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The effect of thyroxine on thermoregulation in the mature domestic fowl (Gallus Domesticus)
J. therm. BioL. Vol. 4, pp. 247 to 249 C) Per#ninon Press Ltd 1979. Printed in Great Britain
0306-4565/79 0701-O247502.00/0
THE EFFECT OF THYROXINE ON THERMOREGULATION IN THE MATURE DOMESTIC FOWL (GALLUS DOMESTICUS) A. ARIELI and A. BERMAN* The Hebrew University. Faculty of Agriculture, Rehovot, Israel
(Received 7 December 1978; revised 4 January 1979; accepted 31 January 1979) Abstract--l. Thermoregulatory effects of 10, 30 and 100 #g/kg day L-thyroxine were examined in mature domestic fowls at 4, 21 and 32°C. 2. Daily doses of 30 and 1(30 gg/kg elevated metabolic rate when administered over 1 week or longer. 3. The apparent metabolic effect of thyroxine increased with the ambient temperature and the dose level. 4. A possible role for endogenous thyroxine in the control of long-term metabolic response to cold in the domestic fowl is suggested.
INTRODUCTION
fowls were exposed to the three test temperatures during any one day; each fowl was thus examined 3-4 times at 48-h intervals. After determining control levels the fowls were randomly distributed to 4 groups, 3-4 fowls in each group. The fowls in each group were then daily intramuscularly administered 0.5 ml of saline, or 10, 30, 100/~g/kg of thyroxine (L-thyroxine sodium salt. Sigma) in a 0.5 ml volume of saline, Following 7 days of such treatment, the fowls were again examined for their thermoregulatory responses at the forementioned ambient temperatures 4--12h after the injections. This was repeated after 2 and 3 wks. For the determination of the responses at the different temperatures, the fowls were placed into darkened metabolic cages in a freezer-incubator (Forma Scientific model M 23) at 20°C. The temperature was then reduced to 4°C over 2-3h. Function measurements started at least 1 h after reaching 4°C. Determination of responses lasted about 10rain per fowl. Following the completion of measurements at this temperature, the temperature was gradually raised over 30 min to 21°C. The same procedure was repeated to determine responses at 21 and 32°C. Methods for the determination of I~O2 and Tb were as earlier described (Arieli et al., 1978). Respiratory rate (RR) was measured using a pressure transducer (Mercury Electronics, model M4, Argyle, Scotland) and recorded on a Gilson polygraph.
THYROID secretion rate is enhanced by chronic exposure to cold in both m a m m a l s and birds (Assenreacher, 1973; Hoch, 1974). Fluctuations in thyroid secretion affect 1)O2 and metabolic heat production (Hoch, 1974), thereby modifying B M R of m a m m a l s and birds (Himms-Hagen, 1976). Similar increases in thyroid activity from summer to winter were observed in both m a m m a l s (Hensel et al., 1973) and birds (Falconer, 1971). In mammals, thyroid h o r m o n e s are indispensable for survival in the cold, but it seems that they are not involved in the control of thermoregulatory nonshivering thermogenesis (Jansky, 1973). In chicks, on the other hand, evidence has been brought for an immediate calorigenic response to thyroxine, which has been interpreted to suggest the presence of a thermoregulatory N S T mechanism under thyroid control (Freeman, 1971). This report presents a study of exogenous thyroxine effects on thermoregulatory responses in the mature fowl. MATERIALS AND METHODS
Animals
Calculations The effect of the treatments was determined by comparison with the control values. Since no significant differences were observed between values obtained after 1, 2 and 3 wks of treatment, these were pooled for the assessment of treatment effects, by the Student's t-test. Control values of fowls assigned to the different treatment groups did not differ significantly; they were therefore pooled to yield the temperature effects, to which effects of treatments were compared.
