SEARCH · PubMed Health

Results for “Hyperthyroidism”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 73 records · Page 4Linked to original sources

PubMed1990

Enhanced activity of the tricarboxylate carrier and modification of lipids in hepatic mitochondria from hyperthyroid rats.

The effect of hyperthyroidism on the activity of the mitochondrial tricarboxylate carrier has been studied. The activity of this transporting system in liver mitochondria was quantitatively determined by the rate of malate-[14C]citrate exchange using the 1,2,3-benzene-tricarboxylate inhibitor stop technique. It has been found that the rate of citrate uptake is significantly enhanced in liver mitochondria from hyperthyroid rats as compared to that obtained in mitochondria from control rats. Kinetic analysis of the malate-citrate exchange reaction indicates that only the Vmax of this transporting process is enhanced, while there is practically no change in the Km values. Inhibitor titrations with the inhibitor palmitoyl-CoA show that mitochondria from hyperthyroid rats require the same concentrations of inhibitor to produce 100% inhibition of citrate uptake as control mitochondria, suggesting that the amount of functional translocase enzyme present is unaffected. The Arrhenius plot characteristics differ for tricarboxylate carrier activity in mitochondria from hyperthyroid rats as compared with control rats in that the break point of the biphasic plot decreases from 18.1 +/- 1.4 degrees C in controls to 12.9 +/- 1.2 degrees C in hyperthyroid animals. The hepatic mitochondrial lipid composition is altered significantly in hyperthyroid rats; the total cholesterol decreases and the phospholipids increase. The liver mitochondrial phospholipid composition is altered significantly in hyperthyroid rats. In particular negatively charged phospholipid cardiolipin increases by more than 50%. Minor alterations were found in the pattern of fatty acids. The thyroid hormone induced change in the activity of the tricarboxylate carrier can be ascribed either to a general modification of membrane lipid composition which increases the membrane fluidity and in turn the mobility of the carrier or to a more localized change of lipid domain (cardiolipin content) surrounding the carrier molecule in the mitochondrial membrane.

Animals↗

PubMed1991

Relationships between fatty acid synthesis and lipid secretion in the isolated perfused rat liver: effects of hyperthyroidism, glucose and oleate.

Various studies on the effects of thyroid status on hepatic fatty acid synthesis have produced conflicting results. Several variables (e.g., plasma free fatty acid and glucose concentrations) are altered simultaneously by thyroid status and can affect fatty acid synthesis. To evaluate the effects of these variables, hepatic fatty acid synthesis (lipogenesis) was studied in isolated perfused livers from normal and triiodothyronine-treated rats. Livers were perfused with media containing either 5.5 or 25 mM glucose without fatty acid, or 5.5 mM glucose and 0.7 mM oleate. Rates of lipogenesis were determined by measurement of incorporation of 3H2O into fatty acids. Lipogenesis in livers from hyperthyroid animals exceeded that of controls, when perfused with 5.5 mM glucose with or without oleate. Perfusion with 25 mM glucose increased lipogenesis in both euthyroid and hyperthyroid groups to the same level, abolishing this difference between them. Perfusion with oleate reduced rates of lipogenesis by livers from euthyroid and hyperthyroid rats to a similar extent, but stimulated secretion of radioactive fatty acid in phospholipid and free fatty acid fractions. Oleate increased ketogenesis by livers from normal and triiodothyronine-treated rats, with higher rates of ketogenesis in the triiodothyronine-treated group. When oleate was omitted, ketogenesis in the presence of 5.5 mM glucose by the hyperthyroid group was similar to that of euthyroid controls, while ketogenesis was decreased in the hyperthyroid group relative to controls when perfused with 25 mM glucose. About 30% of the radioactivity incorporated into the total fatty acid of both groups was recovered in palmitate, with the remainder in longer chain saturated and unsaturated fatty acids. In both euthyroid and hyperthyroid groups, the ratio of triacylglycerol:phospholipid fatty acid radioactivity was not only less than predicted (based on synthetic rates of PL and TG) but also was decreased in perfusions with exogenous oleate compared to perfusions without oleate. In perfusions with oleate, both groups incorporated twice as much radioactivity into phospholipid as into triacylglycerol. The data suggest the following concepts: while hepatic fatty acid synthesis and oxidation are increased simultaneously in the hyperthyroid state, de novo synthesized fatty acids seem to be poorer substrates for oxidation than are exogenous fatty acids, and are preferentially incorporated into phospholipid, while exogenous fatty acids are better substrates for oxidation and esterification to triacylglycerol. The preferential utilization of de novo synthesized fatty acid for phospholipid synthesis may be an important physiologic adaptation insuring a constant source of fatty acid for membrane synthesis.

