Plasma Thyroid Hormone Concentrations Research Articles

Diurnal rhythms of plasma growth hormone, somatostatin, thyroid hormones, cortisol and glucose concentrations in rainbow trout, Oncorhynchus mykiss, during progressive food deprivation

Abstract The diurnal patterns of changes in plasma cortisol, growth hormone (GH), somatostatin‐14 (SRIF), thyroid hormones (L‐thyroxine, T4 and triiodo‐L‐thyronine, T3) and glucose were investigated in rainbow trout, Oncorhynchus mykiss, both during single meal‐feeding and during a progressive fast of 13 weeks. All measured variables exhibited a diurnal pattern in fed rainbow trout, most of which appeared to be correlated with the time of feeding (30–60 min after the onset of light), while additional changes, associated with the scotophase were also found for cortisol. Although fasting had no affect on mean daily plasma cortisol or SRIF concentrations, there was a progressive increase in mean daily plasma GH concentrations and a progressive decrease in mean daily plasma thyroid hormone and glucose concentrations associated with fasting. However, for GH, significant changes were not evident until week 10 of the fast. In addition, fasting appeared to phase‐shift the diurnal patterns of plasma GH, cortisol a...

Increased leucine flux and leucine oxidation during the luteal phase of the menstrual cycle in women

Possible changes in protein metabolism during the menstrual cycle were examined in eight healthy women who received an intravenous infusion of L-[1-13C]leucine on time during the follicular phase of the menstrual cycle and one time during the luteal phase. Enrichment of plasma [13C]ketoisocaproate and expired 13CO2 were measured to determine leucine flux and oxidation. Continuous respiratory gas exchange measurements were made for the determination of CO2 production, O2 uptake, and energy expenditure. The day of the tests, plasma thyroid hormone concentrations were measured as well as plasma and urinary cortisol. Leucine flux was higher during the luteal than during the follicular phase (2.25 +/- 0.39 vs 2.01 +/- 0.42 mumol.kg-1.min-1; P < 0.01), and leucine oxidation was also increased during the luteal phase [0.52 +/- 0.14 vs. 0.44 +/- 0.05 mumol.kg-1.min-1 (P < 0.05) for luteal and follicular phases, respectively]. Resting energy expenditure was increased during the luteal phase compared with the follicular phase (218 +/- 22 and 199 +/- 12 kJ/h, respectively). Plasma free triiodothyronine (T3) and the ratio triiodothyronine/reverse triiodothyronine (T3/rT3) were both significantly higher during the luteal phase [7.7 +/- 0.6 vs. 7.1 +/- 0.8 and 4.65 +/- 0.80 vs. 3.93 +/- 0.70 for T3 and T3/rT3, respectively (P < 0.05 for both comparisons)]. This study shows small changes in protein metabolism during the menstrual cycle in women, with an increase in oxidative leucine metabolism during the luteal phase. The concomitant increase observed in circulating free T3 raises the possibility that fluctuations in protein metabolism and thyroid hormones throughout the menstrual cycle are causally related.

Toxic Potency of 3,3′,4,4′,5-Pentachlorobiphenyl Relative to and in Combination with 2,3,7,8-Tetrachlorodibenzo-p-dioxin in a Subchronic Feeding Study in the Rat

Toxic and biochemical potencies of 3,3′,4,4′,5-pentachlorobiphenyl (PCB 126) were studied relative to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in a 13-week feeding study in female Sprague-Dawley rats. To study possible interactive effects the combinations of both compounds were administered. The diets were supplemented with PCB 126 (7, 50, or 180 μg/kg diet), with TCDD (0.4 or 5 μg/kg diet), or with combinations of both compounds. An estimated daily intake of 0.47 μg PCB 126/kg body weight/day caused thymic atrophy, a dramatic loss in he patic retinoids, and a marked induction in CYP1A1 and CYP1A2 activities. At a daily intake of 3.18 μg PCB 126/kg body weight/day a decrease in body weight gain, liver enlarge ment, and plasma thyroid hormone concentrations occurred. Based on a simultaneous subchronic feeding study with TCDD, a toxic equivalency factor range between 0.01 and 0.1 was estimated for PCB 126 for the mentioned effects. Antagonism was found between TCDD and PCB 126 for hepatic retinol levels and CYP1A2 activity. At the same time, TCDD and PCB 126 liver residue levels were slightly decreased by coadministration. However, these antagonistic effects occurred at maximum induction levels of CYP1A1 and CYP1A2, which are not likely to occur at levels relevant for humans.

