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Thyroid function in laying, incubating, and broody bantam hens
GENERAL
AND
Thyroid
COMPARATIVE
47, 492-496 (1982)
ENDOCRINOLOGY
Function
in Laying, H. KLANDOW,’
incubating, R. W. LEA,
and Broody
Bantam
Hens
AND P. J. SHARP
A.R.C. Poultry ResearchCentre,Roslin.Midlothiun,EH2S9PS,Scotland Accepted October 2, 1981 The concentration of plasma triiodothyronine (TJ increased in broody bantam hens within 1 or 2 days of the onset of incubation and rose further after the chicks hatched. In a separate study, blood samples were taken from hens over a 24-hr period (14L: 1OD) when they were laying, incubating, or brooding chicks. The concentrations of plasma T3 tended to drop during the dark period in laying, incubating, and brooding birds, while the converse changes were observed in the concentration of plasma thyroxine (T4). A daily rhythm in the levels of plasma T4 was not observed in incubating bantams. The possibility that prolactin is involved in the regulation of thyroid function during broodiness was investigated by measuring the concentrations of plasma thyroid hormones after an injection of bovine prolactin. The concentration of plasma T, was not affected by the injection of prolactin, whereas the concentration of T3 in laying and incubating bantam hens was significantly increased after 60 min. This study suggests that one of the factors which influences thyroid function in broody bantams may be the increase in prolactin secretion.
In birds, thyroid function may be affected by several factors including the pattern of food intake and changes in the concentrations of plasma gonadal steroids and prolactin. Thus, in the hen, the level of plasma triiodothyronine (T3) falls while that of plasma thyroxine (T4) increases after withdrawal of food (May, 1978; Klandorf er al., 1981a,b). Conversely, the level of plasma T:< increases after hens have eaten at the end of a prolonged fast (Brake et al., 1979). This effect of food intake on thyroid function may account for the diurnal variations in the concentrations of plasma T3 and T4 seen in the hen (Newcomer, 1974; Klandorf et al., 1978). Gonadal steroids may affect thyroid function by altering the concentrations of thyroid-binding proteins in the blood. In support of this view, in the quail, the concentrations of plasma T3 and T4 fall in intact but not in gonadectomized birds after photostimulation (Sharp and Klandorf, 1981).
’ Present address: The Wolfson Institute, University of Hull, Hull, North Humberside HU6 7RX, England.
Injections of prolactin induce hypertrophy of the thyroid glands in the Japanese quail (Wadaet ul., 1975) and immature cockerels (Maiti and Chakraborty, 1980), and depress the levels of plasma T, in the quail (Wada et al., 1975). An effect of prolactin on thyroid function has also been observed in other nonmammalian vertebrates. Thus, injections of prolactin cause thyroid gland hypertrophy in the lizard (An& carolinensis) (Licht and Jones, 1967), the eel (Olivereau, 1966), and the teleost Pterophyllum scafare (Osewald and Fiedler, 1968). Further, Singh and Singh (1976) found that in the teleost Heteropneustes fossilis prolactin reduced both pituitary TSH levels and the uptake of 1311into the thyroid gland. In another teleost, the rainbow trout (Safmo gairdneri), Milne and Leatherland (1978) found that injections of pro&tin increased the concentrations of plasma T:, but did not affect levels of plasma T,. A combination of changes in food intake and alterations in plasma levels of ovarian steroids and prolactin occur in broody bantam hens and might be expected to affeet thyroid function. In incubating ban-
492 00166480/82/080492-OS$Ol .OO/O Copyright 0 1982 by Academic Press, Inc. All rights of reproduction in any form reserved.