Animals↗

PubMed1986

Basal and glucose- and arginine-stimulated serum concentrations of insulin, C-peptide, and glucagon in hyperthyroid patients.

The effect of oral glucose and arginine infusion on plasma glucose, glucagon, serum insulin, and C-peptide concentrations was evaluated in 16 patients with hyperthyroid Graves' disease and in ten euthyroid age- and sex-matched normal subjects. Basal plasma glucose concentrations were significantly higher in the hyperthyroid patients, but the plasma glucose response following glucose and arginine administration was similar in the two groups. The insulin response was similar in the hyperthyroid and normal subjects after glucose administration and significantly lower during arginine infusion in the hyperthyroid patients. The serum C-peptide response to both glucose and arginine administration was markedly blunted in the hyperthyroid patients, and the plasma glucagon response to arginine infusion was decreased. These results suggest that pancreatic beta and alpha cell secretory function is impaired in hyperthyroidism as assessed by C-peptide and glucagon secretion following oral glucose administration and arginine infusion. The apparent discrepancy between C-peptide and insulin secretion in the hyperthyroid patients following glucose administration might be due to diminished hepatic extraction of insulin or enhanced metabolism of C-peptide.

Adult↗

PubMed1991

Pharmacokinetics of methimazole in normal cats and cats with hyperthyroidism.

The intravenous and oral disposition of the antithyroid drug methimazole was determined in 10 clinically normal cats and nine cats with naturally occurring hyperthyroidism. After intravenous administration of 5 mg methimazole, the mean residence time was significantly (P less than 0.05) shorter in the cats with hyperthyroidism than in the normal cats, but there was no significant difference between the mean values for total body clearance (CL), steady state volume of distribution (Vdss), terminal elimination rate constant (ke), or serum terminal half-life (t1/2) in the two groups of cats. After oral administration, the mean bioavailability of methimazole was high in both the normal cats (77.6 per cent) and cats with hyperthyroidism (79.5 per cent). The values for mean residence time, ke and serum terminal t1/2 after oral dosing were significantly shorter in the cats with hyperthyroidism than in the normal cats. However, after oral administration of methimazole there were no significant differences between the mean values for CL, Vdss, bioavailability and maximum serum concentrations or the time for maximal concentrations to be reached in the two groups of cats. Overall, most pharmacokinetic parameters for methimazole were not altered by the hyperthyroid state. However, the cats with hyperthyroidism did show a trend toward faster elimination of the drug compared with the normal cats, similar to what has been previously described for the antithyroid drug propylthiouracil in cats. These results also indicate that methimazole is well absorbed when administered orally and has a higher bioavailability than that of propylthiouracil in cats with hyperthyroidism.(ABSTRACT TRUNCATED AT 250 WORDS)

Absorption↗

PubMed1987

Lack of circulating thyroid stimulating immunoglobulins in cats with hyperthyroidism.

Although feline hyperthyroidism has become a commonly diagnosed disorder of older cats, the underlying etiology remains unknown. Pathological findings of adenomatous hyperplasia involving both thyroid lobes in most hyperthyroid cats suggests the possibility that feline hyperthyroidism may be similar to human Graves' disease, which results from high circulating levels of thyroid stimulating immunoglobulins (TSIs). To exclude high circulating levels of TSIs as the cause of feline hyperthyroidism, we measured intracellular concentrations of cyclic adenosine monophosphate (cAMP) in functioning rat thyroid cells (FRTL-5) incubated with IgG extracted from hyperthyroid cat serum. Since TSIs stimulate thyroid hormone secretion through activation of cAMP, their presence can be evidenced in vitro by generation of high cAMP concentrations in cultured thyroid cells. No significant difference was found in intracellular cAMP concentrations in FRTL-5 cells incubated with IgG from normal versus hyperthyroid cats. In contrast, IgG from a human patient with Graves' disease caused substantially more cAMP generation than either normal human IgG or IgG from the cats of this study. These results indicate that feline hyperthyroidism does not result from high circulating concentrations of TSI and, in that respect, is not analogous to Graves' disease.