The experiment was carried out on 14 crossbred Leghorn-Rhode Island layers, aged 2.5yr, mean weight 2.3 _+ 0.1 kg SE. The fowls were kept in an open shed lit 14 h/day, and were fed a commercial mixture. The experiment was performed through March-June, during which period the mean daily ambient temperature increased from 16 to 22°C, and the diurnal fluctuation in temperature was 13 deg.
Measurements During March-April, thermoregnlatory responses (I)O2, Tb and respiratory rate) were determined at 4, 21 and 32°C ( + I°C) prior to any treatment, to serve as control values. These responses were determined on 7 fowls at any one time; 3-4 replicates at each temperature. For this purpose,
* To whom all correspondence should be addressed.
RESULTS In preliminary experiments the response to different doses of T4 was examined over 10 h following its administration at room temperature. N o metabolic response could be discerned within this time period.
247
248
A. ARIELI and A. BI R~aA~, Table 1. Control values (means _ S.E.) of ox?gen consumption (|;O_,1 bod.~ temperature ITs) and respiratory rate [RRI at 4. 21 and 32 C Ambient temp.
Parameter t"O_, Th RR
(ml O_, min kg)
(C) Ibreaths'min)
4C
21 C
32 C
14.3 _+ 0.4* 41.4 4- 0.1 33 4- 2
11.1 4` 0.3 41.5 4- 0.1 32 4- 1
11.6 + 0.3 42.2* 4- 0.1 222* 4- 13
* Significantly differing (P < 0.001) of value at 21 C. In the later experiments, ~;O2 was examined starting from 1 wk after the first T,~ administration. Control values for 1702. Tb and RR at the three ambient temperatures are presented in Table 1. The lcvels measured at 21-'C are within the range normal for the female domestic fowl (Whittow, 1965). Exposing the fowl to 4°C increased | " O , by _9,, o (P < 0.001), RR by 3~o (NS) and reduced Th by 0.1:C (NS) as compared to 21~C. The exposure to 3 2 C increased VO2 by 5% (NS) and a seven-fold increase was noted in RR (P < 0.001), while Th was elevated by 0.7~C (P < 0.001). The responses at either 4 or 32=C were within the range common for such ambient conditions (Whittow, 1965). Daily treating the fowl with either saline or a T,~ dose of 101tg/kg had no significant effect on 9 0 2 at any of the ambient temperatures. The 30 l~g/kg T4 dose had similar I702 enhancing effects at either 21 and 32°C (4-22-25%, P < 0.01). The 100,ug/kg dose of T4 significantly increased 1702 at the three ambient temperatures (P < 0.01). hs effect gradually increased with rising ambient temperature:it was + 15°/, at 4~C, +26% at 21°C and +39~ o at 32°C (Fig. 1). The saline, l0 and 301~g/kg doses of T4, did not significantly affect T~ at the different ambient temperatures, while the 100~ug/kg dose induced a 0.6 ~
150 []
S
1~.0 [ ] r3
.¢
~30
it ~I~
10(
~N
21 AIR TEMPERATURE (°C)
32
Fig. 1. Relative effects of daily administration of saline (S), 10 (TIL 30 (Tz) and 100 (T~) /tg/kg L-thyroxine on 170 z at 4, 21 and 32°C. Mean + S.E. Significant differences (P<0.01) between pretreatment and treatment levels designated by **.
