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Serotonin effect on deiodinating activity in the rat.
No full textSerotonin (5-HT) and thyroid hormones are part of a complex system modulating eating behaviour and energy expenditure. 5-Deiodinase (5-D) converts the relatively inactive thyroxine (T4) to triiodothyronine (T3), and its activity is an indirect measure of T3 production in peripheral tissues, particularly in the brain, intrascapular brown adipose tissue (IBAT), heart, liver, and kidney. We evaluated the effect of 5-HT on 5'-D activity during basal conditions and after short (30 min) cold exposure (thyroid stimulating hormone stimulation test, TST). 5'-D activity was assessed in the liver, heart, brain, kidney, and IBAT. TST increases 5'-D activity in the brain, heart, and IBAT and decreases it in kidney, leaving it unchanged in the liver. 5-HT alone did not modify 5'-D activity in the organs under study but decreased it in the IBAT, heart, and brain when injected before the TST was administered. Our results confirm the important role of 5-HT in thermoregulation, given its peripheral site of action, in modulating heat production controlling intracellular T3 production. These effects are more evident when heat production is upregulated during cold exposure in organs containing type II 5'-D, such as the brain, heart, and IBAT, which are able to modify their function during conditions that alter energy balance. In conclusion, 5-HT may also act peripherally directly on the thyroid and organs containing type II 5'-D, thus controlling energy expenditure through heat production
Changes in eating behavior and thermogenic activity following inhibition of nitric oxide formation
No full textTriiodothyronine deiodinating activity in brown adipose tissue after short cold stimulation test in trained and untrained rats.
No full textInterscapular brown adipose tissue (IBAT) activity is controlled by sympathetic nervous system, and factors that influence thermogenesis appear to be centrally connected to the sympathetic outflow to IBAT. Cold exposure produces a rise in BAT temperature, which is associated with an increased thyroid activity, elevated serum levels of 3,5,3'-triiodothyronine (T3), and an increased rate of T3 production. This study evaluated the effect of swimming training on 5'-triiodothyronine deiodinase (5'-D) activity in IBAT under normal environmental conditions and after short (30 min) cold exposure (TST stimulation test). 5'-D activity is lower in trained rats at basal condition, and TST increases 5'-D in IBAT of both untrained and trained rats. However, this increase is lower in trained rats. Training reduces the deiodinating activity in normal environmental conditions as well as after short cold exposure. Probably, other compensatory mechanisms of heat production are active in trained rodents
Chronic peripheral administration of serotonin inhibits thyroid function in the rat.
No full textWe studied the effect of chronic intraperitoneal (ip) administration of serotonin (5-HT) and thyroid function. We injected daily intraperitoneally for 10 days different doses of 5-HT, and measured plasma thyroid hormones and TSH levels. There was a decrease in the plasma levels of T3 and T4 with medium doses of 5-HT (0.2 and 0.4 mg/Kg bw for T3, and 0.2 for T4). No effects were evidenced on the plasma levels of TSH. In normal environmental conditions, the site action of 5-HT outside the blood-brain barrier is active when the 5-HT is injected at defined doses. This is probably a result of down-regulation independent of the hypothalamus-pituitary-thyroid axis
Deiodinating activity in the brown adipose tissue of rats following short cold exposure after strenuous exercise.
No full textInterscapular brown adipose tissue (IBAT) activity is controlled by the sympathetic nervous system, and factors that influence thermogenesis appear to act centrally to modify the sympathetic outflow to IBAT. Cold exposure produces a rise in IBAT temperature as a result of the increase in sympathetic outflow to IBAT. This is associated with an increased thyroid activity. 3,5,3'-triiodothyronine (T3) and T4 levels increase during strenuous exercise, and, at the end of the exercise bout, a decrease of T3 and T4 levels, with an increase in TSH during the following 4-5 days, is seen. We evaluated the effect of strenuous exercise on 5'-deiodinase (5'-D) activity in IBAT in normal environmental conditions and after short (30 min) cold exposure. 5'-D activity is lower in rats at basal condition. Short cold exposure (SCE) increases 5'-D in IBAT both in exercising rats and in sedentary rats. However, this increase is lower in exercising animals. Strenuous exercise can reduce 5'-D activity in normal environmental conditions and after SCE. Probably, other compensatory mechanisms of heat production are active in exercising rodents
Sucrose rich diet modifies thermogenic response to injection of muscimol into the posterior hypothalamus in the rat
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