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Measurement of the Thyroid Hormone Secretion Rate of Individual Fowls*†
36
H. S. WEISS Am. J. Physiol. 174:405^07. Sturkie, P. D. ; H. S. Weiss and R. K. Ringer, 1954. Effects of injections of acetylcholine and ephedrine upon components of the hen's egg. Poultry Sci. 33: 18-24. Weiss, H. S., and P. D. Sturkie, 1951. An indirect method for measuring blood pressure in the fowl. Poultry Sci. 30: 587-592. Wiggers, C. J., 1949. Physiology in Health and Disease. 5th ed. Lea & Febiger, Philadelphia, Pennsylvania.
Measurement of the Thyroid Hormone Secretion Rate of Individual Fowls* t G. W. PIPES, B. N. PREMACHANDRA AND C. W. TURNER Department of Dairy Husbandry, University of Missouri, Columbia (Received for publication June 17, 1957)
S
INCE the rate of thyroid hormone; secretion is an important factor ini growth rate (Winchester and Davis, 1952)I and egg production (Winchester andl Scarborough, 1953), studies were undertaken to develop methods for determination of the thyroxine secretion rate in intact fowls. The earlier techniques of simultaneousi administration of thyroxine and thiouracil1 (Mixner et al., 1944) require sacrifice off the fowls and can be used only to measure; the average thyroid hormone secretionl rate of groups rather than of individual1 fowls. When I131 became available, Pipes et al. (1950) proposed that the thyroxine secretion rate could be determined in the intact rat by the injection of graded1 amounts of thyroxine up to the level1 which would inhibit thyrotropin secre* Contribution from the Missouri Agr. Exp. Sta. Journal Series No. 1761. Approved by the Director. , t Aided-in-part by a grant from the U.S. Atomic Energy Commission Contract No. AT(11-1)-301.
tion. This level would be shown by the effect upon the collection of I131 by the thyroid gland and the amount of proteinbound-P 31 in the blood. This plan of measuring thyroxine secretion has been explored by Pipes and Turner (1956) in cattle, by Henneman et al. (1952) in sheep and by Biellier and Turner (1957) in fowls. The method developed in this laboratory for the measurement of the thyroid hormone secretion rate of individual fowls by the use of I131 required serial blood sampling. In addition, due to lack of sufficiently sensitive detecting apparatus, the dosage of I131 sufficient to be detected in the blood approached the level that might damage the function of the thyroid glands (Biellier and Turner, 1957). With more sensitive detecting apparatus available, the possibility of measuring thyroid hormone secretion rate in individual birds by means of an in vivo method was explored. In this method, the two above difficulties would be eliminated.
Downloaded from http://ps.oxfordjournals.org/ at Uniwersytet Warszawski Biblioteka Uniwersytecka on June 20, 2015
Nalbandov, A. V., and M. F. James, 1949. The blood-vascular system of the chicken ovary. Am. J. Anat. 85: 347-378. Romanoff, A. L., and A. L. Romanoff, 1949. The Avian Egg. John Wiley & Sons, Inc., New York, N . Y. Sturkie, P. D., R. K. Ringer and H. S. Weiss, 1956. Inheritance of blood pressure and its relationship to mortality in chickens. Fed. Proc. 15: 182. Sturkie, P. D., H. S. Weiss and R. K. Ringer, 1953. Effects of age on blood pressure in the chicken.