rise at 3 2 C ambient tNSL Respirator) rate was not significantl', modified by the administration of saline. or the 10 and 30/.tg/kg doses of T.,. The highest T., dose caused a 3.5-fold rise in the respiratory response at 2 1 C ambient (P < 0.05). No significant changes in body weight were observed in the course of this experiment. DISCUSSION
The results indicated an enhancement of thermoneutral (21 C ) 170, in response to the daily administration of T4, the response becoming evident after 1 wk of daily administrations. A similar rise in metabolic rate had been observed following 3 wks of thyroprotein feeding in White Leghorn cockerels (Heller & Snapir, 1970). The metabolic response increased with both the dose of T.~ administered and the ambient temperature. At 4=C, the control t?O_, was 29°0 higher than at thermoneutral 21~C. At 4 C . only the highest dose, 100ug/kg, had a significant effect in elevating 1702 beyond the control level, while at higher temperatures the intermediate dose enhanced metabolic rate. These suggest that the thermogenic effects of cold and thyroxine were complementary to each other and not additive at the lowest temperature, similar to the effects of cold and catecholamines in mammals (Jansky, 1973). A possible role for thyroxine in the response to cold might be inferred in the fowl. At 21=C. a temperature thermoneutral for the control fowl and those treated at the lowest T4 dose, panting was observed in the 100/~g kg dose treated fowl; a slightly higher body temperature (NS) was noted in the later group at 32:C ambient. This is in line with the suggestion (Collins & Weiner. 1968) that changes in BMR modify the upper critical temperature. The I702 was increased at 4=C by the highest dose only, and at 21=C by the tv.o higher doses: this may be interpreted to suggest that thyroxine induces also a decrease in the lower critical temperature. The lowest T4 dose administered in this experiment, i.e. 10 Ftg/kg day, did not modify the responses of the fowls at any of the three ambient temperatures. It may hence be assumed that this dose is close to the endogenous TSR in these fowls. Such inference is supported by the 10-20 mg/kg day range reported for TSR in the fowl (Assenmacher, 1973). The results presented here are in line with a calorigenie action of thyroid hormones, characterized by a long latent period (Hoch, 1974). The)', contrast, however, the calorigenic action occurring within 0.%2 h in 7"3 and T.~ treated chicks (Singh et al., 1968; Freeman, 1971). The immediate calorigenic response was interpreted as indicating a thermoregulatory NST in
Thyroxine effects on thermoregulation in the mature fowl the chick (Freeman, 1971). Since in the adult birds there is no conclusive evidence for thermoregulatory NST, it was suggested that in the fowl a shift occurs from thermoregulatory NST to shivering in course of its ontogeny (Freeman, 1971). Such view may find support in circumstantial evidence. During the first weeks of life, the white fibers in the muscles of the fowl multiply at the expense of the red fibres (Wittenberg et al., 1977). In the latter type a lipolytic activity predominates, which prevails during NST; in the white fibers, on the other hand, a capacity for glycogenolysis, which prevails during shivering, is more developed (Thomas & George, 1975). Also, free T~ serum levels in the fowl decrease by 25~o from the neonate stage to 3-7wks of age and remain stable thereafter (Davison, 1976). In the adult fowl evidence has been brought for an increase in thermoneutral I/O., on cold acclimation (Arieli et al., 1979). This might suggest a possible role for thyroxine which is compatible with its latency.
REFERENCES
ARIELI A., BERMAN A. & MELTZER A. (1978) Indication for nonshivering thermogenesis in the adult (Gallus domesticus). Comp. Biochem. Physiol. 60C, 33-36. ARIELI A., BERMANA. & MELTZERA. (1979) Cold thermogenesis in the summer acclimatized and cold acclimated domestic fowl. Comp. Biochem. Physiol, 63C, 7-12. ASSENMACHER I (1973). The peripheral endocrine glands. In Avian Biology (Edited by FARNER D. S. & KING J. R.), Vol. 3, pp. 183-386. Academic Press, New York. COLLINS K. J. • WEINER J. S. (1968) Endocrinological aspects of exposure to high environmental temperatures. Physiol. Re~'. 48, 785-839. DAVlSONT. F. (1976) Circulating thyroid hormones in the chicken before and after hatching. Gen. comp. Endocr. 29, 21-27.
