Effect of Ambient Salinity,Food-deprivation and Prolactin on the Thyroidal Response to TSH,and in vitro Hepatic T4 to T3 Conversion in Yearling Coho Salmon,Oncorhynchus kisutch

This study examines the effect of food deprivation, increased ambient salinity and prolactin administration on the thyroidal response to ovine TSH, and in vitro hepatic monodeiodination of T4 to T3 in coho salmon, Oncorhynchus kisutch. Fed fish and fish food-deprived for 18 days showed similar significant increases in plasma T4 9 and 24 h after a single injection of TSH. Plasma T3 levels were also elevated in both fed and food-deprived fish 9 h after the TSH injection but plasma T3 levels in the food-deprived fish were markedly lower than in the fed salmon. The increase in T4 and T3 evident in freshwater-acclimated fish after TSH administration was not found in salmon acclimated to 65% sea water. Prolactin, given alone (either as a single injection or a series of three daily injections) had no effect on plasma T4 or T3 levels. When given together with TSH prolactin prolonged the T4 and T3 elevating effect of TSH. Food-deprived salmon had lower in vitro hepatic T4 to T3 conversion rates than fed groups but T4 to T3 conversion did not appear to be affected by increased ambient salinity, or by prolactin and/or TSH administration.     

Effect of ovine TSH, thiourea, ovine prolactin and bovine growth hormone on plasma thyroxine and tri-iodothyronine levels in rainbow trout,Salmo gairdneri

Summary A single injection of ovine TSH (1.1 g or 2.2 g/g body weight) effected a significant (P<0.01) increase in plasma T₄ levels in rainbow trout within 9 h and 1 h respectively. In fish given the higher dose the T₄ levels were still significantly higher (P<0.01) than in the controls 24 h after the injection. Ovine TSH had no significant effect on plasma T₃ levels. Plasma T₃/T₄ ratios in fish given the higher TSH dose were significantly lower than the controls at 3 h (P<0.01), 6 h (P=0.01), 9 h and 24 h (P<0.05) while in fish given the lower dose they were significantly lower than in controls at 3 h (P<0.01), 6 h (P=0.01) and 9 h (P<0.05).T₄ levels in TSH-injected fish were significantly higher (P<0.05) than in controls after 3 and 11 injections but were not significantly different after 16 injections. Plasma T₃ and T₃/T₄ ratios did not differ significantly in fish given multiple injections of either TSH or saline.Plasma T₄ levels in fish treated with thiourea were significantly lower (Pº0.01) than in comparable controls after 6, 9 and 15 days and plasma T₃ levels were lower (P<0.05) after 15 days treatment. T₃/T₄ ratios did not differ significantly at any time period.A single injection of bovine STH (10 g/g body weight) effect a significant rise in plasma T₄ levels 9 h (P=0.05) and 24 h (P<0.01) after the injection while ovine prolactin in a similar dose was without effect. Plasma T₃ levels in saline injected fish showed a steady decline over the 24 h following the injection whereas levels in prolactin and STH injected animals tended to rise. T₃ levels in the saline-injected fish were significantly higher (P<0.01) than in prolactin and STH injected animals 1 h after the injection but were significantly lower (P<0.01) than in the hormone-treated fish 24 h after the injection. There were no significant differences in T₃/T₄ ratios in any of the groups. Multiple injections of STH effected a significant increase (P<0.05) in plasma T₄ compared with the controls; prolactin had no significant effect. There was no significant differences in plasma T₃ concentration or T₃/T₄ ratios in any of the groups.     

Studies on the relationship between osmotic or ionic regulation and thyroid gland activity in two salmonid fishes, Salmo gairdneri Richardson and Oncorhynchus kisutch Walbaum

In freshwater-acclimated rainbow trout a single intraperitoneal injection of ovine TSH significantly elevated plasma thyroxine (T₄) levels within 1 h after the injection. In seawater adapted trout the increase in T₄ after TSH-treatment was not evident until 6 h after the injection. TSH caused a transient fall in plasma Na⁺ and Cl^- between 3 h and 9 h after the injection in seawater-adapted fish and plasma Na⁺ was lowered in freshwater-adapted trout 24 h after the injection. Although there were clear histological changes in the thyroid gland of freshwater-adapted trout after TSH-injection, no such changes were evident in seawater-adapted fish.
Plasma thyroid hormone levels and thyroid histology in freshwater-adapted rainbow trout and coho salmon transferred to sea water, and seawater-adapted trout transferred to fresh water showed no consistent changes compared with controls.
The data are interpreted to indicate that although ambient salinity may have indirect effects on thyroid activity there is no direct involvement in ionic or osmotic regulation in the two species.     