THYROID
HORMONES
rig/ml
tams, food intake drops (Savory, 1979; Sherry et al., 1980) and prolactin levels increase (Sharp et al., 1979; Lea et al., 1981). After the chicks hatch, food intake increases (Savory, 1979; Sherry et al., 1980) and prolactin levels tend to fall (Sharp ef al., 1979). The
ovary regresses (Sharp and
Lea, 1981) and plasma progesterone levels fall (Sharp et al., 1979) at the onset of incubation, and ovarian function remains depressed until the hen stops brooding her chicks. The present study was designed to examine the changes in thyroid function in laying, incubating, and brooding bantam hens and to investigate the possible regulatory role of plasma prolactin. MATERIALS
AND METHODS
Experiment 1. The purpose of this study was to measure the concentration of plasma T3 during the onset of incubation and when the birds began brooding their young. Bantam hens aged between 18 and 24 months were kept in floor pens with free access to food and water and exposed to 14 hr light/day. Blood samples (2 ml) were taken at the same time of day for 1 week before and for 1 week after the onset of incubation and again for 9 days after the chicks had hatched. Experiment 2. The purpose of this experiment was to compare the daily rhythms in the concentrations of plasma thyroid hormones in bantam hens when they were laying, incubating eggs, and brooding young. The birds were sampled on the first day of incubation, when the mean daily food intake drops significantly (Savory, 1979) and the concentration of plasma prolactin is elevated (Lea et al., 1980), and again 9 or 10 days after hatch, when the mean daily food intake is significantly increased (Savory, 1979). Blood samples (1 ml) were taken every 3 hr for a period of 24 hr from the hens (n = 7) during each of these periods. Experiment 3. The purpose of this study was to determine the effect of an injection of prolactin on the concentrations of plasma T3 and T+ Bovine prolactin (NIHPB9) (200 pg in 0.5 ml of 0.9% saline solution) was injected iv into six laying and six incubating bantam hens (Day 20, 21 of incubation). Blood samples were taken at 0, 30, 45, and 60 min. Measurement of plasma T3 and T,,. Plasma thyroxine (TJ and triiodothyronine (T3) were measured by radioimmunoassay as described by Seth et al. (1976). All the samples from each study were measured in single assays. The minimal detectable doses of T, and T3 were 0.13 and 0.10 &ml, respectively.
493
IN BROODY BANTAMS LAYING
.. 3;
jlN ICUBATINC
BROODING YOUNG
3.c T3
-6
+1
a II’
+7 +22
+30
DWS FIG. 1. Variations in the concentration of plasma T3 in bantam hens when they were in lay, during the first week of incubation, and during the first 9 days the hens were brooding their young. Each point represents a mean value (?-SEM) for six hens.
Statistical analyses of the T, and T3 data were carried out using the method described by Halberg et al. (1972) and Student’s t test.
RESULTS Changes in the concentration of plasma T3 during the onset of incubation and brooding of young. The concentration of
plasma T3 did not vary significantly during the days prior to the onset of incubation but increased on the first or second day of incubation and continued to increase during the following week (Fig. 1). When the hens began brooding their young, the concentration of plasma T3 continued to increase. Changes in plasma T4 and T3 over 24 hr.
When bantams were laying, incubating, or brooding their young, the concentration of plasma T3 showed significant daily variations (Table 1): they increased during the light period and fell during the dark period. The mean levels of plasma T3 were similar in birds while they were laying and at the onset of incubation (1.42 +_ 0.1 and 1.37 +-
494
KLANDORF,
LEA, AND SHARE TABLE
CHARACTERISTICS OF SINUSOIDAL VARIATIONS OF THYROXINE
1
CURVES FITTED BY THE LEAST SQUARES METHOD TO DESCRIBE THE DAILY (T,) AND TRIIODOTHYRONINE (T,) IN LAYING, INCUBATING, AND BROODING BANTAM HENS (n = 7)
Laying l-4 Level (&ml) Amplitude Acrophase (hr) from onset of light P
T3
12.5 1.21
1.42 0.21
23.93
16.56
0.16
Incubating
4.13 x 10-S
T4 12.4
Brooding Young T3 1.37
T4 10.5
0.02
0.21
1.37
20.51 0.999
16.29 0.057
22.61 0.049
T3 2.18
0.56 14.52 2.93 x 1O-6
Note. Bantams were serially sampled every 3 hr during a 14L:lOD lighting cycle. The level is the intercept of the theoretical curve, the amplitude is the maximal deviation of the theoretical curve from the level, and the acrophase (hours expressed as a decimal fraction) is the time which the maximal positive deviation of the curve from the level occurs. The value of P (set at the 0.05 level) is used to test the null hypothesis that the amplitude is equal to zero.
