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Difference in thyroid function between male and female frogs (Rana temporaria L.) with increasing temperature
GENERAL
AND
COMPARATIVE
ENDOCRINOLOGY
36,
598403
(1978)
Difference in Thyroid Function between Male and Female (Rana ~~~~~~~~~a I-) with InGr~asing Te~p~r~tur~ R. CEUSTERS,
V. M. DARRAS,
Naamsestraat
AND
Frogs
E. R. KBHN
61, B-3000 Leuven, Belgium
Accepted September
19, I978
In Rana temporaria acclimation to higher environmental temperatures results in an increased lz51 uptake by the thyroid glands but only in males. Both male and female frogs have comparabIe excretion rates for ‘9 which increase with consecutive elevations of temperature. December frogs had the lowest thyroidal uptake rates and the increased uptake percentage following acclimation to higher temperature was less pronounced compared to October or January frogs. In males 1z51uptake was more pronounced in skin, stomach, and liver, whereas in females up to 21.5% of iodine injected was accumulated in the ovaries. Thyroxine content of thyroids in December frogs was about five times as high as in March frogs. No triiodothyronine was detectable in thyroids of December frogs and in March frogs only minims amounts could be found. In frogs tested in March, the ~yroxine content of male thyroids at 22” was only half that at 4”, whereas the level of thyroxine remained unchanged at both temperatures in females. The results support the hypothesis that the lower r*sXthyroid uptake in ferna& is not caused by an accumuIat~on of ‘9 in the ovaries but by competition at the thyroidal site with iodine released from the ovaries.
In poikilothe~s the evidence for the homeostatic role of the thyroid in calorigenesis is considered to be equivocal (Gorbman, 1964: Barrington, 1975; Bentley, 1976). So, TSH or thyroxine will be able to increase iodine uptake by the thyroid glands, stimulate oxygen consumption, and decrease the liver glycogen reserves but only at higher temperatures, whereas these effects are switched off at lower temperatures (Hoar, 1966; Maher, 1965; McNabb, 1969; Packard and Randall, 2975). This is the reverse of what happens in homeotherms. However, some data are present concerning a neurohormonal control of acclimation to lower temperatures in Rana ternporaria (Locker and Weish, 1966; Harri, 1973; Lagerspetz et al., 1974). In the following study the iodine uptake rate of the thyroid gland was investigated in winter specimens of R. te~~ora~~a acclimated to different environmental tempera(T3) and tures. The triiodothyronine thyroxine (TJ concentration of the thyroid
gland was also munoassay . MATERIAL
Copyright @ 1978 by Academic Press, Inc. AI1 rights of reproduction in any form reserved.
by
radioim-
AND METHODS
Adult frogs were obtained in September and November from R. Stein (Lauingen, G. F. R.) and maintained in plastic tanks in a nonheated room. Thereafter, they were allowed to acclimate each one in a separate box with 50 ml of tap water in a thermoregulated (2 1”) cage and this for 7 days. The fatlowing incubation temperatures were used: 5, 10, 15, 20, and 25”..Food (meal worms) was available, though feeding ceased in December and January. In March, food uptake was normal again. NO spawning Wcurred, though gonads were well developed. Injection of I*&1 was made into the ventral lymph sac (about 100,000 counts in a y-counter (Tracerlab) or -t 0.075 PCi). Two days later the thyroid glands were excized and the radioactivity measured. The radjoactivity of different tissues (skin, liver, stomach, gonads) and of the water was also counted. Radioimmunoassay of T, and T, was performed using kits obtained from the Diagnostic Division of Abbott Pharmaceuticals with the following adaptations: for T,, only one-half of the reagents mentioned was used; the tubes for AG-AB reaction were incubated at room tempe~ture for 24 hr; cent~fugation at 598
0016-648ofj78fo364-0598$01.~/0
measured
