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Enhanced potency of desiccated thyroid powder
TOXICOLOGY
AND APPLIED PHARMACOLOGY14,48-53
Enhanced MARTIN
Potency
W. WILLIAMS,
(1969)
of Desiccated
Thyroid
Powder
JACK C. TOWNE, AND CHARLES S. WILLIAMS
Veterans Administration
Hospital, Tucson, Arizona 82713
Received January 12,1968
Enhanced Potency of Desiccated Thyroid Powder. WILLIAMS, MARTIN W., TOWNE, JACK C., and WILLIAMS, CHARLES S. (1969). Toxicol. Appl. Pharmacol. 14,48-53. Thyroid Powder, USP, when aged in uitro at room temperatures for 19 months, was found to be significantly more potent in the production of hyperthyroidism in female SwissWebster mice when fed ad libitum at approximately 3000 ppm in ground Purina Lab Chow, than a similar sample kept in a deep freeze at -23”. Potency was based upon the oxygen consumption-stimulating ability of the thyroid preparations. No significant difference in potency was noted between the freezer-stored thyroid sample and the original. Because of the seeming variations from lot to lot in the potency of thyroid powder, USP, fed to mice on tumor experiments (Williams and Williams, 1965; Williams et al., 1966), which was measured by oxygen consumption, an experiment was designed to determine whether, at room temperature, in vitro changes in potency with time could be observed. For many years the use of pelleted desiccated thyroid powder or other similar thyroid preparations to increase body metabolism has been considered a safe, reproducible, and inexpensive substitute for the more expensive purified thyroactive drugs, such as thyroxine, and indeed it may have some advantages (Goodman and Gilman, 1965). Standard potency has been assured, it was assumed, by control of iodine content as characterized in the U. S. Pharmacopeia (1965), which specifies that the iodine content be not less than 0.17 or more than 0.23 % and that this iodine be in thyroid combination, not in the form of iodide. The general consensus expressed (Krantz and Carr, 1961; Goodman and Gilman, 1965) has been that thyroid powder is stable for many years, losing neither iodine nor calorigenic potency. The improbability of increasing potency with in vitro age has apparently not been considered. The purpose of this work was to determine the changes, if any, in potency of similar samples of thyroid powder from the same lot both at the beginning of the experiment and again 19 months later. One sample was kept at ambient room temperatures and the second sample was kept in a deep freeze at -23”. METHODS In March, 1966, a IO-kg sample of desiccated thyroid powder USP was purchased.1 A sample of 43 g of this lot was separated from the remainder and put on the shelf in a 1 Nutritional Biochemicals, Cleveland, Ohio. 48
POTENCY OF THYROtD POWDER
49
brown chemical bottle at ambient temperature. The remaining powder was placed in a deep freeze, samples being removed as required for other experiments. Initial observations were made in April, 1966. Later assays were made in November and December, 1967. Mice used were female Swiss Websters, the average starting weight being 23.8 g (i.e., young adults). All animals were procured from a commercial supplier.2 All diets were given ad libitum and were prepared from ground lab chow,3 to which was added 3000 ppm of thyroid powder where needed. Control animals received ground chow only. Oxygen consumption observations on individual animals were made in a respirometer previously described (Williams et al., 1965). All oxygen consumption figures were converted to standard temperature and pressure (STP). Duplicate observations were made in all cases, thus the tabular data represent the averages of duplicate observations in all cases. The statistical method used was the Student’s t test, analysis being based upon the number of animals tested, not on the number of observations. Water content of the desiccated thyroid powders was determined by the difference in weight loss for the samples dried in aacuo over potassium hydroxide at room temperature for 72 hours. Amino acid analysis of acid and alkaline hydrolyzed samples was made in amino acid analyzer4 and tested for 17 amino acids. Free iodide and total iodide content of the anhydrous samples were determined by the methods of the U. S. Pharmacopeia (1965, p. 718).
