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Photoperiodic control of the thermogenic capacity in brown adipose tissue of the Djungarian hamster
J. therm. Biol. Vol. 10, No. 3, pp. 167-170, 1985
0306-4565/8553.00+0.00 Pergamon Press Ltd
Printed in Great Britain
PHOTOPERIODIC CONTROL OF THE THERMOGENIC CAPACITY IN BROWN ADIPOSE TISSUE OF THE D J U N G A R I A N HAMSTER J. RAFAELand P. VSIANSKY Institut f'tir Biochemie I der Universit/it Heidelberg, Neuenheimer Feld 328, 6900 Heidelberg, F.R.G. (Received 6 August 1984; accepted in revised form 23 February 1985)
Abstraet--l. Specific GDP-binding in brown adipose tissue (BAT) mitochondria is increased by 50° in Djungarian hamsters after 70 days of exposure to a short photoperiod at 23°C ambient temperature; total GDP-binding in BAT is elevated by 300%. GDP-binding remains unchanged during exposure to a long photoperiod. 2. The increase of GDP-binding in response to a short day is less than 30% if compared to the increase induced by additional cold influence (outdoor/winter). 3. GDP-binding in BAT, as a measure of the thermogenic capacity in BAT, is correlated to the NST capacity of the animals and the significance of BAT during NST is discussed. Key Word lndex--Brown adipose tissue; non-shivering thermogenesis; GDP-binding; mitochondria;
Djungarian hamster. INTRODUCTION
Small mammals have been shown to increase their capacity for non-shivering thermogenesis (NST) in response to cold influence (cold-induced NST) (Smith and Horwitz, 1969; Chaffee and Roberts, 1971) as well as in reaction to overfeeding (diet-induced NST) (Rothwell and Stock, 1979). Both regulatory influences have been shown to affect the thermogenic capacity of brown adipose tissue (BAT) (Foster and Frydman, 1978, Rothwell and Stock, 1979; Trayhurn and James, 1984), thus directing considerable attention on this tissue as a possibly dominant site of NST--for a review see Nicholls and Locke (1984). Heat production in BAT is regulated by a specific nucleotide-binding protein in the inner mitochondriai membrane (Heaton et al., 1978) which provides the proton conductance pathway required by the chemiosmotic modification (Nicholls, 1974) of the original hypothesis. The thermogenic capacity of BAT correlates with the total amount of this regulatory protein (Rafael and Heldt, 1976; Sundin and Cannon, 1980), which is determined by the specific GDP-binding capacity of BAT mitochondria (nmol/mg protein) and the total amount of organelles in the tissue. A further stimulus of NST capacity has been demonstrated recently in Djungarian hamsters (Phodopus sungorus): a short photoperiod increases the thermogenic capacity of these animals in later summer and fall (Heidmaier et al., 1981). It was the purpose of this study to establish photoperiod as an environment regulator of the thermogenic capacity in BAT. The influence of varying photoperiod was measured on GDP-binding in BAT of Djungarian hamsters in correlation to the NST capacity of the animals in response to noradrenaline (NA).
