Experimental Hyperthyroidism Research Articles

Experimental thyrotoxicosis: effects of graded doses of T4 plus T3.

Earlier studies have shown marked species specific differences of the effects of thyroid hormones on the basal metabolic rate (BMR) and on the induction of enzyme biosynthesis (1, 2). In order to produce experimental thyrotoxicosis closely resembling the pathophysiological conditions of human thyrotoxicosis, T4 plus T3 were applicated in a ratio of 3:1 (w/w), given for a period as long as 30 days and finally used in dosages ranging from very low to high.

Influence of inhibitory and facilitatory structures of the medulla on segmental reflexes in experimental thyrotoxicosis

Influence of inhibitory and facilitatory structures of the medulla on segmental reflexes in experimental thyrotoxicosis

Morphological changes in tooth tissues in experimental thyrotoxicosis

Morphological changes in tooth tissues in experimental thyrotoxicosis

Thyroxine elimination by peritoneal dialysis in experimental thyrotoxicosis.

In previous studies (Herrmann et al. 1971) the beneficial effect of peritoneal dialysis (P.D.) in 3 patients with thyroid storm has been shown. Consequently the mechanism of thyroxine (T4) elimination by P.D. was studied in a series of 200 thyrotoxic rats in greater detail: Male Sprague-Dawley rats were injected subcutaneously with 50 µg T4/100 gm body weight daily. After 2 and 8 days, 50 ml of a conventional peritoneal dialysis fluid (Peritosteril-H® were injected intraperitoneally, the fluid remaining for 2 and 8 hours. After 8 days of T4-injection the serum T4-concentration had risen to 56.9 ± 8.3 µg% (C.P.B.-analysis according to Murphy). The T4-concentration fell to 39.1 ± 7.2 µg% after an 8-hour-dialysis period. Half-concentration times of radioactive T4 under these conditions were considerably less (7.6 ± 1.7 hours) than in thyrotoxic rats without P.D. (13.2 ± 5.7 hours). There was a significant positive linear correlation between the amounts of T4 in the dialysate and the decrease of serum-T4-concentrations (r = 0.714 2a < 0.05). An equally positive linear correlation has been found for the amounts of protein in the dialysate and eliminated T4 (r = 0.810 2a < 0.01).

State of neuromuscular transmission in experimental thyrotoxicosis

State of neuromuscular transmission in experimental thyrotoxicosis

Microphotometric determination of enzyme activity in single cells in cryostat sections. I. Application of the gel film technique to microphotometry and studies on the intralobular distribution of succinate dehydrogenase and lactate dehydrogenase activities in rat liver.

A gel film technique was adopted for kinetic enzyme activity determination in single cells using cryostat sections by means of a microscope photometer. The main principle of the method is a comparative activity determination, based on bipositional recording of initial reaction kinetics in two preselected measuring fields in the same tissue section. Systematic model experiments were performed to prove the fulfillment of the following conditions: ( a) validity of Beer's law; ( b) optimal concentrations of substrates, cosubstrates and dye within the reaction film, including evidence that the reaction rate is not limited by insufficient diffusion of these compounds; ( c) proportionality between local enzyme concentration or thickness of tissue sections and the recorded reaction rate; and ( d) specificity of the method as demonstrated by studying reaction rates in the absence of the substrate as well as in the presence of substrate and a specific inhibitor. The validity of the method was also examined by comparing the levels of succinate dehydrogenase activity in various rat tissues, as measured microphotometrically, with the enzyme levels as determined in homogenates. Microphotometric assays for nicotinamide adenine dinucleotide phosphate isocitrate dehydrogenase, lactate dehydrogenase and succinate dehydrogenase are described. Using these techniques it was found that: the periportal and central areas of the hepatic lobule in rat contain the same level of lactate dehydrogenase activity; succinate dehydrogenase activity is 1.6 times higher in the periportal area as compared to the centrilobular area. In experimental thyrotoxicosis, the ratio of enzyme activities in the periportal and central areas was 1.1.

Changes in cholinesterase activity in spinal motoneurons of rats in experimental thyrotoxicosis

Changes in cholinesterase activity in spinal motoneurons of rats in experimental thyrotoxicosis

Histochemical changes in L-glycerol-3-phosphate: Menadione-tetrazolium oxidoreductase activity in the liver of albino rats with experimental thyrotoxicosis

Histochemical changes in L-glycerol-3-phosphate: Menadione-tetrazolium oxidoreductase activity in the liver of albino rats with experimental thyrotoxicosis

Regression of cardiac hypertrophy following experimental hyperthyroidism in rats.

SummaryHyperthyroidism was induced in male, albino rats by subcutaneous injection of T3 daily for 2 weeks. The day following the last injection, groups of control and experimental animals were killed; the hearts were removed, weighed, and the average amount of cardiac hypertrophy was determined. The hearts were then partitioned and the ventricles were weighed separately. To determine when the hearts returned to normal size, groups of rats were killed at about 5-day intervals up to 35 days. The data were subjected to linear regression analysis. It was observed that the hearts returned to normal size in 13 days; this also held approximately for each ventricle despite the fact that the right ventricle was hypertrophied significantly more, proportionally, than the left ventricle.

