triiodothyronine--reverse and Starvation

Topics: Adult; Catecholamines; Child; Diet; Dietary Carbohydrates; Female; Humans; Male; Nutritional Physiological Phenomena; Pituitary Gland; Starvation; Thyroid Gland; Thyroid Hormones; Thyrotropin; Thyroxine; Triiodothyronine; Triiodothyronine, Reverse; Vanilmandelic Acid

The influence of an inhibitor of iodothyronines' extrathyroidal conversion on T4, T3 and rT3 deiodination by adult pig pituitary and cerebral cortical homogenates has been investigated. The homogenates were incubated with T4, T3 and rT3 in the presence of 5 mM dithiothreitol and evaporated diethyl ether extracts of sera obtained from fed and starved (1-14 days) rabbits. The extracts had no influence either on T4 to T3 or on T4 to rT3 conversion in cerebral cortex. Deiodination of rT3 to 3,3'-T2 in that tissue was significantly inhibited only by the extracts of sera obtained from 4 days starved rabbits. Inner-ring deiodination of both rT3 and T3 was not changed by the extracts got from short-term (1-4 days) fasted animals but was significantly reduced by the extracts from long-term (7-14 days) food-deprived subjects. Pituitary conversion of T4 to T3 was diminished by 35% in the presence of sera extracts gained from 1-9 days fasted rabbits and by about 50% on day 14 of fasting, but only the latter change was statistically significant. Short-term fasting inhibited T4 to rT3 conversion on days 2 and 4. Both deiodinations of rT3 and 5-deiodination of T3 were affected by extracts of sera collected during long-term fasting.

Topics: Animals; Cerebral Cortex; Diiodothyronines; In Vitro Techniques; Iodide Peroxidase; Pituitary Gland, Anterior; Rabbits; Starvation; Swine; Thyronines; Thyroxine; Tissue Extracts; Triiodothyronine; Triiodothyronine, Reverse

To find out whether an inhibitor of extrathyroidal conversion of iodothyronines is present in sera of starved animals, pig liver and kidney homogenates were incubated with T4, T3 or rT3 and dithiotreitol in the presence of evaporated diethyl ether extracts of sera obtained from fed and starved (1-12 days) rabbits. Sera extracts of short-term (1-4 days) starved rabbits caused a significant inhibition of T4 to T3 conversion (54% on day 3) and T4 to rT3 deiodination (52% on day 2) in liver homogenates. Extracts of sera from long-term (8 and 12 days) starved animals diminished only liver T4 to T3 conversion on day 8 and had no influence on liver T4 to rT3 conversion. 5'-deiodination of rT3 (to 3,3'-T2) in liver was gradually decreased by extracts of sera from animals starved during 2-12 days. Liver rT3-5-deiodination (to 3',5'-T2) was significantly impaired on day 4 and totally depressed by long-term starvation. In vitro T3 to 3,3'-T2 conversion in liver was markedly (59-103%) increased by ether extracts of sera from short-term fasted rabbits and considerably inhibited (62-72%) by long-term fasting. T4 to T3 conversion in kidney was significantly influenced by sera extracts obtained neither from short-term fasted rabbits and considerably inhibited (62-72%) by long-term fasting. T4 to T3 conversion in kidney was significantly influenced by sera extracts obtained neither from short-term nor from long-term fasted rabbits but T4-5-deiodination (to rT3) was reduced by sera extracts of short-term fasted animals.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Animals; Glucose; In Vitro Techniques; Iodide Peroxidase; Kidney; Liver; Rabbits; Starvation; Swine; Thyroxine; Triiodothyronine; Triiodothyronine, Reverse

Topics: Acclimatization; Disease; Fasting; Female; Fetus; Humans; Infant, Newborn; Kinetics; Obesity; Pregnancy; Receptors, Cell Surface; Receptors, Thyroid Hormone; Starvation; Temperature; Thyroxine; Triiodothyronine; Triiodothyronine, Reverse