described by Heldmaier and Steinlechner (1981). Adult animals, born in spring of the same year, were investigated. Photoperiodic conditions were as indicated in the text. NST capacity was estimated from O2-consumption under noradrenaline (NA) (0.4 mg NA/kg body wt, s.c.) and basal respiration in nonanaesthetized hamsters at 14°C ambient temperature (Heldmaier and Steinlechner, 1981). BAT deposits were pooled and water, lipid and fat-free dry matter (practically representing the tissue protein) of the combined fat pads were determined as recently described by Rafael et al. (1984). Mitochondria were isolated according to Rafael et al. (1984). Activity of cytochrome oxidase (EC 1.9.3.1) was measured polarographically in the homogenate of the pooled fat pads (Rafaei, 1983b). The specific amount of mitochondrial protein in BAT was determined from the cytochrome oxidase activity in the tissue and in the isolated organelles, respectively. Protein was determined by the biuret method. GDP-binding of BAT mitochondria was measured as described earlier (Rafael and Heldt, 1976); the specific binding capacity (nmol GDP/mg mitochondrial protein) was determined from Scatchard plots using 7 different concentrations of GDP (l-8/aM) at pH 7.1. Radioactivity was measured in a Philips LSA counter. Lubroi (type WX), cytochrome c (type III) and TMPD were from Sigma Chemic, Miinchen, F.R.G. [~H]GDP and [14C]sucrose were obtained from Amersham Buchler GmBH, Braunschweig, F.R.G. All other reagents were of the highest purity commercially available. RESULTS AND DISCUSSION
MATERIALS AND METHODS
Djungarian dwarf hamsters (P. sungorus), were bred and kept under thermoneutrai conditions as
The thermogenic capacity of BAT, expressed as the GDP-binding capacity of the tissue mitochondria, was measured in Djungarian hamsters after exposure 167
J. RAFAELand P. VSIANSKY
168
Table 1. Effect of photoperiod on body weight, NST and BAT in Djungarianhamsters as compared to values measured in hamsters under outdoor conditionsin winter Long Short Winter Control photopcriod photoperiod outdoor Body weight (g) 41.0 + 0.9 40.0 4. 0.7 28.0 4. 1.6 26.9 ± 0.8 NST capacity (mW) 999 4. 74 1,0264. 53 1,1604-36 1,5694. 39" BAT (g) 2.1 4.0.1 1.9_+0.1 1.1 4 . 0 . 1 0.94_+0.03 BAT mitochondria 32 4- 2.5 33 4-2.2 58 ~-2.7 91.8 4-2.8 (rag protein) NST capacityffimaximumNA-inducedheat productionminusbasal metabolicrate. Data per animalsare expressed as means+ SEM as obtainedfrom 8 individuals.Detailsand photoperiodicconditionswere as describedin the text. All differencesbetweencontrolsand hamsters kept at short photoperiodwere found significantlydifferent (P < 0.01) according to Student's double-tailedt-test. "Data from Heldmaieret al. (1982). to varying photoperiod. GDP-binding in BAT was However, the significance of these thermotropic correlated to the increase of O:-consumption induced changes is considerably enhanced by the finding of a by NA, as a measure of the NST capacity of the photoperiodic control of GDP-binding in BAT. animals. Control hamsters, kept under natural pho- GDP-binding/mg mitochondrial protein is increased toperiodic conditions, were investigated at the end of by 50~o, total GDP-binding by almost 300%, whereas July, i.e. when NST and respiratory capacity in BAT no change of GDP-binding capacity is observed in are still at the lowest seasonal level (Heldmaier et al., BAT after long photopcriod (Table 2). Specific prop1982; Rafael et al., 1984). At the same time two erties of the binding site, as expressed by the disgroups of hamsters were exposed either to 16 h of sociation constant KD (Lin and Klingenberg, 1982) light/day (long photoperiod) or to 8 h of light/day remain unchanged in all groups investigated. (short photoperiod). Results measured after 70 days In addition to cold and dietary influence, short of photopcriodic treatment were compared to control photopvriod is thus indicated as a further stimulus of data as well as to maximum values measured under thermogenic capacity in BAT (photoperiod-induced winter/outdoor conditions (Heldmaivr et al., 1982; NST). Though nothing is known on the exact timeRafael et al., 1984). Photoperiodic experiments were course of photopcriod-controlled adaptive changes in performed at this time of the year because the BAT, the thermotropic reaction of the tissue appears thermotropic response in Djungarian hamsters to a rather slow in comparison to the effect of other short day has been detectable during late summer and regulatory influences. Fast response of BAT to de. fall, but not in spring and early summer (Heldmaier creased ambient temperature may be vital for the maintenance of body temperature, and a prompt et al., 1981). Body weight and total mass of BAT in hamsters kept at short photoperiod are reduced almost to minimum levels observed in winter/outdoor animals (Table I). Both parameters remain close to control values at long photoperiod. Reduction of BAT in response to short photoperiod is a consequence of the extensive lipid depletion of the tissue, accompanied by an increase of protein and water (Fig. I). Tissue components remain virtually unchanged at long pho-r toperiod. Extensive reduction of body weight and ~omass of BAT, concomitant with an extensive decrease of tissue lipid, has recently been found in hamsters ! during seasonal acclimatization in fall (Rafael et al., 1984). Results of this study confirm that these seasonal changes are basically controlled by photoperiod. The NST capacity of the hamsters is increased by 20% and the amount of BAT mitochoodria by 80°/0 Long Short C0ntr0~ pp Igo under the influence of short photoperiod, whereas no increase is registered under conditions of long photo- Fig. 1. Effect of long and short photoperiod (pp) on Lh¢ period (Table l). This agrees, in principle, with earlier amount of lipid ([2), water (1) and protein (•) in BAT of Djungarian hamsters. results (Heldmaier et al., 1981; Rafacl et al., 1984).