INDIVIDUAL THYROXINE SECRETION RATE
secretion rates for rapid growth and high egg production. EXPERIMENTAL PROCEDURE AND RESULTS
The Determination of Thyroidal I131.— The bird is placed in a weighing funnel of suitable size. Portions of the side of the funnel were removed to expose the thyroid area. Measurements of thyroidal I131 are made with a scintillation counter which included a 1"X1" N a l crystal and which is connected by a twenty foot coaxial cable to a combination analytical ratemeter and scaler. The scintillation counter is mounted on a flexible arm of local design. Attached to the front of the scintillation counter is a plastic spacer which maintains a distance of 15 centimeters between the counter and the bird. In operation the top of the plastic spacer is placed at the point of the keel bone (Figure 1). Highest counting rates were consistently observed in this area. Since the thyroid gland lies within the body of the bird, it is apparently impossible to measure thyroidal I131 without measuring some body radiation. Little change was noticed between the ratio of thyroidal I131 to body I131 after 24 hours and most of the I131 is concentrated in the thyroid at that time. Conventional corrections are made for radioactive decay through the use of I131 standards and for background readings. All results are expressed as percent of injected dose. Carrier free Nal 131 is injected either by the subcutaneous or intraperitoneal route. Measurements of thyroidal I131 are made at 24 hour intervals. Maximum accumulation of I131 in the thyroid gland ranged from 24 hour or less to 48 hours. Measurement of Rate of Release of Thyroidal Im.—Following the rapid uptake of P 31 by the bird's thyroid glands during
Downloaded from http://ps.oxfordjournals.org/ at Uniwersytet Warszawski Biblioteka Uniwersytecka on June 20, 2015
The amount of I131 injected into each bird could be reduced, and the measurement of the amount of I131 released by the thyroid gland eliminated the need of serial blood sampling and serious disturbance to the birds involved. The object of the present paper is to describe a method by which these improvements in technique are made possible. The measurement of the individual thyroxine secretion rates of growing and laying birds is now feasible. Uses of the Method.—While growth rate and egg production have been shown to be dependent upon thyroxine secretion, it will now be possible to directly determine the influence of increasing thyroxine secretion upon the growth rate. The thyroxine secretion rate of individual chicks may be determined and then correlated with their growth rate. If it can be shown that the growth rate increases with increasing thyroxine secretion rate, then the birds with low thyroxine secretion rate may be discarded and only birds of high thyroxine secretion rate selected for breeding purposes. Similarly, the individual thyroxine secretion rate of pullets going into lay can be determined and their egg laying capacity can be related to their thyroxine secretion rate. If there is a close correlation between thyroxine secretion rate and egg production, the value of the thyroxine secretion rate as a selective index will be indicated. Finally, if these two characters, growth and egg production, are shown to be influenced by the thyroxine secretion rate, it will be possible to determine the mode of inheritance of thyroxine secretion rate by ma tings of highXhigh, highXlow, etc., and note the average thyroxine secretion rate of the progeny. This information should make possible the selection and breeding of birds of optimal thyroxine
37
38
G. W. PIPES, B. N. PREMACHANDRA AND C. W. TURNER
RATE METER
® /SPACER /
(10CM.)
^LEXIBLE ARM
MEASURMENT OF THYROIDAL I IN THE FOWL
FIG. 1. Measurement of thyroidal I131 in the fowl with scintillation counter and rate meter.
the first 2 days or less, the I131 is converted into Il31-labeled thyroglobulin. I131-tagged thyroxine is then gradually released into the blood stream reducing the amount of radioactivity in the thyroid glands (Figure 2). Daily measurements of the radioactivity of the thyroid glands then indicate the rate of discharge of thyroxine. It might be thought that the rate of decline of radioactivity in the thyroid glands would serve as an index of thyroxine secretion. However, there is a complicating factor in such measurements. As I131-tagged thyroxine is discharged into the blood and is utilized by the tissues of the body, it is metabolized and some of the I131 is set free from the thyroxine molecule by a process of deiodination. The inorganic I131 passes from the cells into the blood and may again be picked up, in part, by the thyroid glands. This process is called "reutilization" or "recycling" of I131. Since the I131 which is recycled cannot be distinguished from the original injected I131, the rate of release of
I131-tagged thyroxine from the thyroid glands is obscured by the continuous uptake of I131 from metabolized thyroxine. In order to obtain the true rate of release of thyroxine-I131 from the thyroid glands, it is necessary to block the recycling of I131 from metabolized thyroxine. The use of the goitrogens such as thiouracil was, therefore, explored. The amount of thiouracil required to block the synthesis of thyroxine by the fowl thyroid gland has been determined (Schultze and Turner, 1945). The Effect oj Thiouracil upon the Apparent Release of Thyroidal Im.—Since thiouracil inhibits the further formation of thyroxine from inorganic iodine, the thyroid gland loses its ability to hold inorganic iodine (Adams and Purves, 1951) which, in effect, prevents the thyroid from utilizing iodine from metabolized hormone as well as from the diet. Under these conditions the net rate of release of thyroidal I131 is accelerated. Three mature New Hampshire hens
Downloaded from http://ps.oxfordjournals.org/ at Uniwersytet Warszawski Biblioteka Uniwersytecka on June 20, 2015
•WEIGHING FUNNEL
39
INDIVIDUAL THYROXINE SECRETION RATE
so • THIOURACIL 0,1% Or RATION
1
0
•
1
•
2
•
3
'
4
•
5
6 DArS
'
'
7
I
8
I
9
L-
10
FIG. 2. The effect of thiouracil on the apparent rate of release of thyroidal I131 (thyroid hormone) from the gland. After measurements were made for a five day control period, all fowls were fed thiouracil and measurements continued. Thiouracil inhibited the reutilization of I m from metabolized hormone and thyroid hormone secretion consisted of stored hormone only.