0.2 @ml, respectively) but increased almost twofold while the birds were brooding their young (2.18 1- 0.1 @ml). The concentration of plasma T3 tended to be depressed in the samples taken 24 hr after the first in laying, incubating, and brooding birds (Fig. 1). Significant daily variations in plasma Tq, with an increase occurring in the dark period, were observed when the birds were laying or brooding young but not when they were incubating eggs (Fig. 2, Table 1). The mean level of T, over 24 hr was lower when they were brooding young than when they were laying or at the onset of incubation (Table 1). The effect of repeated sampling of the same bird appeared to result in a depression in the amplitude and concentration of plasma T, over the 24-hr sampling period (Fig. 2) (Klandorf et al., 1978). Effect of bovine prolactin on the concentration of plasma T3 and T*. Concentrations of plasma T, did not differ significantly in either laying or incubating birds after an injection of saline solution or prolactin (Fig. 3). In laying birds, circulating T3 levels were significantly increased (P < 0.001) between 30 and 60 min after prolactin administration. The concentration of plasma .T3 was not significantly increased in incubating
birds after an injection of prolactin (P < 0.1). No changes in T3 levels were observed after an injection of saline solution. DISCUSSION
An increase in the concentration of plasma T, was first noted after the hens began to incubate their eggs. The depressive effect of reduced food consumption on plasma T3 levels thus appears to have been countered either by the stimulating effect of increased plasma prolactin levels or by an increase in thyroid-binding protein caused by the fall in levels of plasma ovarian steroids (see Introduction). In mammals a reduction in food intake results in a decrease in the peripheral metabolism of T, to T3 (Balsam and Ingbar, 1979); a similar mechanism may occur in birds, since in fasted hens the concentration of plasma T3 decreases in association with an increase in plasma T4 (May, 1978; Klandorf et al., 1981). The decline in the concentration of plasma T3 in fasting hens has been shown to be correlated with a reduction in the rate of heat production (Klandorf et al., 1981b). Thus, the decline in food intake during incubation in bantams would also be expected to lead to a decrease in plasma T3 and heat production. Such a de-
THYROID
HORMONES
(0-o)
.,,
ndml
nalml
T3 nglml
,:,:,:.:.:.:.::::::~~~:.:::::.:::.
LAYING
495
IN BROODY BANTAMS
INCUBATING
LAYING 3.5.
4,o .
(
T3
........................ ...........
..................... ...................... ..: ..............................
INCUBATING
0
YOUNG
lack
0800
:, :,
:::,
::::: ::::.
..,........... .,....... ‘:.‘:::::::::::::. ::: ;. :::. :I:I:l:I:I:I~:J:I:j:1:I :i;,lj;,;,;c;;lj;;;/
BROODING 15
::::
0 60 Minutes
30
60
FIG. 3. Effect of an iv injection of 200 pg bovine prolactin on plasma T4 and T3 levels in laying and incubating bantam hens (Day 20,21 of incubation). Each point represents a mean value (SEM) for five or six hens.
1 ::, .‘,‘.‘,‘.‘.‘.~.‘.’ ::, :::;. ,.......
9t
30
lated T3 production. Because the levels of .‘.~.‘_‘_‘.‘. v:. T4 did not change after the administration of ...~...~.t.t,t.~,t.,.rt~:~:~:~~~~~~,~~ ,o
1400
0200
2000 Time
of
0800
day
FIG. 2. Variations in the concentrations of plasma thyroxine (TJ and triiodothyronine (T3) in bantam hens when they were in lay, on the first day of incubation, and brooding young. Each point represents the mean (SEM) hormone level in serial samples taken from seven hens. The birds were maintained on a lighting cycle of 14L: 10D with the stippled area representing the period of darkness.
crease would be inappropriate in incubating birds because body heat is required to maintain the temperature of the eggs. Elevated levels of T3 may thus be important in preventing heat production from dropping below that required for optimal incubating conditions; it has been shown that incubation temperature critically determines the duration of the incubation period (Romanoff et al., 1938; Decuypere et al., 1979). The possibility that prolactin plays a role in maintaining the elevated levels of plasma T3 in broody bantams is supported by the finding that an injection of prolactin stimu-
prolactin, the present observations suggest that prolactin might be exerting a peripheral effect on the metabolism of T, to T3. This view is supported by the finding of Milne and Leatherland (1978), who found that in the rainbow trout the concentration of TX but not of T, increased after an injection of prolactin. The increase in plasma TS levels in bantam hens observed after their chicks had hatched was similar to that observed in hens given access to food after a prolonged fast (Brake et al., 1979). Savory (1979) has shown that in the bantam the increase in food intake at the onset of brooding young is associated with the recovery of body weight lost during incubation. At this time, food consumption is greater than when the hens were laying. Although the elevated levels of plasma prolactin would have been falling (Sharp, 1980), they may be involved in the generation of T3 in brooding bantams. However, it is more likely that the principal factor causing the increase in the concentration of T3 at this time would be the increased level of food intake.