Effects of gonadectomy on prolactin and LH secretion and the pituitary-thyroid axis in male dogs

The effects of gonadectomy on the secretion of prolactin, LH, TSH, and thyroxine were investigated. Blood serum hormone concentrations were analysed before and at 20, 120, and 180 min after a single iv TRH injection in each of eight healthy intact and castrated male beagle dogs before (control) and after 4-week treatment with the dopamine-2 receptor agonist cabergoline. Under control conditions the mean prolactin, TSH, and thyroxine concentrations were similar in intact and gonadectomised dogs, and administration of TRH provoked a significant (p < 0.01) increase in concentrations of the three hormones. The overall inhibitory effect of cabergoline treatment on prolactin secretion was more pronounced in the castrated dogs compared with the intact group. Cabergoline significantly suppressed the TRH-induced prolactin increase in each group (p < 0.01). Corresponding TRH-stimulated TSH concentrations were not affected by cabergoline. In the gonadectomised dogs, thyroxine concentrations before and at 120 and 180 min after TRH injection were significantly lower than under control conditions. LH concentrations were always higher (p < 0.01) in gonadectomised dogs compared with the intact dogs, but appeared to be affected neither by TRH nor by cabergoline administration. It can thus be concluded from the results, that gonadectomy does not result in hyperprolactinaemia in male dogs, while LH concentrations are significantly increased due to missing androgen feedback. Thyroid function remains unaffected by gonadectomy. Testicular steroids appear to interact with central dopaminergic and probably other neuroendocrine mechanisms regulating the secretion of prolactin, TSH, and thyroxine. Thus, long-term dopamine-2 receptor agonistic treatment may lead to a hypothyroid condition in castrated male dogs.     

Twenty-four-Hour Rhythms of Serum Acth,Prolactin, Growth Hormone,and Thyroid-Stimulating Hormone,and of Median-Eminence Norepinephrine,Dopamine, and Serotonin,in Rats Injected with Freund's Adjuvant

The effect of Freund's adjuvant injection on 24-h variation of circulating ACTH, prolactin, growth hormone (GH), and thyroid-stimulating hormone (TSH) levels, and of norepinephrine (NE) content, and dopamine (DA) and serotonin (5HT) turnover in median eminence, was examined in adult rats kept under light between 0800 and 2000 h daily. Groups of 6–10 animals Freund's complete adjuvant or its vehicle at 1 lOOh 3 days before sacrifice and were killed by decapitation at six different time intervals throughout a 24-h cycle. In rats injected with adjuvant's vehicle, serum ACTH and prolactin exhibited peak values around the light-dark transition (p < 0.0001 and < 0.04, respectively), while the maximum in TSH was found in the late afternoon (p < 0.0001, one-way ANOVA). GH levels did not vary on a 24-h basis. In Freund's adjuvant-injected rats, 24-h variations of TSH levels became blunted, while 24-h variations of prolactin and ACTH persisted. Freund's adjuvant augmented serum ACTH and prolactin levels, and decreased GH and TSH levels (p < 0.0007, factorial ANOVA). Median-eminence NE content, and turnover of DA, assessed by measuring dihydroxyphenylacetic acid, DOPAC/DA ratio, and of 5HT, assessed by measuring 5-hydroxyindoleacetic acid, HIAA/5HT ratio, varied on a 24-h basis in rats receiving adjuvant's vehicle (p < 0.02). Median-eminence NE content attained its maximum at 1600–2000 h, while maxima in DOPA/DA and HIAA/5HT ratios occurred at 0400 h. Injection with Freund's adjuvant reduced the amplitude of the daily variation of NE content, shifted the maximum of DOPAC/DA ratio toward the light-dark transition, and blunted the daily variation in HIAA/5HT ratio in median eminence. The administration at 1200 of the immunosuppressant drug cyclosporine (5 mg/kg, 5 days) restored the augmented ACTH and prolactin levels (p < 0.0001, factorial ANOVA) and depressed GH and TSH levels (p < 0.02) found in Freund's adjuvant-injected rats. Cyclosporine was also effective in restoring 24-h rhythmicity of serum ACTH and TSH, but not of prolactin, levels. Cyclosporine did not modify the effect of Freund's adjuvant on time-of-day changes of median-eminence NE content, but it was effective in counteracting the changes of DA and 5HT turnover found after immunization. The results are compatible with a significant effect of immune-mediated inflammatory response at an early phase after Freund's adjuvant injection on ACTH, GH, prolactin, and TSH release, which is partially sensitive to immunosuppression by cyclosporine. (Chronobiology International, 14(3), 253–265, 1997)     

