Several metabolic alterations were studied in rats submitted to either an 80% jejunoileal resection or an 80% jejunoileal bypass. After a 1 00-day observation, the weight curve, daily food intake, stomach wet weight, liver glycogen and serum glucose, and free fatty acid and insulin concentrations were evaluated. The animals submitted to jejunoileal bypass showed decreased […]
The role of glucocorticoids in the stress-induced reduction of extrathyroidal 3,5,3′-triiodothyronine generation in rats.
Serum concentrations of T4, T3, and rT3 as well as liver and kidney 5′-deiodinase activity, have been examined in rats stressed by restraint. After immobilization, serum concentrations of T3 decreased significantly (6 hr, -33 +/- 1%; 8 h, -42 +/- 3%), while serum rT3 increased (6 h, +55 +/- 3%; 8 h, +75 +/- 5%). […]
Intracellular Conversion of Thyroxine to Triiodothyronine Is Required for the Optimal Thermogenic Function of Brown Adipose Tissue.
The effect of thyroxine (T4) and triiodothyronine (T3) on the expression of uncoupling protein (UCP) in rat brown adipose tissue (BAT) has been examined. Thyroidectomized rats have a threefold reduction in basal UCP levels. When exposed to cold, they become hypothermic and show a fivefold lower response of UCP than euthyroid controls. T3 augments the […]
Nuclear 3,5,3′-triiodothyronine (T3) in brown adipose tissue: receptor occupancy and sources of T3 as determined by in vivo techniques.
The amount and sources of T3 associated with high affinity, low capacity cellular nuclear receptors in brown adipose tissue (BAT) have been estimated by in vivo pulse-labeling techniques. Maximal binding capacity was measured by in vivo saturation analysis. Nuclear receptor occupancy at endogenous levels of T3 and T4 in euthyroid rats was estimated from the […]
Extrathyroidal conversion of thyroxine to 3,5,3′-triiodothyronine in cold-acclimated thyroxine-maintained thyroidectomized rats.
Chronic exposure of rats to cold (4 degrees C) leads to thyroid gland hyperactivity as a compensatory mechanism for activating body heat production. There is increased extrathyroidal production of T3 from T4 in parallel to thyroid hormone hypersecretion. Since the 5′-deiodination (5′-D) of T4 can be modulated by thyroid hormones, it has been suggested that […]
The properties of the sarcoplasmic reticulum membranes isolated from slow-twitch type I soleus and fast-twitch type II psoas muscles of control and thyroxine treated rabbits were comparatively studied. Membrane yield, maximal calcium storing capacity, ATP-supported calcium uptake, calcium-dependent ATPase activity and calcium-dependent phosphoprotein formation were found to be 3-10 fold higher in psoas than in […]
We have examined the effect of hypothalamic extracts of rats fed cholesterol excess (1%) on TSH and Prl secretions from in vitro incubated pituitaries derived from normal rats. The TSH activity in the hypothalamic extracts from rats fed cholesterol excess was greater than that observed in the control extracts, indicating that increased Prl and TSH […]
The role of mast cells on thyroid gland function was studied with respect to two sites of thyroid control: 1. the thyroid gland; 2. the hypothalamus pituitary system. It was observed that the treatment with disodium cromoglycate (mast cells stabilizer) partially blocked the TSH actions on thyroid gland, thus evidencing the thyroidal mast cells as […]