Eur J Appl Physiol (1982) 48:355-359 European Journal of

Applied Physiology and Occupational Physiology �9 Spdnger-Verlag 1982

Effects of Physical Training on Hypothalamic Obesity in Rats

R. R. Jenkins and D. R. Lamb

Biology Department, Ithaca College, Ithaca, NY 14850, USA Exercise Physiology Laboratory, Purdue University, West Lafayette, IN 47906, USA

Summary. Forthy-eight male rats either underwent sterotaxic placement of electrolytic lesions in the ventromedial nucleus of the hypothalamus or had a sham operation and, after a recovery period of at least two weeks, were assigned to either a trained or untrained condition. Training consisted of treadmill running for 120 min per day, 5 days per week, for 12 weeks. At which point all rats were sacrificed to allow the determination of carcass analysis and fat pad lipolysis rates. Both untrained and trained animals with lesions had significantly increased carcass fat. The increased fat content not be attributed to an increased intake since the average daily food consumption of the four groups was not different. Training significantly reduced the fat content in both the lesioned and unlesioned rats. However, the loss in the lesioned rats was about one third less than that of the unlesioned. Training also increased the rate of lipolysis irrespective of whether an animal was lesioned or not. However, the amount of increase was about one third less than in trained normals. Destruction of the ventromedial nucleus of the hypothalamus apparently does not destroy the ability of exercise to alter body composition. The lesions may diminish the capacity of endurance programs to reduce carcass fat. Since the findings relative to lipolysis result from an in vitro investigation, they do not necessarily reflect the events occurring in the in vivo state.

Key words: Physical training - Obesity - Lipolysis - Carcass composi- tion

Obesity is a common malady of the general American populace and a reduction of body fatness is regarded as important for cosmesis, for reduction of risk to

Offprint requests to: Robert R. Jenkins, Ithaca College (address see above)

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356 R.R. Jenkins and D. R. Lamb

c a r d i o v a s c u l a r - r e n a l d i sease and for the e n h a n c e m e n t of r ehab i l i t a t i ve mea - sures. A p p r o p r i a t e hab i tua l exerc ise can dec rease b o d y fat b o t h by inc reas ing ca lor ic e x p e n d i t u r e and by depress ing calor ic i n t ake (Oscai and Ho l lo szy 1969). I t has also b e e n sugges ted tha t phys ica l ly t r a ined an imals have a g rea t e r ab i l i ty to mob i l i ze fats due to an inc reased capac i ty for ad rena l ine - sens i t i ve l ipolysis (Osca i and H o l l o s z y 1969). H o w e v e r , the me c ha n i sms unde r ly ing the t ra in- i ng - induced a l t e ra t ions in food i n t ake and fat mob i l i z a t i on are unc lea r .

B e c a u s e an in tac t h y p o t h a l a m u s is i m p o r t a n t in food i n t ake r e gu l a t i on ( R e e v e r s and P l u m 1969) and has b e e n r e p o r t e d to con ta in a l ip id mobi l i z ing fac tor ( R e d d i n g and Schal ly 1970), it is conce ivab le tha t the exerc i se effect on food c o n s u m p t i o n and fat mob i l i za t i on is m e d i a t e d t h rough the h y p o t h a t a m u s and tha t les ions of the h y p o t h a l a m u s might ob l i t e r a t e these exerc i se responses . W e now r e p o r t the resul ts of an e x p e r i m e n t de s igned to d e t e r m i n e the effects of phys ica l t r a in ing on carcass weight , carcass fat and wa te r , food c o n s u m p t i o n , and ad rena l i ne - sens i t i ve l ipolysis of n o r m a l rats and to c o m p a r e these effects wi th t hose o b s e r v e d in ra ts wi th e lec t ro ly t i c les ions of the h y p o t h a l a m u s .

Materials and Methods

Sixty male, 41 week old Sprague-Dawley rats (Sprague-Dawley, Inc. Madison, Wisconsin) were housed individually in standard wire cages at 22 ~ C with alternating 12-h light and dark cycles. They were provided ad libitum acces to water and standard lab chow. Body weights and food consumption were recorded daily. The animals had exhibited similar growth rates prior to the experimental procedure.