Hind-limb protein metabolism in growing sheep; effects of acute and chronic infusion of clenbuterol by close arterial and systemic routes

1. Close arterial infusion of clenbuterol (0.7 μg/hr) for a 3 hr period led to decreased protein synthesis and degradation (both P < 0.05) across the hind-limb of sheep.2. Systemic infusion of the drug (14 μg/hr) for a similar period increased blood flow (P < 0.001) through the hind-limb and decreased protein degradation (P < 0.05).3. Following chronic (7 day) close-arterial infusion of clenbuterol (1.9 μg/hr) hind-limb protein synthesis and degradation again declined (P < 0.05) but this was apparently not recovered during 7 days of drug withdrawal.4. In consequence, during subsequent systemic infusion of the drug (62 μg/hr) the lower rates of protein metabolism were not altered significantly, despite improved whole nitrogen retention (+ 30%, P < 0.01).5. The results are discussed with reference to the differential actions of β-agonists on the various tissues of the hind-limb.     

Involvement of β3-adrenergic receptors in in vivo cardiovascular regulation in rainbow trout (Oncorhynchus mykiss)

Currently, we have little information concerning the involvement of β₃-adrenergic receptors (AR) in cardiovascular regulation in fishes. The goal of this study was to investigate the effect of β₃-AR ligands on in vivo cardiovascular function in larval and adult rainbow trout (Oncorhynchus mykiss). In adult fish, injection of BRL₃₇₃₄₄ (β₃-AR agonist) resulted in an increase in heart rate (f_H) (~ 31%) while stroke volume (Sv) was reduced (? 25.9%). Injection of SR_59230A (β₃-AR antagonist) and propranolol (β₁/β₂-AR antagonist) resulted in increases in dorsal aorta blood pressure (P_DA) with differing effect on cardiac variables (f_H and Sv). To confirm specificity of the results, BRL₃₇₃₄₄ was injected following sequential injections of phentolamine (α₁-AR antagonist), atropine (muscarinic antagonist), propranolol and SR_59230A. While phentolamine had no effect on BRL₃₇₃₄₄, atropine completely abolished the influence of BRL₃₇₃₄₄ on f_H, Sv and cardiac output (Q). In larval trout, BRL₃₇₃₄₄ (10 and 100 μM) induced a significant concentration-dependent increase in f_H while SR_59230A (1 and 10 μM) and propranolol (1 and 10 μM) separately caused a significant concentration-dependent decrease. These data suggest that β₃-ARs have an important role in regulation of cardiovascular function, and provide evidence for a potential interaction between muscarinic and adrenergic receptors in rainbow trout.     

The use of intramuscularly administered methyl-TRH to evaluate the pituitary-thyroid axis.