2.0:- -~ 1.5-
o
05
m
Table 2. Effectof photoperiod on GDP-binding in B A T mitochondda of Djungarian hamsters as compared to values measured in hamsCm~ und~ ou;do~r conditions in winter
G D P bound (nmol/mg
mitochondrialprotein) GDP bound (nmol total)
Control
Long photoperiod
Short photoperiod
Winter outdoor
0.21 ± 0.02
0.20 ± 0.02
0.31 ± 0.02
0.55 4-0.03
6.4 ± 0.7 6.6 4-0.6 18.1 + 1.2 50.4± 1.8 4.5±0.2 4.8 ± 0.3 4.74.0.5 4.1 4.0.3 Means4. SEM from 8 animals.Experimentaldetails are as described in Materials and Methods. KD
Photoperiodic control of NST capacity in BAT
reaction to overfeeding appears meaningful in order to prevent obesity by the wasting of food energy as heat. In contrast to other effc~:tors, short photoperiod stimulates the thermogenic capacity in BAT without any actual need for NST. The seasonal decrease of photoperiod might serve as a long-term environmental signal indicating the approach of increased NST requirement; hamsters become prepared for a rapid temperature decrease in fall, especially common in their natural environment in the Siberian steppe. Photoperiodic regulation of the thermogenic mechanism in BAT adds a further aspect to the hormonal control of this mechanism. Photoperiodic influence is likely to be mediated via the pineal-endocrinal function. In fact, melatonin, a compound released by the pineal, has been shown to mimic the effect of short photoperiod on the NST capacity and the amount of BAT mitochondria, when applied to Djungarian hamsters kept at thermoneutrality in summer (Heldmaier et al., 1981). Melatonin therefore appears as a promising candidate for direct or indirect control of GDP-binding in BAT. The increase of total GDP-binding and NST capacity in response to a short day represents only 25-30% of the maximum increase measured in hamsters kept outdoors in winter (Tables 1 and 2), thus emphasizing the additional effect of cold on both parameters. It is striking, however, that short-day exposure increases the absolute NST capacity by 16% but elevates the total GDP-binding capacity in BAT by almost 200% (Table 2). Accordingly, maximum NST capacity in winter/outdoor hamsters is only 57% higher than in controls, whereas GDP-binding is increased by about 700%. Correlation of the NST capacity and the total amount of nucleotide-binding protein as indicated by total GDP-binding, is demonstrated in Fig. 2. Though this correlation is based on three points only, extrapolation to zero GDP-binding permits speculation on the NST capacity independent of BAT. Linear extrapolation to zero GDP-binding results in a relatively small reduction of the NST capacity in warm-adapted controls (Fig. 2). This would indicate a substantial thermogenic response of warm-adapted hamsters to NA independent of BAT and agrees with the limited thermoregnlatory significance of BAT in these animals indicated by biochemical parameters in the tissue (Rafael,
1500 --
~
,
outdOOr
..J -- 1000 Controls, long pp
E 5OO
I
10
I
30
I 50
nmol GDP BOUND/ANIMAL
Fig. 2. Correlation of GDP-binding in BAT and NST capacity in Djungarian hamsters. Data are taken from Tables 1 and 2.
