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The relation between thyroid activity and responsiveness to adrenaline during cold acclimation in the frog, Rana temporaria
Comp. Gen. Pharmac., 1974, Vol. 5, PP. 305 to 309 . Pergamon Press. Printed in Great Britain
305
THE RELATION BETWEEN THYROID ACTIVITY AND RESPONSIVENESS TO ADRENALINE DURING COLD ACCLIMATION IN THE FROG, RAWA TEMPORARIA M I K K O N. E. H A R R I Zoophysiological Laboratory, Department of Zoology, University of Turku, 8F-oo5oo Turku 5o, Finland
(Received03 3uly z973) ABSTRACT I. In 25 ° C-acclimated winter frogs which were transferredto 5°C, the basal metabolic rate was significantlyincreased onc day and the metabolic response to adrenaline two days after the transfer. o. The blood sugar Icvel decreased, following a small initialrisc, after 4 days of cold exposurc. The hypcrglycacmic response to adrenaline was significantby thc 4th day. 3. Thc basic heart rate fell bctween the ond and 4th days, but the chronotropic sensitivityto adrcnalinc within the two firstdays fellto the Icvcltypicalfor frogs acclimated to 5°C. 4. A significant activation of the thyroid, as judged from its histological state, was observablc within 4 days of cold exposurc. 5. It is concluded that the thyroid hormone m a y be important in regulating the responsiveness to catccholamincs in amphibians.
IN cold-acclimated winter flogs, the utilization I954). This was assumed to indicate that of tissue catecholamines is increased (Harri, the thyroid hormone potentiates the hyperi972 ). Furthermore, the increment of the glycaemic effect of released endogenous oxygen consumption caused by adrenaline adrenaline. The aim of the present study was to gain as well as the hyperglycaemic response to adrenaline are more pronounced in cold- further evidence about the thyroid-cateacclimated than in warm-acclimated frogs cholamine interaction and about the role Harri & Hedenstam, x972; Harri & of adrenerglc mechanisms in the initiation Lindgren, I972 ). On the other hand, the of cold acclimation in amphibians by a chronotropic sensitivity to some sympathomi- comparision of the time-course of the changes tactic amines is lowered in hearts from in responsiveness to adrenaline and of the cold-acclimated animals (Tirri, Harri & activation of the ~hyroid during cold Laitinen, i974 ). These results suggest the acclimation. importance of adrenergic processes in the temperature acclimation of amphibians. MATERIAL AND METHODS The thyroid gland apparently participates • Winter frogs of both sexes were acclimated to in the mediation of the compensatory m5°C for at least two weeks before use (warmchanges in oxidative metabolism during acclimated frogs), and then transferred to 5°C temperature acclimation in amphibians for times of different duration. The experiments were performed in December-January. In (Lagerspetz, Harri & Okslahti, x974). In addition, some animals had been kept at 5-xo°C mammals, the thyroid also participates in since autumn (cold-acclimated frogs). The producing the metabolic responsiveness to animals were not fed. Oxygen consumption was measured at 25°C catecholamines (Swanson, i956 ). Correspondingly, a significant correlation between with Pauling's paramagnetic oxygen analyzer (Beckman E 2), using an open circuit system. the blood sugar level and thyroid condition The metabolic increment caused by adrenaline is found in the frog, Rana temporaria (Smith, was calculated by comparing the oxygen con-
Gomp. Gen. Pharmac.
I-IARRI
306
sumption after the injection of adrenaline to that after the previously injected saline. A dose o f o.I rag. per kg. was injected into the dorsal lymph sac. This dose was chosen because it was shown to give the maximum responses (Harri & Hedemtam, x972). The determination of the blood glucose was performed according to Hultman's (I959) micromethod for aldosaccharides from o.2 ml. of blood. The hyperglycaemic response to adrenaline was tested by using a dose of o"5 rag. per kg. with a period of x hour between the drug administration
and the killing of the animals (Harri & Lindgren, x972). The basic heart rate and the chronotropic respome to adrenaline were measured at 12°C from pithed frogs. Adrenaline was injected into the abdominal vein and the cumulative doseresponse curves were prepared as described elsewhere (Tirri et al., t974). The doses which gave 5o ~o of the maximum chronotropic response (EDso) were used as an indication of the sensitivity to adrenaline. The ED60-values presented are from Tirri et al. (x974).