496
KLANDORF,
LEA, AND SHARP
REFERENCES Balsam, A., and Ingbar, S. H. (1979). Observations on the factors that control the generation of triiodothyronine from thyroxine and liver and the nature of the defect induced by fasting. J. C/in. Invrsf. 63, 1145-1156. Brake, J., Thaxton, P., and Benton, E. H. (1979). Physiological changes in caged layers during a forced molt. 3. Plasma thyroxine, plasma triiodothyronine, adrenal cholesterol, and total adrenal steroids. Poult. Sci. 58, 1345-1350. Decuypere, E., Nouwen, E. J., Kuhn, E. R., Geers, R., and Michels, H. (1979). Iodohormones in the serum of chick embryos and post-hatching chickens as influenced by incubation temperature. Relationship with the hatching process and thermogenesis. Ann. Biol. Anim. Biochem. Biophys. 19, 1713- 1723. Halberg, F., Johnson, E. A., Nelson, W., Reiner, W.. and Southern, R. (1972). Autorhythmetryprocedures for physiological self measurements and their analysis. Physiol. Teacher 1 (4), 1- 11. Klandorf, H., Sharp, P. J., and Sterling, R. (1978). Induction of thyroxine and triiodothyronine release by thyrotrophin-releasing hormone in the hen. Gen.
Comp.
Endocrinol.
34, 377-379.
Klandorf, H., Sharp, P. J., and Duncan, 1. .I. H. (1978). Variations in levels of plasma thyroxine and triiodothyronine in juvenile female chickens during 24- and 16-hour lighting cycles. Gen. Comp.
Endocrinol.
36, 238-243.
Klandorf, H., Sharp, P. J., and Newcomer, W. S. (198la). The influence of feeding patterns on daily variations in the concentrations of plasma thyroid hormones in the hen. IRCS Med. Sci. 9, 82. Klandorf, H., Sharp, P. J., and MacLeod, M. G. (198lb). The relationship between heat production and concentrations of plasma thyroid hormones in the domestic hen. Gen. Comp. Endocrinol.. 4.5, 513-520. Lea, R. W., Sharp, P. J., Klandorf, H., and Chadwick, A. (1980). Diurnal rhythms in plasma prolactin and thyroid hormones in broody bantams. Gen.
Comp.
Endocrinol.
40, 333.
Lea, R. W., Dods, A. S. M., Sharp, P. J., and Chadwick, A. (1981). The possible role of prolactin in the regulation of nesting behaviour and the secretion of luteinizing hormone in broody bantams. J. Endocrinol., 91, 89- 99. Licht, P., and Jones, R. E. (1967). Effects of exogenous prolactin on reproduction and growth in adult males of the lizard, Anofis carolinensis. Gen.
Comp.
Endocrinol.
8, 228-244.
Maiti, B. R., and Chakraborty, S. (1980). The mitogenic action of prolactin on some endocrine organs in chicks. Arch. Histol. Jap. 43, 341-346. May, J. D. (1978). Effect of fasting on T3 and Tq concentrations in chicken serum. Cert. Comp. Endocrinol.
34. 323-327.
Milne, R. S., and Leatherland, J. F. (1978). Effect of ovine TSH, thiourea, ovine prolactin and bovine growth hormones on plasma thyroxine and triiodothyronine in rainbow trout, Salmo gairdneri. J. Comp. Physiol. 124, 105-110. Newcomer, W. S. (1974). Diurnal rhythms of thyroid function in chicks. Gen. Comp. Endacrinol. 24, 65-73. Olivereau, M. (1966). Action de la prolactin chez l’anguille intacte et hypophysectomisee. I. Systeme hypophysio-thyroidien et pigmentation. Gen. Comp. Endocrinol. 6, 130-143. Osewald, T., and Fiedler, K. (1968). Die Wirkung von Sauger-Prolactin auf die Shilddriise des Segelflossers Pterophyllum scalare (Chichlidae, Teleostei). Z. Zellforsch. Mikrosk. Anat. 91, 617-632. Romanoff, A. L., Smith, L. L., and Sullivan, R. A. (1938). Biochemistry and biophysics of the developing hen’s egg. II. Influence of temperature. Cornell Univ. Agric. Exp. Stat. Mem. 216, l-42. Savory, C. J. (1979). Changes in food intake and body weight of bantam hens during breeding. Appl. Anim.
Ethol.
5, 283-288.