249
FALCONER 1. R. (1971) The thyroid glands. In Physiolotty and Biochemistry of the Domestic Fowl (Edited by BELL D. S. & FREEMANB. M.), Vol. 1, pp. 459-472. Academic Press, London. FREEMAN B. M. (19711 Non-shivering thermogenesis in birds. In Nonshirering Thermogenesis (Edited by JANSKY L.), pp. 83-93. Academia, Prague. HELLER E. D. & SNAPlR N. (1970) Evaluation of thyroid activity in cockerels by the in vitro radio 3-triiodothyronine erythrocyte uptake test. Gen. comp. Endocr. 14. 290-294. HENSEL H., Bgt~'C~ K. & RA~r~s P. (1973) Homeothermic organisms. In TemperanJre and Lift, (Edited by PRECH'r H.. CHRos'roPHERSENJ., HENSELH. & LARCHERW.), pp. 503-761. Springer, Berlin. HtMMS-HAGEN I. (1976) Cellular thermogenesis. A. Rer. Physiol. 38. 315-351. HocH F. L. (1974) Metabolic effects of thyroid hormones. In Hamlbook of Physioloyy, Sect. 7, Endocrinology. Thyroid, Vol. 3 (Edited by GaEER M. A. & SOLOMO.~ D. H.), pp. 391-411. American Physiological Societ?, Washington D.C. JANSKVL. (1973) Non-shivering thermogenesis and its thermoregulatory significance. Biol. Rer. 48, 85-132. SI,'~GH A.. REINEKE P. & RINGER R. K. (19681 Influence of thyroid status of the chick on growth and metabolism. with observations on several parameters of thyroid function~ Poultry Sci. 47, 212-219. THOMASV. G. & GEORGEJ. C. (1975) Changes in plasma. liver and muscle metabolite levels in Japanese quail exposed to different cold stress situations. J. Comp. Physiol. 100, 297-306. WHir'row G. C. (1965) Regulation of body temperature. In Atian Physiology. 2nd edn (Edited by Srt;gKIE P. D.). pp. 186-238. Cornell University Press, Ithaca. Wlan'ENBEaG C,. COPREAND. & POPESCUV. (1977) On the carbohydrate metabolism of pectoral muscle in the ontogeny of chicken. Comp. Biochem. Physiol. 58B. 141-146.
Key ~brd Index--Domestic fowl; thyroxine; calorigenesis; metabolic rate; cold response; cold acclimation: thermoregulation.
0306-4565/79 0701-O247502.00/0
THE EFFECT OF THYROXINE ON THERMOREGULATION IN THE MATURE DOMESTIC FOWL (GALLUS DOMESTICUS) A. ARIELI and A. BERMAN* The Hebrew University. Faculty of Agriculture, Rehovot, Israel
(Received 7 December 1978; revised 4 January 1979; accepted 31 January 1979) Abstract--l. Thermoregulatory effects of 10, 30 and 100 #g/kg day L-thyroxine were examined in mature domestic fowls at 4, 21 and 32°C. 2. Daily doses of 30 and 1(30 gg/kg elevated metabolic rate when administered over 1 week or longer. 3. The apparent metabolic effect of thyroxine increased with the ambient temperature and the dose level. 4. A possible role for endogenous thyroxine in the control of long-term metabolic response to cold in the domestic fowl is suggested.
INTRODUCTION
fowls were exposed to the three test temperatures during any one day; each fowl was thus examined 3-4 times at 48-h intervals. After determining control levels the fowls were randomly distributed to 4 groups, 3-4 fowls in each group. The fowls in each group were then daily intramuscularly administered 0.5 ml of saline, or 10, 30, 100/~g/kg of thyroxine (L-thyroxine sodium salt. Sigma) in a 0.5 ml volume of saline, Following 7 days of such treatment, the fowls were again examined for their thermoregulatory responses at the forementioned ambient temperatures 4--12h after the injections. This was repeated after 2 and 3 wks. For the determination of the responses at the different temperatures, the fowls were placed into darkened metabolic cages in a freezer-incubator (Forma Scientific model M 23) at 20°C. The temperature was then reduced to 4°C over 2-3h. Function measurements started at least 1 h after reaching 4°C. Determination of responses lasted about 10rain per fowl. Following the completion of measurements at this temperature, the temperature was gradually raised over 30 min to 21°C. The same procedure was repeated to determine responses at 21 and 32°C. Methods for the determination of I~O2 and Tb were as earlier described (Arieli et al., 1978). Respiratory rate (RR) was measured using a pressure transducer (Mercury Electronics, model M4, Argyle, Scotland) and recorded on a Gilson polygraph.