169
1983a). Measurement of the total NST capacity in Djungarian hamsters permits no estimate of relative changes of NST capacity in different thermogenic sites, but NST independent of BAT may well respond to photoperiod and cold, concomitant with the response of NST capacity in BAT (Rafael et al., 1984). Increased knowledge about quantitative changes in nucleotide-controlled heat production in BAT will help to answer this question.
Acknowledgements--The authors would like to thank Prolessor G. Heidmaier who kindly offered all the facilities for O,.-consumption measurements in his laboratory in Marburg. Expert technical assistance was provided by Ms Gabriele Miiller. This work was supported by a grant from the Deutsche Forschungsgemeinschafi.
REFERENCES
Chaffee R. R. J. and Roberts J. C. (1971) Temperature acclimation in birds and mammals. A. Rev. Physiol. 33, 155-202. Foster D. O. and Frdyman M. (1978) Non-shivering thermogenesis in the rat: measurements of blood flow with microspheres point to brown adipose tissue as the dominant site of calorigenesis induced by noradrenaline. Can. J. Physiol. Pharmac. 56, 110-122. Heaton G. M., Wagenford R. J., Kemp A. Jr and Nicholls D. G. (1978) Brown-adipose-tissuemitochondria: photoaffinity labelling of the regulatory site of energy dissipation. Fur. J. Biochem. 82, 515-521. Heldmaier G. and Steinlechner S. (1981) Seasonal control of energy requirements for thermoregulation in the Djungarian hamster (Phodopus sungorus), living in natural photoperiod. J. comp. Physiol. 142, 429-437. Heldmaier G., Steinlechner S., Rafael J. and Vsiansky P. (1981) Photoperiodic control and effects of melatonin on nonshivering thermogenesis and brown adipose tissue. Science 212, 917-919. Heldmaier G., Steinlechner S. and Rafael J. (1982) Nonshivering thermogenesis and cold resistance during seasonal acclimatization in the Djungarian hamster. J. comp. Physiol. 149, I-9. Lin C.-S. and Klingenberg M. (1982) Characteristics of the isolated purine nucleotide binding protein from brown fat mitochondria. Biochemistry 21, 2950-2956. Nicholls D. G. (1974) Hamster brown-adipose-tissue mitochondria. The control of respiration and the proton electrochemical potential gradient by possible physiological effectors of the proton conductance of the inner membrane. Fur. J. Biochem. 49, 573-583. Nicholls D. G. and Locke R. M. (1984) Thermogenic mechanism in brown fat. Physiol. Rev. 64, 1--64. Rafael J. (1983a) Biochemical aspects of the thermoregulatory role of brown adipose tissue. J. therm. Biol. 8, 410--412. Rafael J. (1983b) Cytochrome oxidase. In Methods of Enzymatic Analysis, Vol. 3 (Edited by Bergmeyer H. U.), pp. 266-273. Verlag Chemie, Weinheim, F.R.G. Rafael J. and Heldt H.-W. (1976) Binding of guanine nucleotides to the outer surface of the inner membrane of guinea-pig brown fat mitochondria in correlation with the thermogenic capacity of the tissue. FEBS Lett. 63, 304-308. Rafael J., Vsiansky P. and Heldmaier G. (1984) Seasonal adaptation of brown adipose tissue in the Djungarian hamster. J. comp. Physiol. 155, 521-528. Rothweil N. J. and Stock M. J. (1979) A role for brown
170
J. RAFAEL and P. VSIANSKY
adipose tissue in diet-induced thermogenesis. Nature 281, 31-35. Smith R. E. and Horwitz B. A. (1969) Brown fat and thermogenesis. Physiol. Ret'. 49, 330-425. Sundin U. and Cannon B. (1980) GDP-binding to the
brown fat mitochondria of developing and cold-adapted rats. Comp. Biochem. Physiol. 65B, 463--471. Trayhurn P. and James W. P. T. (1984) Thermogenesis and obesity. In Mammalian Thermogenesis (Edited by Girardier L. and Stock M. J.). Chapman & Hall, London.