animals fp < O.01)(Fig. 1)and this for ternperatureshigher than IO”. No difference in body weight between sexes was present. Total 125Iexcretion into the water after 2 days for ah groups aIso did not differ between mates (41.71i 12.61%)and fernates (38.05r ~~.~%),butincreasesiu both sexes with increasing temperatures 0, < 0.01) (Table 1). A second seriesof experimentswas rua 01 in December.No differencein body weight a 5 to 15 20 25 tcmperabrurt l t between sexes was present. Both females f%G. 1. 1251uptake (%) 2 SEM in the thyroid and rualeshad a significantly lower thyroiglands of &ma temporaria as measured 2 days after da1iodine uptake comparedto the Qctober injection in the ventral lymph sac of 0.075 &i. All frogs but a moderate increase in uptake animals have been acclimated to the indicated tempercentage with increasing te~~rat~re peraures for 7 days. was seenonly in majes Q7< 0.05)(Fig. 21. SO00 rpm for 10 min at 20”; for T,: only one-@& of the In a separateexperiment‘I’, and TJ levels of reagents mentioned was used. thyraid glands were,assayedafter au adcliBlood levels for T, and T, were below the sensitivmation period,af 7 days (Table 2) High and ity of the assay. In the thyroid glands very low Ta variable levels of T4 were found ‘in the values were found. Since in the ~dio~mmun~assay the addition of IO0 ng T, to the TX antiserum results in thyroid glands of male and femafe,frogs at an j~ibitj?n eq&dent to 0.7 ng of T, a TJ’T4 ratio every te~~eratnre i used. No d~te~t~b~e higber’tlian 0.007 is required in order to ensure a T, amounts of T, were found in the thyroi&, measurement. Ia the T3 values given, no correction since the T3fT, ratio was ldzrverthan 0. for tbis T, cross-reactivity has been made. The J25Iexcretion did not differ between Increases in thyroidal iodine uptake with consecutive elevations of temperature have been evaluated sexesbut it in&eased with incre&ng temstitristically by he-way analysis of variance. Coinperature (p < @AH)(Table I). parisons between two groups were made using StuIn a third series of exper~~~~tsmado in dent’s t test. January, iodine, uptake of thyroid boards RESULTS and other tissues have been compared beIn a first seriesof experiments(October) tween males and feP;inales acclimated for 7 an increasein iodine uptake with increasing days &t 22” (Table 3) Uptake,~er~~~tag~s te~peratnr~ was observedbut only in male were det~~~~ed 3 days foIl~~~g’~z~~in&~
October frogs 6 0 December frogs 6 0
5”
ftl”
If
20”
25”
37.7 r 6.9”(4)h 33.2 c 4.5 (3)
-
31.7 ” 3.0 (3) 35.8 I?Z6.7 (4)
40.5 2 3.0 (3) 31.6 rt: 10.2 (4)
s5.0 -t- 16.0 (4) 54.1 r 3.3 (3)
33.6 -i- 10.1 (3) 33.7 -c x2 (4)
27.8 + 3.9 (3) 33.4 Ifi 6.8 (4)
35.8 T.k4.3 (4) 34.5 + 3.3 (3)
49.1 -c 7.7 (4) 53.2 t 8.1 (3)
52.0 2 6.3 (3) 60.8 Ir 5.1 (3)
a Mean f SEM. * Number of animals in parentheses.
600
CEUSTERS,
DARRAS,
AND K6HN
thyroxine level in the thyroids was only about one-fifth that of the December frogs. Males had a lower T, content at both temperatures used. At 4” the difference between males and females was not present when expressed in gram body weight but a decrease in thyroidal content is seen in males acclimated to 22”. No change in thyroxine concentration occurs in females. DISCUSSION
Our results indicate that in winter frogs an increase in iodine uptake by the thyroid glands occurs when the temperature of the environment is raised but only in male animals. Both male and female frogs have comparable excretion tion. In the January frogs, males had a sig- rates for rz51which increase with consecunificantly lower body weight. Total iodine tive rises in temperature. Controversial results are reported in the uptake by the thyroid gland again was more elevated in males than in females, the total literature on the influence of temperature amount being comparable to the October on thyroid function in poikilotherms (Janfrogs. The iodine excretion in water during kowsky, 1960, 1964; Leloup and Fontaine, 1960; Locker and Weish, 1966; Lagerspetz 3 days was the same in males and females, but males had a higher lZ51count/g of skin, et al., 1974). However, it is generally acstomach, and liver, whereas the ovaries had cepted that thyroid activity (Hoar, 1966), effects (Maher, 196.5; a higher uptake (on a g weight basis) com- and thyroid-mediated NcNabb, 1969; Packard and Randall, 1975) pared to’the testes. Since the total ovarian vary with body temperature. Therefore it weight was 4.61 -+ 0.66 g (E = 7), this represeems likely that, as in our experiments, the sents 21.5% of the total injected lz51. Total low level of metabolic activity present at weight of testes was only 0.21 4: 0.03 g (rz = low temperatures in amphibians will result 7) representing 0.22% of total injected jz51. In a last experiment (March) male and in a lower rate of iodine uptake by the female frogs were acclimated to 4 and 22” thyroids as observed in males or a lower and their thyroidal concentration of T3 and excretion rate as observed both in males Td was assayed. The results are sum- and females. So, these results can be exmarized in Table 4. In these frogs, the plained by an action of temperature on the Ia51 uptake (%) k glands of Rana temporaria as injection in the ventral lymph animals have been acclimated peratures for 7 days. FIG.