RESULTS
AND DISCUSSION
The results of the 1966 study on the original sample of desiccated thyroid powder are shown in Table 1. The expected increase in oxygen consumption is seen from day 1I onward, although a significant increase was seen at day 6. Results of the 1967 study are shown in Table 2. Here again the expected increase is in evidence both in the freezer thyroid and the ambient temperature stored thyroid, but the percentages above control are greater for the ambient stored than for the freezer material. A statistical comparison of the ambient versus freezer thyroid powder (1967 study; Table 2), indicates a significant increase of the former over the latter in every case, i.e., days 8, 15, 17, 22, and 29, where comparisons are possible except at day 2. A cross comparison of the freezer thyroid sample (1967) with the original sample (1966) (Table 1) indicates no significant difference between the two at days 4 and 11 or when close time periods are compared, i.e., day 15 freezer sample versus day 16 original sample; or day 22 freezer sample versus day 23 original sample. From these data we may conclude that the freezer sample (tested in 1967) has the same potency (not statistically different) as the original sample when run in 1966. A comparison of data from the original sample tested in 1966 with the ambient temperature sample tested in 1967 can be made as shown in Table 3. 2 Simonsen Laboratories, 3 Purina. 4 Spinco Model 120B.
Gilroy, California.
50
WILLIAMS,
TOWNE, AND WILLIAMS
It is evident from Table 3 that, although on days 6 and 22-23 no significant difference is seen, the means in all cases are higher in the ambient than in the original sample, this being indicative of the trend. In all four other cases a highly significant difference is seen to exist. The hypothesis that elevated ambient temperatures, i.e., up to 120”F, or bacterial activity may have enhanced the conversion of thyroxine to triiodothyronine is a possibility. Wiberg et al. (1962) have shown thyroid powder to owe much of its thyromimetic effect to its contained triiodothyronine. TABLE 1 OXYGEN CONSUMED, MILLILITERS/GRAM/HOUR
Day number
CORRECTED TO STP (1966 STUDY)
Thyroid f SE original sample, Control f SE
3OOOppm
%
P”
2
3.7 i 0.29
4.2 f 0.19
+13.5
4
(lQb 4.2 & 0.43 (10)
(6)
6
9 11 13 16 23 32
3.5 Ito.
(10) 3.7 * 0.50 (10) 3.7 f 0.49 (10) 3.5 f 0.40 (10) 4.2zkO.18
4.6 dc0.22
+ 9.5
(10) 5.5 rk 0.80
>o.os NS’ BO.05 NS
$57.1
co.05
t-29.7
10.05
$54.0
co.02
5.6 f 0.42
+60.0
co.02
(10) 6.1 f 0.35
+45.2
+58.9
to.01
(8)
4.8 zt 0.92
(8)
5.7 it.45
(10)
(10) 3.9 + 0.18 (10) 3.2 ho.39
(10) 6.8 f 0.93
(10)
(8)
b Number of determinations c NS, not significant.
NS
03)
6.2 f 0.42
+112.5
CO.01
on half this number of animals; n = number of animals.
Mean deviation for water content (&standard deviation) of the freezer sample compared with the ambient stored sample were 4.71 f 0.083 and 9.69 f 0.103 %, respectively. No correction was made for water content of the powder in any of these studies. Thus 3000 ppm of weighed water-containing powder used in the 1966 study was actually 2859 ppm of water-free sample, while the corrected ambient temperature sample contained 2739 ppm of water-free material. Cross comparisons between the two studies thus cannot be exact, but the increases seen in the ambient stored sample will be slightly greater (about +4x) than indicated by the data. Both samples contained the total expected iodide content (&standard deviation) and were indistinguishable one from the other, 0.185 & 0.0048 % (freezer stored) and 0.184 & 0.0047 % (ambient stored). No free iodide was found in either sample.
4.3 f 0.23 (24)b 3.9 * 0.44 (10) 4.7 f 0.26 (12) 4.4 f 0.21 (24) 4.1 + 0.31 (12) 4.7 f 0.24 (12) 4.6 f 0.15 (24) 4.6 rt 0.12 (24) 4.3 It 0.17 (24 4.1 + 0.12 (24
Control f SE
o t test. b Number of determinations c NS, not significant.
