12.04.1991 | 9:48 AM
Central role of brown adipose tissue thyroxine 5′-deiodinase on thyroid hormone-dependent thermogenic response to cold.

Millions of levothyroxine-treated hypothyroid patients complain of impaired cognition despite normal TSH serum levels. This could reflect abnormalities in the type-2 deiodinase (D2)-mediated T4-to-T3 conversion, given their much greater dependence on the D2 pathway for T3 production. T3 normally reaches the brain directly from the circulation or is produced locally by D2 in astrocytes. Here […]

05.12.1988 | 9:52 AM
Triiodothyronine amplifies norepinephrine stimulation of uncoupling protein gene transcription by a mechanism not requiring protein synthesis.

Transcription of the uncoupling protein (UCP) gene in rat brown adipose tissue has been evaluated by a nuclear run-on transcription assay. Nuclei from euthyroid rats treated with norepinephrine (NE) exhibited a 3-4-fold increase in transcription 2 h after the injection, whereas the UCP mRNA abundance increased 2-3-fold during the same interval. In contrast, neither UCP […]

12.10.1988 | 10:04 AM
Cold exposure rapidly induces virtual saturation of brown adipose tissue nuclear T3 receptors.

Cold exposure induces a rapid increase in uncoupling protein (UCP) concentration in the brown adipose tissue (BAT) of euthyroid, but not hypothyroid, rats. To normalize this response with exogenous 3,5,3′-triiodothyronine (T3), it is necessary to cause systemic hyperthyroidism. In contrast, the same result can be obtained with just replacement doses of thyroxine (T4) and, in […]

12.09.1987 | 11:17 AM
Optimal response of key enzymes and uncoupling protein to cold in BAT depends on local T3 generation.

We have examined the activity of three lipogenic enzymes [malic enzyme (ME), glucose-6-phosphate dehydrogenase (G-6-PD), and acetyl coenzyme A (CoA) carboxylase], the activity of the mitochondrial FAD-dependent alpha-glycerolphosphate dehydrogenase (alpha-GPD), and the mitochondrial concentration of uncoupling protein (UCP) in brown adipose tissue (BAT) of euthyroid and hypothyroid rats, both at room temperature and in response […]

01.09.1987 | 10:11 AM
Metabolic Changes in Rats Submitted to Extensive Intestinal Resection or jejunoileal Bypass.

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 […]

19.01.1987 | 9:35 AM
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 […]

19.01.1987 | 9:27 AM
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 […]

19.08.1986 | 9:48 AM
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 […]

19.10.1985 | 10:00 AM
Thyroxine induced transformation in sarcoplasmic reticulum of rabbit soleus and psoas muscles.

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 […]