2.
SEM in the thyroid measured 2 days after sac of 0.075 $3. AII to the indicated tem-
(R. temporaria)
TABLE THYROXINE
CONTENT
(ng)~~
5” 215.7
k 33.9
(5 + 5Y
2
GLANDS OF DECEMBER TEM~E~~URES
788.9 -+ 210.Y (15)~ 517 5 ~ 145 5 (5)
a Mean + SEM. b Number of animals in parentheses. c Male and female frogs put together by mistake.
FROGS ACCLIMATEDTO
15
10”
CT 0
THYROID
385.9 830.0
-s 84.8 rt 418.5
DIFFERENT
20" (5) (5)
648.1 292.7
c 519.4 (5) c 13.1 (5)
25" 824.3 416.7
+ 299.7 {6) + 134.6 (4)
THYROID
FUNCTION
TABLE ~~~XUPTAKE/~TI~SUE(~)~DA~~F~LLOWING~N~ECTION~F~LC~INJANUARY DAYS&
IN
Rana
601
3 FROGS
6 Body weight (g) Thyroid glands (total) Skin Stomach Liver Gonads Oviduct Blood (/ml) Excretion
2 ” -+ I I‘-
28.74 5.83
1.93 1.76 1.63 1.03
0 1.97”
P
ztz3+46 -+ 0.69 -c 0.13 2 0.04 t 0.06 rt 0.83 0.10 -+ 0.02 0.32 * 0.05 (4) 54.75 It 3.36
38.27 2.72 0.39 0.41 1.02 5.02
0.75
0.50 0.41 0.13 0.22
0.83 57.49
ACCLIMA~EDTo22FOR7
= 7)
-c 0.18 (6)” k 3.14
KS. n.s.
a Mean r SEM. b IZ = 7 except for numbers in parentheses. C Not significant.
kinetics of the reaction involved. ~uiesc~nt or hibernating ectotherms are found to have a low level of metabolic activity which is markedly independent of experimental temperature (Newell, 1973). This could explain the low uptake rates of 125I in our December frogs and the inability of males to respond to increasing temperatures in the same way as frogs in October or January. In our results an inverse relationship exists between thyroxine content of the thyroid glands and the iodine uptake rate. So, high levels of thyroxine are found in December with a low iodine uptake. Histological evidence has indicated the existence of seasonally varying secretory activity in the adenohypophysis of R. temTABLE T, LEVELS
~~~~~
4
OFFROGSACCLIMATEDFORY
DAYSTO~
ANDRE'
Weight of gonads (54
T,
T4
28.9 rt 2.5" 2 3.3
0.179 Y!z0.014 L 0.762
f 0.50 2 0.38 n.s.b 0.91 t 0.27 0.97 2 0.25 l3.s.