The mean weight of the rats was 554 + 20.4 prior to the study. Hypothalamic lesions were placed in the ventromedial nuclei of 30 randomly selected animals. The rats were anesthetized by a 50 mg - kg -1 body weight intraperitoneal injection of Nembutal. Stereotaxic coordinates were taken from the atlas of DeGroot (1959). Holes were drilled in the skull, and an anodal current of 1.5 mA was delivered for 10 s through an insulated monopolar electrode 0.5 mm in diameter bared of insulation for 0.5 mm from the tip. The remaining 30 rats received sham operations with the eletrodes inserted into the brain but without the administration of the current. The placement of the lesions was verified by histological examination at the termination of the study.

Daily records of post operative weight gain and food consumption were made for at least 2 weeks. A rat was considered successfully lesioned if its average daily weight gain exceeded its preoperative average weight gain by 2 g or more, The 24 rats that met this criterion wer assigned at random to a trained or untrained condition with 12 in each group. Twenty-four sham-operated animals were also randomly assigned to either a trained or untrained condition. The average weight gain for the sham-operated animals was not significantly different from their preoperative gain.

After at least 2 weks of postoperative recovery, the training began by running on a rodent treadmill according to the protocol of Askew et al. (1975). After 12 weeks of running, the rats were killed by decapitation and exsanguination. The gastrointestinal tract of each animal was removed, cleaned of its contents and replaced in the carcass which was then weighed. Carcass composition was determined by the method of Mickelson and Anderson (1959). Isolated adipose cells were prepared and analyzed for adrenaline-sensitive lipolysis by the method of Askew et al. (1975). Twenty micrograms of adrenaline were added to the incubation medium and the glycerol released was determined by Korn's (1955) procedure. Protein was determined by Hartree's modification of the Lowry method (Hartree 1972).

The range of coefficients of variation for all procedures was between 2% and 5 %, and recoveries of known amounts of glycerol and protein averaged 95% and 98%, respectively. Data for carcass fat and lipolysis were analyzed by a two-way analysis of variance and Student-Newman-Keuls test for multiple comparisons (Wirier 1962).

Physical Training and Hypothalamic Obesity 357

Table 1. Effects of physical training and hypothalamic lesion placement on carcass weight, fat, and food consumption. The values given are the mean + standard error of the mean. The letters refer to differences (p < 0.05) from the following values (b) untrained normal, (c) trained normal, (d) untrained lesioned, and (e) trained lesioned. Number of animals in parenthesis

Untrained Trained

Normal (12) Lesioned (12) Normal (12) Lesioned (12)

Caracass weight (g) 559.10 4- 23.1 c,d,e 650.00 4- 31.4 b,c,e 410.00 4- 18.2 b,d,e 598.00 4- 28.6 b,c,d Caracass fat (g) 202.59 4- 28.2 ~,a,e 261.2 4- 18.4 b,c,e 110.48 4- 16.4 b,d,e 226.52 4- 22.1 b'c'd Caracass water (g) 268.58 + 14.1 c,a,e 276.4 + 15.4 ~ 220.49 + 6.3 b,d,e 269.28 + 9.1 ~ Other 87.93 + 4.1 d,e 112.4 + 3.3 b,c 79.03 __. 4.3 d,e 102.204- 6.0 c Food consumption 19.00 + 2.0 20.00 + 4.1 20.00 + 2.0 20.00 + 2.1 (g. day -1)

Table 2. Glycerol release from adrenalin stimulated fat pad samples, figures are the means + SEM. The letters refer to differences (p < 0.05) from the following values (b) untrained normal. (c) trained normal, (d) untrained lesioned, and (e) trained lesioned. Number of animals in parenthesis

Untrained Trained

Sham (12) Lsioned (12) Sham ( 1 2 ) Lesioned (I2)

~xmol �9 mg protein - h -1 0.06 4- 0 .16c ,d ,e 0.16 4- 0 . 3 b'c'e 1.80 -t- 0 .2b,d , e 0.47 4- 0.2 c'a gmol (cell x 106) �9 h -1 0.98 __ 0 . 2 c'd'e' 0.39 4- 0.1 b,c,r 1.87 -t- 0 .3b,d , e 0.70 + 0.2 c'a

Resul t s

T h e d a t a for the effects of the h y p o t h a l a m i c les ion and exerc i se on carcass c o m p o s i t i o n and food c o n s u m p t i o n are shown in T a b l e 1. A s e x p e c t e d , the p l a c e m e n t of les ions in the h y p o t h a l a m u s resu l t ed in g rea t e r carcass weights , m o r e carcass fat and a d e c r e a s e d p e r c e n t carcass wa te r , r ega rd les s of phys ica l t r a in ing s ta tus . A l t h o u g h the a m o u n t of fat weight was s ignif icant ly d i f fe ren t b e t w e e n the n o r m a l cont ro l s and l e s ioned t r a i ne d an imals , the p e r c e n t fat was no t d i f fe ren t and thus the carcass c o m p o s i t i o n was s imi lar in those two groups . T h e r e was no d i f fe rence b e t w e e n the food c o n s u m p t i o n of e i the r the l e s ioned or t r a i ned rats .