THYROID secretion rate is enhanced by chronic exposure to cold in both m a m m a l s and birds (Assenreacher, 1973; Hoch, 1974). Fluctuations in thyroid secretion affect 1)O2 and metabolic heat production (Hoch, 1974), thereby modifying B M R of m a m m a l s and birds (Himms-Hagen, 1976). Similar increases in thyroid activity from summer to winter were observed in both m a m m a l s (Hensel et al., 1973) and birds (Falconer, 1971). In mammals, thyroid h o r m o n e s are indispensable for survival in the cold, but it seems that they are not involved in the control of thermoregulatory nonshivering thermogenesis (Jansky, 1973). In chicks, on the other hand, evidence has been brought for an immediate calorigenic response to thyroxine, which has been interpreted to suggest the presence of a thermoregulatory N S T mechanism under thyroid control (Freeman, 1971). This report presents a study of exogenous thyroxine effects on thermoregulatory responses in the mature fowl. MATERIALS AND METHODS
Animals
Calculations The effect of the treatments was determined by comparison with the control values. Since no significant differences were observed between values obtained after 1, 2 and 3 wks of treatment, these were pooled for the assessment of treatment effects, by the Student's t-test. Control values of fowls assigned to the different treatment groups did not differ significantly; they were therefore pooled to yield the temperature effects, to which effects of treatments were compared.
The experiment was carried out on 14 crossbred Leghorn-Rhode Island layers, aged 2.5yr, mean weight 2.3 _+ 0.1 kg SE. The fowls were kept in an open shed lit 14 h/day, and were fed a commercial mixture. The experiment was performed through March-June, during which period the mean daily ambient temperature increased from 16 to 22°C, and the diurnal fluctuation in temperature was 13 deg.
Measurements During March-April, thermoregnlatory responses (I)O2, Tb and respiratory rate) were determined at 4, 21 and 32°C ( + I°C) prior to any treatment, to serve as control values. These responses were determined on 7 fowls at any one time; 3-4 replicates at each temperature. For this purpose,
* To whom all correspondence should be addressed.
RESULTS In preliminary experiments the response to different doses of T4 was examined over 10 h following its administration at room temperature. N o metabolic response could be discerned within this time period.
247
248
A. ARIELI and A. BI R~aA~, Table 1. Control values (means _ S.E.) of ox?gen consumption (|;O_,1 bod.~ temperature ITs) and respiratory rate [RRI at 4. 21 and 32 C Ambient temp.
Parameter t"O_, Th RR
(ml O_, min kg)
(C) Ibreaths'min)
4C
21 C
32 C
14.3 _+ 0.4* 41.4 4- 0.1 33 4- 2
11.1 4` 0.3 41.5 4- 0.1 32 4- 1
11.6 + 0.3 42.2* 4- 0.1 222* 4- 13
* Significantly differing (P < 0.001) of value at 21 C. In the later experiments, ~;O2 was examined starting from 1 wk after the first T,~ administration. Control values for 1702. Tb and RR at the three ambient temperatures are presented in Table 1. The lcvels measured at 21-'C are within the range normal for the female domestic fowl (Whittow, 1965). Exposing the fowl to 4°C increased | " O , by _9,, o (P < 0.001), RR by 3~o (NS) and reduced Th by 0.1:C (NS) as compared to 21~C. The exposure to 3 2 C increased VO2 by 5% (NS) and a seven-fold increase was noted in RR (P < 0.001), while Th was elevated by 0.7~C (P < 0.001). The responses at either 4 or 32=C were within the range common for such ambient conditions (Whittow, 1965). Daily treating the fowl with either saline or a T,~ dose of 101tg/kg had no significant effect on 9 0 2 at any of the ambient temperatures. The 30 l~g/kg T4 dose had similar I702 enhancing effects at either 21 and 32°C (4-22-25%, P < 0.01). The 100,ug/kg dose of T4 significantly increased 1702 at the three ambient temperatures (P < 0.01). hs effect gradually increased with rising ambient temperature:it was + 15°/, at 4~C, +26% at 21°C and +39~ o at 32°C (Fig. 1). The saline, l0 and 301~g/kg doses of T4, did not significantly affect T~ at the different ambient temperatures, while the 100~ug/kg dose induced a 0.6 ~
150 []
S
1~.0 [ ] r3
.¢
~30
it ~I~
10(
~N
21 AIR TEMPERATURE (°C)
32
Fig. 1. Relative effects of daily administration of saline (S), 10 (TIL 30 (Tz) and 100 (T~) /tg/kg L-thyroxine on 170 z at 4, 21 and 32°C. Mean + S.E. Significant differences (P<0.01) between pretreatment and treatment levels designated by **.