123.3 f 9.7 200.5 lir: 34.4 <0.05 67.1 j, 15.7 264.7 c 59.9 co.01
P 22" 22*
IN THYROIDS
Body weight (g) 6 (fl = 7) 9 (n = 6)
4* 4O
(ng)
with maxims activity o~cur~ng at the end of hibernation, but secretory granules will only be released during the reproduction period, which dar&els the seasonal changes in gonads, thyroid, etc. (van Oordt et al., 1968). Therefore we ‘beIieve that the high thyroxine level in the December frogs is not accompanied by a high thyroxine release from the gland. These results do not support the hypothesis of Lagerspetz et al. (1974) that the thyrbid participates in the a~~lirnatio~ process at lower temperatures in winter frogs. In our experiments, females do not react in the same way as males to an’increase in temperature. It has long been known that the ovary accumulates most of tht injected ~~~a~i~
d (n = 7) 0 (rl = 7)
P u Mean + SEM. b Not significant,
43.4
6.523
1.73 1.12
T,ig body wt “_ 0.4 +- 0.9 n.s. 2.5 rf: 0.5 8.2 i- 1.7 io.01
4.4 4.7
602
CEUSTERS,
DARRAS,
iodine (Robertson and Chancy, 1953; Leloup and Fontaine, 1960; Lindsay et al., 1966; Tarrant, 1971). However, we do not think that this phenomenon removes the injected Iz51 from the circulation in a way that the iodine uptake by the thyroids will decrease compared to males for the following reasons. (1) Excretion rates up to 50% are found and the amounts of lzsI excreted do not differ between male and female frogs at any of the temperatures used. Apparently enough rA51 is circulating to saturate the iodine-uptake capacity of the thyroid giands of both sexes. Since iodine accumulation by the .ovaries does not seem to influence the excretion rate, it is unlikely that it will be responsible for the lack of response to higher temperature in iodine uptake by the thyroids. (2) The high T, content of the thyroids found in December is p~a~~e~fed by low iodine uptake by both males and females. In March frogs, the thyroidal concentration of thyroxine in both sexes is lower than was found in December frogs, but the concentrations in females are still twice those of males and remain unchanged with increasing temperature, whereas in males a sharp decrease is seen. This could mean that males release thyroxine from the thyroid gland with increasing temperature, thereby facilitating uptake of 123. ACKNOWLEDGMENTS We would like to thank the Diagnostic Division of Abbott Pharma~euticais (Antwerp) for their provision of the kits for radioimmunoassay of T8 and T,.
REFERENCES Barrington, E. J. W. (1975). “An Intr~uction to General and Comparative Endocrinology.” Clarendon, Oxford. Bentley, P. J. (1976). “Comparative Vertebrate Endocrinology.” Cambridge Univ. Press, LondonlNew York. Gorbman, A. (1964). Endocrinology of the Amphibia. In “Physiology of the Amphibia” (J. A. Moore, ed.), pp. 371-425. Academic Press, New York. Harri, M. N. E. (1973). Neural control of tem~~ture
AND
KtiHN
adaptation in Rana temporariu. In “Effects of Temperature on Ectothermic Organisms. Ecological Implications and Mechanisms of Compensation” (W. Wieser, ed.), pp. 35-43. SpringerVerlag, Berlin, New York. Hoar, W. S. (1966). Hormonal activities of the pars distalis in cyclostomes, fish and Amphibia. In “The Pituitary Gland” (G. W. Harris, and B. T. Donovan, eds.), pp. 242-294. Butterworths, London. Jankowsky, H. D. (1960). Ueber die hormonale Beeinflussung der Temperaturadaptation beim Grasfrosch (Raaa ~em~ara~~a L.) Z. Vergi. f’hysiot.
43, 392-410.
Jankowsky, H. D. (1964). Die Bedeutung der Hormone fur die Temperaturanpassung im normalen Temperaturberei~h. He~go~~~der Wiss. ~eer~su~~ers.
9, 412-419.
Lagerspetz, K. Y. H., Harri, M. N. E., and Qkslahti, R. (1974). The role of the thyroid in the temperature acclimation of the oxidative metabolism in the frog Rana ~em~araria. crinol. 22, 169-176.
Gen.
Camp.
Endo-
Leloup, J., and Fontaine, M. (1960). Iodine metabolism in lower vertebrates.Ann. Iv’. Y. Acad. Sci. 86, 316-353.
Lindsay, R. H., Romine, C., Zacharewicz, P., Dup ree, H. K., and Sneed, K. E. (1966). Accumulation of Ir3’ by channel catfish (Zctalurus punctatus) ovaries in viva and in vitro. Gen. Camp. Endocrinol.
6, 231-238.
Locker, A., and Weish, P. (1966). Quantitative aspects of cold-adaptation and its thyroxine model in coldand warm-blooded animals. Helgoliinder Wiss. Meeresunters.
14, 503-513.
Maher, M. J. (1965). The role of the thyroid gland in the oxygen consumption of lizards. Gen. Comp. Endocrinol.
5, 320-325.
McNabb, R. A. (1969). The effects of thyroxine on glycogen stores and oxygen consumption in the leopard frog, Rana pipiens. Gen. Camp. Endocrinol.
