Thyroid response to dexamethasone: A study on normal controls and patients with psychogenic sexual dysfunction: Der Einfluß von Dexamethason auf die Schilddrüsenfunktion bei Patienten mit erektiler Dysfunktion und gesunden Männern

Pre- and postdexamethasone triiodothyronine (T3), thyroxine (T4), and TSH levels of thirteen patients with psychogenic sexual dysfunction and thirteen controls were studied. Patients showed lowered T4 levels in comparison with the control group whereas T3 and TSH levels did not differ significantly. Dexamethasone had a suppressive effect on TSH in patients and in controls while T3 levels were suppressed in the control group only. Patients scored significantly higher on the Hamilton Depression Scale than controls. These results compared with results obtained in patients recovered from major depression might point to endocrinological as well as clinical interrelations between psychogenic sexual dysfunction and minor depression.     

Inducing coproporphyria in rat hepatocyte cultures using cyclic AMP and cyclic AMP-releasing agents

Cyclic AMP (c-AMP), added on its own to rat hepatocyte cultures, caused a marked accumulation of coproporphyrin III. The results obtained by comparing the effect of c-AMP to that of exogenous 5-aminolevulinate (ALA), and from adding c-AMP and ALA together, indicated that the coproporphyrinogen III metabolism was blocked, even though no inhibition of the relevant enzyme, coproporphyrinogen oxidase, could be demonstrated. Preferential accumulation of coproporphyrin could also be produced in cultures of rat hepatocytes by agents that raise the cellular levels of cyclic AMP, such as glucagon. The effect of supplementing the culture medium with triiodothyronine (T3) on the response of rat hepatocytes to c-AMP was also investigated. T3, which is known to stimulate mitochondrial respiration, uncoupling O₂ consumption from ATP synthesis, produced a c-AMP-like effect when given on its own and potentiated the effect of c-AMP, with an apparent increase in the severity of the metabolic block. It is suggested that an oxidative mechanism may be activated in c-AMP and T₃-induced coproporphyria, preferentially involving the mitochondrial compartment, leading to oxidation of porphyrinogen intermediates of haem biosynthesis, especially coproporphyrinogen. Coproporphyin, the fully oxidized aromatic derivative produced, cannot be metabolized and will therefore accumulate.     

Diurnal patterns of cortisol and thyroid hormones in the Harbor seal (Phoca vitulina) during summer and winter seasons

A leading hypothesis for the dramatic population decline of the Alaskan harbor seal over the last 2-3 decades have related environmental changes to a decrease in the quality or quantity of available prey. If harbor seals are experiencing some sort of nutritional stress, it is important to understand the physiological and endocrine mechanisms controlling metabolic homeostasis in this species. The purpose of this research project was to determine whether circadian patterns of cortisol and total and free thyroxine (T(4)) and triiodothyronine (T(3)) are present in the harbor seal during the summer and winter seasons, and identify how they might alter metabolic rate and maintenance of body reserves. This study was carried out at the Alaska SeaLife Center in Seward, Alaska in June 2000 and January 2001. Blood samples were obtained every 2-3 h over a 24-h period through in-dwelling catheters inserted the day before sampling. The presence of a diurnal rhythm was determined by comparing levels between ante meridian (12 am to noon) and post meridian (noon to 12 midnight) time periods. Mean daily cortisol concentrations were not significantly different between seasons, but cortisol displayed a circadian rhythm only during the summer. Mean concentrations of cortisol (51.5 ng/ml+/-20.3) in the summer hours of ante meridian differed significantly from levels in the hours of post meridian (28.5 ng/ml+/-17.4). Neither total and free T(4), nor T(3), displayed a diurnal rhythm in either season. However, tT(4), tT(3), and fT(3) levels were significantly higher in the winter than in the summer. There was no seasonal effect on fT(4) levels. The absence of a circadian rhythm of cortisol during the winter may have been a result of the limited amount of daylight as well as the continual need to produce metabolic heat as a by-product of gluconeogenesis. Higher levels of thyroid hormones in the winter indicate an adaptive mechanism to cope with the low temperatures of winter.     