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Fzo. z.--The time-course of the changes in respomiveness to adrenaline and in thyroid activity after transferring the 25°C-acclimated frogs (©) to 5°C for different lengths of time; (a) the oxygen consumption of intact animals before (O) (from Harri, i973) , and after (©) the injection of o'I rag. per kg. of adrenaline; (b) the blood sugar level before (O), and after the injection ofo. 5 rag. per kg. of adrenaline (O) ; (c) the basic heart rate (O), and the chronotropic sensitivity to adrenaline, measured as EDs0-values (O, scale on the right; from Tirri et d . , I974); (d) the percentage amount of epithelium in the thyroid. W = winter frogs which had been kept at 5-io°C since autumn: The number of experimental animals is indicated at each point on the graph. Vertical bars indicate+ S.E.
z974, 5
THYROID--CATECHOLAMINEINTERACTION
307
The thyroids with the adjacent tissues were removed from the pithed animals, fixed in Bouin's fluid and stained with Weigert's hematoxylin and Domagk's thiazine red-picric acid solutions. The relative amounts of epithelium, colloid and stroma were measured from the thyroid sections prepared according to the linear method of Uotila & Karmas (t952). Student's t-test was used in the statistical evaluation of the differences.
for frogs maintained at a low temperature since autumn, o n the other hand, the chronotropic sensitivity to adrenaline began to decrease even during the first day at 5°(3, which was shown by the increase of the EDs0-values. The change was significant (P< o.o2) after 2 days. Later changes were not significant.
RESULTS CHANGES IN RESPONSIVENESSTO ADRENALINEDURmO COLD ACCLIMATION
ACTIVATION OF THE TH'zRom Gnaa~ DmuNo CoLD ACCLn~ATmN The results in Fro. z (d) and FIO. 2 indicate that the mean percentage amount of glandular epithelium, which was used to indicate the thyroid activity, increased after transferring the warm-acclimated frogs to a low temperature. The thickness of the epithelium was significantly higher than that in the warm-acclimated animals by the 4th day (P
Oxygen consumption FIOURE z(a) shows that in frogs acclimated to 25°C, a very rapid increase in the oxygen consumption (measured at 25°(3) was observable within the first day after transferring them to cold conditions (P
Blood glucose Fxom~z I (b) shows that after transferring the warm-acclimated frogs to 5°C, the basic blood sugar level increased, reaching its maximum 4 days after the transfer (P < o.o5). The typical blood sugar level of winter frogs acclimated to cold was not seen until they had been at a temperature of 5°C for 8 days. The hyperglycaemic response to adrenaline was significant (P < o.oo5) by the 4th day. Later, when the basic blood sugar level was lowered, the hyperglycaemic response to adrenaline was slightly elevated.
Heart rate In winter frogs acclimated to 25°(3 and then transferred to 5°(3, the basic heart rate increased slightly but not significantly in 2 days (FIo. zc). Between the 2nd and 4th day in the cold, however, there was a significant (P< o.o5) lowering to the level typical
DISCUSSION The results show that the metabolic as well as the hypcrglycacmic response to adrenaline-increased very rapidly after transferring the warm-acclimated frogs to a low temperature. These reactions were also rapid at the beginning of the exposure and slowed down after 2-4 days very markedly. Furthermore, the metabolic sensitization to adrenaline m a y be cvcn more rapid than that observed. As the utilization of catccholamines is increased irnrncdiatcly after placing the frogs into a cold environment (Harri, t972), it is possible
308
HARR!
Comp. Gen. Pharmaz.