Animals↗

PubMed1991

The effect of external calcium concentration on the negative inotropic action of dantrolene in isolated hyperthyroid and euthyroid heart.

The effect of altering external calcium concentration [Ca2+]o on the negative inotropic action of dantrolene was tested in Langendorff-perfused hearts from euthyroid and hyperthyroid rats. Elevated contractility was demonstrated in the hyperthyroid hearts at all the [Ca2+]o tested. At a [Ca2+]o of 1.25 mM (physiological), dantrolene (5 x 10(-5) M) significantly reduced contractility (dP/dtmax) in hyperthyroid but not in euthyroid hearts (-42% and -4% of zero-time values at 12 min perfusion, respectively). When hearts from both groups were paced at 375 beats/min, dantrolene again exerted a greater negative inotropic action in the hyperthyroid preparations, showing that the effect was not heart rate related. Elevating the [Ca2+]o did not further affect the time course of dantrolene action in hyperthyroid hearts. In euthyroid hearts, however, raising the [Ca2+]o to 2.5 and 3.75 mM caused a progressive increase in the negative inotropic action of dantrolene (-15% and -56% of zero-time values at 12 min perfusion, respectively). Our results demonstrate that dantrolene exerts a negative inotropic action which at physiological [Ca2+]o is greater in the hyperthyroid than in the euthyroid heart thus indicating that calcium handling by the myocardium is altered in the hyperthyroid state. However, dantrolene action in the rat myocardium is more complex than was at first believed; as in euthyroid hearts, its negative inotropic action appears to be increased rather than reduced by increases in [Ca2+]o.

Animals↗

PubMed1989

Kinetics of drug action in disease states. XXXI. Effect of experimental hyperthyroidism on the hypnotic activity of a benzodiazepine (oxazepam) in rats.

This investigation was designed to determine the effect of experimental hyperthyroidism on the hypnotic activity of a benzodiazepine and on the binding characteristics of the benzodiazepine receptor complex. Rats were made hyperthyroid by subcutaneous implantation of slow release pellets containing L-thyroxine. This treatment produced the characteristic symptoms of hyperthyroidism: increased serum thyroxine concentrations, increased heart weight and body temperature, and decreased serum protein concentrations. The hyperthyroid rats and a parallel group of normal animals (with drug-free pellets implanted subcutaneously) were slowly infused intravenously with oxazepam until they lost their righting reflex. The hyperthyroid rats required a significantly larger dose of the benzodiazepine and their total serum and cerebrospinal fluid concentrations of oxazepam (but not the serum concentration of free drug and the brain concentration) at the onset of loss of the righting reflex were modestly but statistically significantly lower than those of the normal rats. The receptor density and affinity for diazepam in hyperthyroid rats were not significantly different from those of the normal animals. Hyperthyroidism apparently affects the pharmacokinetics of oxazepam but has, at best, only a small effect on the pharmacodynamics (hypnotic activity) of the drug.

Animals↗

PubMed1989

Brain chemiluminescence and oxidative stress in hyperthyroid rats.