12, 276-281.
Newell. R. C. (1973). Environmental factors affecting the acchmatory responses of ectotherms. In “Effects of Temperature on Ectothermic Organisms. Ecological Implications and Mechanisms of Compensation” (W. Wieser, ed.), pp. 151-164. Springer-Verlag, Berlin/New York. Packard G. C., and Randall, J. G. (1975). The influence of thyroxine and acclimation temperature on glycogen reserves of the frog Rana pipiens. J. Exp. Zool. 191, 365-369. Robertson, 0. H., and Chaney, A. L. (1953). Thyroid hyperplasia and tissue iodine content in spawning rainbow trout: A comparative study of lake Michigan and California sea-run trout. Physiol. 2001. 26, 328-340. Tarrant, R. M. (1971f. Seasonal variation in the ac-
THYROID
FUNCTION
cumulation and loss of 1311by tissues of adult female channel catfish, Ictalurus punctatus (Rafinesque). Trans. Amer. Fish. Sot. 2,237-246. van Oordt, P. G. W. .I., van Dongen, W. J., and Lofts,
IN
Rum
603
B. (1968). Seasonal changes in endocrine organs of the male frog Rana tempouaria: i, The pars distalis of the adenohypophysis. Z. Zeliforsch. 88, 549-559.
AND
COMPARATIVE
ENDOCRINOLOGY
36,
598403
(1978)
Difference in Thyroid Function between Male and Female (Rana ~~~~~~~~~a I-) with InGr~asing Te~p~r~tur~ R. CEUSTERS,
V. M. DARRAS,
Naamsestraat
AND
Frogs
E. R. KBHN
61, B-3000 Leuven, Belgium
Accepted September
19, I978
In Rana temporaria acclimation to higher environmental temperatures results in an increased lz51 uptake by the thyroid glands but only in males. Both male and female frogs have comparabIe excretion rates for ‘9 which increase with consecutive elevations of temperature. December frogs had the lowest thyroidal uptake rates and the increased uptake percentage following acclimation to higher temperature was less pronounced compared to October or January frogs. In males 1z51uptake was more pronounced in skin, stomach, and liver, whereas in females up to 21.5% of iodine injected was accumulated in the ovaries. Thyroxine content of thyroids in December frogs was about five times as high as in March frogs. No triiodothyronine was detectable in thyroids of December frogs and in March frogs only minims amounts could be found. In frogs tested in March, the ~yroxine content of male thyroids at 22” was only half that at 4”, whereas the level of thyroxine remained unchanged at both temperatures in females. The results support the hypothesis that the lower r*sXthyroid uptake in ferna& is not caused by an accumuIat~on of ‘9 in the ovaries but by competition at the thyroidal site with iodine released from the ovaries.
In poikilothe~s the evidence for the homeostatic role of the thyroid in calorigenesis is considered to be equivocal (Gorbman, 1964: Barrington, 1975; Bentley, 1976). So, TSH or thyroxine will be able to increase iodine uptake by the thyroid glands, stimulate oxygen consumption, and decrease the liver glycogen reserves but only at higher temperatures, whereas these effects are switched off at lower temperatures (Hoar, 1966; Maher, 1965; McNabb, 1969; Packard and Randall, 2975). This is the reverse of what happens in homeotherms. However, some data are present concerning a neurohormonal control of acclimation to lower temperatures in Rana ternporaria (Locker and Weish, 1966; Harri, 1973; Lagerspetz et al., 1974). In the following study the iodine uptake rate of the thyroid gland was investigated in winter specimens of R. te~~ora~~a acclimated to different environmental tempera(T3) and tures. The triiodothyronine thyroxine (TJ concentration of the thyroid
gland was also munoassay . MATERIAL
Copyright @ 1978 by Academic Press, Inc. AI1 rights of reproduction in any form reserved.