Thyroid hormone concentrations in the gonads of wild chum salmon during maturation

Changes in gonadal and plasma concentrations of thyroid hormones were examined at various stages of maturation in chum salmon (Oncorhynchus keta) caught in the Bering Sea and the Bay of Alaska. Plasma concentrations of thyroxine (T4) were less than 5 ng ml(-1), and those of 3,5,3'-triiodo-L-thyroxine (T3) were less than 2 ng ml(-1) I in both males and females, regardless of the degree of sexual maturity or the gonadosomatic index (GSI).There was no clear relationships between circulating thyroid hormone levels and tissue levels. The ovarian T4 concentrations were undetectable (less than 0.2 ng g(-1)) or less than 2 ng g(-1) when GSI was lower than 1%, but increased thereafter and reached a plateau of 8-10 ng g(-1) when GSI became 2%. The ovarian T3 concentrations were about 5 ng g(-1) when GSI was 1%, increased to a maximum level (20 ng g(-1)) when GSI was about 2%, and decreased to a constant level of 10 ng g(-1) thereafter. The T4 and T3 content in single oocyte increased proportionally to the oocyte volume, indicating a constant incorporation of the hormones into the oocyte.The T4 concentrations in the testis were 1 ng g(-1) or less regardless of the GS1. On the other hand, the T3 concentrations were highest (15 ng g(-1)) when the GSI was less than 1%, decreased thereafter when spermatocytes appeared in the testis, and became about 5 ng g(-1) I in testes containing spermatozoa, raising the possibility of a role for T3 during early gamete and/or gonad maturation of testes.

Does the time of feeding affect the diurnal rhythms of plasma hormone and glucose concentration and hepatic glycogen content of rainbow trout?

The diurnal rhythms of plasma glucose, cortisol, growth hormone (GH) and thyroid hormone (T4, T3) concentrations and hepatic glycogen content were measured in rainbow trout that had been entrained to a specific time of daily feeding (post-dawn, midday, pre-dusk); the purpose of the study was to investigate the significance of feeding time on hormones and metabolite patterns. Plasma GH, cortisol and T4 concentrations all showed evidence of a diurnal rhythm in some treatment groups. There was a significant interaction between the time of feeding and plasma GH and cortisol concentration rhythms; for GH, this appeared to be related to the phase-shifting of the post-prandial increases in plasma GH concentrations, and for cortisol, the rhythms were only evident in fish fed in the post-dawn period [diurnal rhythms were not evident in treatment groups fed in at midday or pre-dusk]. Peak plasma T4 concentrations were evident during the photophase in all three treatment groups; however, the time of feeding had a negligible effect on the timing of those peaks. There were no apparent diurnal rhythms of plasma T3 and glucose concentrations, hepatic glycogen content or hepatosomatic index in any of the three treatment groups.

Circadian and ultradian rhythms of plasma thyroid hormone concentrations in lactating dairy cows.

Circadian and ultradian rhythms of thyroxine and triiodothyronine were analyzed by radioimmunoassay on integrated 15-min blood samples collected for 48 h from six lactating dairy cows. Body temperatures were recorded every 1.4 min using radiotelemetry. The cows were housed in an environmental chamber at 19.0 +/- 0.5 degrees C (lights on between 0700 and 2300 h), fed daily at 0900 h, and milked at 0800 and 2000 h. Mean concentrations of plasma triiodothyronine and thyroxine exhibited similar circadian rhythms with minima (0500-1300 h) and maxima (1700-0200 h) separated by 12 h. Triiodothyronine peaked 2 h before thyroxine. The thyroxine circadian rhythm preceded a circadian body temperature rhythm by 2 h. Superimposed on the circadian rhythm was an ultradian rhythm with a 90-min period that was 15-20% of the mean thyroid hormone concentrations. Peak thyroxine and triiodothyronine concentrations were 50 +/- 2 and 1.58 +/- 0.17 ng/ml, and minimal concentrations were 42 +/- 2 and 0.94 +/- 0.17 ng/ml, respectively. Our data indicate that peripheral triiodothyronine is regulated independently of peripheral thyroxine concentration.