Newborn Wistar rats were made hyperthyroid by injection of tri-iodothyronine and assayed for survival, brain oxygen uptake, brain chemiluminescence and activity of antioxidant enzymes. Brain chemiluminescence was measured (1) by removing the parietal bones or (2) through the translucid parietal bones. Control animals showed a brain chemiluminescence of 130 +/- 12 c.p.s./cm2 and 99 +/- 10 c.p.s./cm2 for procedures (1) and (2) respectively. Hyperthyroid rats showed increases in the spontaneous brain photoemission of 46 and 70% compared with controls, measured by procedures 1 and 2 respectively. The hyperthyroid state did not modify the oxygen-dependent chemiluminescence of brain homogenates. The hyperthyroid animals showed a 30% increase in the oxygen uptake of brain slices and a dramatic shortening of life-span to about 16 weeks. Superoxide dismutase (the Cu-Zn enzyme), catalase and Se-dependent glutathione peroxidase activities of brain homogenates were increased by 18, 36 and 30% respectively in the hyperthyroid animals. Isolated brain mitochondria produced 0.18-0.20 nmol of H2O2/min per mg of protein in state 4 in the presence of succinate as substrate. No difference was observed between control and hyperthyroid animals. It is concluded that hyperthyroidism leads to hypermetabolism and oxidative stress in the brain. The increased levels of oxygen and peroxyl radicals may contribute to premature ageing in these animals.

Animals↗

PubMed1992

Amelioration of some metabolic effects produced by hyperthyroidism in late pregnant rats and their fetuses. Effects on lipids and proteins.

We have studied the effect of 40-45 days administration of 1 mg/kg thyroxine on protein and lipid metabolism in liver, heart, lungs, kidneys and adrenal glands of virgin and 21-day pregnant rats and their fetuses and placentae. The chronic administration of thyroid hormone produced significant increases in serum T3 and T4 in both groups as well as in organ weights and protein concentrations in virgin rats, but much smaller modifications in pregnant ones. Hyperthyroidism decreased the weight of fetal livers and increased that of placentae; protein content was increased in all fetal organs. Hyperthyroidism induced increases in phospholipid concentrations in all the organs and in total lipids only in liver and heart of adult rats, which were not counteracted by pregnancy. Pregnant rats had increases in total lipids in liver and kidneys and in adrenal phospholipids. In hyperthyroid fetuses there was an increase in hepatic total lipids and no changes in phospholipids. Hepatic lipogenesis (measured by in vivo incorporation of 3H2O into lipids) was increased by hyperthyroidism in virgin and pregnant rats, but the increase was significantly smaller in the pregnant hyperthyroid rats compared with the virgin ones. Fetal lipogenesis in liver and lung was not changed. In addition, an increase was observed in lipogenic enzyme (fatty acid synthetase and glucose-6-phosphate dehydrogenase) activities in hyperthyroid virgin rats which was prevented by pregnancy. In fetuses only pulmonary glucose-6-phosphate dehydrogenase was increased when expressed in terms of tissue weight. Our results indicate that the metabolic effect of hyperthyroidism is attenuated in pregnant rats and their fetuses, when compared with adult virgin rats, in most of the parameters studied.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1977

Comparison between serum thyroxine and triiodothyronine estimation and the TRH test in the routine diagnosis of hyperthyroidism.

Serum T3 and T4 levels have been determined by a radioimmunoassay technique and the TRH test has been performed in 50 patients in whom hyperthyroidism could not be ruled out by the first clinical examination alone. Each patient was then further evaluated in order to establish the state of the thyroid function. The extent to which the determination of T3 or T4 could replace the TRH test in the routine diagnosis of hyperthyroisism was evaluated. The results showed that 26 of the 50 patients had normal thyroid function and 24 had hyperthyroidism. No patient in the normal groups and all but one in the hyperthyroid group had T3 levels above the upper normal limit (2 S.D.). Two of the patients in the normal group and 19 in the hyperthyroid group had T4 levels above the upper normal limit (2 S.D.). Twenty of the patients in the normal group showed a normal TSH response to TRH (increment is greater than 3.0 micronU/ml); the remaining 6 showed an impaired or absent response. Twenty of the hyperthyroid patients had no response and four had a slightly positive response to TRH. No hyperthyroid patient had a TSH response exceeding 3.0 micronU/ml. It is concluded that the determination of T3 is superior to both the determination of T4 and the TRH test for the laboratory discrimination between eu- and hyperthyroidism.

Adult↗

PubMed1992

Serum levels of free and bound testosterone in hyperthyroidism.