T h e n o r m a l t r a ined an imals h a d lower carcass weights , less carcass fa t and a g r ea t e r p e r c e n t carcass wa te r t han bo th the n o r m a l u n t r a i n e d g roups and b o t h g roups of l e s ioned rats . T h e l e s ioned ra ts r e s p o n d e d to exerc i se in a s imi lar m a n n e r . H o w e v e r , the changes were s ignif icant ly less than those of n o r m a l t r a i ned rats .

T h e ad rena l ine - sens i t i ve l ipolysis of n o r m a l an imals was g r e a t e r t han tha t of the l e s i o n e d animals . Tra in ing also i nc reased l ipolysis in b o t h n o r m a l and l e s ioned an imals t h o u g h this effect was less m a r k e d in the l a t t e r (Tab l e 2).

358 R.R. Jenkins and D. R. Lamb

Discussion

In general, exercise exerted a typical influence on the carcass composition of both the lesioned and normal rats. Carcass weight and fat content were reduced in both groups and percent carcass water increased in both trained groups. However, the lesioned rats lost nearly one third less carcass fat than the shamoperated animals.

There was no difference between the food consumption of either the lesioned rats or the trained rats. It is well knwon that hypothalamic obesity may develop independently of an increased food intake (Goldman et al. 1974; Hart 1963; Hart 1967). It appears that the reduction of spontaneous activity accounts for a large proportion of the weight gain in hypothalamic obese animals (Gladfelter and Brobeck 1962; Gladfelter 1978). The finding that exercise reduced the carcass weight and fat of normal rats without a suppression of food intake is in accord with a previous study (Oscai et al. 1974).

The effect of exercise on hormone-stimulated lipolysis remains unsettled. The findings from several labs (Askew et al. 1975; Gollnick and Williams 1969; Parizkova and Stankova 1964) originally were in agreement that training resulted in a significant increase in lipolysis. However, McGarr et al. (1976) and Howle and Barnard (1976) reported that no significant difference was noted when the results were expressed on a per cell basis. Our findings on normal rats indicate that training does increase hormone-sensitive lipolysis when the data are expressed on a per cell or per milligram protein basis. This finding is in agreement with that of Askew et al. (1975). The discrepancy between our findings and those of earlier investigators who have reported no training effect is very likely due to a difference in the analysis technique for the enzyme. Notably, we have followed the fat cell isolation and incubation procedure of Askew et al. (1975) which utilized a 1 ml fat cell suspension in the incubation medium while Howle and Barnard (1976) used pieces of fat pads. The use of tissue pieces may impose a diffusion barrier.

The lesioned non-trained rats of this study released only 26% as much free glycerol as the normal rats when expressed on a per mg protein basis and 39% when compared per fat cell. Haessler and Crawford (1967) have also reported a reduced rate of lipolysis in lesioned rats. Therefore, rats with hypothalamic lesions exhibited greater carcass fat stores than normals in the absence of hyperphagia. This finding was probably a result of a greater rate of fat incorporation (Holm et al. 1973) and a reduction of spontaneous motor activity (Gladfelter and Brobeck 1962; Gladfelter 1978). Trained lesioned rats had a carcass fat loss which was only 38% that of the normal rats. The lower rate of fat loss in the lesioned rats is very likely explained by the reduced rate of adrenaline stimulated lipolysis of the lesioned animals.

It should be mentioned that, in a previous unpublished experiment we failed to observe either a reduction of carcass fat or a response to adrenaline in lesioned animals. Swimming was used as the exercise in that study and 200 mg samples of fat pads were incubated to study lipolysis. The difference in the results of that experiment and the present one illustrates that care must be taken to impose a suitable vigorous exercise, especially when using animals of varying

Physical Training and Hypothalamic Obesity 359

body composition. It also demonstrates the need to use very small samples or preferably, isolated cells when investigating lipolysis of tissues with low levels of enzyme activity.

In conclusion, our data suggest that rats made obese by hypothalamic lesions will respond to imposed exercise by lowering fat stores, but that the ability to lower fat is poorer due to a reduced sensitivity of the adrenaline-sensitive lipase activity.

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Accepted November 26, 1981