29
22
17
15
13
11
8
6
4
2
number
Day
CONSUMED,
on half
this
+48.7
+39.5
‘r47.8
4.001
-
+39.1
+43.9
CO.01
+34.1
-
-135.9
P”
>0.05 NS” 40.05
+20.9
Percent variation from control
MILLILITERS/GRAM/HOUR
2 TO
7.6 i 0.28 (12) 7.7 f 0.26 (12) 7.9 i 0.32 (12) 7.3 i 0.42 (1.3 7.2 zk 0.38 (12)
6.1 -I 0.32 (12) 7.0 dz0.29 (12) -
5.5 f 0.20 (12) -
STUDY)
t75.6
+69.7
+71.7
1-67.4
t61.7
+59.1
10.001
<0.001
10.001
CO.05
co.05
CO.05
10.02
-
(0.02
-
>0.05 NS -
____~_
Ambient versus Freezer Pa
(0.001
CO.01
-
+29.8
P”
+27.9
Percent variation from control
STP (1967
Ambient temp. stored thyroid i SE, 3000 ppm
CORRECTED
number of animals; n = number of animals.
6.4 + 0.39 W) 6.8 + 0.28 (12) 6.0 f 0.28 (12) 6.1 f 0.23 WI
5.9 f 0.25 w 5.9 f 0.27 (12) -
5.2 i 0.23 02) 5.3 h 0.31 (12) -
Freezer-stored thyroid f SE, 3000 pm
OXYGEN
TABLE
i
8 Q
g i3
5 k-3
21 3
52
WILLIAMS,
TOWNE,
AND
WILLIAMS
By our procedure the water content of the ambient temperature stored samples was found to deviate from the USP standard of not more than 6 %. Despite this difference, its thyromimetic potency is enhanced over short-period testing. It is also evident that the biological testing procedure is more effective in determining standards of potency than the official chemical procedures of the USP. TABLE 3 OXYGEN
Day 2 6 9” 13 16” 23”
CONSUMPTION WITH
OF THE ORIGINAL THYROID SAMPLE AMBIENT TEMPERATURE SAMPLE
COMPARED
Original sample 1966 f SE
Day
Ambient temp. sample 1967 f SE
4.2 f 0.19 5.5 f 0.80
2 6
5.5 f 0.20 6.1 f 0.32
4.8 5.6 6.1 6.2
f zt zt zt
0.92 0.42 0.35 0.42
8” 13 17” 22”
7.0 7.6 7.9 7.3
f f zt f
0.29 0.28 0.32 0.42
P co.01 20.05 NS*0.05 NS
a Days compared: 9 and 8; 16 and 17; 23 and 22 (one day separation in time). * NS, not significant. No difference in 17 amino acid levels were found between the ambient-stored sample and the freezer-stored sample. It is conceivable that a deiodination of thyroxine to triiodothyronine (T3 is a possible explanation of these findings. T3 is 20 times more potent than thyroxine (U. S. Pharmacopeia, 1965, pp. 622, 624) and a conversion of 1-2 % of thyroxine in thyroid to T3 with the loss of free iodine would produce a more active substance without notable chemical changes. Such may be the case here, as a 2% change would produce a substance having a calculated 138 % potency relative to the unchanged material. ACKNOWLEDGMENT We gratefully acknowledge the assistance of Dr. William F. McCaughey, Professor of Biochemistry, University of Arizona, in the amino acid analysis of the thyroid samples. REFERENCES GOODMAN, L. S., and GILMAN, A. (1965). ThePharmacologicalBasisof Therapeutics,3rd ed., pp. 1, 480. Macmillan, New York. KRANTZ, J. C., and CARR, C. J. (1961). ThePharmacologicPrinciplesof MedicalPractice, 5th ed., pp. 1, 334. Williams & Wilkins, Baltimore, Maryland. U. S. Pharmacopeia (1965). 17th Revision, Mack Publ., Easton, Pennsylvania. WIBERG?::G. S., DEVLIN, W. F., STEPHENSON, N. R., CARTER, J. R., and BAYNE, A. J. (1962). A comp&ison of the thyroxine tri-iodothyronine content and biological activity of thyroid from various species. J. Pharm. Pharmacol.14, 777-783.
POTENCY OF THYROID POWDER
53
WILLIAMS, M. W., and WILLIAMS, C. S. (1965). Depression of growth of Sarcoma 180 by hyperthyroidism. Cancer Chem. Rept. 34, l-4. WILLIAMS,M. W., WILLIAMS,C. S., and DEWITT, G. R. (1965).Temperatureand subspecies variation on the oxygen consumptionof the desertant Pogonomyrmex barbatus. Life Sci. 4, 603-606. WILLIAMS,M. W., WILLIAMS,C. S., and DEWIIT, G. R. (1966).Activity, weight and oxygen consumptionof hyperthyroid mice bearing Sarcoma180. Life Sci. 5, 545-549.