Connection between changes in the parafollicular system of the thyroid and in bone tissue in experimental thyrotoxicosis

Connection between changes in the parafollicular system of the thyroid and in bone tissue in experimental thyrotoxicosis

Functional and morphological studies of the gastric mucosa in dogs with experimental thyrotoxicosis

Functional and morphological studies of the gastric mucosa in dogs with experimental thyrotoxicosis

Presynaptic inhibition and dorsal root potentials in cats with experimental thyrotoxicosis

Presynaptic inhibition and dorsal root potentials in cats with experimental thyrotoxicosis

Augmentation of myocardial oxygen consumption in hyperthyroid cats.

To clarify the effects of hyperthyroidism on myocardial oxygen consumption (VO 2 ), a polarographic method was employed to compare the VO 2 of isolated papillary muscles from 13 normal euthyroid cats with that of 11 hyperthyroid cats. Basal VO 2 was greater in the hyperthyroid group (3.03±0.20 vs. 2.36±0.19 SE filter-ing dry wrr 1 · hour 1 , P &lt; 0.05). In muscles studied under afterloaded isotonic conditions, hyperthyroidism shifted the forcevelocity curve upward and to the right, with an increase in both extent and velocity of shortening at equivalent loads. These changes in myocardial behavior in hyperthyroidism were associated with an increase in myocardial VO 2 . Isometrically contracting muscles from hyperthyroid animals demonstrated significant increases in both developed tension (6.3±0.7 vs. 4.7±0.4 g/mm 2 , P &lt; 0.05) and rate of tension development (32.6±3.5 vs. 19.4±1.5 g/mm 2 · second- 1 , P &lt; 0.01), as compared to the euthyroid group. Myocardial VO 2 , expressed per g/mm 2 isometric developed tension, was significantly greater in the hyperthyroid group (0.641±0.09 vs. 0.42±0.04 milliter · mg dry wt- 1 · beat-, P &lt; 0.02). Thus, experimental hyperthyroidism augments myocardial VO 2 whether measured in resting or contracting cardiac muscle. This increase can be attributed, at least in part, to $ie altered contractile function of the heart in hyperthyroidism.

Atrial electrophysiology in experimental hyperthyroidism in rabbits.

Male rabbits received l -thyroxine (250 µg/kg) subcutaneously for 7 days and exhibited marked tachycardia, elevation of protein-bound iodine levels and a 26% mean weight loss. Their hearts were isolated and perfused by the Langendorff technique. In 8 thyroid-treated rabbits the mean heart rate before they were killed and also after 30 minutes of perfusion was much higher than that of 10 controls; threshold in late diastole was lower, and the mean effective refractory period was shorter: 109 msec (95 to 116) as compared with 147 msec (130 to 170). The atrial multiple-response threshold was strikingly lower, and strength-interval curves were shifted to the left without overlap or change in contour. Atropine, 7 µg/liter, did not significantly affect these changes. Acute perfusion of four hearts with l -thyroxine (500 µg/liter) produced similar, but less consistent, results. Perfusion with either epinephrine or norepinephrine, regardless of concentration, could not reproduce the changes seen with thyroid treatment. It is concluded that thyroxine profoundly alters electrophysiologic variables of atrial tissue independently of the autonomic nervous system and that these changes are responsible for many cardiac effects of hyperthyroidism, including the enhanced susceptibility to atrial fibrillation in thyrotoxicosis.

Electrophysiological analysis of the state of the autonomic nerves in experimental thyrotoxicosis

Electrophysiological analysis of the state of the autonomic nerves in experimental thyrotoxicosis

Contractile function of the heart in rabbits with experimental thyrotoxicosis

Contractile function of the heart in rabbits with experimental thyrotoxicosis

Effect of experimental thyrotoxicosis on development of compensatory adrenal hypertrophy

Effect of experimental thyrotoxicosis on development of compensatory adrenal hypertrophy

Indices of carbohydrate metabolism in the myocardium in experimental thyrotoxicosis

Indices of carbohydrate metabolism in the myocardium in experimental thyrotoxicosis

Size of cardiac ventricles in experimental hyperthyroidism in the rat.

SummaryExperimental hyperthyroidism was induced in male white rats by the administration of T3. A significant degree of cardiac hypertrophy was produced. The hearts were fixed in a 4% solution of formaldehyde, and the ventricles were partitioned and weighed. The right ventricle showed proportionally a greater degree of hypertrophy (on a percentage basis almost twofold) than the left.

Regression of cardiac hypertrophies of various origin.

Enlargement of the heart was produced in rats by four methods: (a) unilateral nephrectomy with DOC pellet implantation and salt loading, (b) experimental hyperthyroidism, (c) experimental aortic coarctation, and (d) nutritional anemia. All enlargements proved to be reversible if the provoking stimulus was removed. In hearts enlarged by anemia up to 80–100%, the extra protein and RNA synthesized during the process of accelerated growth of the heart disappeared as the size of the heart reverted to normal. In this way, the concentration of these two macromolecules remained the same, in spite of the changes in the size of the heart. On the other hand, a large part of the new DNA was not removed during regression.