by
radioim-
AND METHODS
Adult frogs were obtained in September and November from R. Stein (Lauingen, G. F. R.) and maintained in plastic tanks in a nonheated room. Thereafter, they were allowed to acclimate each one in a separate box with 50 ml of tap water in a thermoregulated (2 1”) cage and this for 7 days. The fatlowing incubation temperatures were used: 5, 10, 15, 20, and 25”..Food (meal worms) was available, though feeding ceased in December and January. In March, food uptake was normal again. NO spawning Wcurred, though gonads were well developed. Injection of I*&1 was made into the ventral lymph sac (about 100,000 counts in a y-counter (Tracerlab) or -t 0.075 PCi). Two days later the thyroid glands were excized and the radioactivity measured. The radjoactivity of different tissues (skin, liver, stomach, gonads) and of the water was also counted. Radioimmunoassay of T, and T, was performed using kits obtained from the Diagnostic Division of Abbott Pharmaceuticals with the following adaptations: for T,, only one-half of the reagents mentioned was used; the tubes for AG-AB reaction were incubated at room tempe~ture for 24 hr; cent~fugation at 598
0016-648ofj78fo364-0598$01.~/0
measured
animals fp < O.01)(Fig. 1)and this for ternperatureshigher than IO”. No difference in body weight between sexes was present. Total 125Iexcretion into the water after 2 days for ah groups aIso did not differ between mates (41.71i 12.61%)and fernates (38.05r ~~.~%),butincreasesiu both sexes with increasing temperatures 0, < 0.01) (Table 1). A second seriesof experimentswas rua 01 in December.No differencein body weight a 5 to 15 20 25 tcmperabrurt l t between sexes was present. Both females f%G. 1. 1251uptake (%) 2 SEM in the thyroid and rualeshad a significantly lower thyroiglands of &ma temporaria as measured 2 days after da1iodine uptake comparedto the Qctober injection in the ventral lymph sac of 0.075 &i. All frogs but a moderate increase in uptake animals have been acclimated to the indicated tempercentage with increasing te~~rat~re peraures for 7 days. was seenonly in majes Q7< 0.05)(Fig. 21. SO00 rpm for 10 min at 20”; for T,: only one-@& of the In a separateexperiment‘I’, and TJ levels of reagents mentioned was used. thyraid glands were,assayedafter au adcliBlood levels for T, and T, were below the sensitivmation period,af 7 days (Table 2) High and ity of the assay. In the thyroid glands very low Ta variable levels of T4 were found ‘in the values were found. Since in the ~dio~mmun~assay the addition of IO0 ng T, to the TX antiserum results in thyroid glands of male and femafe,frogs at an j~ibitj?n eq&dent to 0.7 ng of T, a TJ’T4 ratio every te~~eratnre i used. No d~te~t~b~e higber’tlian 0.007 is required in order to ensure a T, amounts of T, were found in the thyroi&, measurement. Ia the T3 values given, no correction since the T3fT, ratio was ldzrverthan 0. for tbis T, cross-reactivity has been made. The J25Iexcretion did not differ between Increases in thyroidal iodine uptake with consecutive elevations of temperature have been evaluated sexesbut it in&eased with incre&ng temstitristically by he-way analysis of variance. Coinperature (p < @AH)(Table I). parisons between two groups were made using StuIn a third series of exper~~~~tsmado in dent’s t test. January, iodine, uptake of thyroid boards RESULTS and other tissues have been compared beIn a first seriesof experiments(October) tween males and feP;inales acclimated for 7 an increasein iodine uptake with increasing days &t 22” (Table 3) Uptake,~er~~~tag~s te~peratnr~ was observedbut only in male were det~~~~ed 3 days foIl~~~g’~z~~in&~
October frogs 6 0 December frogs 6 0
5”
ftl”
If
20”
25”
37.7 r 6.9”(4)h 33.2 c 4.5 (3)
-
31.7 ” 3.0 (3) 35.8 I?Z6.7 (4)
40.5 2 3.0 (3) 31.6 rt: 10.2 (4)
s5.0 -t- 16.0 (4) 54.1 r 3.3 (3)
33.6 -i- 10.1 (3) 33.7 -c x2 (4)
27.8 + 3.9 (3) 33.4 Ifi 6.8 (4)
35.8 T.k4.3 (4) 34.5 + 3.3 (3)
49.1 -c 7.7 (4) 53.2 t 8.1 (3)
52.0 2 6.3 (3) 60.8 Ir 5.1 (3)
a Mean f SEM. * Number of animals in parentheses.