Seth, J., Toft, A. O., and Irvine, W. J. (1976). Simple solid-phase radioimmunoassays for total triiodothyronine and thyroxine in serum, and their clinical evaluation, Clin. Chem. Acta 68, 291-301. Sharp, P. J., Scanes, C. Cl., Williams, J. B.. Harvey, S., and Chadwick, A. (1979). Variation in concentrations of prolactin, luteinizing hormone, growth hormone and progesterone in the plasma of broody bantams (Gal/us domesticus). J. Enducrinol. 80, 51-57. Sharp, P. J. (1980). Female reproduction. In “Avian Endocrinology” (A. Epple and M. H. Stetson, eds.), pp. 435-455. Academic Press, New York. Sharp, P. J., and Klandorf, H. (1981). The interaction between day length and the gonads in the regulation of levels of plasma thyroxine and triiodothyronine in the Japanese Quail. Gen. Camp. Endocrinol., 45, 504-512. Sharp, P. J., and Lea, R. W. (1981). The response of the pituitary gland to luteinizing hormonereleasing hormone in broody bantams. Gen. Comp. Endocrinol.. 45, 131-133. Sherry, D. F., Mrosovsky, N., and Hosan, J. H. (1980). Weight loss and anorexia during incubation in birds. J. Comp. Physiol. Psychol. 94, 89-98. Singh, R., and Singh, T. P. (1976). Effect of prolactin administration on ovarian and thyroid activity in relation to gonadotrophic and thyrotrophic potency in a freshwater catfish, Heterapneustes (Bloch). Endokrinotagie 68, 27-34. Wada, M., Arimatsu, Y., and Kobayashi, H. (1975). Effect of prolactin on thyroid function in Japanese Quail (Corturnix corturnix japonica) Gen. Camp. Endocrinol.
27, 28-33.
AND
Thyroid
COMPARATIVE
47, 492-496 (1982)
ENDOCRINOLOGY
Function
in Laying, H. KLANDOW,’
incubating, R. W. LEA,
and Broody
Bantam
Hens
AND P. J. SHARP
A.R.C. Poultry ResearchCentre,Roslin.Midlothiun,EH2S9PS,Scotland Accepted October 2, 1981 The concentration of plasma triiodothyronine (TJ increased in broody bantam hens within 1 or 2 days of the onset of incubation and rose further after the chicks hatched. In a separate study, blood samples were taken from hens over a 24-hr period (14L: 1OD) when they were laying, incubating, or brooding chicks. The concentrations of plasma T3 tended to drop during the dark period in laying, incubating, and brooding birds, while the converse changes were observed in the concentration of plasma thyroxine (T4). A daily rhythm in the levels of plasma T4 was not observed in incubating bantams. The possibility that prolactin is involved in the regulation of thyroid function during broodiness was investigated by measuring the concentrations of plasma thyroid hormones after an injection of bovine prolactin. The concentration of plasma T, was not affected by the injection of prolactin, whereas the concentration of T3 in laying and incubating bantam hens was significantly increased after 60 min. This study suggests that one of the factors which influences thyroid function in broody bantams may be the increase in prolactin secretion.
In birds, thyroid function may be affected by several factors including the pattern of food intake and changes in the concentrations of plasma gonadal steroids and prolactin. Thus, in the hen, the level of plasma triiodothyronine (T3) falls while that of plasma thyroxine (T4) increases after withdrawal of food (May, 1978; Klandorf er al., 1981a,b). Conversely, the level of plasma T:< increases after hens have eaten at the end of a prolonged fast (Brake et al., 1979). This effect of food intake on thyroid function may account for the diurnal variations in the concentrations of plasma T3 and T4 seen in the hen (Newcomer, 1974; Klandorf et al., 1978). Gonadal steroids may affect thyroid function by altering the concentrations of thyroid-binding proteins in the blood. In support of this view, in the quail, the concentrations of plasma T3 and T4 fall in intact but not in gonadectomized birds after photostimulation (Sharp and Klandorf, 1981).
’ Present address: The Wolfson Institute, University of Hull, Hull, North Humberside HU6 7RX, England.
Injections of prolactin induce hypertrophy of the thyroid glands in the Japanese quail (Wadaet ul., 1975) and immature cockerels (Maiti and Chakraborty, 1980), and depress the levels of plasma T, in the quail (Wada et al., 1975). An effect of prolactin on thyroid function has also been observed in other nonmammalian vertebrates. Thus, injections of prolactin cause thyroid gland hypertrophy in the lizard (An& carolinensis) (Licht and Jones, 1967), the eel (Olivereau, 1966), and the teleost Pterophyllum scafare (Osewald and Fiedler, 1968). Further, Singh and Singh (1976) found that in the teleost Heteropneustes fossilis prolactin reduced both pituitary TSH levels and the uptake of 1311into the thyroid gland. In another teleost, the rainbow trout (Safmo gairdneri), Milne and Leatherland (1978) found that injections of pro&tin increased the concentrations of plasma T:, but did not affect levels of plasma T,. A combination of changes in food intake and alterations in plasma levels of ovarian steroids and prolactin occur in broody bantam hens and might be expected to affeet thyroid function. In incubating ban-
492 00166480/82/080492-OS$Ol .OO/O Copyright 0 1982 by Academic Press, Inc. All rights of reproduction in any form reserved.