Effects of dexamethasone on muscle protein homeostasis and on calpain and calpastatin activities and gene expression in rabbits

The objectives were to investigate the mechanisms by which glucocorticoids control proteolysis in muscle cells and the relationship between the calpain:calpastatin system and proteolysis in muscle. Female rabbits were treated with 1 mg dexamethasone (Dex)/kg body weight per day for 0, 1, 2 or 4 days after which animals were killed and muscle samples taken for analyses. Dex reduced urinary N tau-methylhistidine (NMH) 48% (day 4 versus day 1 of Dex treatment) and muscle NMH concentrations by 49% (day 1) to 40% (day 2) respectively, suggesting that protein degradation was reduced. To investigate whether the changes in apparent proteolysis were related to calpains, we examined the effects of Dex on muscle calpain and calpastatin activities. These were unaffected by Dex. This implies that Dex-dependent changes in degradation are not mediated by changes in muscle calpain or calpastatin activities. We studied the effects of Dex on calpain and calpastatin gene expression as a means of clarifying the relationships between proteinase gene expression and proteinase activities. mu-Calpain mRNA concentration was unaffected by Dex but m-calpain mRNA and calpastatin mRNA concentrations were reduced by 42-55% and 40% respectively. Dex had a similar effect on beta-actin mRNA. Although calpain and calpastatin genes behaved as house-keeping genes, changes in their expression mimicked apparent changes in proteolysis. The observation that calpain and calpastatin activities were unchanged indicates that additional regulation of the calpain:calpastatin system exists at other sites in muscle cells. To determine whether Dex-dependent changes in proteolysis were mediated indirectly, we assayed the effects of Dex on plasma thyroid hormone concentrations.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of ambient temperature during 1st day of life on thermoregulation in lambs delivered by cesarean section

We examined the effect of delivering near-term twin lambs by cesarean section into a warm (30 degrees C) or cool (15 degrees C) ambient temperature on the control of thermoregulation. Heat production was measured 20-30 h after birth during non-rapid-eye-movement sleep at 29 and 14 degrees C. At 29 degrees C there was no difference in heat production between groups, but at 14 degrees C cool-delivered (CD) lambs exhibited a 62% greater metabolic response. Irrespective of delivery temperature, 15 of the 18 lambs used shivering thermogenesis during cold exposure, indicating a reduction in the ability to use nonshivering thermogenesis in brown adipose tissue (BAT). Mean plasma concentrations of thyroxine and triiodothyronine were 35 and 45% greater, respectively, in CD lambs than in warm-delivered lambs. The level of guanosine 5'-diphosphate binding in BAT was lower than in normally delivered lambs and was not different between CD and warm-delivered lambs. Cesarean section delivery prevents the rise in BAT thermogenic activity, which results in an increased reliance on shivering thermogenesis to maintain colonic temperature. Under these conditions, delivery into a cool environment increases the plasma concentration of thyroid hormones, which benefits the neonate by enabling a greater thermogenic response via shivering.

Thyroid hormone concentrations in the plasma of fed and fasted Brahman and Hereford steers

Plasma concentration patterns of thyroxine (TJ, free T4 (FT4), triiodothyronine (T3), and free T3 (FT3) were determined in Brahman steers fed lucerne hay ad libitum and in Brahman and Hereford steers fed restricted intakes of lucerne hay at the rate of either 208 g/h before fasting for 72 h or 250 g/h before fasting for 96 h. In Brahmans fed ad libitum, the plasma concentrations of all thyroid hormone fractions were significantly (P&lt;0.01) correlated with one another and with feed intake. Within breeds, the concentrations of thyroid hormones were higher (P&lt;0.001) when animals were fed at 250 g k than at 208 g/h. During both hourly feeding regimes T4, FT4, T3, and FT3 concentrations were higher (P&lt;0.001) in Brahmans than in Herefords. Fasting after both hourly feeding regimes lowered (P&lt;0.001) the concentrations of T4 about 53% in Brahmans and 30% in Herefords, while FT4, T3, and FT3 were lowered about 68% in Brahmans and 50% in Herefords. Consequently, thyroid hormone concentrations were significantly lower in Brahmans than in Herefords after 72 h fasting but did not differ significantly between breeds after 96 h fasting. The present results, together with those of our previous work showing breed differences in rumen metabolism, support the concept that, in Hereford and Brahman steers fed the same amount of hay in a thermoneutral environment, breed differences in plasma concentrations of thyroid hormones originate from quantitative differences in the supply of nutrients from the rumen to body tissues.