0306-4565/8553.00+0.00 Pergamon Press Ltd
Printed in Great Britain
PHOTOPERIODIC CONTROL OF THE THERMOGENIC CAPACITY IN BROWN ADIPOSE TISSUE OF THE D J U N G A R I A N HAMSTER J. RAFAELand P. VSIANSKY Institut f'tir Biochemie I der Universit/it Heidelberg, Neuenheimer Feld 328, 6900 Heidelberg, F.R.G. (Received 6 August 1984; accepted in revised form 23 February 1985)
Abstraet--l. Specific GDP-binding in brown adipose tissue (BAT) mitochondria is increased by 50° in Djungarian hamsters after 70 days of exposure to a short photoperiod at 23°C ambient temperature; total GDP-binding in BAT is elevated by 300%. GDP-binding remains unchanged during exposure to a long photoperiod. 2. The increase of GDP-binding in response to a short day is less than 30% if compared to the increase induced by additional cold influence (outdoor/winter). 3. GDP-binding in BAT, as a measure of the thermogenic capacity in BAT, is correlated to the NST capacity of the animals and the significance of BAT during NST is discussed. Key Word lndex--Brown adipose tissue; non-shivering thermogenesis; GDP-binding; mitochondria;
Djungarian hamster. INTRODUCTION
Small mammals have been shown to increase their capacity for non-shivering thermogenesis (NST) in response to cold influence (cold-induced NST) (Smith and Horwitz, 1969; Chaffee and Roberts, 1971) as well as in reaction to overfeeding (diet-induced NST) (Rothwell and Stock, 1979). Both regulatory influences have been shown to affect the thermogenic capacity of brown adipose tissue (BAT) (Foster and Frydman, 1978, Rothwell and Stock, 1979; Trayhurn and James, 1984), thus directing considerable attention on this tissue as a possibly dominant site of NST--for a review see Nicholls and Locke (1984). Heat production in BAT is regulated by a specific nucleotide-binding protein in the inner mitochondriai membrane (Heaton et al., 1978) which provides the proton conductance pathway required by the chemiosmotic modification (Nicholls, 1974) of the original hypothesis. The thermogenic capacity of BAT correlates with the total amount of this regulatory protein (Rafael and Heldt, 1976; Sundin and Cannon, 1980), which is determined by the specific GDP-binding capacity of BAT mitochondria (nmol/mg protein) and the total amount of organelles in the tissue. A further stimulus of NST capacity has been demonstrated recently in Djungarian hamsters (Phodopus sungorus): a short photoperiod increases the thermogenic capacity of these animals in later summer and fall (Heidmaier et al., 1981). It was the purpose of this study to establish photoperiod as an environment regulator of the thermogenic capacity in BAT. The influence of varying photoperiod was measured on GDP-binding in BAT of Djungarian hamsters in correlation to the NST capacity of the animals in response to noradrenaline (NA).