The increasing amounts of exogenous thyroxine gradually suppresses the secretion of the thyrotropic hormone of each bird in relation to their endogenous secretion rates. When an amount of thyroxine is injected equal to the bird's secretion rate, the further discharge of thyrotropin is blocked. The lack of thyrotropin in the blood then inhibits the further discharge of thyroxine. This point is indicated when the daily reading of radioactivity does not change. The level of thyroxine injection at which endogenous thyroxine discharge is blocked is believed to indicate the equivalent thyroxine secretion rate of the bird. It is not necessary to completely block the uptake of recycled I131 with thiouracil, but only to inhibit uptake to the point
Downloaded from http://ps.oxfordjournals.org/ at Uniwersytet Warszawski Biblioteka Uniwersytecka on June 20, 2015
were injected with 50 microcuries of I131 and daily measurements of thyroidal I131 were made for 5 days (Figure 2). At the end of this period thiouracil was fed as 0.1% of the ration. As had been anticipated, a more rapid apparent rate of release of thyroidal I131 was observed. In both phases of the experiment observed values followed the predicted values very closely, indicating small standard deviations. These data indicate the technique was sufficiently sensitive to measure small day-to-day reductions in thyroidal I131 as thyroxine is discharged into the blood. As further synthesis of thyroxine is blocked by the goitrogen, the rate of release of the preformed thyroxine is measured. Since it is shown that rate of release follows a regular course, the time required to deplete the supply of stored hormone can be estimated. Differences in the rate of release of thyroxine in individual birds provides a qualitative measure of differences in thyroxine secretion rate, however, it does not provide a quantitative measure. To estimate the amount of thyroxine secreted per day, the following method was developed. Estimation of the Daily Thyroxine Secretion Rate.—Three mature New Hampshire hens were injected with 50 microcuries of I131 and daily thyroid counts were made for 6 days. At this time thiouracil was fed as 0.1 percent of the ration. Once again all birds responded to thiouracil by an increase in the apparent rate of release of thyroidal I131 (Figure 3). On the third day of thiouracil feeding, purified Lthyroxine was injected subcutaneously with the dose being increased daily as follows: 0.5, 1.0, 1.5, 2.0, 4.0, 5.0 and 6 micrograms per 100 grams body weight. As shown in Figure 3, two birds showed a complete inhibition of I131-tagged hormone release at 2.0 micrograms while one required 5.0 micrograms.
40
G. W. PIPES, B. N. PREMACHANDRA AND C. W. TURNER
80THIOURACIL
60
0.1 %
OF RATION
THYROXINE 1.0
40
X / 1 0 0 GRAMS 2.0
THYROXINE SECRETION
Q20
7516 Ibid 7585
i 10-
< g
o
cc >- 6I
° * •
NEW HAMPSHIRE
V V
I
7
8 9 [>AYS
10
11-12
13
_1_
14
_l_
15
FIG. 3. The method of estimating the thyroid hormone secretion rate of the fowl. Arrows indicate the dosage of L-thyroxine which blocked the secretion of thyrotropic hormone and, consequently, the release of radiothyroxine from the gland as shown by the measurement on the following day.