Thyroid hormones are required for the expression of seasonal changes in red deer (Cervus elaphus) stags.

Experiment 1, from 6 July 1990 (winter) to 8 November 1990 (spring), examined the effect of an early elevation of plasma thyroid hormone concentrations on the expression of seasonal changes in 20-month-old stags. Four stags were injected subcutaneously with 1 mg thyroxine (T4) daily, and four with vehicle only. Plasma T4 concentration was elevated by injection of T4; the mean concentration 24 h after injection was 192 +/- 31 nmol L-1 compared with 58 +/- 5 nmol L-1 in controls on 21 September. However, live weight, testicular diameter, plasma testosterone concentration and moulting underwent similar changes in both groups of animals. Experiment 2 tested the hypothesis that thyroid hormones are required for the expression of changes that occur during spring and early summer in red deer stags. Thyroidectomized (THX) stags (n = 4) of mixed age (> 22 months old) were given a replacement dosage of T4 or vehicle only (controls) during spring (from 7 September). T4-treated THX stags underwent testicular regression, antler regeneration and spring moult during spring and early summer (October-December), whereas control THX stags did not display these changes. During spring and summer, T4-treated stags gained more live weight (P < 0.05) than control stags. These results show that, in stags, thyroid hormones are required for the expression of seasonal changes and that these changes are not caused by the seasonal elevation of plasma concentrations of thyroid hormones.

Nitrogen and sulfur metabolism and plasma thyroid hormone concentrations in fleeceweight-selected and control Romney sheep at two ambient temperatures

This study was conducted to determine the effect of ambient temperature on nitrogen and sulfur metabolism in 7-month-old rams from the Massey University fleeceweight-selected (FW) and control (C) lines of Romney sheep. Eight rams from each line were exposed to either 6�C or 25�C ambient temperature under a constant photoperiod. Detailed studies of sulfur metabolism were made on four of the rams from each line at each ambient temperature. Intake and faecal output of dry matter and nitrogen were lower at 25�C than at 6�C, but there was no effect of ambient temperature on digestibility of either dry matter or nitrogen. Nitrogen balance was lower at 25�C than at 6�C, but none of the parameters relating to nitrogen balance was influenced by selection line. There were also no effects of ambient temperature or selection line on clearance rates of urea or creatinine. Blood samples were collected from the animals at 2 h intervals over a 24 h period to determine plasma concentrations of urea, creatinine, thyroxine and triiodothyronine. Although the between-line differences in concentrations of these hormones and metabolites varied throughout the 24 h period, and with ambient temperature, there were no consistent interactions between the effects of selection line and ambient temperature. There were no consistent effects of selection line, or interactions of selection line with ambient temperature, on sulfur and sulfate balances, concentrations of leucine, cyst(e)ine and glutathione in whole blood or on irreversible loss rates of leucine and cyst(e)ine. However, when considered across lines and ambient temperatures, both the whole blood concentrations (P &lt; 0.10) and the irreversible loss rates (P &lt; 0.05) of leucine and cyst(e)ine were positively related to midside wool growth. The only significant (P &lt; 0.05) interaction between selection line and ambient temperature was observed in the wool sulfur concentration which was lower in the FW rams than in the C rams at 6�C, but not at 25�C. It is concluded that none of the metabolic measurements made in this study explains previous inconsistencies observed in metabolic differences between sheep from lines divergently selected on the basis of fleeceweight. Wool sulfur content was again shown to be a potentially useful predictor of genetic merit for fleeceweight, but no clear metabolic basis for differences between the lines could be demonstrated even with detailed measurements of sulfur metabolism.

