- Email: [email protected]
Comparison of the Effect of Feeding Thiobarbital and Thiouracil on the Thyroid Gland of the Chick*,1
Comparison of the Effect of Feeding Thiobarbital and Thiouracil on the Thyroid Gland of the Chick*1 C. W.
TURNER
Department of Dairy Husbandry, University of Missouri (Received for publication May 6, 1946)
I
N PREVIOUS reports from this laboratory (Mixner, Reineke and Turner, 1944; Schultze and Turner, 1945), comparisons have been made of the goitrogenicity of thiourea and thiouracil when fed to chicks of various ages. Due to the narrow margin between the toxic and physiological dosage and the low potency of thiourea (Reineke and Turner, 1945), this compound has been eliminated from further consideration by most investigators. The practical value of goitrogenic agents in the fattening of broilers is suggested by the observations of Kempster and Turner (1945) and Andrews and Schnetzler (1946). Many compounds of a diverse nature have been assayed biologically in order to find more active preparations. Of these, thiobarbital was reported by Astwood et al. (1945) to be somewhat more effective than thiouracil in the rat, and twice as active in inhibiting the function of the thyroid gland in man (Astwood, 1945). McGinty and Bywater (1945) gave thiobarbital a rating of 123 in comparison with thiouracil which was rated as 100 in tests using the reduction in thyroid iodine in the immature rat as * Contribution from the Missouri Agricultural Experiment Station, Journal Series No. 1004. 1 1 am indebted to Dr. E. E. Sweebe of Abbott Laboratories for a supply of thiobarbital, and to Dr. Mark Welsh of Lederle Laboratories for the thiouracil. 517
the basis of comparison. Astwood et al. (1945) recently rated thiobarbital as 170, using rats and a technique based upon thyroid size and iodine reduction. These observations indicate the desirability of further study of this compound in influencing the thyroids of fowls and as an agent to accelerate the fattening rate of broilers. The present paper has as its object to report upon a comparison of the goitrogenicity of thiobarbital and thiouracil in White Plymouth Rock chicks using the average thyroid weight as an index of activity. For comparison, the previous observations from our laboratory upon the goitrogenicity of thiourea for both White Plymouth Rocks and White Leghorns will be included. EXPERIMENTAL
Ten groups of approximately 20 White Plymouth Rock chicks each were placed in two adjoining brooders. Thiouracil and thiobarbital were mixed with the complete ration in the following amounts: 0.1, 0.05, 0.025, 0.0125, and 0.00625%. The highest concentration of each substance was fed to the chicks in the top pens and other concentrations of the two substances were fed at comparable levels of the brooders so that environmental factors would be similar for chicks fed the two compounds. After a three-week feeding period, the chicks were weighed, sacrificed, and the
518
C. W. TURNER
TABLE 1.—Comparison of thiouracil and thiobarbital on the thyroid gland of 3-week-old White Rock chicks 0 . 1 % Level Thiouracil No. of chicks & sex
Ave. bo. wt. gm.
21 12 M 9F
131.5 131.3 131.9
Thiobarbital
Ave. Thyroid wt. thyroid — • wt. mg. 100 gm. body wt. 53.93 48.78 60.78
41.01 37.16 46.08
No. of chicks & sex
Ave. bo. wt. gm.
Ave. Thyroid wt. thyroid wt. mg. 100 gm. body wt.
21 7M 14 F
98.1 91.9 101.2
64.2 33.25 79.65
65.4 36.20 78.69
134.4 131.9 138.7
74.9 64.1 93.6
55.73 48.59 67.48
164.2 165.1 163.2
87.74 87.73 87.75
53.43 53.13 53.76
182.4 194.4 173.4
40.94 40.93 40.95
22.44 21.05 23.61
198.5 203.2 196.8
39.23 39.08 39.29
"19.76 19.23 19.96
0.05% Level 20 8M 12 F
157.0 160.8 154.4
84.38 76.93 87.76
53.74 47.82 56.83
19 12 M 7F 0.025% Level
21 8M 13 F
170.8 165.0 174.3
58.07 63.35 54.82
33.99 38.39 31.43
19 10 M 9F
0,0125% Level 21 13 M 8F
187.7 187.9 187.3 '
22.48 23.36 21.03
11.97 12.43 11.22
21 9M 12 F
0.00625% Level 19 13 M 6F
204.4 206.5 200.0
24.78 23.60 27.35
12.12 11.42 13.67
thyroids weighed and sex determined. These observations are summarized in Table 1. It will be seen that thiobarbital at the 0.1% level restricted body weight rather markedly and with decreasing levels of substance, the body weight increased rather regularly. The average body weight of the chicks on 0.1% thiouracil was somewhat heavier than those on thiobarbital. They also increased in average body weight with decreasing dosage. The maximum increase in actual thyroid weight or relative weight in relation to body weight for thiouracil was observed at the 0.05% level of feeding. It was still quite effective at the 0.025% level but dropped off rapidly to the control level on lower dosages.