The effect of different thyroid states on glucose homeostasis was investigated during metabolic adaptation to starvation in the conscious unrestrained miniature pig. Moderate hyperthyroidism increased the rate of glucose turnover, whereas hypothyroidism was without effect. Glucose recycling was elevated in hyperthyroid pigs, and reduced after thyroidectomy. Supplementary doses of T4 normalized total glucose recycling. Glucose metabolic clearance rate and pool size were unaffected by thyroid hormones. During starvation serum insulin showed a similar decrease in all thyroid states; glucagon increased in euthyroid and hypothyroid pigs, although it was already elevated in the hyperthyroid fed state. Serum cortisol levels although varying were enhanced in hyperthyroid and hypothyroid-T4-treated pigs. Glucogenic precursor concentration and cumulative urinary N-excretion were increased in hyperthyroid pigs. It is concluded that 1) even a moderate hyperthyroidism produces an increase in glucose turnover and a concomitant acceleration in protein breakdown, and 2) thyroid hormone is essential for the starvation-induced total glucose recycling.

Topics: Animals; Blood Glucose; Glucagon; Hyperthyroidism; Hypothyroidism; Insulin; Kinetics; Lipids; Male; Starvation; Swine; Swine, Miniature; Thyroid Gland; Thyroxine; Triiodothyronine; Triiodothyronine, Reverse

The effects of short-term starvation (up to 5 days) on hepatic ketone body production was investigated in the conscious unrestrained miniature pig in vivo. Starvation induced an increase in arterial free fatty acid concentration (0.2-0.7 mM) with a concomitant elevation in hepatic free fatty acid extraction [-1.4-5.7 mumol/kg. minute),r = 0.53, P less than 0.005]. Ketone body production (sum of acetoacetate + beta-hydroxybutyrate) increased from 1.5 to 5.8 mumol/(kg . minute) in parallel (r = 0.71, P less than 0.0005). During starvation arterial insulin levels decreased, glucagon increased, cortisol remained unchanged and a "low T3 state' was observed. These data differ in some aspects from those reported for humans and dogs. Thus a species-specific variation in the fuel economy of the pig's body is proposed.

Topics: Animals; Fatty Acids, Nonesterified; Glucagon; Insulin; Ketone Bodies; Lipid Metabolism; Liver; Male; Starvation; Swine; Thyroxine; Triiodothyronine; Triiodothyronine, Reverse

Topics: Animals; Diiodothyronines; Dithiothreitol; Edetic Acid; Hyperthyroidism; Hypothyroidism; Iodide Peroxidase; Kinetics; Liver; Male; NADP; Peroxidases; Propylthiouracil; Rats; Starvation; Thyroidectomy; Thyronines; Triiodothyronine; Triiodothyronine, Reverse

During starvation the response of TSH to TRH decreases in many subjects. This could be due to an increased sensitivity to TSH secretion to circulating thyroid hormones. To study this hypothesis, 13 subjects were starved twice for 2-day periods. After both starvation periods, a standard TRH test (200 micrograms TRH, iv) was performed; during 1 starvation period 15 micrograms T3 were injected iv 24 h before the TRH test. The TRH tests were also performed while on normal nourishment, once without pretreatment and once 24 h after the iv injection of 15 micrograms T3. The spontaneous decrease of the TSH response to TRH was seen in 10 of 13 subjects. In these 10 subjects it decreased from 18.0 +/- 1.9 to 9.7 +/- 1.2 microU/ml (mean +/- SEM; P < 0.001). The additional inhibition of the TRH test with T3 was small compared with the one observed under normal conditions. In starvation, T3 decreased the maximal TSH response from 9.7 +/- 1.2 to 8.4 +/- 1 microU/ml (P = NS), while during the control period the maximal TSH response fell from 18.0 +/- 1.9 to 11.4 +/- 1.3 microU/ml (P < 0.001). These data indicate a diminished effectiveness of T3 in inhibiting TSH secretion and are consistent with the hypothesis of a more generalized resistance of target organs to T3 during starvation in man.