Roles of skeletal muscle morphology and activity in determining Na(+)-K(+)-ATPase concentration in young pigs

It has been demonstrated previously that the Na(+)-K(+)-adenosinetriphosphatase (Na(+)-K(+)-ATPase) concentration (total concentration of [3H]ouabain-binding sites = maximal [3H]ouabain-binding capacity, Bmax) in longissimus dorsi muscle is higher in young pigs living in a cold than in a warm environment, with the effect being even greater in those on a low rather than a high energy intake in the cold. The importance of thyroid status, myofiber type and size, and muscular activity in determining the concentration of Na(+)-K(+)-ATPase has therefore been assessed in longissimus dorsi, semitendinosus, and soleus muscles from 8-wk-old littermate pigs, which had been living 35 or 10 degrees C on either a high or a low energy intake for 3-4 wk. Changes in neither plasma thyroid hormone concentrations nor myofiber type could account for the greater Bmax at 10 vs. 35 degrees C observed in all three muscles; instead, it was possibly related to the greater muscular activity associated with shivering in the cold. More than 50% of the increase in Bmax on the low compared with the high intake in the cold could be attributed to the smaller fiber size and hence greater membrane area in animals on the low intake, and it is concluded that membrane surface area must be assessed in studies of membrane-bound enzymes.

The effects of thyroid hormones on the heart following global ischemia. A clinical and experimental study.

Cardiopulmonary bypass is associated with a reduction in plasma thyroid hormone concentrations in patients undergoing cardiac surgery. However, studies of the effects of cardiopulmonary bypass on thyroid function are limited and many studies report conflicting data concerning only the period of cardiopulmonary bypass. In this study, we tried to clinically determine the effects of cardiopulmonary bypass on concentrations of thyroid hormones by comprehensive thyroid function tests in 10 patients before and after surgery, and observed the benefits of triiodothyronine supplementation after global ischemia on myocardial function experimentally in guinea pigs. In patients undergoing surgery, concentrations of total triiodothyronine and free triiodothyronine decreased progressively on the institution of cardiopulmonary bypass and remained below normal levels until 24 hours postoperatively. In the guinea pig hearts studied in a Langendorf perfusion apparatus, T3 supplementation enhanced percentage recovery of ventricular contractile force, heart work and heart rate with respect to other groups receiving no T3 supplementation or T3 supplementation without any ischemic interval.

Plasma Concentrations of Corticosterone and Thyroid Hormones in Broilers Provided Various Lighting Schedules

The purpose of this study was to measure plasma corticosterone and thyroid hormone concentrations in broilers exposed to various photoschedules. Day-old male broilers were placed on litter floors in light-controlled chambers. Four chambers were randomly assigned to each of four light treatments: 1) 23 h light (L):1 h dark (D) from 1 to 56 d of age (designated extended, E); 2) 1L:3D from 1 to 56 d (intermittent, I); 3) 6L:18D from 1 to 14 d and 1L:3D from 15 to 56 d (brief-I, BI); and 4) 6L:18D from 1 to 14 d and 23L:1D from 15 to 56 d (brief-E, BE). Blood samples were collected 0, 4, and 20 h after lights-on (1200 h) at 13, 41, and 55 d of age. Corticosterone concentration did not differ among light treatments or collection times and was decreased at 41 d compared with 13 d (.65 vs 2.11 ng/mL). Triiodothyronine (T3) increased and thyroxine (T4) decreased with age. At 13 d, there were light treatment by sampling time interactions for T3 and T4. Plasma T3 was elevated in Treatments BI (3.11 ng/mL) and BE (3.40 ng/mL) compared with Treatments E (2.39 ng/mL) and I (2.30 ng/mL) at 0 h; the former two treatments showed decreased T3 concentrations at 4 and 20 h compared with 0 h. Plasma T4 showed reciprocal changes to T3. There were no differences in T3 or T4 for light treatments or sampling times at 41 and 55 d. The light treatments did not cause severe stress, and elevated T3 concentrations in Treatments BI and BE at 13 d were most likely associated with feeding during the dark period.