AND APPLIED PHARMACOLOGY14,48-53
Enhanced MARTIN
Potency
W. WILLIAMS,
(1969)
of Desiccated
Thyroid
Powder
JACK C. TOWNE, AND CHARLES S. WILLIAMS
Veterans Administration
Hospital, Tucson, Arizona 82713
Received January 12,1968
Enhanced Potency of Desiccated Thyroid Powder. WILLIAMS, MARTIN W., TOWNE, JACK C., and WILLIAMS, CHARLES S. (1969). Toxicol. Appl. Pharmacol. 14,48-53. Thyroid Powder, USP, when aged in uitro at room temperatures for 19 months, was found to be significantly more potent in the production of hyperthyroidism in female SwissWebster mice when fed ad libitum at approximately 3000 ppm in ground Purina Lab Chow, than a similar sample kept in a deep freeze at -23”. Potency was based upon the oxygen consumption-stimulating ability of the thyroid preparations. No significant difference in potency was noted between the freezer-stored thyroid sample and the original. Because of the seeming variations from lot to lot in the potency of thyroid powder, USP, fed to mice on tumor experiments (Williams and Williams, 1965; Williams et al., 1966), which was measured by oxygen consumption, an experiment was designed to determine whether, at room temperature, in vitro changes in potency with time could be observed. For many years the use of pelleted desiccated thyroid powder or other similar thyroid preparations to increase body metabolism has been considered a safe, reproducible, and inexpensive substitute for the more expensive purified thyroactive drugs, such as thyroxine, and indeed it may have some advantages (Goodman and Gilman, 1965). Standard potency has been assured, it was assumed, by control of iodine content as characterized in the U. S. Pharmacopeia (1965), which specifies that the iodine content be not less than 0.17 or more than 0.23 % and that this iodine be in thyroid combination, not in the form of iodide. The general consensus expressed (Krantz and Carr, 1961; Goodman and Gilman, 1965) has been that thyroid powder is stable for many years, losing neither iodine nor calorigenic potency. The improbability of increasing potency with in vitro age has apparently not been considered. The purpose of this work was to determine the changes, if any, in potency of similar samples of thyroid powder from the same lot both at the beginning of the experiment and again 19 months later. One sample was kept at ambient room temperatures and the second sample was kept in a deep freeze at -23”. METHODS In March, 1966, a IO-kg sample of desiccated thyroid powder USP was purchased.1 A sample of 43 g of this lot was separated from the remainder and put on the shelf in a 1 Nutritional Biochemicals, Cleveland, Ohio. 48
POTENCY OF THYROtD POWDER
49
brown chemical bottle at ambient temperature. The remaining powder was placed in a deep freeze, samples being removed as required for other experiments. Initial observations were made in April, 1966. Later assays were made in November and December, 1967. Mice used were female Swiss Websters, the average starting weight being 23.8 g (i.e., young adults). All animals were procured from a commercial supplier.2 All diets were given ad libitum and were prepared from ground lab chow,3 to which was added 3000 ppm of thyroid powder where needed. Control animals received ground chow only. Oxygen consumption observations on individual animals were made in a respirometer previously described (Williams et al., 1965). All oxygen consumption figures were converted to standard temperature and pressure (STP). Duplicate observations were made in all cases, thus the tabular data represent the averages of duplicate observations in all cases. The statistical method used was the Student’s t test, analysis being based upon the number of animals tested, not on the number of observations. Water content of the desiccated thyroid powders was determined by the difference in weight loss for the samples dried in aacuo over potassium hydroxide at room temperature for 72 hours. Amino acid analysis of acid and alkaline hydrolyzed samples was made in amino acid analyzer4 and tested for 17 amino acids. Free iodide and total iodide content of the anhydrous samples were determined by the methods of the U. S. Pharmacopeia (1965, p. 718).