Topics: Adult; Blood Glucose; Body Weight; Female; Humans; Hydroxybutyrates; Kinetics; Male; Prolactin; Starvation; Thyrotropin; Thyrotropin-Releasing Hormone; Triiodothyronine; Triiodothyronine, Reverse

Topics: Animals; Bile; Chromatography, High Pressure Liquid; Diiodothyronines; Male; Rats; Starvation; Thyronines; Thyroxine; Triiodothyronine; Triiodothyronine, Reverse

The effect of starvation on thyroid hormones was studied during a starvation period of 48 h in 10 young bulls. Mean thyroxine degradation rate decreased from K/day 0.32 during feeding to 0.23 during fasting. Mean plasma concentration of T4 decreased to 75% of normal, and it was calculated that the mean thyroxine secretion rate during the starvation period was 24% of normal. Plasma concentration of free thyroxine decreased to 54% of normal, indicating that the concentration of binding protein was not decreased. T3 and reverse T3 decreased to about 60% of normal. This indicated a parallel decrease in the secretion of all 3 hormones. We did not find evidence of an inactivating pathway for T4 as has been shown in humans during starvation. TSH decreased to 85% of normal.

Topics: Animals; Cattle; Male; Starvation; Thyrotropin; Thyroxine; Time Factors; Triiodothyronine; Triiodothyronine, Reverse

Caloric deprivation (feeding 50 and 25% of the original maintenance requirement for 126 days), followed by overnutrition (feeding 133 and 200% of the original maintenance requirement) for 37 days, were induced in 7 adult sheep. Before and after the periods of undernutrition and after overnutrition the animals were fasted (total energy withdrawal) for 5 days. Energy- and nitrogen-balances were determined and related to concentrations of thyroxine (total: T4; free: FT4), 3,5,3'-triiodothyronine (total: T3; free FT3) and 3,3',5'-triiodothyronine (reverse T3,rT3). caloric deprivation led to decreased T3 and FT3 levels, overnutrition to increased T3 and FT3 concentration. T3 was significantly correlated with energy- and nitrogen-balances (r = 0.73 and 0.71, respectively; P less than 0.001). T4 and FT4 behave similar to T3, but correlations between T4 levels and energy- and nitrogen-balances were low. In contrast to T3, rT3 levels increased during energy withdrawal and decreased during overnutrition. After an overnutrition for months, an additional fasting for 5 days did not increase rT3 levels, however, rT3 was significantly correlated with energy- and nitrogen-balances (r = -0.50 and -.50, respectively; P less than 0.01).

Topics: Animal Nutritional Physiological Phenomena; Animals; Body Weight; Energy Intake; Energy Metabolism; Male; Nitrogen; Sheep; Starvation; Thyroid Hormones; Thyroxine; Triiodothyronine; Triiodothyronine, Reverse

To investigate the effect of nutrition on catecholamine metabolism, four subjects were initially energy-restricted for three weeks and then refed a high-carbohydrate diet, salt intake being kept constant. Energy restriction was associated with a reduction in plasma noradrenaline, urinary excretion of 4-hydroxy 3-methoxymandelic acid (HMMA), serum triiodothyronine (T3), systolic and diastolic pressures, pulse and resting metabolic rate (RMR). Within 72 hours of refeeding there was a significant increase in the urinary excretion of HMMA, serum T3, blood pressure, pulse and the RMR. Thus catecholamine metabolism is affected both in semistarvation and during the first few days of refeeding.