OBJECTIVE: The aim of this study was to improve knowledge about the relationships between free and bound forms of testosterone in serum and the major testosterone-binding proteins during hyperthyroidism. DESIGN: Nine men and 11 women were studied when hyperthyroid due to Graves' disease and again after at least 3 months of euthyroidism. MEASUREMENTS: The serum concentrations of free T3, free T4, TSH, sex hormone-binding globulin (SHBG), LH, progesterone and free, non-SHBG bound and total testosterone were determined. RESULTS: For both sexes, hyperthyroidism was associated with significant elevations of the mean total testosterone and sex hormone-binding globulin (SHBG) levels and significant depressions of the mean percentage and concentration of non-SHBG-bound testosterone and the mean percentage of free testosterone. For women, the mean free testosterone concentration was significantly lower during hyperthyroidism than during euthyroidism; no significant difference in mean free testosterone concentration was observed between hyperthyroid and euthyroid men. When the experimentally derived data were analysed according to a model based on the binding constants of testosterone with SHBG and albumin, the simulated results for each patient when hyperthyroid and euthyroid paralleled the actual results. However, the model consistently overestimated the actual amounts of non-SHBG-bound testosterone. There was a significant correlation between SHBG concentration and the severity of thyrotoxicosis as measured by the change in thyroid hormone levels between euthyroidism and hyperthyroidism. CONCLUSIONS: Our results support the following pathogenetic sequence: thyrotoxicosis leads to a rise in serum SHBG concentration which is accompanied by an increase in testosterone concentration, a fall in the concentration of non-SHBG-bound testosterone and little or no change in the concentration of free testosterone.

Adolescent↗

PubMed1989

Electrophysiological abnormalities and enhanced reperfusion arrhythmias in the isolated hearts of hyperthyroid rats.

1. The influence of hyperthyroidism on electrophysiological characteristics and on reperfusion arrhythmias was examined in rat hearts. 2. Electrophysiological studies were performed with glass microelectrodes, and the experiments on reperfusion arrhythmias were done in isolated perfused hearts. 3. Ventricular muscle from hyperthyroid rats was more prone than that from euthyroid rats to develop triggered activity under conditions believed to cause myoplasmic Ca2+ overload. 4. The severity of reperfusion arrhythmias was significantly enhanced in hyperthyroid preparations as compared with euthyroid ones. 5. The enhanced reperfusion arrhythmias in hyperthyroid rats were significantly reduced by propranolol (3 x 10(-7) M), lignocaine (1 x 10(-5) M) and verapamil (3 x 10(-8) M), but not by nadolol (3 x 10(-7) M) or prazosin (3 x 10(-7) M). 6. These results suggest that increased heart rate due to hyperthyroidism and responses mediated via either alpha- or beta-adrenoceptors were not dominant causes of enhanced reperfusion arrhythmias in hyperthyroid hearts. 7. The increased tendency to develop triggered activity which was observed in the electrophysiological study, may be one possible explanation of enhanced reperfusion arrhythmias in hyperthyroid hearts.

Action Potentials↗

PubMed1978

Thyroid function tests in elderly hyperthyroid patients.

Several tests of thyroid function were performed in 35 hyperthyroid patients over the age of 65 (elderly). The results were compared to those of similar tests in 48 hyperthyroid patients under the age of 65 (young). Total serum thyroxine (T4) was within the normal range in 14 percent of the elderly and 11 percent of the young hyperthyroid patients. The free thyroxine index (FTI) was within the normal range in 11 percent of both groups. The triiodothyronine uptake (T3U) proved to be a poor test in both groups. Although elevation of the triiodothyronine (T3) level allowed a diagnosis of "T3-toxicosis" in 2 elderly and 3 young hyperthyroid patients, the T3 level was normal in 34 percent of the elderly and 13 percent of the young subjects. Correction of the T3 range for age reduced the number of normal T3 values to 12.5 percent in the elderly hyperthyroid patients. The 24-hour uptake of radioactive iodine was normal in 12 percent of the young hyperthyroid patients, 27 percent of the elderly patients with Graves' disease, and 70 percent of the elderly patients with toxic nodular goiter, despite recent readjustment of the normal range for the test. It is concluded that the diagnosis of hyperthyroidism in the elderly may be difficult and that no single test can be relied upon to exclude the diagnosis.

Adult↗

PubMedDate not supplied

Hypertension in cats with chronic renal failure or hyperthyroidism.