described by Heldmaier and Steinlechner (1981). Adult animals, born in spring of the same year, were investigated. Photoperiodic conditions were as indicated in the text. NST capacity was estimated from O2-consumption under noradrenaline (NA) (0.4 mg NA/kg body wt, s.c.) and basal respiration in nonanaesthetized hamsters at 14°C ambient temperature (Heldmaier and Steinlechner, 1981). BAT deposits were pooled and water, lipid and fat-free dry matter (practically representing the tissue protein) of the combined fat pads were determined as recently described by Rafael et al. (1984). Mitochondria were isolated according to Rafael et al. (1984). Activity of cytochrome oxidase (EC 1.9.3.1) was measured polarographically in the homogenate of the pooled fat pads (Rafaei, 1983b). The specific amount of mitochondrial protein in BAT was determined from the cytochrome oxidase activity in the tissue and in the isolated organelles, respectively. Protein was determined by the biuret method. GDP-binding of BAT mitochondria was measured as described earlier (Rafael and Heldt, 1976); the specific binding capacity (nmol GDP/mg mitochondrial protein) was determined from Scatchard plots using 7 different concentrations of GDP (l-8/aM) at pH 7.1. Radioactivity was measured in a Philips LSA counter. Lubroi (type WX), cytochrome c (type III) and TMPD were from Sigma Chemic, Miinchen, F.R.G. [~H]GDP and [14C]sucrose were obtained from Amersham Buchler GmBH, Braunschweig, F.R.G. All other reagents were of the highest purity commercially available. RESULTS AND DISCUSSION
MATERIALS AND METHODS
Djungarian dwarf hamsters (P. sungorus), were bred and kept under thermoneutrai conditions as
The thermogenic capacity of BAT, expressed as the GDP-binding capacity of the tissue mitochondria, was measured in Djungarian hamsters after exposure 167
J. RAFAELand P. VSIANSKY
168
Table 1. Effect of photoperiod on body weight, NST and BAT in Djungarianhamsters as compared to values measured in hamsters under outdoor conditionsin winter Long Short Winter Control photopcriod photoperiod outdoor Body weight (g) 41.0 + 0.9 40.0 4. 0.7 28.0 4. 1.6 26.9 ± 0.8 NST capacity (mW) 999 4. 74 1,0264. 53 1,1604-36 1,5694. 39" BAT (g) 2.1 4.0.1 1.9_+0.1 1.1 4 . 0 . 1 0.94_+0.03 BAT mitochondria 32 4- 2.5 33 4-2.2 58 ~-2.7 91.8 4-2.8 (rag protein) NST capacityffimaximumNA-inducedheat productionminusbasal metabolicrate. Data per animalsare expressed as means+ SEM as obtainedfrom 8 individuals.Detailsand photoperiodicconditionswere as describedin the text. All differencesbetweencontrolsand hamsters kept at short photoperiodwere found significantlydifferent (P < 0.01) according to Student's double-tailedt-test. "Data from Heldmaieret al. (1982). to varying photoperiod. GDP-binding in BAT was However, the significance of these thermotropic correlated to the increase of O:-consumption induced changes is considerably enhanced by the finding of a by NA, as a measure of the NST capacity of the photoperiodic control of GDP-binding in BAT. animals. Control hamsters, kept under natural pho- GDP-binding/mg mitochondrial protein is increased toperiodic conditions, were investigated at the end of by 50~o, total GDP-binding by almost 300%, whereas July, i.e. when NST and respiratory capacity in BAT no change of GDP-binding capacity is observed in are still at the lowest seasonal level (Heldmaier et al., BAT after long photopcriod (Table 2). Specific prop1982; Rafael et al., 1984). At the same time two erties of the binding site, as expressed by the disgroups of hamsters were exposed either to 16 h of sociation constant KD (Lin and Klingenberg, 1982) light/day (long photoperiod) or to 8 h of light/day remain unchanged in all groups investigated. (short photoperiod). Results measured after 70 days In addition to cold and dietary influence, short of photopcriodic treatment were compared to control photopvriod is thus indicated as a further stimulus of data as well as to maximum values measured under thermogenic capacity in BAT (photoperiod-induced winter/outdoor conditions (Heldmaivr et al., 1982; NST). Though nothing is known on the exact timeRafael et al., 1984). Photoperiodic experiments were course of photopcriod-controlled adaptive changes in performed at this time of the year because the BAT, the thermotropic reaction of the tissue appears thermotropic response in Djungarian hamsters to a rather slow in comparison to the effect of other short day has been detectable during late summer and regulatory influences. Fast response of BAT to de. fall, but not in spring and early summer (Heldmaier creased ambient temperature may be vital for the maintenance of body temperature, and a prompt et al., 1981). Body weight and total mass of BAT in hamsters kept at short photoperiod are reduced almost to minimum levels observed in winter/outdoor animals (Table I). Both parameters remain close to control values at long photoperiod. Reduction of BAT in response to short photoperiod is a consequence of the extensive lipid depletion of the tissue, accompanied by an increase of protein and water (Fig. I). Tissue components remain virtually unchanged at long pho-r toperiod. Extensive reduction of body weight and ~omass of BAT, concomitant with an extensive decrease of tissue lipid, has recently been found in hamsters ! during seasonal acclimatization in fall (Rafael et al., 1984). Results of this study confirm that these seasonal changes are basically controlled by photoperiod. The NST capacity of the hamsters is increased by 20% and the amount of BAT mitochoodria by 80°/0 Long Short C0ntr0~ pp Igo under the influence of short photoperiod, whereas no increase is registered under conditions of long photo- Fig. 1. Effect of long and short photoperiod (pp) on Lh¢ period (Table l). This agrees, in principle, with earlier amount of lipid ([2), water (1) and protein (•) in BAT of Djungarian hamsters. results (Heldmaier et al., 1981; Rafacl et al., 1984).