The present study was carried out to evaluate the effectiveness of intramuscular administration of methyl-TRH, a potent analogue of thyrotropin-releasing hormone, for assessing pituitary reserve of TSH and prolactin and for distinguishing euthyroid, hypothyroid and hyperthyroid individuals. Serum samples were taken for 24 hours after intramuscular injection of methyl-TRH, 200 microgram, in 19 euthyroid subjects, 9 hypothyroid men and 9 hyperthyroid men. The mean serum prolactin and TSH concentrations were significantly elevated over baseline levels at 30 min in the euthyroid individuals and remained elevated for 3 to 4 hours. The serum TSH, T3 and T4 responses after intramuscular methyl-TRH in euthyroid subjects were clearly distinguishable from those of hyperthyroid and hypothyroid patients. Significant elevation of the serum T3 and T4 concentrations at 24 hours after intramuscular injection of methyl-TRH shows the sustained effect of this TRH analogue in euthyroid subjects.     

Suppression of plasma thyroid hormone concentrations by cortisol in the European eel Anguilla anguilla

Female European eels, Anguilla anguilla, were given a single intra-arterial injection via a catheter of cortisol hemisuccinate at doses ranging from 3.5 to 35 micrograms (15 to 150 micrograms/kg body wt), yielding mean plasma cortisol levels of 87-410 ng/ml 2 hr after injection. Cortisol treatment (17.5 and 35 micrograms) significantly decreased plasma levels of thyroxine (T4) and triiodothyronine (T3) within 24 hr relative to those in control fish. Cortisol treatment (35 micrograms) appeared to increase the clearance rate of 125I-T3 from plasma and the proportionate uptake of radioactivity in certain tissues after injection of 125I-T3. Cortisol treatment had no apparent effect on the plasma clearance of 125I-T4 or tissue distribution of radioactivity after injection of 125I-T4.     

The effect of carbon tetrachloride on the total plasma protein concentration of rainbow trout,Salmo gairdneri

1. The effect of a single i.p. injection of CCl₄ on total plasma protein and albumin concentrations was measured in the rainbow trout.2. CCl₄ treatment caused a significant reduction in total plasma protein concentration at 12, 24 and 36 hr post-treatment.3. At 24 hr post-treatment plasma albumin concentration was significantly reduced only in fish given the highest dose of CCl₄ (2.0 ml/kg).4. Several factors, including intestinal inflammation and hemorrhages, could have contributed to the decreased plasma protein concentration in the trout.     

Effect of central injection of bradykinin and bradykinin potentiating factor upon release of anterior pituitary hormones in ovariectomized female rats

The effects of third ventricular (IVT) injection of 25 μg of bradykinin (BK) upon plasma levels of LH, FSH, TSH, GH and prolactin were investigated in conscious ovariectomized female rats bearing indwelling jugular cannulae. Some animals were pretreated with bradykinin potentiating factor (BPF). Intravenous administration of BK had no effect upon hormone levels. IVT injection of BK significantly depressed plasma prolactin levels at 15 and 30 min post-drug, with levels returning to control values by 60 min. Pretreatment of animals with BPF (75 μg/3 μl) prolonged the prolactin suppression induced by BK for up to two hours. Plasma LH, FSH, TSH and GH levels in BK-rats were not significantly different from those of saline-injected animals at any time point measured. Neither BPF alone nor in conjunction with BK had any effects upon plasma levels of TSH; however, BK plus BPF suppressed FSH concentrations at 75 min post-BPF, while BPF alone appeared to increase GH levels at 45 min. In vitro incubation of hemipituitaries with 0.083, 0.83 or 8.33 μg/ml BK had no effect upon the release of LH, TSH or prolactin compared to control values. However, the secretion of GH and FSH was suppressed by the lowest dose of BK tested. These results suggest that BK may play a physiological inhibitory role in the regulation of prolactin, which can be augmented by preventing its degradation, i.e. via BPF. The effect of the peptide seems to be mediated by the CNS since neither intravenous injection of BK nor in vitro incubation of pituitaries with the peptide modified prolactin release.     