Seasonal variation in plasma thyroid hormone concentrations in coastal versus inland populations of juvenile American alligators (Alligator mississippiensis): influence of plasma iodide concentrations

Thyroid hormones, essential for normal growth and health, are associated with changes in temperature, photoperiod, and reproduction. Iodide, a necessary element for thyroid hormone production, varies in diet, and is more abundant in estuarine environments, which could alter thyroid hormone variation. However, associations between thyroid hormone concentrations in animals from marine versus freshwater environments, which could become more pertinent with rising sea levels associated with global climate change, are not well studied. To determine the importance of dietary iodide in seasonal variation of plasma thyroid hormone concentrations, we analyzed seasonal variation of plasma thyroxine (T₄) and triiodothyronine (T₃) concentrations in juvenile alligators from an estuarine habitat (Merritt Island National Wildlife Refuge; MI) and a freshwater habitat (Lake Woodruff National Wildlife Refuge; LW) and compared these results to plasma inorganic iodide (PII) concentrations. Alligators from MI did not display seasonal variation in plasma T₄, but exhibited a seasonal pattern in plasma T₃ concentrations similar to alligators from LW. Plasma thyroid hormone concentrations were consistently higher at MI than at LW. PII concentrations were correlated with plasma T₄ and T₃ concentrations in juvenile alligators from LW but not MI. The data on plasma T₄ and T₃ concentrations suggest altered iodide metabolism in estuarine alligators. Differences in thyroid hormone concentrations between the populations could be due to differences in dietary iodide, which need to be further evaluated.     

Myocardial concentration of cardiac troponin T as an early discriminator of mechanisms of cardiac hypertrophy

Measurement of myocardial concentration of the myofibrillar protein, cardiac troponin T (cTnT), was used as a biochemical correlate of myocardial myofibrillar volume fraction to confirm and extend results of histomorphometric studies of changes in myofibrillar density during hypertrophy. Rat models were used to study concentric cardiac hypertrophy due to pressure overload (spontaneous hypertension), eccentric cardiac hypertrophy due to volume overload (administration of minoxidil for 4 weeks), and mixed cardiac hypertrophy due to growth factor stimulation (administration of triiodothyronine for 4 weeks). Mean myocardial cTnT concentration was 583±60 g/g wet weight tissue in 40 control rats aged 10–20 weeks. We confirmed that pressure overload increased myofibrillar density by up to 30%, whereas volume overload decreased myofibrillar density, in our study, by up to 15%. Growth factor-induced hypertrophy was confirmed to occur by a mixture of processes; while myofibrillar density had increased by 31% at 1 week, it had normalised by 4 weeks. Minoxidil-induced hypertrophy was also confirmed to occur by a mixture of the processes, with myofibrillar density first decreased by 15% at 1 week before normalising by 4 weeks. Progressive, pathological hypertrophy, as modelled with spontaneous hypertension, was confirmed to be associated with abnormal myocardial myofibrillar density. We conclude that myocardial cTnT concentration may be used as a simple and precise biomarker of myofibrillar volume density, which, assessed over time, discriminates early physiological mechanisms involving myocyte thickening from those involving myocyte elongation and may discriminate between physiological and pathological hypertrophy.     

The Influences of Thermal Stress on Serum Biochemical Parameters of Dromedary Camels and Their Correlation with Thyroid Activity

In order to study the influences of thermal stress on serum biochemical parameters of dromedary camels and their correlation with thyroid activity, blood samples were taken from the jugular vein of 40 clinically healthy Iranian dromedary camels from December to February (3 times: mean temperature 11°C) and from June to August (3 times: mean temperature 41°C). There were significant differences in the concentrations of serum total protein, glucose, blood urea nitrogen (BUN), sodium, potassium, calcium, inorganic phosphorus, triiodothyronine (T3) and thyroxine (T4) and the activities of aspartate aminotransferase (AST), alanine aminotransferase (ALT), alkaline phosphatase (ALP), creatine kinase (CK) and lactate dehydrogenase (LD) in heat stress and cold stress conditions (p<0.05). The concentrations of BUN, sodium, potassium, calcium, inorganic phosphorus and the activities of CK and LD in winter months were higher than summer months, and in contrast, the concentrations of total protein, glucose, T3 and T4 and the activities of AST, ALT and ALP were higher in summer than in winter (p<0.05). Thyroidal hormones (T3 and T4) showed significant correlations with serum total protein, glucose, BUN, AST, ALT, ALP, LD and CK. Our results revealed that very hot and cold conditions had a profound effect on serum biochemical parameters.     

妊娠期单纯低甲状腺素血症的危险因素和对母婴结局的影响

妊娠期单纯低甲状腺素血症又称妊娠期低甲状腺素(thyroxine,T4)血症,是指妊娠妇女甲状腺自身抗体阴性、血清促甲状腺激素(thyroid stimulating hormone,TSH)水平正常但血清游离甲状腺素(free thyroxine,FT4)水平低于妊娠期特异性参考范围下限.目前,妊娠期低T4血症的病因...     

Relationship between triiodothyronine and proinflammatory cytokines in chronic heart failure

Cytokines and thyroid hormones are involved in the biochemical changes associated to heart failure (HF).