600
CEUSTERS,
DARRAS,
AND K6HN
thyroxine level in the thyroids was only about one-fifth that of the December frogs. Males had a lower T, content at both temperatures used. At 4” the difference between males and females was not present when expressed in gram body weight but a decrease in thyroidal content is seen in males acclimated to 22”. No change in thyroxine concentration occurs in females. DISCUSSION
Our results indicate that in winter frogs an increase in iodine uptake by the thyroid glands occurs when the temperature of the environment is raised but only in male animals. Both male and female frogs have comparable excretion tion. In the January frogs, males had a sig- rates for rz51which increase with consecunificantly lower body weight. Total iodine tive rises in temperature. Controversial results are reported in the uptake by the thyroid gland again was more elevated in males than in females, the total literature on the influence of temperature amount being comparable to the October on thyroid function in poikilotherms (Janfrogs. The iodine excretion in water during kowsky, 1960, 1964; Leloup and Fontaine, 1960; Locker and Weish, 1966; Lagerspetz 3 days was the same in males and females, but males had a higher lZ51count/g of skin, et al., 1974). However, it is generally acstomach, and liver, whereas the ovaries had cepted that thyroid activity (Hoar, 1966), effects (Maher, 196.5; a higher uptake (on a g weight basis) com- and thyroid-mediated NcNabb, 1969; Packard and Randall, 1975) pared to’the testes. Since the total ovarian vary with body temperature. Therefore it weight was 4.61 -+ 0.66 g (E = 7), this represeems likely that, as in our experiments, the sents 21.5% of the total injected lz51. Total low level of metabolic activity present at weight of testes was only 0.21 4: 0.03 g (rz = low temperatures in amphibians will result 7) representing 0.22% of total injected jz51. In a last experiment (March) male and in a lower rate of iodine uptake by the female frogs were acclimated to 4 and 22” thyroids as observed in males or a lower and their thyroidal concentration of T3 and excretion rate as observed both in males Td was assayed. The results are sum- and females. So, these results can be exmarized in Table 4. In these frogs, the plained by an action of temperature on the Ia51 uptake (%) k glands of Rana temporaria as injection in the ventral lymph animals have been acclimated peratures for 7 days. FIG.
2.
SEM in the thyroid measured 2 days after sac of 0.075 $3. AII to the indicated tem-
(R. temporaria)
TABLE THYROXINE
CONTENT
(ng)~~
5” 215.7
k 33.9
(5 + 5Y
2
GLANDS OF DECEMBER TEM~E~~URES
788.9 -+ 210.Y (15)~ 517 5 ~ 145 5 (5)
a Mean + SEM. b Number of animals in parentheses. c Male and female frogs put together by mistake.
FROGS ACCLIMATEDTO
15
10”
CT 0
THYROID
385.9 830.0
-s 84.8 rt 418.5
DIFFERENT
20" (5) (5)
648.1 292.7
c 519.4 (5) c 13.1 (5)
25" 824.3 416.7
+ 299.7 {6) + 134.6 (4)
THYROID
FUNCTION
TABLE ~~~XUPTAKE/~TI~SUE(~)~DA~~F~LLOWING~N~ECTION~F~LC~INJANUARY DAYS&
IN
Rana
601
3 FROGS
6 Body weight (g) Thyroid glands (total) Skin Stomach Liver Gonads Oviduct Blood (/ml) Excretion
2 ” -+ I I‘-
28.74 5.83
1.93 1.76 1.63 1.03
0 1.97”
P
ztz3+46 -+ 0.69 -c 0.13 2 0.04 t 0.06 rt 0.83 0.10 -+ 0.02 0.32 * 0.05 (4) 54.75 It 3.36
38.27 2.72 0.39 0.41 1.02 5.02
0.75
0.50 0.41 0.13 0.22
0.83 57.49
ACCLIMA~EDTo22FOR7
= 7)
-c 0.18 (6)” k 3.14
KS. n.s.
a Mean r SEM. b IZ = 7 except for numbers in parentheses. C Not significant.
kinetics of the reaction involved. ~uiesc~nt or hibernating ectotherms are found to have a low level of metabolic activity which is markedly independent of experimental temperature (Newell, 1973). This could explain the low uptake rates of 125I in our December frogs and the inability of males to respond to increasing temperatures in the same way as frogs in October or January. In our results an inverse relationship exists between thyroxine content of the thyroid glands and the iodine uptake rate. So, high levels of thyroxine are found in December with a low iodine uptake. Histological evidence has indicated the existence of seasonally varying secretory activity in the adenohypophysis of R. temTABLE T, LEVELS
~~~~~
4
OFFROGSACCLIMATEDFORY
DAYSTO~
ANDRE'
Weight of gonads (54
T,
T4
28.9 rt 2.5" 2 3.3
0.179 Y!z0.014 L 0.762
f 0.50 2 0.38 n.s.b 0.91 t 0.27 0.97 2 0.25 l3.s.