The rapid change of the "histological that the elevated basal metabolic rate as well as the delay in the lowering of the heart rate picture of the thyroid gland is not an at the beginning of cold exposure are due unexpected phenomenon, because in mamto the increased release of endogenous mals, the histological changes are shown adrenaline. Furthermore, the basic blood to appear as early as within ½ hour to 2 sugar level elevated at the beginning of cold hours from beginning of exposure to cold (Ariel exposure. Became this elevation was accom- & Warren, I943; Del Conte & Stux, i954). Although the increased thyroid activity parried by the increased hyperglycaemic sensitivity to adrenaline, the increased release is probably responsible for the increased of endogenous adrenaline may be responsible metabolic sensitivity to adrenaline, the mechanism for the lowered chronotropic also for this elevation. The lowering of the basic heart rate and sensitivity to adrenaline in hearts from blood sugar level after 2 and 4 days respective- cold-acclimated frogs may be different. It ly of cold exposure may, on the other hand, has been recently suggested that this lowered indicate that after the initial rise, the sensitivity could be explained by decreased release of endogenous adrenaline later receptor sensitivity and by increased metareturns to a lower level. This has been boric rate and catechol-0-methyl transferase shown previously for the utilization of activity in heart tissue caused by increased adrenal adrenaline in cold-exposed winter sympathetic activity at low temperatures (Tirri et al., I974 ). frogs (Harri, i972 ). Recently, it has been shown that repeated However, the possibility that the thyroid dally adrenaline injections to frogs kept also participates in producing lowered in the warm causes an increase in the sensitivity of the heart to adrenaline has to thyroid activity and in the succinic dehydro- be considered. The lowered sensitivity genase activity of skeletal and heart muscle seems to be mediated by a-adrenoreceptors homogenates, similar to those induced by in the frogs (Tirri et al., x974), whereas the cold acclimation (Lagerspetz et al., I974). hyperglycaemic and probably also the response Thus, the increased utilization of adrenaline of the oxygen consumption to catecholamines in the brains of cold-exposed frogs (Harri, result from t-receptor stimulation (Harri x972) leads to thyroid activation either & Lindgren, i972 ). It has recently been directly (Melander & Sundler, I972; found that a-adrenergic responses are Mdander, Nilsson & Sundler, I972 ) or enhanced in the aorta from hypothyroid through TSH, the release of which may be rabbits (Rosenquist & Boreus, x972). It is affected b y the neurochemical changes thus possible that the hyperthyroid state found during temperature acclimation. In of cold-accrimated frogs is responsible for addition, the results of the present study the lowered chronotropic sensitivity of the show that the length of time required for heart's ot-adrenoreceptors. The importance thyroid activation at low temperature, as of the thyroid hormone in the control of the judged from thickening of t h e glandular form of the temperature-heart rate curve of epithelium and appearance of marginal the isolated frog's heart has been reported vacuoles in the follicles, corresponds to that earlier (Carter , 1933; Smith, I95i ). of the development of the metabolic and The changes observed in this study of the hyperglycaemic respons e to adrenaline. responsiveness to adrenaline and in thyroid Thus, t h e increased thyroid hormone activity after transferring frogs to a low secretion may be responsible also for the temperature were much more rapid than elevated metabolic and hyperglyaemic those observed previously in the tissue sensitivity to adrenaline in cold-acclimated metabolism (Lagerspetz et al., I974 ). This frogs. This view is also supported by the supports the assumption that the early results of Smith (x954), which show a phases of the adaptive changes associated significant correlation between the blood with cold acclimation in amphibians are sugar level and thyroid condition. results of temperature-induced changes in
Fro. m--Photomicrographs of thyroid glands of -05°C-acclimated winter frogs before (O) and after transferring them to 5°C for I, 4 or I8 days. Weigert's hematoxylin and Domagk's thiazine red-picric acid. Magnification × -064.
I974, 5
THYROID.-CATECH OLAMINE INTERACTION
c o o r d i n a t i n g mechanisms, r a t h e r t h a n direct effects o f t e m p e r a t u r e on the tissues. T h e present results also lead to the conclusion t h a t the adrenergic nervous system together with the thyroid gland are a f u n d a m e n t a l p a r t o f the mechanisms o f t e m p e r a t u r e acclimation in the frog. ACKNOWLEDGEMENTS I wish to express m y t h a n k s to Professor K. Y. H.
Lagerspetz for helpful criticism. My thanks are also due to Miss Hanna Kurppa for technical assistance and to Mrs Sinikka Hillgren for the drawings. This study has been supported by the Emil Aaltonen Foundation.