19 5M 14 F
The thiobarbital was effective in stimulating large thyroid weight increases down to the 0.025% level. Even at the two lower levels of administration, the thyroids . were still about twice the size of normal White Plymouth Rock chicks and compare with the goitrogenicity of thiourea at its optimum level. These data are interpreted as indicating that thiobarbital possesses about twice the goitrogenicity of thiouracil when administered orally to White Plymouth Rock chicks at the 0.025% level. Since high physiological activity is exhibited at this low level, thiobarbital should be an effectiye fattening agent when incorporated in the fattening ration of broilers in that amount. It suggests further that thiouracil at the 0.05% level should be
519
E F F E C T OF T H I O B A R B I T A L AND T H I O U R A C I L ON T H Y R O I D
effective in the fattening ration. To present a summary of our data in graphic form, the average thyroid weight per 100 gm. body weight of each sex has been added together and the product
0 NH„
HC—NH
C=S
HC C=S
1 1
NH2 Thiourea
II 1
C—NH
X/
11
1
C
0=C—NH Thiouracil
II
C2H5
C=S
/ \ C2H6
1 C—NH
II
0 Thiobarbital (S-5-diethyl-2-thiobar bituric acid) com• It will be noted that these three
pounds have in common the HN—C—NH
.006.012 -OiS .02$
.037
.OSO
.0?i
CONTENT IN RATION-PCR CENT
FIG. 1. Comparison of the goitrogenic action of thiourea, thiouracil and thiobarbital in varying concentration in the feed of White Plymouth Rock chicks measured at three weeks of age.
divided by 2. This should approximate the effect of the compounds in a population of equal numbers of the two sexes (Fig. 1). DISCUSSION
Since the discovery of the goitrogenicity of thiourea and its derivatives and many related compounds, a vast amount of research work has been conducted to determine their mode of action and the most effective compounds. It is now quite generally agreed that these compounds inhibit the secretion of thyroxine by the thyroid gland. Thus, there is produced a condition comparable to the removal of the thyroid glands, i.e., a chemical thyroidectomy. Under these conditions, the energy metabolism is reduced, the tendency toward growth is reduced, and the deposition of fat is accelerated. The structural formula of the three compounds studied most extensively using chicks are presented herewith:
radicle which appears to be essential for highest goitrogenic action. The present data indicates that thiourea is very inferior to the other compounds. At the 0.05% level thiouracil and thiobarbital are about equal in goitrogenic action. The difference between these two compounds in the chick is the equally high activity of thiobarbital at the 0.025% level, whereas thiouracil is only slightly more than § as effective. SUMMARY
The goitrogenicity of thiouracil and thiobarbital was determined by feeding graded amounts of these two compounds in the starter ration of White Plymouth Rock day-old chicks for a period of three weeks. At the 0.1 and 0.05% levels, the thyroid weights of the chicks per 100 gm. body weight were only slightly larger where thiobarbital was fed. The significant difference in activity of these two compounds was observed at the 0.025% level. The average thyroid weights of the group fed thiobarbital were still the same as at higher levels, whereas the average thyroid weights of the thiouracil-fed group were considerably lighter. As goitrogenic agents, it is suggested that thiobarbital at the 0.025% level and thiouracil at the 0.05% level should be equally effective when added to a broiler ration.
520
.
C. W, TURNER
REFERENCES
Andrews, F. N. and E. E. Schnetzler, 1946. The influence of thiouracil on growth and fattening in broilers. Poultry Sci., 25: 124-129. Astwood, E. B., 1945. Some observations on the use of thiobarbital as an antithyroid agent in the treatment of Graves' disease. J. Clin. Endocrinology. 5: 345-352. — , A. Bissell, and A. M. Hughes, 1945. The antithyroid activity of thiobarbital (5,5-diethyl-2thiobarbituric acid). Endocrinology. 36: 72-74. , 1945. Further studies on the chemical nature of compounds which inhibit the function of the thyroid gland. Endocrinology. 37:456-481. Kempster, H. L. and C. W. Turner, 1945. The effect
of feeding thiouracil on the fleshing of New Hampshire broilers. Poultry Sci. 24: 94-96. McGinty, D. A. and W. G. Bywater, 1945. Antithyroid studies. I. The goitrogenic activity of some thioureas, pyrimidines and miscellaneous compounds. J. Pharm. & Exp. Therap. 84: 342357. Mixner, J. P., E. P. Reineke, and C. W. Turner, 1944. Effect of thiouracil and thiourea on the thyroid gland of the chick. Endocrinology. 34: 168-174. Schultze, A. B. and C. W. Turner, 1945. The determination of the rate of thyroxine secretion by certain domestic animals. Mo. Agr. Exp. Sta. Res. Bui. 392.