RESULTS
AND DISCUSSION
The results of the 1966 study on the original sample of desiccated thyroid powder are shown in Table 1. The expected increase in oxygen consumption is seen from day 1I onward, although a significant increase was seen at day 6. Results of the 1967 study are shown in Table 2. Here again the expected increase is in evidence both in the freezer thyroid and the ambient temperature stored thyroid, but the percentages above control are greater for the ambient stored than for the freezer material. A statistical comparison of the ambient versus freezer thyroid powder (1967 study; Table 2), indicates a significant increase of the former over the latter in every case, i.e., days 8, 15, 17, 22, and 29, where comparisons are possible except at day 2. A cross comparison of the freezer thyroid sample (1967) with the original sample (1966) (Table 1) indicates no significant difference between the two at days 4 and 11 or when close time periods are compared, i.e., day 15 freezer sample versus day 16 original sample; or day 22 freezer sample versus day 23 original sample. From these data we may conclude that the freezer sample (tested in 1967) has the same potency (not statistically different) as the original sample when run in 1966. A comparison of data from the original sample tested in 1966 with the ambient temperature sample tested in 1967 can be made as shown in Table 3. 2 Simonsen Laboratories, 3 Purina. 4 Spinco Model 120B.
Gilroy, California.
50
WILLIAMS,
TOWNE, AND WILLIAMS
It is evident from Table 3 that, although on days 6 and 22-23 no significant difference is seen, the means in all cases are higher in the ambient than in the original sample, this being indicative of the trend. In all four other cases a highly significant difference is seen to exist. The hypothesis that elevated ambient temperatures, i.e., up to 120”F, or bacterial activity may have enhanced the conversion of thyroxine to triiodothyronine is a possibility. Wiberg et al. (1962) have shown thyroid powder to owe much of its thyromimetic effect to its contained triiodothyronine. TABLE 1 OXYGEN CONSUMED, MILLILITERS/GRAM/HOUR
Day number
CORRECTED TO STP (1966 STUDY)
Thyroid f SE original sample, Control f SE
3OOOppm
%
P”
2
3.7 i 0.29
4.2 f 0.19
+13.5
4
(lQb 4.2 & 0.43 (10)
(6)
6
9 11 13 16 23 32
3.5 Ito.
(10) 3.7 * 0.50 (10) 3.7 f 0.49 (10) 3.5 f 0.40 (10) 4.2zkO.18
4.6 dc0.22
+ 9.5
(10) 5.5 rk 0.80
>o.os NS’ BO.05 NS
$57.1
co.05
t-29.7
10.05
$54.0
co.02
5.6 f 0.42
+60.0
co.02
(10) 6.1 f 0.35
+45.2
+58.9
to.01
(8)
4.8 zt 0.92
(8)
5.7 it.45
(10)
(10) 3.9 + 0.18 (10) 3.2 ho.39
(10) 6.8 f 0.93
(10)
(8)
b Number of determinations c NS, not significant.
NS
03)
6.2 f 0.42
+112.5
CO.01
on half this number of animals; n = number of animals.
Mean deviation for water content (&standard deviation) of the freezer sample compared with the ambient stored sample were 4.71 f 0.083 and 9.69 f 0.103 %, respectively. No correction was made for water content of the powder in any of these studies. Thus 3000 ppm of weighed water-containing powder used in the 1966 study was actually 2859 ppm of water-free sample, while the corrected ambient temperature sample contained 2739 ppm of water-free material. Cross comparisons between the two studies thus cannot be exact, but the increases seen in the ambient stored sample will be slightly greater (about +4x) than indicated by the data. Both samples contained the total expected iodide content (&standard deviation) and were indistinguishable one from the other, 0.185 & 0.0048 % (freezer stored) and 0.184 & 0.0047 % (ambient stored). No free iodide was found in either sample.
4.3 f 0.23 (24)b 3.9 * 0.44 (10) 4.7 f 0.26 (12) 4.4 f 0.21 (24) 4.1 + 0.31 (12) 4.7 f 0.24 (12) 4.6 f 0.15 (24) 4.6 rt 0.12 (24) 4.3 It 0.17 (24 4.1 + 0.12 (24
Control f SE
o t test. b Number of determinations c NS, not significant.
29
22
17
15
13
11
8
6
4
2
number
Day
CONSUMED,
on half
this
+48.7
+39.5
‘r47.8
4.001
-
+39.1
+43.9
CO.01
+34.1
-
-135.9
P”
>0.05 NS” 40.05
+20.9
Percent variation from control
MILLILITERS/GRAM/HOUR
2 TO
7.6 i 0.28 (12) 7.7 f 0.26 (12) 7.9 i 0.32 (12) 7.3 i 0.42 (1.3 7.2 zk 0.38 (12)
6.1 -I 0.32 (12) 7.0 dz0.29 (12) -
5.5 f 0.20 (12) -
STUDY)
t75.6
+69.7
+71.7
1-67.4
t61.7
+59.1
10.001
<0.001
10.001
CO.05
co.05
CO.05
10.02
-
(0.02
-
>0.05 NS -
____~_
Ambient versus Freezer Pa
(0.001
CO.01
-
+29.8
P”
+27.9
Percent variation from control
STP (1967
Ambient temp. stored thyroid i SE, 3000 ppm
CORRECTED
number of animals; n = number of animals.