REFERENCES ARmL, I., & WARREN, S. L. (1943), ' Studies on the effect of hypothermia. II. The active role of the thyroid gland in hypothermic states in the rabbit ', Cancer. Res., 3, 454-463 • C~a~a~R, G. S. (1933), ' O n the control of the level of activity of the animal body. I. The endocrine control of seasonal variations of activity in the frog ' o7. Exp. Biol., xo, 256-273 . DEL CONTE, E., & STtrX, M. (x954) , 'Rapidity of thyroid reaction to cold ', .Nature, Lond., x73, 83. HARm, M. N. E. (I972), 'Effect of season and temperature acclimation on the tissue catecholamine level and utilization in the frog,
Rana temporaria', Comp. Gen. Pharnu~., 3~ xo I- I 1 2 . H A ~ , M. N. E. (x973), ' The rate of metabolic temperature acclimation in the frog, Rana temporaria', Physiol. Zool., 46~ t48--156. HARm, M. N. E., & HEDENSTAM, R. (x972), 'Calorigenic effect of adrenaline and noradrenaline in the frog, Rana temporaria', Comp. Biochem. Physiol., 4xA, 4o9--419 • ~I, M. N. E., & I_aNDORXN, E. (I972), ' Adrenergic control of carbohydrate metabolism in the frog, Rana temporaria', Comp. Gen. Pharmac., 3, 226-234.
309
Hm.~, E. (x959), ' R a p i d specific method for determination of aldosacchaxides in body fluids ', .Nature, Lond., x83, xoS-xo 9. LAO~mPETZ, K. Y. H., HARm, M. N. E., & O m t a ~ , R. (1974), ' T h e role of the thyroid in the temperature acclimation of the oxidative metabolism in the frog, Rana temporaria ', Gen. Comp. Endocrinol., 22, ,69-*75. MaLANDER, A., & SUNDI~n, F. (1972), ' I n t e r actions between catecholamines, 5-hydroxytryptamine and T S H on the secretion of thyroid hormone ', Endocrinology, 90, t88--x93. MELANDRR, A., NmSSON, E., & StrNDt£R, F. (1972), 'Sympathetic activation of thyroid hormone secretion in mice ', Endocrinology, 9o~ x94-t99. ROSENQtrtST, U., & BoP.Eus, L. O. (x972), ' Enhancement of the alpha adrenergic response in aorta from hypothyroid rabbits', L/~ Sci., xx~ 595--604. SmTH, C. L. (t951), ' The temperature-pulse rate curve of the isolated frog's heart (Rana temporaria) ', aT. Exp. Biol., 28, x4x-164. SmTH, C. L. (I954), ' T h e relation between seasonal hyperglycaemia and thyroid activity in the frog, Rana temporaria ', ,7. Endocr., to, x84-19 I. SWANSON, H. E. (t956), ' Interrelations between thyroxin and adrenalin in the regulation of oxygen consumption in the albino rat ', Endocrinology, 59, 2I 7-225. Txam, R., HARm, M. N. E., & LAITINEN, L. (x974) , 'Lowered chronotropic sensitivity of rat and frog hearts to sympathomimetic amines following cold acclimation ', Acta Physiol. Scand., 90, 5o9-5x2. UOTmA, U., & KANNAS,O. (I952), ' Quantitative histological methods of determining the proportion of the principal components of thyroid tissue ', Acta Endocr., Copenh., xx, 49-60.
Key Word Index: Frog, Rana temporaria, temperature acclimation, adrenaline, oxygen consumption, blood sugar, heart rate, thyroid gland.
305
THE RELATION BETWEEN THYROID ACTIVITY AND RESPONSIVENESS TO ADRENALINE DURING COLD ACCLIMATION IN THE FROG, RAWA TEMPORARIA M I K K O N. E. H A R R I Zoophysiological Laboratory, Department of Zoology, University of Turku, 8F-oo5oo Turku 5o, Finland
(Received03 3uly z973) ABSTRACT I. In 25 ° C-acclimated winter frogs which were transferredto 5°C, the basal metabolic rate was significantlyincreased onc day and the metabolic response to adrenaline two days after the transfer. o. The blood sugar Icvel decreased, following a small initialrisc, after 4 days of cold exposurc. The hypcrglycacmic response to adrenaline was significantby thc 4th day. 3. Thc basic heart rate fell bctween the ond and 4th days, but the chronotropic sensitivityto adrcnalinc within the two firstdays fellto the Icvcltypicalfor frogs acclimated to 5°C. 4. A significant activation of the thyroid, as judged from its histological state, was observablc within 4 days of cold exposurc. 5. It is concluded that the thyroid hormone m a y be important in regulating the responsiveness to catccholamincs in amphibians.