THYROID
HORMONES
rig/ml
tams, food intake drops (Savory, 1979; Sherry et al., 1980) and prolactin levels increase (Sharp et al., 1979; Lea et al., 1981). After the chicks hatch, food intake increases (Savory, 1979; Sherry et al., 1980) and prolactin levels tend to fall (Sharp ef al., 1979). The
ovary regresses (Sharp and
Lea, 1981) and plasma progesterone levels fall (Sharp et al., 1979) at the onset of incubation, and ovarian function remains depressed until the hen stops brooding her chicks. The present study was designed to examine the changes in thyroid function in laying, incubating, and brooding bantam hens and to investigate the possible regulatory role of plasma prolactin. MATERIALS
AND METHODS
Experiment 1. The purpose of this study was to measure the concentration of plasma T3 during the onset of incubation and when the birds began brooding their young. Bantam hens aged between 18 and 24 months were kept in floor pens with free access to food and water and exposed to 14 hr light/day. Blood samples (2 ml) were taken at the same time of day for 1 week before and for 1 week after the onset of incubation and again for 9 days after the chicks had hatched. Experiment 2. The purpose of this experiment was to compare the daily rhythms in the concentrations of plasma thyroid hormones in bantam hens when they were laying, incubating eggs, and brooding young. The birds were sampled on the first day of incubation, when the mean daily food intake drops significantly (Savory, 1979) and the concentration of plasma prolactin is elevated (Lea et al., 1980), and again 9 or 10 days after hatch, when the mean daily food intake is significantly increased (Savory, 1979). Blood samples (1 ml) were taken every 3 hr for a period of 24 hr from the hens (n = 7) during each of these periods. Experiment 3. The purpose of this study was to determine the effect of an injection of prolactin on the concentrations of plasma T3 and T+ Bovine prolactin (NIHPB9) (200 pg in 0.5 ml of 0.9% saline solution) was injected iv into six laying and six incubating bantam hens (Day 20, 21 of incubation). Blood samples were taken at 0, 30, 45, and 60 min. Measurement of plasma T3 and T,,. Plasma thyroxine (TJ and triiodothyronine (T3) were measured by radioimmunoassay as described by Seth et al. (1976). All the samples from each study were measured in single assays. The minimal detectable doses of T, and T3 were 0.13 and 0.10 &ml, respectively.
493
IN BROODY BANTAMS LAYING
.. 3;
jlN ICUBATINC
BROODING YOUNG
3.c T3
-6
+1
a II’
+7 +22
+30
DWS FIG. 1. Variations in the concentration of plasma T3 in bantam hens when they were in lay, during the first week of incubation, and during the first 9 days the hens were brooding their young. Each point represents a mean value (?-SEM) for six hens.
Statistical analyses of the T, and T3 data were carried out using the method described by Halberg et al. (1972) and Student’s t test.
RESULTS Changes in the concentration of plasma T3 during the onset of incubation and brooding of young. The concentration of
plasma T3 did not vary significantly during the days prior to the onset of incubation but increased on the first or second day of incubation and continued to increase during the following week (Fig. 1). When the hens began brooding their young, the concentration of plasma T3 continued to increase. Changes in plasma T4 and T3 over 24 hr.
When bantams were laying, incubating, or brooding their young, the concentration of plasma T3 showed significant daily variations (Table 1): they increased during the light period and fell during the dark period. The mean levels of plasma T3 were similar in birds while they were laying and at the onset of incubation (1.42 +_ 0.1 and 1.37 +-
494
KLANDORF,
LEA, AND SHARE TABLE
CHARACTERISTICS OF SINUSOIDAL VARIATIONS OF THYROXINE
1
CURVES FITTED BY THE LEAST SQUARES METHOD TO DESCRIBE THE DAILY (T,) AND TRIIODOTHYRONINE (T,) IN LAYING, INCUBATING, AND BROODING BANTAM HENS (n = 7)
Laying l-4 Level (&ml) Amplitude Acrophase (hr) from onset of light P
T3
12.5 1.21
1.42 0.21
23.93
16.56
0.16
Incubating
4.13 x 10-S
T4 12.4
Brooding Young T3 1.37
T4 10.5
0.02
0.21
1.37
20.51 0.999
16.29 0.057
22.61 0.049
T3 2.18
0.56 14.52 2.93 x 1O-6
Note. Bantams were serially sampled every 3 hr during a 14L:lOD lighting cycle. The level is the intercept of the theoretical curve, the amplitude is the maximal deviation of the theoretical curve from the level, and the acrophase (hours expressed as a decimal fraction) is the time which the maximal positive deviation of the curve from the level occurs. The value of P (set at the 0.05 level) is used to test the null hypothesis that the amplitude is equal to zero.