Regulation of atrial contraction in the seawater-adapted eel,Anguilla japonica

The atrium isolated from the seawater-adapted eel beats spontaneously in normal Ringer solution for more than 10 hr. The strength of beating was inhibited by acetylcholine (ACh) and the inhibitory effects were blocked by atropine, a muscarinic ACh-receptor antagonist, indicating existence of muscarinic ACh-receptor on the atrium. The atrial contractility was stimulated by catecholamines and their agonists; the order of potency being isoproterenol > adrenaline (AD) = noradrenaline (NA) > phenylephrine > clonidine. The stimulatory effects of AD was completely blocked by propranolol, a β-adrenoceptor antagonist, but not by phentolamine, an α-adrenoceptor antagonist. These data were consistent with characteristics of β-adrenoceptors. Further characterization of the β-receptor was not attempted. The positive inotropic and chronotropic actions of AD were not completely blocked either by atenolol, a β₁-adrenoceptor antagonist, or by ICI 118551, a β₂-adrenoceptor antagonist. When electrical current with a short duration (0.25 msec) was passed through the atrium, the beating was inhibited initially, then enhanced later. The initial inhibition was inhibited by atropine and the later enhancement was blocked by propranolol. These results indicate that the electrical stimulation releases ACh and catecholamine(s) from the nerve endings. The positive inotropic and chronotropic effects of catecholamines were mimicked by tyramine, a catecholamine releaser from sympathetic nerve endings.     

Effects of dietary conjugated linoleic acids on cellular immune response of piglets after cyclosporin A injection

The present study investigated the effects of dietary conjugated linoleic acid (CLA) on the cellular immune response of piglets after cyclosporin A (CsA) treatment. The experimental study had a 2×2 factorial design, and the main factors consisted of diets (0% or 2% CLA) and immunosuppression treatments (CsA or saline injection). CsA injection significantly increased feed : gain (F : G) of piglets (P<0.05); however, dietary CLA significantly decreased F : G of piglets (P<0.05). Dietary CLA partly ameliorated the deterioration of the feed conversion rate caused by CsA treatment (P<0.01). CsA treatment significantly decreased the percentages of CD4⁺ and CD8⁺ T lymphocytes in the thymus (P<0.01). Dietary CLA increased the percentages of CD4⁺ CD8⁺ double-positive and CD8⁺ single-positive T lymphocytes in the thymus (P<0.05), and had the trend to inhibit the decrease of CD4⁺ T lymphocytes in the thymus after CsA injection (P=0.07). CsA treatment significantly depleted the peripheral blood CD3⁺, CD4⁺ and CD8⁺ T lymphocytes (P<0.01). Dietary CLA significantly increased the number of peripheral blood CD8⁺ T lymphocytes and interleukin-2 (IL-2) production (P<0.05), and inhibited the decreases of peripheral blood CD3⁺, CD4⁺ and CD8⁺ T lymphocytes counts (P<0.01) as well as IL-2 production (P<0.05) after CsA treatment. Dietary CLA partly rescued the decrease of lymphocyte proliferation after CsA injection (P<0.05). In summary, dietary CLA effectively ameliorated CsA-induced cellular immunosuppression in piglets.     

B-naphthoflavone induction and its effect on hepatic phospholipid metabolism in rainbow trout (Salmo gairdneri)

1. B-naphthoflavone (BNF) induction of microsomal cytochrome P-488 and its effect on liver phospholipid metabolism were examined in rainbow trout (Salmo gairdneri) 24 and 96 hr after intraperitoneal injection. 2. Cytochrome P-448 content increased at 96 hr to approximately double the cytochrome content of control fish. 3. Computer-analyzed laser densitometry scans of LDS-polyacrylamide gels of 96 hr BNF-treated liver microsomes showed a 90% increase in cytochrome P-448 levels. 4. A 34% increase in microsomal phospholipid (mumol/mg protein) was observed 24 hr after BNF injection, with a marked increase in choline, ethanolamine and inositol phospholipids. 5. Following 96 hr of exposure to BNF some differences in enzyme activity were noted; choline kinase and cytidylyltransferase activities were reduced, while a marked increase was observed in choline phosphotransferase activity. In light of current information on induction of liver microsomal phospholipid metabolism in mammals, the results of the this study suggest that trout do not respond like mammals to inducers of monooxygenase activity.     