TURNER
Department of Dairy Husbandry, University of Missouri (Received for publication May 6, 1946)
I
N PREVIOUS reports from this laboratory (Mixner, Reineke and Turner, 1944; Schultze and Turner, 1945), comparisons have been made of the goitrogenicity of thiourea and thiouracil when fed to chicks of various ages. Due to the narrow margin between the toxic and physiological dosage and the low potency of thiourea (Reineke and Turner, 1945), this compound has been eliminated from further consideration by most investigators. The practical value of goitrogenic agents in the fattening of broilers is suggested by the observations of Kempster and Turner (1945) and Andrews and Schnetzler (1946). Many compounds of a diverse nature have been assayed biologically in order to find more active preparations. Of these, thiobarbital was reported by Astwood et al. (1945) to be somewhat more effective than thiouracil in the rat, and twice as active in inhibiting the function of the thyroid gland in man (Astwood, 1945). McGinty and Bywater (1945) gave thiobarbital a rating of 123 in comparison with thiouracil which was rated as 100 in tests using the reduction in thyroid iodine in the immature rat as * Contribution from the Missouri Agricultural Experiment Station, Journal Series No. 1004. 1 1 am indebted to Dr. E. E. Sweebe of Abbott Laboratories for a supply of thiobarbital, and to Dr. Mark Welsh of Lederle Laboratories for the thiouracil. 517
the basis of comparison. Astwood et al. (1945) recently rated thiobarbital as 170, using rats and a technique based upon thyroid size and iodine reduction. These observations indicate the desirability of further study of this compound in influencing the thyroids of fowls and as an agent to accelerate the fattening rate of broilers. The present paper has as its object to report upon a comparison of the goitrogenicity of thiobarbital and thiouracil in White Plymouth Rock chicks using the average thyroid weight as an index of activity. For comparison, the previous observations from our laboratory upon the goitrogenicity of thiourea for both White Plymouth Rocks and White Leghorns will be included. EXPERIMENTAL
Ten groups of approximately 20 White Plymouth Rock chicks each were placed in two adjoining brooders. Thiouracil and thiobarbital were mixed with the complete ration in the following amounts: 0.1, 0.05, 0.025, 0.0125, and 0.00625%. The highest concentration of each substance was fed to the chicks in the top pens and other concentrations of the two substances were fed at comparable levels of the brooders so that environmental factors would be similar for chicks fed the two compounds. After a three-week feeding period, the chicks were weighed, sacrificed, and the
518
C. W. TURNER
TABLE 1.—Comparison of thiouracil and thiobarbital on the thyroid gland of 3-week-old White Rock chicks 0 . 1 % Level Thiouracil No. of chicks & sex
Ave. bo. wt. gm.
21 12 M 9F
131.5 131.3 131.9
Thiobarbital
Ave. Thyroid wt. thyroid — • wt. mg. 100 gm. body wt. 53.93 48.78 60.78
41.01 37.16 46.08
No. of chicks & sex
Ave. bo. wt. gm.
Ave. Thyroid wt. thyroid wt. mg. 100 gm. body wt.
21 7M 14 F
98.1 91.9 101.2
64.2 33.25 79.65
65.4 36.20 78.69
134.4 131.9 138.7
74.9 64.1 93.6
55.73 48.59 67.48
164.2 165.1 163.2
87.74 87.73 87.75
53.43 53.13 53.76
182.4 194.4 173.4
40.94 40.93 40.95
22.44 21.05 23.61
198.5 203.2 196.8
39.23 39.08 39.29
"19.76 19.23 19.96
0.05% Level 20 8M 12 F
157.0 160.8 154.4
84.38 76.93 87.76
53.74 47.82 56.83
19 12 M 7F 0.025% Level
21 8M 13 F
170.8 165.0 174.3
58.07 63.35 54.82
33.99 38.39 31.43
19 10 M 9F
0,0125% Level 21 13 M 8F
187.7 187.9 187.3 '
22.48 23.36 21.03
11.97 12.43 11.22
21 9M 12 F
0.00625% Level 19 13 M 6F
204.4 206.5 200.0
24.78 23.60 27.35
12.12 11.42 13.67
thyroids weighed and sex determined. These observations are summarized in Table 1. It will be seen that thiobarbital at the 0.1% level restricted body weight rather markedly and with decreasing levels of substance, the body weight increased rather regularly. The average body weight of the chicks on 0.1% thiouracil was somewhat heavier than those on thiobarbital. They also increased in average body weight with decreasing dosage. The maximum increase in actual thyroid weight or relative weight in relation to body weight for thiouracil was observed at the 0.05% level of feeding. It was still quite effective at the 0.025% level but dropped off rapidly to the control level on lower dosages.