Stocking density and cohort sampling effects on endocrine interactions in rainbow trout

Studies were conducted to explore the effect of cohort sampling and stocking density on the interactions between plasma growth hormone (GH), thyroid hormone and cortisol concentrations in rainbow trout. Depending on the experimental design, plasma GH concentrations were either suppressed, or elevated by sequential removal of cohorts from the holding aquarium. Since plasma cortisol concentrations consistently increased during cohort sampling, regardless of experimental design, it would appear that the apparent correlation (direct or inverse) is the result of concomitant changes, i.e. not necessarily a cause-effect relationship. Plasma GH concentrations of rainbow trout were not correlated with eviscerated body weight. Trout stocked at 150 kg m−3 exhibited a significantly lower mean growth rate, hepatosomatic index, hepatic lipid reserve, plasma triiodo-l-thyronine (T3) concentration andin vitro hepatic T3 production than trout stocked at 60 kg m−3. These observations are consistent with the former group being food deprived or ration restricted. Stocking density appeared to have no effect on plasma GH or cortisol concentrations, or on the pituitary-interrenal axis response to stressor challenge, or the thyroid tissue response to exogenous TSH challenge.

Effects of pre- and postnatal exposure to chlorinated dioxins and furans on human neonatal thyroid hormone concentrations.

Animal studies have shown that dioxins influence plasma thyroid hormone concentrations. To investigate the effect of chlorinated dioxins and furans on thyroid hormone concentrations in humans, we studied 38 healthy breast-fed infants. The study population was divided into two groups according to the dioxin concentrations in milk fat of their mothers. Blood samples were taken at birth and at the ages of 1 and 11 weeks. At birth a tendency to higher total thyroxine (tT4) concentrations was found in the high exposure group. At the ages of 1 and 11 weeks the increase of mean tT4 concentrations and tT4/thyroxine-binding globulin ratios in the high exposure group reached significance as compared to the low exposure group. At birth and 1 week after birth, mean thyrotropin (TSH) concentrations were similar in both groups, but at the age of 11 weeks the mean TSH concentrations were significantly higher in the high exposure group. We postulate that the observed plasma tT4 elevation in infants exposed to dioxins before and after birth is the result of an effect on the thyroid hormone regulatory system.

Effects of Pre- and Postnatal Exposure to Chlorinated Dioxins and Furans on Human Neonatal Thyroid Hormone Concentrations

Animal studies have shown that dioxins influence plasma thyroid hormone concentrations. To investigate the effect of chlorinated dioxins and furans on thyroid hormone concentrations in humans, we studied 38 healthy breast-fed infants. The study population was divided into two groups according to the dioxin concentrations in milk fat of their mothers. Blood samples were taken at birth and at the ages of 1 and 11 weeks. At birth a tendency to higher total thyroxine (tT4) concentrations was found in the high exposure group. At the ages of 1 and 11 weeks the increase of mean tT4 concentrations and tT4/thyroxine-binding globulin ratios in the high exposure group reached significance as compared to the low exposure group. At birth and 1 week after birth, mean thyrotropin (TSH) concentrations were similar in both groups, but at the age of 11 weeks the mean TSH concentrations were significantly higher in the high exposure group. We postulate that the observed plasma tT4 elevation in infants exposed to dioxins before and after birth is the result of an effect on the thyroid hormone regulatory system.

Investigation of mechanisms mediating the increase in plasma concentrations of thyroid hormones after a meal in young growing pigs

These studies investigated a number of possible mechanisms which could mediate the increase in plasma concentrations of thyroid hormones after a meal in young growing pigs. It has been established that in animals fed one meal a day, an immediate rise in plasma 3,5,3'-tri-iodothyronine (T3) and a slightly delayed increase in thyroxine (T4) levels are followed by a more sustained peak in both hormones several hours later. The increase in thyroid hormones involves both total and free T3 and T4, and there is no change in plasma albumin, the high-capacity thyroid hormone-binding protein in the pig. It has also been shown that the immediate rise in plasma T3 is not mediated either by an increase in plasma glucose concentration or by neural mechanisms associated with distension of the gastrointestinal tract. However, the finding that plasma T3 increases rapidly after feeding in thyroidectomized animals maintained on a replacement dose of T4 alone, indicates the source of T3 to be non-thyroidal. It is concluded that the rise in plasma thyroid hormones after a meal depends on the energy content of the food but not directly on the circulating glucose levels. The immediate increases in plasma T3 and T4 are probably due largely to a redistribution of the hormonal pools, and peripheral 5'-monodeiodination of T4 may also contribute significantly to the post-prandial rise in T3. The potential significance of these findings in relation to both the metabolic and growth-promoting effects of thyroid hormones is discussed.