where increased accuracy results due to a more rapid apparent rate of release of thyroidal I131 (Premachandra et al., 1958). DISCUSSION
The technique here described for measurement of thyroidal I131 in fowls produces highly reproducible results since the counter is located at a sufficient distance to minimize small variations in thyroid location. The inverse square law, i.e., the intensity of radiation is inversely proportional to the square of the distance between the radiation source and the point of measurement indicates that small variations in thyroid position should not be an important factor when measurements are made at a 15 centimeter distance. If the rate of release of thyroidal I131 were sufficiently rapid, thiouracil could be
omitted from the ration during the test period. In the present work the use of thiouracil increased the sensitivity of the technique and made possible more accurate estimation of the secretion rate since the point of blockage of thyroxine discharge is more clearly indicated. SUMMARY
1. An improved technique for the estimation of the thyroxine secretion rate of fowls is described. It involves the daily measurement of thyroidal-I131 in place of the measurement of blood I131. As thyroxine is discharged into the blood, the amount of thyroidal I131 gradually declines. 2. When thiouracil, at a level of 0.1% of the ration, is fed, the recycling of I131 formed as a product of thyroxine metabo-
Downloaded from http://ps.oxfordjournals.org/ at Uniwersytet Warszawski Biblioteka Uniwersytecka on June 20, 2015
o
1.5
INDIVIDUAL THYROXINE SECRETION RATE
ACKNOWLEDGMENT
The authors wish to express their appreciation to Dr. R. F. Elliott, of the Research Division, American Cyanamid Company, who generously supplied the thiouracil used in these studies; to Mr. E. R. Thompson, Jr., for technical assist-
ance and to Mr. Elbert F. Turner, Jr., for help in care and handling of the animals. REFERENCES Adams, D. D., and H. D. Purves, 1951. The effect of methylthiouracil and of iodine on secretion of radioactive iodine by the human thyroid. Proc. Univ. Otago Medical School Res. Soc. 29(3): 1-2. Biellier, H. V., and C. W. Turner, 1957. The thyroid hormone secretion rate of domestic fowls as determined by the goitrogen and radio-iodine techniques. Missouri Agr. Exp. Sta. Res. Bull. #622. Henneman, H. A., S. A. Griffin and E. P. Reineke, 1952. A determination of thyroid secretion rate in intact individual sheep. J. An. Sci. 11: 794. Mixner, J. P., E. P. Reineke and C. W. Turner, 1944. The effect of thiouracil and thiourea on the thyroid gland of the chick. Endocrinology, 34: 168-174. Pipes, G. W., C. R. Blincoe and Hsieh Kaung-Mei, 1950. Estimation of the thyroid secretion rate without sacrifice of the animal. J. Dairy Sci. 33: 384. Pipes, G. W., and C. W. Turner, 1956. The effect of thyroxine on thyroidjfunction. Missouri Agri. Exp. Sta. Res. Bull. #617. Premachandra, B. N., G. W. Pipes and C. W. Turner, 1957. Thyroxine secretion rates of two strains of New Hampshire chickens selected for high and low response to thiouracil. In press. Schultze, A. B., and C. W. Turner, 1945. The determination of the rate of thyroxine secretion by certain domestic animals. Missouri Agr. Exp. Sta. Res. Bull. #392. Winchester, C. F., and G. K. Davis, 1952. Influence of thyroxine on growth of chickens. Poultry Sci. 31:31-34. Winchester, C. F., and V. C. Scarborough, 1953. The influence of thyroxine on growth and egg production of chickens. Poultry Sci. 32: 423-429.
NEWS AND NOTES {Continued from page 26) Missouri are similarly responsible for four other areas within India. Each area is organized so that the group leaders together with representatives of the Indian and U.S. governments and the colleges and institutes make up an advisory committee for work related to agricultural education and research in India.
In its foreign programs, the University of Illinois holds three contracts with the International Cooperation Administration for work in India. Under these contracts, the University sends its staff members to India, takes Indian scholars for further study in the United States and buys educational equipment and supplies for the Indian institutions.
{Continued on page 123)
Downloaded from http://ps.oxfordjournals.org/ at Uniwersytet Warszawski Biblioteka Uniwersytecka on June 20, 2015
lism is prevented. The apparent rate of thyroxine release from the thyroid gland is increased. 3. The daily injection of L-thyroxine in increasing amounts is then started. When the amount of thyroxine injected equals the daily thyroxine secretion rate of the fowl, the exogenous thyroxine blocks the discharge of thyrotropic hormone from the pituitary. In the absence of circulating thyrotropin, the discharge of thyroidal-I131 is prevented and the decline in radioactivity of the thyroid gland is prevented. The point on the curve where the decline is stopped is considered the Lthyroxine secretion rate equivalent of the fowl. The possibility exists that all of the hormone injected during the test period may not be metabolized. If this situation exists, as it does in the dairy cow (Pipes and Turner, 1956), it will be important to standardize dosage rates and schedules. Regardless of the possibility of accumulation of hormone during the test period, the authors believe that this technique is a sensitive and reliable index of thyroxine secretion rate in fowls.