19 5M 14 F
The thiobarbital was effective in stimulating large thyroid weight increases down to the 0.025% level. Even at the two lower levels of administration, the thyroids . were still about twice the size of normal White Plymouth Rock chicks and compare with the goitrogenicity of thiourea at its optimum level. These data are interpreted as indicating that thiobarbital possesses about twice the goitrogenicity of thiouracil when administered orally to White Plymouth Rock chicks at the 0.025% level. Since high physiological activity is exhibited at this low level, thiobarbital should be an effectiye fattening agent when incorporated in the fattening ration of broilers in that amount. It suggests further that thiouracil at the 0.05% level should be
519
E F F E C T OF T H I O B A R B I T A L AND T H I O U R A C I L ON T H Y R O I D
effective in the fattening ration. To present a summary of our data in graphic form, the average thyroid weight per 100 gm. body weight of each sex has been added together and the product
0 NH„
HC—NH
C=S
HC C=S
1 1
NH2 Thiourea
II 1
C—NH
X/
11
1
C
0=C—NH Thiouracil
II
C2H5
C=S
/ \ C2H6
1 C—NH
II
0 Thiobarbital (S-5-diethyl-2-thiobar bituric acid) com• It will be noted that these three
pounds have in common the HN—C—NH
.006.012 -OiS .02$
.037
.OSO
.0?i
CONTENT IN RATION-PCR CENT
FIG. 1. Comparison of the goitrogenic action of thiourea, thiouracil and thiobarbital in varying concentration in the feed of White Plymouth Rock chicks measured at three weeks of age.
divided by 2. This should approximate the effect of the compounds in a population of equal numbers of the two sexes (Fig. 1). DISCUSSION
Since the discovery of the goitrogenicity of thiourea and its derivatives and many related compounds, a vast amount of research work has been conducted to determine their mode of action and the most effective compounds. It is now quite generally agreed that these compounds inhibit the secretion of thyroxine by the thyroid gland. Thus, there is produced a condition comparable to the removal of the thyroid glands, i.e., a chemical thyroidectomy. Under these conditions, the energy metabolism is reduced, the tendency toward growth is reduced, and the deposition of fat is accelerated. The structural formula of the three compounds studied most extensively using chicks are presented herewith:
radicle which appears to be essential for highest goitrogenic action. The present data indicates that thiourea is very inferior to the other compounds. At the 0.05% level thiouracil and thiobarbital are about equal in goitrogenic action. The difference between these two compounds in the chick is the equally high activity of thiobarbital at the 0.025% level, whereas thiouracil is only slightly more than § as effective. SUMMARY
The goitrogenicity of thiouracil and thiobarbital was determined by feeding graded amounts of these two compounds in the starter ration of White Plymouth Rock day-old chicks for a period of three weeks. At the 0.1 and 0.05% levels, the thyroid weights of the chicks per 100 gm. body weight were only slightly larger where thiobarbital was fed. The significant difference in activity of these two compounds was observed at the 0.025% level. The average thyroid weights of the group fed thiobarbital were still the same as at higher levels, whereas the average thyroid weights of the thiouracil-fed group were considerably lighter. As goitrogenic agents, it is suggested that thiobarbital at the 0.025% level and thiouracil at the 0.05% level should be equally effective when added to a broiler ration.
520
.
C. W, TURNER
REFERENCES
Andrews, F. N. and E. E. Schnetzler, 1946. The influence of thiouracil on growth and fattening in broilers. Poultry Sci., 25: 124-129. Astwood, E. B., 1945. Some observations on the use of thiobarbital as an antithyroid agent in the treatment of Graves' disease. J. Clin. Endocrinology. 5: 345-352. — , A. Bissell, and A. M. Hughes, 1945. The antithyroid activity of thiobarbital (5,5-diethyl-2thiobarbituric acid). Endocrinology. 36: 72-74. , 1945. Further studies on the chemical nature of compounds which inhibit the function of the thyroid gland. Endocrinology. 37:456-481. Kempster, H. L. and C. W. Turner, 1945. The effect
of feeding thiouracil on the fleshing of New Hampshire broilers. Poultry Sci. 24: 94-96. McGinty, D. A. and W. G. Bywater, 1945. Antithyroid studies. I. The goitrogenic activity of some thioureas, pyrimidines and miscellaneous compounds. J. Pharm. & Exp. Therap. 84: 342357. Mixner, J. P., E. P. Reineke, and C. W. Turner, 1944. Effect of thiouracil and thiourea on the thyroid gland of the chick. Endocrinology. 34: 168-174. Schultze, A. B. and C. W. Turner, 1945. The determination of the rate of thyroxine secretion by certain domestic animals. Mo. Agr. Exp. Sta. Res. Bui. 392.