The Doppler ultrasonic recording technique was used to measure systolic and diastolic blood pressures indirectly in 28 cats with naturally occurring renal failure, 39 cats with hyperthyroidism, and 33 clinically normal cats. The mean systolic and diastolic blood pressures in the normal cats were 118.4 +/- 10.6 mm Hg and 83.8 +/- 12.2 mm Hg, respectively. In the cats with chronic renal failure, both the systolic (146.6 +/- 25.4 mm Hg) and diastolic (96.6 +/- 15.2 mm Hg) blood pressures were significantly higher (P less than 0.0001 and P less than 0.01, respectively) than in the normal cats. Elevations in systolic and/or diastolic blood pressure were recorded in 17 (61%) of the 28 cats with chronic renal failure. In the 39 untreated hyperthyroid cats, both the mean systolic (167.9 +/- 28.9 mm Hg) and diastolic (111.6 +/- 21.5 mm Hg) pressures also were significantly higher (P less than 0.0001) than normal. Increased systolic and/or diastolic blood pressure was recorded in 34 (87%) of the 39 hyperthyroid cats. In seven cats with hyperthyroidism that were reevaluated two to four months after successful treatment of the hyperthyroid state, there was a significant fall in mean systolic pressure (P less than 0.05) from a pretreatment value of 159.5 +/- 15.4 mm Hg to a posttreatment value of 132.0 +/- 1.62 mm Hg. Overall, the results of this study indicate that mild to moderate hypertension is common in cats with chronic renal failure and in cats with untreated hyperthyroidism. In addition, the hypertension appears to be reversible following successful treatment of the hyperthyroid state.

Animals↗

PubMed1979

Effect of hypoxia on mechanical properties of hyperthyroid cat papillary muscle.

It has been previously established that hyperthyroid myocardium exhibits increased performance under well-oxygenated conditions. To date, it is not known whether hyperthyroid cardiac muscle can maintain this increased performance during hypoxia. The responses of isolated right ventricular papillary muscles from hyperthyroid and euthyroid kittens to hypoxia were compared under isometric conditions at 31 degrees C. Under well-oxygenated conditions, the hyperthyroid cardiac muscle exhibited both an increased contractility and an accelerated rate of relaxation. A similar degree of acute hypoxic stress for 15 min resulted in a greater decrease in contractility in the hyperthyroid compared with the euthyroid papillary muscle as indicated by a greater fall in both peak tension development (2.2 +/- 0.25 from 4.2 +/- 0.2 vs. 0.9 +/- 0.15 from 3.2 +/- 0.4 g/mm2, P less than 0.01) and +dT/dt (12.9 +/- 2.3 from 25 +/- 3 vs. 4.0 +/- 0.6 from 14 +/- 1 g-s-1-mm-2, P less than 0.01). In addition, compared with the euthyroid data, hypoxia resulted in impaired myocardial relaxation in the hyperthyroid cardiac muscle. Thus, the hyperthyroid compared with the euthyroid papillary muscle exhibits both a greater decrease in contractility and an impairment of myocardial relaxation during hypoxia, indicating a greater susceptibility to a given hypoxic stress.

Animals↗

PubMed1987

Effects of beta-blocking agents on urinary excretion of 3-methylhistidine during experimental hyperthyroidism in rats.

Beta-blocking agents are increasingly used as preoperative treatment of hyperthyroid patients. Relatively little is known about the effects of these drugs on metabolic alterations in hyperthyroidism. The aim of this investigation was to study the effects of two different beta-blocking agents on the urinary excretion of 3-methylhistidine (3-MH) during experimental hyperthyroidism in rats. Experimental hyperthyroidism was induced by daily intraperitoneal injections of triiodothyronine (T3; 100 micrograms/100 g body weight) for 3 days. Control animals were injected with corresponding volumes of solvent. Groups of rats received food enriched with metoprolol (8.8 mmol/kg of diet) or propranolol (3.3 mmol/kg of diet) or food without additions. Urinary 3-MH excretion was increased by about 40% during experimental hyperthyroidism. A similar increase of 3-MH excretion was found in animals receiving T3 + metoprolol, whereas the excretion of 3-MH was reduced to control level in hyperthyroid rats receiving propranolol. No effects of metoprolol or propranolol on 3-MH excretion were found in control animals. Although the source of 3-MH cannot be exactly defined, the present results indicate that increased proteolysis in skeletal muscle and/or other tissues during experimental hyperthyroidism was reduced by propranolol.