rise at 3 2 C ambient tNSL Respirator) rate was not significantl', modified by the administration of saline. or the 10 and 30/.tg/kg doses of T.,. The highest T., dose caused a 3.5-fold rise in the respiratory response at 2 1 C ambient (P < 0.05). No significant changes in body weight were observed in the course of this experiment. DISCUSSION
The results indicated an enhancement of thermoneutral (21 C ) 170, in response to the daily administration of T4, the response becoming evident after 1 wk of daily administrations. A similar rise in metabolic rate had been observed following 3 wks of thyroprotein feeding in White Leghorn cockerels (Heller & Snapir, 1970). The metabolic response increased with both the dose of T.~ administered and the ambient temperature. At 4=C, the control t?O_, was 29°0 higher than at thermoneutral 21~C. At 4 C . only the highest dose, 100ug/kg, had a significant effect in elevating 1702 beyond the control level, while at higher temperatures the intermediate dose enhanced metabolic rate. These suggest that the thermogenic effects of cold and thyroxine were complementary to each other and not additive at the lowest temperature, similar to the effects of cold and catecholamines in mammals (Jansky, 1973). A possible role for thyroxine in the response to cold might be inferred in the fowl. At 21=C. a temperature thermoneutral for the control fowl and those treated at the lowest T4 dose, panting was observed in the 100/~g kg dose treated fowl; a slightly higher body temperature (NS) was noted in the later group at 32:C ambient. This is in line with the suggestion (Collins & Weiner. 1968) that changes in BMR modify the upper critical temperature. The I702 was increased at 4=C by the highest dose only, and at 21=C by the tv.o higher doses: this may be interpreted to suggest that thyroxine induces also a decrease in the lower critical temperature. The lowest T4 dose administered in this experiment, i.e. 10 Ftg/kg day, did not modify the responses of the fowls at any of the three ambient temperatures. It may hence be assumed that this dose is close to the endogenous TSR in these fowls. Such inference is supported by the 10-20 mg/kg day range reported for TSR in the fowl (Assenmacher, 1973). The results presented here are in line with a calorigenie action of thyroid hormones, characterized by a long latent period (Hoch, 1974). The)', contrast, however, the calorigenic action occurring within 0.%2 h in 7"3 and T.~ treated chicks (Singh et al., 1968; Freeman, 1971). The immediate calorigenic response was interpreted as indicating a thermoregulatory NST in
Thyroxine effects on thermoregulation in the mature fowl the chick (Freeman, 1971). Since in the adult birds there is no conclusive evidence for thermoregulatory NST, it was suggested that in the fowl a shift occurs from thermoregulatory NST to shivering in course of its ontogeny (Freeman, 1971). Such view may find support in circumstantial evidence. During the first weeks of life, the white fibers in the muscles of the fowl multiply at the expense of the red fibres (Wittenberg et al., 1977). In the latter type a lipolytic activity predominates, which prevails during NST; in the white fibers, on the other hand, a capacity for glycogenolysis, which prevails during shivering, is more developed (Thomas & George, 1975). Also, free T~ serum levels in the fowl decrease by 25~o from the neonate stage to 3-7wks of age and remain stable thereafter (Davison, 1976). In the adult fowl evidence has been brought for an increase in thermoneutral I/O., on cold acclimation (Arieli et al., 1979). This might suggest a possible role for thyroxine which is compatible with its latency.