2.0:- -~ 1.5-
o
05
m
Table 2. Effectof photoperiod on GDP-binding in B A T mitochondda of Djungarian hamsters as compared to values measured in hamsCm~ und~ ou;do~r conditions in winter
G D P bound (nmol/mg
mitochondrialprotein) GDP bound (nmol total)
Control
Long photoperiod
Short photoperiod
Winter outdoor
0.21 ± 0.02
0.20 ± 0.02
0.31 ± 0.02
0.55 4-0.03
6.4 ± 0.7 6.6 4-0.6 18.1 + 1.2 50.4± 1.8 4.5±0.2 4.8 ± 0.3 4.74.0.5 4.1 4.0.3 Means4. SEM from 8 animals.Experimentaldetails are as described in Materials and Methods. KD
Photoperiodic control of NST capacity in BAT
reaction to overfeeding appears meaningful in order to prevent obesity by the wasting of food energy as heat. In contrast to other effc~:tors, short photoperiod stimulates the thermogenic capacity in BAT without any actual need for NST. The seasonal decrease of photoperiod might serve as a long-term environmental signal indicating the approach of increased NST requirement; hamsters become prepared for a rapid temperature decrease in fall, especially common in their natural environment in the Siberian steppe. Photoperiodic regulation of the thermogenic mechanism in BAT adds a further aspect to the hormonal control of this mechanism. Photoperiodic influence is likely to be mediated via the pineal-endocrinal function. In fact, melatonin, a compound released by the pineal, has been shown to mimic the effect of short photoperiod on the NST capacity and the amount of BAT mitochondria, when applied to Djungarian hamsters kept at thermoneutrality in summer (Heldmaier et al., 1981). Melatonin therefore appears as a promising candidate for direct or indirect control of GDP-binding in BAT. The increase of total GDP-binding and NST capacity in response to a short day represents only 25-30% of the maximum increase measured in hamsters kept outdoors in winter (Tables 1 and 2), thus emphasizing the additional effect of cold on both parameters. It is striking, however, that short-day exposure increases the absolute NST capacity by 16% but elevates the total GDP-binding capacity in BAT by almost 200% (Table 2). Accordingly, maximum NST capacity in winter/outdoor hamsters is only 57% higher than in controls, whereas GDP-binding is increased by about 700%. Correlation of the NST capacity and the total amount of nucleotide-binding protein as indicated by total GDP-binding, is demonstrated in Fig. 2. Though this correlation is based on three points only, extrapolation to zero GDP-binding permits speculation on the NST capacity independent of BAT. Linear extrapolation to zero GDP-binding results in a relatively small reduction of the NST capacity in warm-adapted controls (Fig. 2). This would indicate a substantial thermogenic response of warm-adapted hamsters to NA independent of BAT and agrees with the limited thermoregnlatory significance of BAT in these animals indicated by biochemical parameters in the tissue (Rafael,
1500 --
~
,
outdOOr
..J -- 1000 Controls, long pp
E 5OO
I
10
I
30
I 50
nmol GDP BOUND/ANIMAL
Fig. 2. Correlation of GDP-binding in BAT and NST capacity in Djungarian hamsters. Data are taken from Tables 1 and 2.