IN cold-acclimated winter flogs, the utilization I954). This was assumed to indicate that of tissue catecholamines is increased (Harri, the thyroid hormone potentiates the hyperi972 ). Furthermore, the increment of the glycaemic effect of released endogenous oxygen consumption caused by adrenaline adrenaline. The aim of the present study was to gain as well as the hyperglycaemic response to adrenaline are more pronounced in cold- further evidence about the thyroid-cateacclimated than in warm-acclimated frogs cholamine interaction and about the role Harri & Hedenstam, x972; Harri & of adrenerglc mechanisms in the initiation Lindgren, I972 ). On the other hand, the of cold acclimation in amphibians by a chronotropic sensitivity to some sympathomi- comparision of the time-course of the changes tactic amines is lowered in hearts from in responsiveness to adrenaline and of the cold-acclimated animals (Tirri, Harri & activation of the ~hyroid during cold Laitinen, i974 ). These results suggest the acclimation. importance of adrenergic processes in the temperature acclimation of amphibians. MATERIAL AND METHODS The thyroid gland apparently participates • Winter frogs of both sexes were acclimated to in the mediation of the compensatory m5°C for at least two weeks before use (warmchanges in oxidative metabolism during acclimated frogs), and then transferred to 5°C temperature acclimation in amphibians for times of different duration. The experiments were performed in December-January. In (Lagerspetz, Harri & Okslahti, x974). In addition, some animals had been kept at 5-xo°C mammals, the thyroid also participates in since autumn (cold-acclimated frogs). The producing the metabolic responsiveness to animals were not fed. Oxygen consumption was measured at 25°C catecholamines (Swanson, i956 ). Correspondingly, a significant correlation between with Pauling's paramagnetic oxygen analyzer (Beckman E 2), using an open circuit system. the blood sugar level and thyroid condition The metabolic increment caused by adrenaline is found in the frog, Rana temporaria (Smith, was calculated by comparing the oxygen con-
Gomp. Gen. Pharmac.
I-IARRI
306
sumption after the injection of adrenaline to that after the previously injected saline. A dose o f o.I rag. per kg. was injected into the dorsal lymph sac. This dose was chosen because it was shown to give the maximum responses (Harri & Hedemtam, x972). The determination of the blood glucose was performed according to Hultman's (I959) micromethod for aldosaccharides from o.2 ml. of blood. The hyperglycaemic response to adrenaline was tested by using a dose of o"5 rag. per kg. with a period of x hour between the drug administration
and the killing of the animals (Harri & Lindgren, x972). The basic heart rate and the chronotropic respome to adrenaline were measured at 12°C from pithed frogs. Adrenaline was injected into the abdominal vein and the cumulative doseresponse curves were prepared as described elsewhere (Tirri et al., t974). The doses which gave 5o ~o of the maximum chronotropic response (EDso) were used as an indication of the sensitivity to adrenaline. The ED60-values presented are from Tirri et al. (x974).
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Fzo. z.--The time-course of the changes in respomiveness to adrenaline and in thyroid activity after transferring the 25°C-acclimated frogs (©) to 5°C for different lengths of time; (a) the oxygen consumption of intact animals before (O) (from Harri, i973) , and after (©) the injection of o'I rag. per kg. of adrenaline; (b) the blood sugar level before (O), and after the injection ofo. 5 rag. per kg. of adrenaline (O) ; (c) the basic heart rate (O), and the chronotropic sensitivity to adrenaline, measured as EDs0-values (O, scale on the right; from Tirri et d . , I974); (d) the percentage amount of epithelium in the thyroid. W = winter frogs which had been kept at 5-io°C since autumn: The number of experimental animals is indicated at each point on the graph. Vertical bars indicate+ S.E.
z974, 5
THYROID--CATECHOLAMINEINTERACTION
307
The thyroids with the adjacent tissues were removed from the pithed animals, fixed in Bouin's fluid and stained with Weigert's hematoxylin and Domagk's thiazine red-picric acid solutions. The relative amounts of epithelium, colloid and stroma were measured from the thyroid sections prepared according to the linear method of Uotila & Karmas (t952). Student's t-test was used in the statistical evaluation of the differences.
for frogs maintained at a low temperature since autumn, o n the other hand, the chronotropic sensitivity to adrenaline began to decrease even during the first day at 5°(3, which was shown by the increase of the EDs0-values. The change was significant (P< o.o2) after 2 days. Later changes were not significant.