REFERENCES
ARIELI A., BERMAN A. & MELTZER A. (1978) Indication for nonshivering thermogenesis in the adult (Gallus domesticus). Comp. Biochem. Physiol. 60C, 33-36. ARIELI A., BERMANA. & MELTZERA. (1979) Cold thermogenesis in the summer acclimatized and cold acclimated domestic fowl. Comp. Biochem. Physiol, 63C, 7-12. ASSENMACHER I (1973). The peripheral endocrine glands. In Avian Biology (Edited by FARNER D. S. & KING J. R.), Vol. 3, pp. 183-386. Academic Press, New York. COLLINS K. J. • WEINER J. S. (1968) Endocrinological aspects of exposure to high environmental temperatures. Physiol. Re~'. 48, 785-839. DAVlSONT. F. (1976) Circulating thyroid hormones in the chicken before and after hatching. Gen. comp. Endocr. 29, 21-27.
249
FALCONER 1. R. (1971) The thyroid glands. In Physiolotty and Biochemistry of the Domestic Fowl (Edited by BELL D. S. & FREEMANB. M.), Vol. 1, pp. 459-472. Academic Press, London. FREEMAN B. M. (19711 Non-shivering thermogenesis in birds. In Nonshirering Thermogenesis (Edited by JANSKY L.), pp. 83-93. Academia, Prague. HELLER E. D. & SNAPlR N. (1970) Evaluation of thyroid activity in cockerels by the in vitro radio 3-triiodothyronine erythrocyte uptake test. Gen. comp. Endocr. 14. 290-294. HENSEL H., Bgt~'C~ K. & RA~r~s P. (1973) Homeothermic organisms. In TemperanJre and Lift, (Edited by PRECH'r H.. CHRos'roPHERSENJ., HENSELH. & LARCHERW.), pp. 503-761. Springer, Berlin. HtMMS-HAGEN I. (1976) Cellular thermogenesis. A. Rer. Physiol. 38. 315-351. HocH F. L. (1974) Metabolic effects of thyroid hormones. In Hamlbook of Physioloyy, Sect. 7, Endocrinology. Thyroid, Vol. 3 (Edited by GaEER M. A. & SOLOMO.~ D. H.), pp. 391-411. American Physiological Societ?, Washington D.C. JANSKVL. (1973) Non-shivering thermogenesis and its thermoregulatory significance. Biol. Rer. 48, 85-132. SI,'~GH A.. REINEKE P. & RINGER R. K. (19681 Influence of thyroid status of the chick on growth and metabolism. with observations on several parameters of thyroid function~ Poultry Sci. 47, 212-219. THOMASV. G. & GEORGEJ. C. (1975) Changes in plasma. liver and muscle metabolite levels in Japanese quail exposed to different cold stress situations. J. Comp. Physiol. 100, 297-306. WHir'row G. C. (1965) Regulation of body temperature. In Atian Physiology. 2nd edn (Edited by Srt;gKIE P. D.). pp. 186-238. Cornell University Press, Ithaca. Wlan'ENBEaG C,. COPREAND. & POPESCUV. (1977) On the carbohydrate metabolism of pectoral muscle in the ontogeny of chicken. Comp. Biochem. Physiol. 58B. 141-146.
Key ~brd Index--Domestic fowl; thyroxine; calorigenesis; metabolic rate; cold response; cold acclimation: thermoregulation.