6.4 + 0.39 W) 6.8 + 0.28 (12) 6.0 f 0.28 (12) 6.1 f 0.23 WI
5.9 f 0.25 w 5.9 f 0.27 (12) -
5.2 i 0.23 02) 5.3 h 0.31 (12) -
Freezer-stored thyroid f SE, 3000 pm
OXYGEN
TABLE
i
8 Q
g i3
5 k-3
21 3
52
WILLIAMS,
TOWNE,
AND
WILLIAMS
By our procedure the water content of the ambient temperature stored samples was found to deviate from the USP standard of not more than 6 %. Despite this difference, its thyromimetic potency is enhanced over short-period testing. It is also evident that the biological testing procedure is more effective in determining standards of potency than the official chemical procedures of the USP. TABLE 3 OXYGEN
Day 2 6 9” 13 16” 23”
CONSUMPTION WITH
OF THE ORIGINAL THYROID SAMPLE AMBIENT TEMPERATURE SAMPLE
COMPARED
Original sample 1966 f SE
Day
Ambient temp. sample 1967 f SE
4.2 f 0.19 5.5 f 0.80
2 6
5.5 f 0.20 6.1 f 0.32
4.8 5.6 6.1 6.2
f zt zt zt
0.92 0.42 0.35 0.42
8” 13 17” 22”
7.0 7.6 7.9 7.3
f f zt f
0.29 0.28 0.32 0.42
P co.01 20.05 NS*
a Days compared: 9 and 8; 16 and 17; 23 and 22 (one day separation in time). * NS, not significant. No difference in 17 amino acid levels were found between the ambient-stored sample and the freezer-stored sample. It is conceivable that a deiodination of thyroxine to triiodothyronine (T3 is a possible explanation of these findings. T3 is 20 times more potent than thyroxine (U. S. Pharmacopeia, 1965, pp. 622, 624) and a conversion of 1-2 % of thyroxine in thyroid to T3 with the loss of free iodine would produce a more active substance without notable chemical changes. Such may be the case here, as a 2% change would produce a substance having a calculated 138 % potency relative to the unchanged material. ACKNOWLEDGMENT We gratefully acknowledge the assistance of Dr. William F. McCaughey, Professor of Biochemistry, University of Arizona, in the amino acid analysis of the thyroid samples. REFERENCES GOODMAN, L. S., and GILMAN, A. (1965). ThePharmacologicalBasisof Therapeutics,3rd ed., pp. 1, 480. Macmillan, New York. KRANTZ, J. C., and CARR, C. J. (1961). ThePharmacologicPrinciplesof MedicalPractice, 5th ed., pp. 1, 334. Williams & Wilkins, Baltimore, Maryland. U. S. Pharmacopeia (1965). 17th Revision, Mack Publ., Easton, Pennsylvania. WIBERG?::G. S., DEVLIN, W. F., STEPHENSON, N. R., CARTER, J. R., and BAYNE, A. J. (1962). A comp&ison of the thyroxine tri-iodothyronine content and biological activity of thyroid from various species. J. Pharm. Pharmacol.14, 777-783.
POTENCY OF THYROID POWDER
53
WILLIAMS, M. W., and WILLIAMS, C. S. (1965). Depression of growth of Sarcoma 180 by hyperthyroidism. Cancer Chem. Rept. 34, l-4. WILLIAMS,M. W., WILLIAMS,C. S., and DEWITT, G. R. (1965).Temperatureand subspecies variation on the oxygen consumptionof the desertant Pogonomyrmex barbatus. Life Sci. 4, 603-606. WILLIAMS,M. W., WILLIAMS,C. S., and DEWIIT, G. R. (1966).Activity, weight and oxygen consumptionof hyperthyroid mice bearing Sarcoma180. Life Sci. 5, 545-549.