Adrenergic beta-Antagonists↗

PubMed1992

Effect of arginine on the GHRH-stimulated GH secretion in patients with hyperthyroidism.

Patients with hyperthyroidism have reduced GH responses to pharmacological stimuli and reduced spontaneous nocturnal GH secretion. The stimulatory effect of arginine on GH secretion has been suggested to depend on a decrease in hypothalamic somatostatin tone. The aim of our study was to evaluate the effects of arginine on the GH-releasing hormone (GHRH)-stimulated GH secretion in patients with hyperthyroidism. Six hyperthyroid patients with recent diagnosis of Graves' disease [mean age +/- SEM, 39.2 +/- 1.4 years; body mass index (BMI) 22 +/- 0.4 kg/m2] and 6 healthy nonobese volunteers (4 males, 2 females; mean age +/- SEM, 35 +/- 3.5 years) underwent two experimental trials at no less than 7-day intervals: GHRH (100 micrograms, i.v.)-induced GH secretion was evaluated after 30 min i.v. infusion of saline (100 ml) or arginine (30 g) in 100 ml of saline. Hyperthyroid patients showed blunted GH peaks after GHRH (13.2 +/- 2.9 micrograms/l) as compared with normal subjects (23.8 +/- 3.9 micrograms/l, p < 0.05). GH peaks after GHRH were only slightly enhanced by arginine in hyperthyroid subjects (17.6 +/- 2.9 micrograms/l), whereas, in normal subjects, the enhancement was clear cut (36.6 +/- 4.4 micrograms/l; p < 0.05). GH values after arginine + GHRH were still lower in hyperthyroid patients with respect to normal subjects. Our data demonstrate that arginine enhances but does not normalize the GH response to GHRH in patients with hyperthyroidism when compared with normal subjects. We hypothesize that hyperthyroxinemia may decrease GH secretion, both increasing somatostatin tone and acting directly at the pituitary level.

Adult↗

PubMed1987

Plasma atriopeptin concentrations in hyperthyroidism, euthyroidism, and hypothyroidism: studies in man and rat.

Atriopeptin (AP) is a polypeptide produced by atrial myocytes that is capable of inducing diuresis, natriuresis, and vasodilatation. Because thyroid dysfunction is known to be associated with alterations in both renal function and vasomotor control, we investigate the possible effects of varying thyroid function on AP in humans and rats. Plasma AP concentrations were determined in hyperthyroid and hypothyroid patients and normal subjects. Plasma AP was also measured in some patients after the iv infusion of 1 L 150 mmol/L NaCl and after treatment of hyperthyroidism or hypothyroidism. Plasma and atrial AP concentrations were measured in hyperthyroid, euthyroid, and hypothyroid rats. Plasma AP concentrations did not differ in the hyperthyroid (n = 22), euthyroid (n = 45), and hypothyroid (n = 16) subjects [47.1 +/- 18.2 (mean +/- SD), 45.1 +/- 28.9, and 42.4 +/- 20.0 pg/mL, respectively]. After NaCl infusion, mean plasma AP concentrations did not increase significantly in any of the three groups. Treatment of hyperthyroidism and hypothyroidism did not result in a significant change in plasma AP levels. In contrast, plasma AP concentrations were significantly higher in T4-treated (hyperthyroid) rats than in either euthyroid or propylthiouracil-treated (hypothyroid) rats [621 +/- 17 vs. 266 +/- 41 (P less than 0.01) and 210 +/- 28 pg/mL (P less than 0.001), respectively], whereas atrial AP contents were similar in the three groups of rats. We conclude that hyperthyroidism and hypothyroidism in man are not associated with significantly altered plasma AP concentrations. The higher plasma AP levels in T4-treated rats may reflect the relatively shorter duration or greater severity of thyroid dysfunction or thyroid hormone-induced myocardial hypertrophy in the animals.

Adult↗