0.38 _ 0.1 6.0 _+ 0.2
16.1 -+ 0.8 1.32 _+ 0.03 0.41 _+ 0.01* 5.6 -+ 0.2
9.9 0.86 0.25 3.9
__ 0.4 __ 0.02 x 0.01 _+ 0.1
10.4 0.97 0.30 3.6
_+ 0.3 _+ 0.02* _+ 0.02* _+ 0.1
Groups of 9 rats were used. Asterisks indicate significant differences from values for the sedentary group (/7<0.05).
902
T O K U Y A M A , SAI'IO ,~ND O K U I ) A TABLE 2 BODY COMPOSITION Female
Body Weight (g) Fat(g) Water(g) Non-fat Solid (g)
Male
Sedentary
Exercising
Sedentary
Exercising
285 _+ 8
263 _+ 5*
472 _+ 13
428 _+ 12"
47_+ 8 170_+ 5 68_+ 2
31 _+ 3* 165_+ 4 67 + 1
70_+ 5 287_+ 8 114+ 3
49_+ 6* 272_+_ 5 107_+ 3
Body weights measured after exsanguination from the jugular vein. Body weights of female sedentary, female exercising, male sedentary and male exercising rats measured before exsanguination were 292 _+ 8, 271 _+ 5, 482 _+ 13 and 438 _+ 12 g, respectively. Groups of 9 animals were used. Asterisks indicate significant differences from values for the sedentary group (/)<0.05).
the case, there should be a positive correlation between running wheel activity and rate of increase in food intake in males and females, and in fact we found good correlations in both sexes. There was no significant difference in the slopes of regression lines for males and females. These findings suggest that the sex difference in running wheel activity contributes at least in part to the sex difference in the rate of increase in food intake elicited by wheel running. Rolls and Rowe [15] also found a sex difference in the effect of wheel running on food intake. In their experiment food intake of males in the exercising group decreased while that of females increased 10 weeks after the beginning of wheel running. But recently, Mondon et al. [8] reported that food intake of males in their exercising group increased 7 weeks after the beginning of wheel running. Mondon et al.
[8] selected rats that ran more than 2 milesMay on days l i after the beginning of wheel running and measured their food intake. Thus the discrepancy between the results of Rolls and Rowe [15] and Mondon et al. 18] can be partly explained by the difference in the running wheel activities of the rats in their experiments. The decrease in food intake of males in the exercising group of Roils and Rowe could not be explained by our regression line for running wheel activity and food intake. In our experiment, wheel running was started after a preliminary 10-day period. During this period, we confirmed that there was no significant difference in the food intakes or body weights of sedentary and exercising groups. Rolls and Rowe began their experiment by transferring rats of the exercising group to cages with a running wheel. Therefore, in their experiment the rats in the exercising group may have been affected not only by wheel running itself but also by transfer to the new cage. We did not detect any effect of transfer to a new cage on food intake or body weight gain, but Routtenberg et al. [16] reported that food intake decreased significantly when rats were transferred to cages with a locked running wheel. Although food intake increased as a ['unction of the amount of wheel running, the increase in food intake was not sufficient to compensate for the increase in energy expenditure elicited by wheel running. Thus both males and females in the exercising group gained weight slower than sedentary rats. These findings suggest that wheel running not only increased energy expenditure but also decreased the set-point of energy balance that regulates the amount of food intake 11, 6, 9, 2O]. In both males and females the body fat contents of exercising rats were significantly lower than those of sedentary rats, but there was no significant difference in the body water or non-fat solid contents of the two groups. Consistent with this finding, the adipose tissue weights of exercising rats were significantly lower than those of sedentary rats. Further study is necessary to elucidate the effect of wheel running on lipid metabolism.
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