RESULTS CHANGES IN RESPONSIVENESSTO ADRENALINEDURmO COLD ACCLIMATION
ACTIVATION OF THE TH'zRom Gnaa~ DmuNo CoLD ACCLn~ATmN The results in Fro. z (d) and FIO. 2 indicate that the mean percentage amount of glandular epithelium, which was used to indicate the thyroid activity, increased after transferring the warm-acclimated frogs to a low temperature. The thickness of the epithelium was significantly higher than that in the warm-acclimated animals by the 4th day (P
Oxygen consumption FIOURE z(a) shows that in frogs acclimated to 25°C, a very rapid increase in the oxygen consumption (measured at 25°(3) was observable within the first day after transferring them to cold conditions (P
Blood glucose Fxom~z I (b) shows that after transferring the warm-acclimated frogs to 5°C, the basic blood sugar level increased, reaching its maximum 4 days after the transfer (P < o.o5). The typical blood sugar level of winter frogs acclimated to cold was not seen until they had been at a temperature of 5°C for 8 days. The hyperglycaemic response to adrenaline was significant (P < o.oo5) by the 4th day. Later, when the basic blood sugar level was lowered, the hyperglycaemic response to adrenaline was slightly elevated.
Heart rate In winter frogs acclimated to 25°(3 and then transferred to 5°(3, the basic heart rate increased slightly but not significantly in 2 days (FIo. zc). Between the 2nd and 4th day in the cold, however, there was a significant (P< o.o5) lowering to the level typical
DISCUSSION The results show that the metabolic as well as the hypcrglycacmic response to adrenaline-increased very rapidly after transferring the warm-acclimated frogs to a low temperature. These reactions were also rapid at the beginning of the exposure and slowed down after 2-4 days very markedly. Furthermore, the metabolic sensitization to adrenaline m a y be cvcn more rapid than that observed. As the utilization of catccholamines is increased irnrncdiatcly after placing the frogs into a cold environment (Harri, t972), it is possible
308
HARR!
Comp. Gen. Pharmaz.
The rapid change of the "histological that the elevated basal metabolic rate as well as the delay in the lowering of the heart rate picture of the thyroid gland is not an at the beginning of cold exposure are due unexpected phenomenon, because in mamto the increased release of endogenous mals, the histological changes are shown adrenaline. Furthermore, the basic blood to appear as early as within ½ hour to 2 sugar level elevated at the beginning of cold hours from beginning of exposure to cold (Ariel exposure. Became this elevation was accom- & Warren, I943; Del Conte & Stux, i954). Although the increased thyroid activity parried by the increased hyperglycaemic sensitivity to adrenaline, the increased release is probably responsible for the increased of endogenous adrenaline may be responsible metabolic sensitivity to adrenaline, the mechanism for the lowered chronotropic also for this elevation. The lowering of the basic heart rate and sensitivity to adrenaline in hearts from blood sugar level after 2 and 4 days respective- cold-acclimated frogs may be different. It ly of cold exposure may, on the other hand, has been recently suggested that this lowered indicate that after the initial rise, the sensitivity could be explained by decreased release of endogenous adrenaline later receptor sensitivity and by increased metareturns to a lower level. This has been boric rate and catechol-0-methyl transferase shown previously for the utilization of activity in heart tissue caused by increased adrenal adrenaline in cold-exposed winter sympathetic activity at low temperatures (Tirri et al., I974 ). frogs (Harri, i972 ). Recently, it has been shown that repeated However, the possibility that the thyroid dally adrenaline injections to frogs kept also participates in producing lowered in the warm causes an increase in the sensitivity of the heart to adrenaline has to thyroid activity and in the succinic dehydro- be considered. The lowered sensitivity genase activity of skeletal and heart muscle seems to be mediated by a-adrenoreceptors homogenates, similar to those induced by in the frogs (Tirri et al., x974), whereas the cold acclimation (Lagerspetz et