41
H. S. WEISS Am. J. Physiol. 174:405^07. Sturkie, P. D. ; H. S. Weiss and R. K. Ringer, 1954. Effects of injections of acetylcholine and ephedrine upon components of the hen's egg. Poultry Sci. 33: 18-24. Weiss, H. S., and P. D. Sturkie, 1951. An indirect method for measuring blood pressure in the fowl. Poultry Sci. 30: 587-592. Wiggers, C. J., 1949. Physiology in Health and Disease. 5th ed. Lea & Febiger, Philadelphia, Pennsylvania.
Measurement of the Thyroid Hormone Secretion Rate of Individual Fowls* t G. W. PIPES, B. N. PREMACHANDRA AND C. W. TURNER Department of Dairy Husbandry, University of Missouri, Columbia (Received for publication June 17, 1957)
S
INCE the rate of thyroid hormone; secretion is an important factor ini growth rate (Winchester and Davis, 1952)I and egg production (Winchester andl Scarborough, 1953), studies were undertaken to develop methods for determination of the thyroxine secretion rate in intact fowls. The earlier techniques of simultaneousi administration of thyroxine and thiouracil1 (Mixner et al., 1944) require sacrifice off the fowls and can be used only to measure; the average thyroid hormone secretionl rate of groups rather than of individual1 fowls. When I131 became available, Pipes et al. (1950) proposed that the thyroxine secretion rate could be determined in the intact rat by the injection of graded1 amounts of thyroxine up to the level1 which would inhibit thyrotropin secre* Contribution from the Missouri Agr. Exp. Sta. Journal Series No. 1761. Approved by the Director. , t Aided-in-part by a grant from the U.S. Atomic Energy Commission Contract No. AT(11-1)-301.
tion. This level would be shown by the effect upon the collection of I131 by the thyroid gland and the amount of proteinbound-P 31 in the blood. This plan of measuring thyroxine secretion has been explored by Pipes and Turner (1956) in cattle, by Henneman et al. (1952) in sheep and by Biellier and Turner (1957) in fowls. The method developed in this laboratory for the measurement of the thyroid hormone secretion rate of individual fowls by the use of I131 required serial blood sampling. In addition, due to lack of sufficiently sensitive detecting apparatus, the dosage of I131 sufficient to be detected in the blood approached the level that might damage the function of the thyroid glands (Biellier and Turner, 1957). With more sensitive detecting apparatus available, the possibility of measuring thyroid hormone secretion rate in individual birds by means of an in vivo method was explored. In this method, the two above difficulties would be eliminated.
Downloaded from http://ps.oxfordjournals.org/ at Uniwersytet Warszawski Biblioteka Uniwersytecka on June 20, 2015
Nalbandov, A. V., and M. F. James, 1949. The blood-vascular system of the chicken ovary. Am. J. Anat. 85: 347-378. Romanoff, A. L., and A. L. Romanoff, 1949. The Avian Egg. John Wiley & Sons, Inc., New York, N . Y. Sturkie, P. D., R. K. Ringer and H. S. Weiss, 1956. Inheritance of blood pressure and its relationship to mortality in chickens. Fed. Proc. 15: 182. Sturkie, P. D., H. S. Weiss and R. K. Ringer, 1953. Effects of age on blood pressure in the chicken.