123.3 f 9.7 200.5 lir: 34.4 <0.05 67.1 j, 15.7 264.7 c 59.9 co.01
P 22" 22*
IN THYROIDS
Body weight (g) 6 (fl = 7) 9 (n = 6)
4* 4O
(ng)
with maxims activity o~cur~ng at the end of hibernation, but secretory granules will only be released during the reproduction period, which dar&els the seasonal changes in gonads, thyroid, etc. (van Oordt et al., 1968). Therefore we ‘beIieve that the high thyroxine level in the December frogs is not accompanied by a high thyroxine release from the gland. These results do not support the hypothesis of Lagerspetz et al. (1974) that the thyrbid participates in the a~~lirnatio~ process at lower temperatures in winter frogs. In our experiments, females do not react in the same way as males to an’increase in temperature. It has long been known that the ovary accumulates most of tht injected ~~~a~i~
d (n = 7) 0 (rl = 7)
P u Mean + SEM. b Not significant,
43.4
6.523
1.73 1.12
T,ig body wt “_ 0.4 +- 0.9 n.s. 2.5 rf: 0.5 8.2 i- 1.7 io.01
4.4 4.7
602
CEUSTERS,
DARRAS,
iodine (Robertson and Chancy, 1953; Leloup and Fontaine, 1960; Lindsay et al., 1966; Tarrant, 1971). However, we do not think that this phenomenon removes the injected Iz51 from the circulation in a way that the iodine uptake by the thyroids will decrease compared to males for the following reasons. (1) Excretion rates up to 50% are found and the amounts of lzsI excreted do not differ between male and female frogs at any of the temperatures used. Apparently enough rA51 is circulating to saturate the iodine-uptake capacity of the thyroid giands of both sexes. Since iodine accumulation by the .ovaries does not seem to influence the excretion rate, it is unlikely that it will be responsible for the lack of response to higher temperature in iodine uptake by the thyroids. (2) The high T, content of the thyroids found in December is p~a~~e~fed by low iodine uptake by both males and females. In March frogs, the thyroidal concentration of thyroxine in both sexes is lower than was found in December frogs, but the concentrations in females are still twice those of males and remain unchanged with increasing temperature, whereas in males a sharp decrease is seen. This could mean that males release thyroxine from the thyroid gland with increasing temperature, thereby facilitating uptake of 123. ACKNOWLEDGMENTS We would like to thank the Diagnostic Division of Abbott Pharma~euticais (Antwerp) for their provision of the kits for radioimmunoassay of T8 and T,.
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AND
KtiHN
adaptation in Rana temporariu. In “Effects of Temperature on Ectothermic Organisms. Ecological Implications and Mechanisms of Compensation” (W. Wieser, ed.), pp. 35-43. SpringerVerlag, Berlin, New York. Hoar, W. S. (1966). Hormonal activities of the pars distalis in cyclostomes, fish and Amphibia. In “The Pituitary Gland” (G. W. Harris, and B. T. Donovan, eds.), pp. 242-294. Butterworths, London. Jankowsky, H. D. (1960). Ueber die hormonale Beeinflussung der Temperaturadaptation beim Grasfrosch (Raaa ~em~ara~~a L.) Z. Vergi. f’hysiot.
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9, 412-419.
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Camp.
Endo-
Leloup, J., and Fontaine, M. (1960). Iodine metabolism in lower vertebrates.Ann. Iv’. Y. Acad. Sci. 86, 316-353.
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6, 231-238.
Locker, A., and Weish, P. (1966). Quantitative aspects of cold-adaptation and its thyroxine model in coldand warm-blooded animals. Helgoliinder Wiss. Meeresunters.
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THYROID
FUNCTION
cumulation and loss of 1311by tissues of adult female channel catfish, Ictalurus punctatus (Rafinesque). Trans. Amer. Fish. Sot. 2,237-246. van Oordt, P. G. W. .I., van Dongen, W. J., and Lofts,
IN
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603
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