169
1983a). Measurement of the total NST capacity in Djungarian hamsters permits no estimate of relative changes of NST capacity in different thermogenic sites, but NST independent of BAT may well respond to photoperiod and cold, concomitant with the response of NST capacity in BAT (Rafael et al., 1984). Increased knowledge about quantitative changes in nucleotide-controlled heat production in BAT will help to answer this question.
Acknowledgements--The authors would like to thank Prolessor G. Heidmaier who kindly offered all the facilities for O,.-consumption measurements in his laboratory in Marburg. Expert technical assistance was provided by Ms Gabriele Miiller. This work was supported by a grant from the Deutsche Forschungsgemeinschafi.
REFERENCES
Chaffee R. R. J. and Roberts J. C. (1971) Temperature acclimation in birds and mammals. A. Rev. Physiol. 33, 155-202. Foster D. O. and Frdyman M. (1978) Non-shivering thermogenesis in the rat: measurements of blood flow with microspheres point to brown adipose tissue as the dominant site of calorigenesis induced by noradrenaline. Can. J. Physiol. Pharmac. 56, 110-122. Heaton G. M., Wagenford R. J., Kemp A. Jr and Nicholls D. G. (1978) Brown-adipose-tissuemitochondria: photoaffinity labelling of the regulatory site of energy dissipation. Fur. J. Biochem. 82, 515-521. Heldmaier G. and Steinlechner S. (1981) Seasonal control of energy requirements for thermoregulation in the Djungarian hamster (Phodopus sungorus), living in natural photoperiod. J. comp. Physiol. 142, 429-437. Heldmaier G., Steinlechner S., Rafael J. and Vsiansky P. (1981) Photoperiodic control and effects of melatonin on nonshivering thermogenesis and brown adipose tissue. Science 212, 917-919. Heldmaier G., Steinlechner S. and Rafael J. (1982) Nonshivering thermogenesis and cold resistance during seasonal acclimatization in the Djungarian hamster. J. comp. Physiol. 149, I-9. Lin C.-S. and Klingenberg M. (1982) Characteristics of the isolated purine nucleotide binding protein from brown fat mitochondria. Biochemistry 21, 2950-2956. Nicholls D. G. (1974) Hamster brown-adipose-tissue mitochondria. The control of respiration and the proton electrochemical potential gradient by possible physiological effectors of the proton conductance of the inner membrane. Fur. J. Biochem. 49, 573-583. Nicholls D. G. and Locke R. M. (1984) Thermogenic mechanism in brown fat. Physiol. Rev. 64, 1--64. Rafael J. (1983a) Biochemical aspects of the thermoregulatory role of brown adipose tissue. J. therm. Biol. 8, 410--412. Rafael J. (1983b) Cytochrome oxidase. In Methods of Enzymatic Analysis, Vol. 3 (Edited by Bergmeyer H. U.), pp. 266-273. Verlag Chemie, Weinheim, F.R.G. Rafael J. and Heldt H.-W. (1976) Binding of guanine nucleotides to the outer surface of the inner membrane of guinea-pig brown fat mitochondria in correlation with the thermogenic capacity of the tissue. FEBS Lett. 63, 304-308. Rafael J., Vsiansky P. and Heldmaier G. (1984) Seasonal adaptation of brown adipose tissue in the Djungarian hamster. J. comp. Physiol. 155, 521-528. Rothweil N. J. and Stock M. J. (1979) A role for brown
170
J. RAFAEL and P. VSIANSKY
adipose tissue in diet-induced thermogenesis. Nature 281, 31-35. Smith R. E. and Horwitz B. A. (1969) Brown fat and thermogenesis. Physiol. Ret'. 49, 330-425. Sundin U. and Cannon B. (1980) GDP-binding to the
brown fat mitochondria of developing and cold-adapted rats. Comp. Biochem. Physiol. 65B, 463--471. Trayhurn P. and James W. P. T. (1984) Thermogenesis and obesity. In Mammalian Thermogenesis (Edited by Girardier L. and Stock M. J.). Chapman & Hall, London.