Induction of ovulation with gonadotropin-releasing hormone during proestrus in cattle: influence on subsequent follicular growth and luteal function

Induction of ovulation by administration of gonadotropin-releasing hormone (GnRH) is commonly practiced in cattle to treat repeat breeders or cows exhibiting long estrous periods. This treatment may, however, disturb normal reproductive functions if timing is incorrect. The objective of the present study was to investigate the effect of exogenous GnRH on estradiol secretion of the ovulatory follicle, occurrence of ovulation, development and function of the corpus luteum (CL) and growth of a dominant follicle after ovulation in the bovine, when GnRH treatment was given before the expected physiological LH-surge. Luteolysis was induced by cloprostenol (PG) in three cows and six heifers. Every animal was assigned once to each of the following treatment or control manipulations, receiving either a single dose (0.1 mg) of GnRH (gonadorelin) at (1) 24 h (T1), (2) 48 h (T2), or (3) 72 h (T3) after PG, or (4) no gonadorelin (control manipulation, C). Ovaries were scanned by ultrasound and blood samples were collected for progesterone (P₄) and estradiol-17β (E-17β) determination. Growth curves of dominant follicles between treatment 1 and the control differed significantly (P<0.01). One day after ovulation, the diameter of the dominant follicle was almost 1 mm larger in T1. This difference remained almost unchanged during the entire follow-up period. The recruitment of a new follicular wave after ovulation seemed to occur earlier. Development of CL and levels and profiles of P₄-production remained unaffected. When GnRH was given 1 day after PG injection, two animals showed significantly different development of CL (P<0.05) and of P₄-production (both in concentrations [P<0.05] and profile [P<0.01]). After normal ovulation and CL development, luteolysis took place on days 5 or 6 after ovulation, and animals ovulated on days 9 and 10. It is suggested that early induction of ovulation with GnRH can cause shortened luteal function in cattle and, ultimately, reduced fertility.     

Effects of tartrate thyrotropin-releasing hormone treatment on serum thyrotropin, free triiodothyronine, free thyroxine and prolactin levels in patients with spinocerebellar degeneration.

The aim of the present study was to investigate the pituitary-thyroid axis function during the long-term (30 days) intramuscular administration of 4 mg/day of thyrotropin-releasing hormone tartrate (TRH-T) in 15 patients with spinocerebellar degeneration. The study was performed as follows: (1) acute 4 mg TRH-T test with hourly prolactin (PRL) and thyroid-stimulating hormone (TSH) level evaluations for 6 h; (2) placebo; and (3) 4 mg/day of TRH-T administration for 30 days with TSH, PRL, and free T3 and T4 (FT3 and FT4) levels evaluated on days 1, 15 and 30. Hormone determination was performed just before and 1 h after placebo or TRH-T administration. The acute administration of TRH-T caused a sustained rise of TSH which lasted until the 6th hour and of PRL which declined after 1 h (p < 0.01). During placebo administration, no change of TSH, PRL, FT3 or FT4 was observed. On the 1st day of treatment, 1 h after the TRH-T injection, a significant increase of both TSH and PRL levels occurred (p < 0.01). As compared to the 1st day, a significant decrease of the TSH (p < 0.01) levels occurred on the 15th and 30th days before TRH-T: the TSH response to TRH-T administration was present although less than on the 1st day (p < 0.01). Moreover, throughout the whole period of treatment, no difference was recorded for PRL levels before or after TRH-T administration.(ABSTRACT TRUNCATED AT 250 WORDS)     

Frequency of Thyroid Hormone Replacement After Lobectomy for Differentiated Thyroid Cancer

ObjectiveTo determine the frequency of levothyroxine (LT4) supplementation after therapeutic lobectomy for low-risk differentiated thyroid cancer (DTC).MethodsThis retrospective cohort study enrolled adult patients with low-risk DTC confirmed using surgical pathology who underwent therapeutic lobectomy at a single institution from January 2016 through May 2020. The outcome measures were postoperative serum thyroid-stimulating hormone (TSH) levels and the initiation of LT4. The predictors of a postoperative TSH level of >2 mU/L and initiation of LT4 were evaluated using Cox proportional hazards models.ResultsPostoperative TSH levels were available for 115 patients (91%), of whom 97 (84%) had TSH levels >2 mU/L after thyroid lobectomy. Over a median follow-up of 2.6 years, a postoperative TSH level of >2 mU/L was associated with older age (median 52 vs 37 years; P = .01), higher preoperative TSH level (1.7 vs 0.85 mU/L; P < .001), and primary tumor size of <1 cm (38% vs 11%, P = .03). Multivariate analysis revealed that only preoperative TSH level was an independent predictor of a postoperative TSH level of >2 mU/L (hazard ratio [HR] 1.53, P = .003). Among patients with a postoperative TSH level of >2 mU/L, 66 (68%) were started on LT4 at a median of 74 days (interquartile range 41-126) after lobectomy, with 51 (77%) undergoing at least 1 subsequent dose adjustment to maintain compliance with current guidelines.ConclusionMore than 80% of the patients who underwent therapeutic lobectomy for DTC developed TSH levels that were elevated beyond the recommended range, and most of these patients were prescribed LT4 soon after the surgery.     