Perinatal Thyroid Hormones and Hepatic 5′Deiodinase in Relation to Hatching Time in Weight-Selected Lines of Chickens

Plasma thyroid hormone concentrations, liver weight, body weight, and hepatic capability for triiodothyronine (T3) production were measured at 8-h intervals on Days 19 through 21 in embryos and chicks from lines selected for high (HW) and low (LW) body weight at 8 wk of age. Embryos were categorized as not having entered the perinatal period (nonpipped, NP) or as being in one of three perinatal stages: embryos that had pipped into the air cell (AC), embryos pipped through the shell (TS), and chicks within 24 h of hatching (H). Both plasma thryoxine (T4) and T3 peaked at the TS stage in embryos of both lines. Embryos had higher concentrations of both hormones and hatched earlier in the LW than in the HW line. This association and evidence from other studies is suggestive that T3 may be playing a role in line differences in hatching time. Hepatic 5′deiodinase (5′D) activity was higher in LW than HW embryos and chicks at the AC, TS, and H stages although the opposite had been the case prior to the perinatal period (NP stage). Hepatic 5′D increased at each stage from AC to TS to H. When the patterns of liver growth and body weight were considered, this pattern and the differences between the lines were exaggerated further. Comparison of the plasma and 5′D patterns during the perinatal period suggests that substrate (T4) supply may be more important than 5′D capability of the liver in determining the pattern of T3 supply during some of these stages.

Low Temperature and Short Days Together Induce Thyroid Activation and Suppression of LH Release in Japanese Quail

We have found in Japanese quail that low ambient temperature is required to terminate breeding activity in the presence of short days (Wada et al., 1990, Gen. Comp. Endocrinol. 80, 465-472; Tsuyoshi and Wada, 1992, Gen. Comp. Endocrinol. 85,424-429). To elucidate the mechanism for photoperiodic and temperature regulation of the release of luteinizing hormone (LH), several serum variables were measured in three groups of mature male birds: (a) birds kept on long days of 16L:8D, 24 hr at 19° as an initial control group (Group IC), (b) birds transferred from long days to short days of 8L:16D, 24 hr at 19° (Group S) for 14 days, and (c) birds transferred to short days of 8L:16D and low temperature cycles of 12 hr, 19°:12 hr, 9° (Group SL) for 14 days. Testicular mass and plasma concentrations of LH significantly decreased to nonbreeding levels in Group SL, but not in Group S, confirming our previous results. Hematocrit, serum osmolarity, and concentrations of Na +, K +, Ca 2+, Mg 2+, and Cl - ions were not different among the three groups. Serum concentrations of free fatty acids were increased in Group SL, but the increase was not statistically significant. On the other hand, plasma concentrations of thyroid hormones changed significantly; thyroxine (T 4), but not triiodothyronine (T 3), increased in Group S, and T 3, but not T 4, increased in Group SL. To follow the changes in plasma levels of LH, T 4, and T 3 during the treatments, blood samples were collected every other day for 2 weeks from birds in the three groups of mature male birds described above. In Group C, plasma concentrations of LH, T 4, and T 3 did not change during the experimental period. In Group S, plasma concentrations of LH remained at relatively high levels and T 4 increased after an initial decrease; T 3 showed a slight increase. In Group SL, plasma concentrations of LH decreased rapidly to the nonbreeding level and T 3 showed a great increase, while changes in T 4 were basically similar to those in Group S. These results indicate that thyroid hormones are involved when a breeding season terminated by short days and low temperature, and they suggest that T 3 and 5′-monodeiodination of T 4 are at least a part of the mechanism.