al., I974). hyperglycaemic and probably also the response Thus, the increased utilization of adrenaline of the oxygen consumption to catecholamines in the brains of cold-exposed frogs (Harri, result from t-receptor stimulation (Harri x972) leads to thyroid activation either & Lindgren, i972 ). It has recently been directly (Melander & Sundler, I972; found that a-adrenergic responses are Mdander, Nilsson & Sundler, I972 ) or enhanced in the aorta from hypothyroid through TSH, the release of which may be rabbits (Rosenquist & Boreus, x972). It is affected b y the neurochemical changes thus possible that the hyperthyroid state found during temperature acclimation. In of cold-accrimated frogs is responsible for addition, the results of the present study the lowered chronotropic sensitivity of the show that the length of time required for heart's ot-adrenoreceptors. The importance thyroid activation at low temperature, as of the thyroid hormone in the control of the judged from thickening of t h e glandular form of the temperature-heart rate curve of epithelium and appearance of marginal the isolated frog's heart has been reported vacuoles in the follicles, corresponds to that earlier (Carter , 1933; Smith, I95i ). of the development of the metabolic and The changes observed in this study of the hyperglycaemic respons e to adrenaline. responsiveness to adrenaline and in thyroid Thus, t h e increased thyroid hormone activity after transferring frogs to a low secretion may be responsible also for the temperature were much more rapid than elevated metabolic and hyperglyaemic those observed previously in the tissue sensitivity to adrenaline in cold-acclimated metabolism (Lagerspetz et al., I974 ). This frogs. This view is also supported by the supports the assumption that the early results of Smith (x954), which show a phases of the adaptive changes associated significant correlation between the blood with cold acclimation in amphibians are sugar level and thyroid condition. results of temperature-induced changes in
Fro. m--Photomicrographs of thyroid glands of -05°C-acclimated winter frogs before (O) and after transferring them to 5°C for I, 4 or I8 days. Weigert's hematoxylin and Domagk's thiazine red-picric acid. Magnification × -064.
I974, 5
THYROID.-CATECH OLAMINE INTERACTION
c o o r d i n a t i n g mechanisms, r a t h e r t h a n direct effects o f t e m p e r a t u r e on the tissues. T h e present results also lead to the conclusion t h a t the adrenergic nervous system together with the thyroid gland are a f u n d a m e n t a l p a r t o f the mechanisms o f t e m p e r a t u r e acclimation in the frog. ACKNOWLEDGEMENTS I wish to express m y t h a n k s to Professor K. Y. H.
Lagerspetz for helpful criticism. My thanks are also due to Miss Hanna Kurppa for technical assistance and to Mrs Sinikka Hillgren for the drawings. This study has been supported by the Emil Aaltonen Foundation.
REFERENCES ARmL, I., & WARREN, S. L. (1943), ' Studies on the effect of hypothermia. II. The active role of the thyroid gland in hypothermic states in the rabbit ', Cancer. Res., 3, 454-463 • C~a~a~R, G. S. (1933), ' O n the control of the level of activity of the animal body. I. The endocrine control of seasonal variations of activity in the frog ' o7. Exp. Biol., xo, 256-273 . DEL CONTE, E., & STtrX, M. (x954) , 'Rapidity of thyroid reaction to cold ', .Nature, Lond., x73, 83. HARm, M. N. E. (I972), 'Effect of season and temperature acclimation on the tissue catecholamine level and utilization in the frog,
Rana temporaria', Comp. Gen. Pharnu~., 3~ xo I- I 1 2 . H A ~ , M. N. E. (x973), ' The rate of metabolic temperature acclimation in the frog, Rana temporaria', Physiol. Zool., 46~ t48--156. HARm, M. N. E., & HEDENSTAM, R. (x972), 'Calorigenic effect of adrenaline and noradrenaline in the frog, Rana temporaria', Comp. Biochem. Physiol., 4xA, 4o9--419 • ~I, M. N. E., & I_aNDORXN, E. (I972), ' Adrenergic control of carbohydrate metabolism in the frog, Rana temporaria', Comp. Gen. Pharmac., 3, 226-234.
309
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Key Word Index: Frog, Rana temporaria, temperature acclimation, adrenaline, oxygen consumption, blood sugar, heart rate, thyroid gland.