0.2 @ml, respectively) but increased almost twofold while the birds were brooding their young (2.18 1- 0.1 @ml). The concentration of plasma T3 tended to be depressed in the samples taken 24 hr after the first in laying, incubating, and brooding birds (Fig. 1). Significant daily variations in plasma Tq, with an increase occurring in the dark period, were observed when the birds were laying or brooding young but not when they were incubating eggs (Fig. 2, Table 1). The mean level of T, over 24 hr was lower when they were brooding young than when they were laying or at the onset of incubation (Table 1). The effect of repeated sampling of the same bird appeared to result in a depression in the amplitude and concentration of plasma T, over the 24-hr sampling period (Fig. 2) (Klandorf et al., 1978). Effect of bovine prolactin on the concentration of plasma T3 and T*. Concentrations of plasma T, did not differ significantly in either laying or incubating birds after an injection of saline solution or prolactin (Fig. 3). In laying birds, circulating T3 levels were significantly increased (P < 0.001) between 30 and 60 min after prolactin administration. The concentration of plasma .T3 was not significantly increased in incubating
birds after an injection of prolactin (P < 0.1). No changes in T3 levels were observed after an injection of saline solution. DISCUSSION
An increase in the concentration of plasma T, was first noted after the hens began to incubate their eggs. The depressive effect of reduced food consumption on plasma T3 levels thus appears to have been countered either by the stimulating effect of increased plasma prolactin levels or by an increase in thyroid-binding protein caused by the fall in levels of plasma ovarian steroids (see Introduction). In mammals a reduction in food intake results in a decrease in the peripheral metabolism of T, to T3 (Balsam and Ingbar, 1979); a similar mechanism may occur in birds, since in fasted hens the concentration of plasma T3 decreases in association with an increase in plasma T4 (May, 1978; Klandorf et al., 1981). The decline in the concentration of plasma T3 in fasting hens has been shown to be correlated with a reduction in the rate of heat production (Klandorf et al., 1981b). Thus, the decline in food intake during incubation in bantams would also be expected to lead to a decrease in plasma T3 and heat production. Such a de-
THYROID
HORMONES
(0-o)
.,,
ndml
nalml
T3 nglml
,:,:,:.:.:.:.::::::~~~:.:::::.:::.
LAYING
495
IN BROODY BANTAMS
INCUBATING
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0 60 Minutes
30
60
FIG. 3. Effect of an iv injection of 200 pg bovine prolactin on plasma T4 and T3 levels in laying and incubating bantam hens (Day 20,21 of incubation). Each point represents a mean value (SEM) for five or six hens.
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9t
30
lated T3 production. Because the levels of .‘.~.‘_‘_‘.‘. v:. T4 did not change after the administration of ...~...~.t.t,t.~,t.,.rt~:~:~:~~~~~~,~~ ,o
1400
0200
2000 Time
of
0800
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FIG. 2. Variations in the concentrations of plasma thyroxine (TJ and triiodothyronine (T3) in bantam hens when they were in lay, on the first day of incubation, and brooding young. Each point represents the mean (SEM) hormone level in serial samples taken from seven hens. The birds were maintained on a lighting cycle of 14L: 10D with the stippled area representing the period of darkness.
crease would be inappropriate in incubating birds because body heat is required to maintain the temperature of the eggs. Elevated levels of T3 may thus be important in preventing heat production from dropping below that required for optimal incubating conditions; it has been shown that incubation temperature critically determines the duration of the incubation period (Romanoff et al., 1938; Decuypere et al., 1979). The possibility that prolactin plays a role in maintaining the elevated levels of plasma T3 in broody bantams is supported by the finding that an injection of prolactin stimu-
prolactin, the present observations suggest that prolactin might be exerting a peripheral effect on the metabolism of T, to T3. This view is supported by the finding of Milne and Leatherland (1978), who found that in the rainbow trout the concentration of TX but not of T, increased after an injection of prolactin. The increase in plasma TS levels in bantam hens observed after their chicks had hatched was similar to that observed in hens given access to food after a prolonged fast (Brake et al., 1979). Savory (1979) has shown that in the bantam the increase in food intake at the onset of brooding young is associated with the recovery of body weight lost during incubation. At this time, food consumption is greater than when the hens were laying. Although the elevated levels of plasma prolactin would have been falling (Sharp, 1980), they may be involved in the generation of T3 in brooding bantams. However, it is more likely that the principal factor causing the increase in the concentration of T3 at this time would be the increased level of food intake.