INDIVIDUAL THYROXINE SECRETION RATE
secretion rates for rapid growth and high egg production. EXPERIMENTAL PROCEDURE AND RESULTS
The Determination of Thyroidal I131.— The bird is placed in a weighing funnel of suitable size. Portions of the side of the funnel were removed to expose the thyroid area. Measurements of thyroidal I131 are made with a scintillation counter which included a 1"X1" N a l crystal and which is connected by a twenty foot coaxial cable to a combination analytical ratemeter and scaler. The scintillation counter is mounted on a flexible arm of local design. Attached to the front of the scintillation counter is a plastic spacer which maintains a distance of 15 centimeters between the counter and the bird. In operation the top of the plastic spacer is placed at the point of the keel bone (Figure 1). Highest counting rates were consistently observed in this area. Since the thyroid gland lies within the body of the bird, it is apparently impossible to measure thyroidal I131 without measuring some body radiation. Little change was noticed between the ratio of thyroidal I131 to body I131 after 24 hours and most of the I131 is concentrated in the thyroid at that time. Conventional corrections are made for radioactive decay through the use of I131 standards and for background readings. All results are expressed as percent of injected dose. Carrier free Nal 131 is injected either by the subcutaneous or intraperitoneal route. Measurements of thyroidal I131 are made at 24 hour intervals. Maximum accumulation of I131 in the thyroid gland ranged from 24 hour or less to 48 hours. Measurement of Rate of Release of Thyroidal Im.—Following the rapid uptake of P 31 by the bird's thyroid glands during
Downloaded from http://ps.oxfordjournals.org/ at Uniwersytet Warszawski Biblioteka Uniwersytecka on June 20, 2015
The amount of I131 injected into each bird could be reduced, and the measurement of the amount of I131 released by the thyroid gland eliminated the need of serial blood sampling and serious disturbance to the birds involved. The object of the present paper is to describe a method by which these improvements in technique are made possible. The measurement of the individual thyroxine secretion rates of growing and laying birds is now feasible. Uses of the Method.—While growth rate and egg production have been shown to be dependent upon thyroxine secretion, it will now be possible to directly determine the influence of increasing thyroxine secretion upon the growth rate. The thyroxine secretion rate of individual chicks may be determined and then correlated with their growth rate. If it can be shown that the growth rate increases with increasing thyroxine secretion rate, then the birds with low thyroxine secretion rate may be discarded and only birds of high thyroxine secretion rate selected for breeding purposes. Similarly, the individual thyroxine secretion rate of pullets going into lay can be determined and their egg laying capacity can be related to their thyroxine secretion rate. If there is a close correlation between thyroxine secretion rate and egg production, the value of the thyroxine secretion rate as a selective index will be indicated. Finally, if these two characters, growth and egg production, are shown to be influenced by the thyroxine secretion rate, it will be possible to determine the mode of inheritance of thyroxine secretion rate by ma tings of highXhigh, highXlow, etc., and note the average thyroxine secretion rate of the progeny. This information should make possible the selection and breeding of birds of optimal thyroxine
37
38
G. W. PIPES, B. N. PREMACHANDRA AND C. W. TURNER
RATE METER
® /SPACER /
(10CM.)
^LEXIBLE ARM
MEASURMENT OF THYROIDAL I IN THE FOWL
FIG. 1. Measurement of thyroidal I131 in the fowl with scintillation counter and rate meter.
the first 2 days or less, the I131 is converted into Il31-labeled thyroglobulin. I131-tagged thyroxine is then gradually released into the blood stream reducing the amount of radioactivity in the thyroid glands (Figure 2). Daily measurements of the radioactivity of the thyroid glands then indicate the rate of discharge of thyroxine. It might be thought that the rate of decline of radioactivity in the thyroid glands would serve as an index of thyroxine secretion. However, there is a complicating factor in such measurements. As I131-tagged thyroxine is discharged into the blood and is utilized by the tissues of the body, it is metabolized and some of the I131 is set free from the thyroxine molecule by a process of deiodination. The inorganic I131 passes from the cells into the blood and may again be picked up, in part, by the thyroid glands. This process is called "reutilization" or "recycling" of I131. Since the I131 which is recycled cannot be distinguished from the original injected I131, the rate of release of
I131-tagged thyroxine from the thyroid glands is obscured by the continuous uptake of I131 from metabolized thyroxine. In order to obtain the true rate of release of thyroxine-I131 from the thyroid glands, it is necessary to block the recycling of I131 from metabolized thyroxine. The use of the goitrogens such as thiouracil was, therefore, explored. The amount of thiouracil required to block the synthesis of thyroxine by the fowl thyroid gland has been determined (Schultze and Turner, 1945). The Effect oj Thiouracil upon the Apparent Release of Thyroidal Im.—Since thiouracil inhibits the further formation of thyroxine from inorganic iodine, the thyroid gland loses its ability to hold inorganic iodine (Adams and Purves, 1951) which, in effect, prevents the thyroid from utilizing iodine from metabolized hormone as well as from the diet. Under these conditions the net rate of release of thyroidal I131 is accelerated. Three mature New Hampshire hens
Downloaded from http://ps.oxfordjournals.org/ at Uniwersytet Warszawski Biblioteka Uniwersytecka on June 20, 2015
•WEIGHING FUNNEL
39
INDIVIDUAL THYROXINE SECRETION RATE
so • THIOURACIL 0,1% Or RATION
1
0
•
1
•
2
•
3
'
4
•
5
6 DArS
'
'
7
I
8
I
9
L-
10
FIG. 2. The effect of thiouracil on the apparent rate of release of thyroidal I131 (thyroid hormone) from the gland. After measurements were made for a five day control period, all fowls were fed thiouracil and measurements continued. Thiouracil inhibited the reutilization of I m from metabolized hormone and thyroid hormone secretion consisted of stored hormone only.