The Association of Thyroid Hormones and Tsh with the Metabolic Syndrome in Euthyroid Taiwanese Individuals

Objective: There are conflicting studies in euthyroid males and females regarding associations between thyroidrelated hormones and parameters of the metabolic syndrome (MetS). We investigated the association between serum thyroid hormones and thyroid-stimulating hormone (TSH) concentrations and MetS in euthyroid men and women.Methods: Taiwanese subjects aged 20 to 65 years who had undergone a voluntary health examination at a preventive examination agency in Taipei were enrolled in this cross-sectional study. The definition of MetS was suggested by the Bureau of Health Promotion, Department of Health, Taiwan. Euthyroidism was defined as TSH and free thyroxine (FT4) levels within the normal reference ranges while not taking any thyroid medication. We conducted multiple logistic regression to identify the ability of serum triiodothyronine (T3), FT4, and TSH concentrations to identify the relative risk for the presence of MetS and components of the MetS in euthyroid Taiwanese individuals.Results: A total of 8,207 Taiwanese subjects (mean age: men, 45.3 ± 9.9 years; women, 43.5 ± 9.3 years) were enrolled in this study. A total of 1,672 subjects (20.4%) were defined as having MetS; these subjects had significantly higher (P<.0001) mean age (48.4 ± 9.1 years vs. 43.6 ± 10.7 years), prevalence of men (78.7% vs. 53.4%), and smoking (16.8% vs. 11.6%) than those without MetS. The median TSH, FT4, and T3 levels in all subjects were 1.70 mIU/L, 1.41 ng/dL, and 1.20 ng/mL, respectively. Higher T3 and lower FT4 values rather than TSH increased the odds ratio for MetS in men and women after adjusting for smoking and age, particularly for the association of T3 and MetS in women (uppermost quartile versus lowermost quartile: odds ratio, 2.4; 95% confidence interval, 1.6 to 3.5; P for trend <.0001).Conclusion: In euthyroid Taiwanese men and women, relatively high serum T3 concentrations was most strongly associated with the presence of the MetS; relatively low serum T4 was less strongly related, and serum TSH levels were not associated with the MetS. It is not known if the relationship of serum T3 and T4 to the MetS is causal.Abbreviations:BMI = body mass indexFT4 = free thyroxineMetS = metabolic syndromeOR = odds ratioT3 = triiodothyronineTSH = thyroid-stimulating hormoneWC = waist circumference     

Influence of chronic thyroxine treatment on plasma hormone and metabolite concentrations and on responses to insulin, glucagon and thyrotrophin releasing hormone in adult sheep

Four adult sheep fed twice daily were given daily subcutaneous injections of saline for four weeks, followed by a similar period of daily L-thyroxine (T4) injection (1 mg/day). T4 treatment increased basal plasma concentrations of T4, triiodothyronine (T3), insulin and glucose, together with T3-uptake and the free thyroxine index, while cholesterol and urea concentrations decreased. T4 treatment reduced the rise in prolactin levels after the morning meal. Thyrotrophin releasing hormone (TRH) injection increased plasma T3 only in the control period and T3-uptake only in the T4 treatment period. T4 treatment did not affect the prolactin response to TRH injection or the insulin and glucose responses to glucagon injection. The increase in insulin concentrations after insulin injection and the secondary hyperglycaemia following initial insulin-induced hypoglycaemia were reduced by T4 treatment.