496
KLANDORF,
LEA, AND SHARP
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Klandorf, H., Sharp, P. J., and Duncan, 1. .I. H. (1978). Variations in levels of plasma thyroxine and triiodothyronine in juvenile female chickens during 24- and 16-hour lighting cycles. Gen. Comp.
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Klandorf, H., Sharp, P. J., and Newcomer, W. S. (198la). The influence of feeding patterns on daily variations in the concentrations of plasma thyroid hormones in the hen. IRCS Med. Sci. 9, 82. Klandorf, H., Sharp, P. J., and MacLeod, M. G. (198lb). The relationship between heat production and concentrations of plasma thyroid hormones in the domestic hen. Gen. Comp. Endocrinol.. 4.5, 513-520. Lea, R. W., Sharp, P. J., Klandorf, H., and Chadwick, A. (1980). Diurnal rhythms in plasma prolactin and thyroid hormones in broody bantams. Gen.
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34. 323-327.
Milne, R. S., and Leatherland, J. F. (1978). Effect of ovine TSH, thiourea, ovine prolactin and bovine growth hormones on plasma thyroxine and triiodothyronine in rainbow trout, Salmo gairdneri. J. Comp. Physiol. 124, 105-110. Newcomer, W. S. (1974). Diurnal rhythms of thyroid function in chicks. Gen. Comp. Endacrinol. 24, 65-73. Olivereau, M. (1966). Action de la prolactin chez l’anguille intacte et hypophysectomisee. I. Systeme hypophysio-thyroidien et pigmentation. Gen. Comp. Endocrinol. 6, 130-143. Osewald, T., and Fiedler, K. (1968). Die Wirkung von Sauger-Prolactin auf die Shilddriise des Segelflossers Pterophyllum scalare (Chichlidae, Teleostei). Z. Zellforsch. Mikrosk. Anat. 91, 617-632. Romanoff, A. L., Smith, L. L., and Sullivan, R. A. (1938). Biochemistry and biophysics of the developing hen’s egg. II. Influence of temperature. Cornell Univ. Agric. Exp. Stat. Mem. 216, l-42. Savory, C. J. (1979). Changes in food intake and body weight of bantam hens during breeding. Appl. Anim.
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Seth, J., Toft, A. O., and Irvine, W. J. (1976). Simple solid-phase radioimmunoassays for total triiodothyronine and thyroxine in serum, and their clinical evaluation, Clin. Chem. Acta 68, 291-301. Sharp, P. J., Scanes, C. Cl., Williams, J. B.. Harvey, S., and Chadwick, A. (1979). Variation in concentrations of prolactin, luteinizing hormone, growth hormone and progesterone in the plasma of broody bantams (Gal/us domesticus). J. Enducrinol. 80, 51-57. Sharp, P. J. (1980). Female reproduction. In “Avian Endocrinology” (A. Epple and M. H. Stetson, eds.), pp. 435-455. Academic Press, New York. Sharp, P. J., and Klandorf, H. (1981). The interaction between day length and the gonads in the regulation of levels of plasma thyroxine and triiodothyronine in the Japanese Quail. Gen. Camp. Endocrinol., 45, 504-512. Sharp, P. J., and Lea, R. W. (1981). The response of the pituitary gland to luteinizing hormonereleasing hormone in broody bantams. Gen. Comp. Endocrinol.. 45, 131-133. Sherry, D. F., Mrosovsky, N., and Hosan, J. H. (1980). Weight loss and anorexia during incubation in birds. J. Comp. Physiol. Psychol. 94, 89-98. Singh, R., and Singh, T. P. (1976). Effect of prolactin administration on ovarian and thyroid activity in relation to gonadotrophic and thyrotrophic potency in a freshwater catfish, Heterapneustes (Bloch). Endokrinotagie 68, 27-34. Wada, M., Arimatsu, Y., and Kobayashi, H. (1975). Effect of prolactin on thyroid function in Japanese Quail (Corturnix corturnix japonica) Gen. Camp. Endocrinol.
27, 28-33.