Topics: Adult; Blood Pressure; Catecholamines; Female; Food; Humans; Middle Aged; Norepinephrine; Obesity; Pulse; Starvation; Thyroid Gland; Thyroxine; Triiodothyronine; Triiodothyronine, Reverse; Vanilmandelic Acid

In order to compare, in vitro, the TSH suppressive effects of iodothyronines, rat pituitary quarters were first preincubated with T4, T3, rT3, or 3,3'-diiodothyronine (T2) in Gey and Gey buffer containing 1% bovine serum albumin for 2 h at 37 C and then incubated at 37 C for 1 h with the iodothyronine under study and TRH. TSH released into the medium during incubation was compared to that released by control pituitary fragments, which were not exposed to iodothyronines. All four iodothyronines (T3, T4, rT3, and T2) were able to significantly inhibit the TRH-induced release of TSH from pituitary fragments in a dose range of 0.015-2.2 microgram/ml. However, much larger doses of sodium iodide (1.25 mg/ml) and diiodotyrosine (10 and 30 microgram/ml) had no significant effect on the release of TSH. Among T3, rT3, and T4, T3 was the most potent and rT3 was the least potent. The relative potency of T3:T4:rT3 appeared to be approximately 100:12:1 when estimated from the lowest doses that caused significant inhibition of TRH-induced release of TSH, and approximately 100:6:0.5 when estimated from the doses that caused 50% inhibition of TSH release; the TSH inhibiting potency of T2 was similar to that of rT3. The activity of T4 could not be explained entirely on the basis of contamination of T4 with T3 or by in vitro conversion of T4 to T3. Similarly, the available data suggested that rT3 and T2 possess some, albeit modest, intrinsic TSH-Suppressive activity. TSH-inhibiting activities of T3, T4, and rT3 were also studied using pituitary fragments from starved and iodine-deficient rats. There was no evidence of a change in the sensitivity of the thyrotroph to either T3 or T4 in starvation. Similarly, comparison of the responses to several doses of rT3 did not indicate any significant abnormality in the sensitivity of the thyrotroph to rT3 in starvation or iodine deficiency. However, comparison of the TSH-suppressive effects of T4 in the iodine-deficient and normal rat indicated a significant increase in the sensitivity of the thyrotroph to T4 in iodine deficiency. A similar trend was also evident in the effect of T3 in iodine deficiency, but it fell short of statistical significance.

Topics: Animals; Diiodothyronines; In Vitro Techniques; Iodine; Male; Pituitary Gland, Anterior; Rats; Starvation; Thyronines; Thyrotropin; Thyrotropin-Releasing Hormone; Thyroxine; Triiodothyronine; Triiodothyronine, Reverse

The effect of starvation on thyroid hormone metabolism was studied in monkey hepatocarcinoma monolayer cultures. Nonphenolic ring monodeiodination of thyroxine, 3, 5, 3'-triiodothyronine and 3, 3'-diiodothyronine was accelerated. Since phenolic ring deiodination of 3, 3',5'-triiodothyronine (reverse T3) was unaffected, this metabolite accumulated in the medium during thyroxine metabolism. This suggests that increased serum reverse T3 in malnourished humans may be caused by enhanced deiodination of thyroxine rather than decreased rT3 catabolism.

Topics: Animals; Cell Line; Glucose; Haplorhini; Starvation; Thyroid Hormones; Thyroxine; Triiodothyronine; Triiodothyronine, Reverse

The effect of starvation on the peripheral metabolism of rT3 was evaluated in four obese euthyroid patients. During starvation, the serum rT3 concentration increased by 69% while the MCR of rT3 decreased in all four patients from control values of 96 +/- 23 (mean +/- SD) to 68 +/- 17 liters/70 kg . day, resulting in a slight increase in the mean production rate of rT3. These findings are in contrast to the marked decrease in T3 production rate associated with fasting, indicating that inner and outer ring deiodination of T4 can be varied independently.

Topics: Female; Humans; Metabolic Clearance Rate; Obesity; Radioimmunoassay; Starvation; Thyroxine; Triiodothyronine; Triiodothyronine, Reverse

Topics: Animals; Male; Metabolic Clearance Rate; Rabbits; Starvation; Thyroxine; Triiodothyronine; Triiodothyronine, Reverse