The increasing amounts of exogenous thyroxine gradually suppresses the secretion of the thyrotropic hormone of each bird in relation to their endogenous secretion rates. When an amount of thyroxine is injected equal to the bird's secretion rate, the further discharge of thyrotropin is blocked. The lack of thyrotropin in the blood then inhibits the further discharge of thyroxine. This point is indicated when the daily reading of radioactivity does not change. The level of thyroxine injection at which endogenous thyroxine discharge is blocked is believed to indicate the equivalent thyroxine secretion rate of the bird. It is not necessary to completely block the uptake of recycled I131 with thiouracil, but only to inhibit uptake to the point
Downloaded from http://ps.oxfordjournals.org/ at Uniwersytet Warszawski Biblioteka Uniwersytecka on June 20, 2015
were injected with 50 microcuries of I131 and daily measurements of thyroidal I131 were made for 5 days (Figure 2). At the end of this period thiouracil was fed as 0.1% of the ration. As had been anticipated, a more rapid apparent rate of release of thyroidal I131 was observed. In both phases of the experiment observed values followed the predicted values very closely, indicating small standard deviations. These data indicate the technique was sufficiently sensitive to measure small day-to-day reductions in thyroidal I131 as thyroxine is discharged into the blood. As further synthesis of thyroxine is blocked by the goitrogen, the rate of release of the preformed thyroxine is measured. Since it is shown that rate of release follows a regular course, the time required to deplete the supply of stored hormone can be estimated. Differences in the rate of release of thyroxine in individual birds provides a qualitative measure of differences in thyroxine secretion rate, however, it does not provide a quantitative measure. To estimate the amount of thyroxine secreted per day, the following method was developed. Estimation of the Daily Thyroxine Secretion Rate.—Three mature New Hampshire hens were injected with 50 microcuries of I131 and daily thyroid counts were made for 6 days. At this time thiouracil was fed as 0.1 percent of the ration. Once again all birds responded to thiouracil by an increase in the apparent rate of release of thyroidal I131 (Figure 3). On the third day of thiouracil feeding, purified Lthyroxine was injected subcutaneously with the dose being increased daily as follows: 0.5, 1.0, 1.5, 2.0, 4.0, 5.0 and 6 micrograms per 100 grams body weight. As shown in Figure 3, two birds showed a complete inhibition of I131-tagged hormone release at 2.0 micrograms while one required 5.0 micrograms.
40
G. W. PIPES, B. N. PREMACHANDRA AND C. W. TURNER
80THIOURACIL
60
0.1 %
OF RATION
THYROXINE 1.0
40
X / 1 0 0 GRAMS 2.0
THYROXINE SECRETION
Q20
7516 Ibid 7585
i 10-
< g
o
cc >- 6I
° * •
NEW HAMPSHIRE
V V
I
7
8 9 [>AYS
10
11-12
13
_1_
14
_l_
15
FIG. 3. The method of estimating the thyroid hormone secretion rate of the fowl. Arrows indicate the dosage of L-thyroxine which blocked the secretion of thyrotropic hormone and, consequently, the release of radiothyroxine from the gland as shown by the measurement on the following day.
where increased accuracy results due to a more rapid apparent rate of release of thyroidal I131 (Premachandra et al., 1958). DISCUSSION
The technique here described for measurement of thyroidal I131 in fowls produces highly reproducible results since the counter is located at a sufficient distance to minimize small variations in thyroid location. The inverse square law, i.e., the intensity of radiation is inversely proportional to the square of the distance between the radiation source and the point of measurement indicates that small variations in thyroid position should not be an important factor when measurements are made at a 15 centimeter distance. If the rate of release of thyroidal I131 were sufficiently rapid, thiouracil could be
omitted from the ration during the test period. In the present work the use of thiouracil increased the sensitivity of the technique and made possible more accurate estimation of the secretion rate since the point of blockage of thyroxine discharge is more clearly indicated. SUMMARY
1. An improved technique for the estimation of the thyroxine secretion rate of fowls is described. It involves the daily measurement of thyroidal-I131 in place of the measurement of blood I131. As thyroxine is discharged into the blood, the amount of thyroidal I131 gradually declines. 2. When thiouracil, at a level of 0.1% of the ration, is fed, the recycling of I131 formed as a product of thyroxine metabo-
Downloaded from http://ps.oxfordjournals.org/ at Uniwersytet Warszawski Biblioteka Uniwersytecka on June 20, 2015
o
1.5
INDIVIDUAL THYROXINE SECRETION RATE
ACKNOWLEDGMENT
The authors wish to express their appreciation to Dr. R. F. Elliott, of the Research Division, American Cyanamid Company, who generously supplied the thiouracil used in these studies; to Mr. E. R. Thompson, Jr., for technical assist-
ance and to Mr. Elbert F. Turner, Jr., for help in care and handling of the animals. REFERENCES Adams, D. D., and H. D. Purves, 1951. The effect of methylthiouracil and of iodine on secretion of radioactive iodine by the human thyroid. Proc. Univ. Otago Medical School Res. Soc. 29(3): 1-2. Biellier, H. V., and C. W. Turner, 1957. The thyroid hormone secretion rate of domestic fowls as determined by the goitrogen and radio-iodine techniques. Missouri Agr. Exp. Sta. Res. Bull. #622. Henneman, H. A., S. A. Griffin and E. P. Reineke, 1952. A determination of thyroid secretion rate in intact individual sheep. J. An. Sci. 11: 794. Mixner, J. P., E. P. Reineke and C. W. Turner, 1944. The effect of thiouracil and thiourea on the thyroid gland of the chick. Endocrinology, 34: 168-174. Pipes, G. W., C. R. Blincoe and Hsieh Kaung-Mei, 1950. Estimation of the thyroid secretion rate without sacrifice of the animal. J. Dairy Sci. 33: 384. Pipes, G. W., and C. W. Turner, 1956. The effect of thyroxine on thyroidjfunction. Missouri Agri. Exp. Sta. Res. Bull. #617. Premachandra, B. N., G. W. Pipes and C. W. Turner, 1957. Thyroxine secretion rates of two strains of New Hampshire chickens selected for high and low response to thiouracil. In press. Schultze, A. B., and C. W. Turner, 1945. The determination of the rate of thyroxine secretion by certain domestic animals. Missouri Agr. Exp. Sta. Res. Bull. #392. Winchester, C. F., and G. K. Davis, 1952. Influence of thyroxine on growth of chickens. Poultry Sci. 31:31-34. Winchester, C. F., and V. C. Scarborough, 1953. The influence of thyroxine on growth and egg production of chickens. Poultry Sci. 32: 423-429.
NEWS AND NOTES {Continued from page 26) Missouri are similarly responsible for four other areas within India. Each area is organized so that the group leaders together with representatives of the Indian and U.S. governments and the colleges and institutes make up an advisory committee for work related to agricultural education and research in India.
In its foreign programs, the University of Illinois holds three contracts with the International Cooperation Administration for work in India. Under these contracts, the University sends its staff members to India, takes Indian scholars for further study in the United States and buys educational equipment and supplies for the Indian institutions.
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lism is prevented. The apparent rate of thyroxine release from the thyroid gland is increased. 3. The daily injection of L-thyroxine in increasing amounts is then started. When the amount of thyroxine injected equals the daily thyroxine secretion rate of the fowl, the exogenous thyroxine blocks the discharge of thyrotropic hormone from the pituitary. In the absence of circulating thyrotropin, the discharge of thyroidal-I131 is prevented and the decline in radioactivity of the thyroid gland is prevented. The point on the curve where the decline is stopped is considered the Lthyroxine secretion rate equivalent of the fowl. The possibility exists that all of the hormone injected during the test period may not be metabolized. If this situation exists, as it does in the dairy cow (Pipes and Turner, 1956), it will be important to standardize dosage rates and schedules. Regardless of the possibility of accumulation of hormone during the test period, the authors believe that this technique is a sensitive and reliable index of thyroxine secretion rate in fowls.
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