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Biomedical subjects

P Rudas

Publications and source records attributed to P Rudas.

At least 55 records · Page 3Linked to original sources
PubMed1986

Comparison of type I 5'-deiodination of thyroxine and of reverse-triiodothyronine in rat and chicken liver homogenates.

The characteristics of 5'-deiodination in the chicken liver have been compared to those in the rat. Using 6-n-propyl-2-thiouracil (PTU) at 1 mM in vitro, it was shown that, in accordance with former in vivo studies, only type I 5'-deiodinase exists in the liver of the chicken. When PTU was used in a concentration (10 microM) close to its Ki species differences could be demonstrated as for PTU sensitivity. 5'-Deiodinase in the chicken liver was more susceptible against the inhibitor. The early thiol-independent phase of deiodination was longer in the chicken than in the rat. Reverse-triiodothyronine (r-T3) seemed to be a more suitable substrate for this enzyme in the chicken when compared to either T4 degradation or r-T3 degradation in the rat. It is concluded that major characteristics of 5'-deiodination in the chicken are similar to those in the rat; however, the slight variances observed might explain some species differences found earlier.

Animals↗
PubMed1986

Acute changes of the conversion of thyroxine to triiodothyronine in hypophysectomized and thyroidectomized chickens exposed to mild cold (10 degrees).

The effect of acute cold (10 degrees) exposure on the tissue level of triiodothyronine (T3) and on the conversion of thyroxine (T4) to triiodothyronine, both in vitro and in vivo, has been investigated in young chickens previously thyroidectomized or hypophysectomized. It was found that cold exposure stimulates T4 to T3 conversion both in vivo and in vitro not only in intact animals but also in hypophysectomized and thyroidectomized ones. It is concluded that peripheral metabolism of thyroid hormones represents a self-standing but not sole route of adaptation to changes in environmental temperature.

Animals↗
PubMed1985

Thyroxine, triiodothyronine, reverse-triiodothyronine, and other physiological characteristics of periparturient cows fed restricted energy.

Eighty-six cows were assigned to two equal groups with group A fed according to National Research Council recommendations for total digestible nutrients for the 8 wk before parturition and group B was fed 21% higher energy in the first 6 wk and 15% higher in the last 2 preparturient wk. Thyroxine in blood serum decreased in both groups 14 days before and on the day of delivery. It was significantly lower in group A. Findings were similar with triiodothyronine. Blood serum concentrations of reverse-triiodothyronine of group A was significantly higher in group A on day 28 and 14 than group B before delivery. Energy intake had little influence on the serum concentrations of other constituents (albumin, total protein, immunoglobulin G, total and free cholesterol, nonesterified fatty acids). Restricted energy intake that does not alter thyrotropin-thyrotropin-releasing hormone secretion results in higher rate of production of reverse-triiodothyronine and in decreased serum concentration of triiodothyronine. Slight changes of energy balance might be indicated readily by reverse-triiodothyronine concentration in blood serum.

Animal Nutritional Physiological Phenomena↗
PubMed1984

Hormonal and environmental interactions on thyroid function in the chick embryo and posthatching chicken.

Recent research has focused on developmental changes in thyroxine (T4) metabolism as well as hormonal and environmental interactions upon peripheral monodeiodination. Toward the end of incubation and the time of air space membrane perforation, concentrations of 3,3', 5'-triiodothyronine T3 increase more rapidly than T4, while reverse T3 (rT3) decreases. Administration of glucocorticoids or prolactin (hormones known to increase at the end of incubation) 2 to 3 days prior to air chamber perforation can induce this change in T4 metabolism. Attention has been focused on two major environmental factors that influence T4 concentrations in posthatch chicks. T4 disappearance rate and peripheral T4 conversion are adjusted during thermal acclimation. More T3 will be generated in cold-exposed chickens, and more rT3 will be produced at higher ambient temperatures. Peripheral T4 metabolism acts as an independent regulation pathway but accompanies changes in hypothalamo-thyroid activity. Changes in thyroid hormone levels following ambient temperature changes, therefore, are the result of a balance between central and peripheral control mechanisms, depending on age of the animal and degree and duration of the temperature change. In the hen, feeding also plays an important role in the regulation of the absolute levels and daily rhythms of plasma thyroid hormones. Fasting results in an increase in circulating T4 levels, but a decrease in T3 levels, owing to a lower 5'deiodinase activity, and also abolishes the circadian circulating T3 rhythm.

Acclimatization↗
PubMed1984

Studies on the conversion of thyroxine to 3,5,3'-triiodothyronine in normal and thyroidectomized chickens.

The possibility of conversion of L-thyroxine (T4) to L-3,5,3'-triiodothyronine (T3) and to 3,3',5'-triiodothyronine (reverse-T3, r-T3) has been investigated in chickens. Reverse-T3 could not be detected in normal animals. Both thyroidectomized and normal animals were able to convert exogenous T4 to T3. The administration of propylthiouracyl blocked this conversion to a greater extent than had been expected from the data on mammals. The conversion ratio is higher than in any other species reported in the literature. Data suggest that, as a result of the adaptation of the peripheral deiodination, thyroidectomized animals were able to convert more T4 to T3 than were normal ones.

Animals↗
PubMed1983

Abnormalities in the plasma concentrations of thyroxine, tri-iodothyronine and growth hormone in sex-linked dwarf and autosomal dwarf White Leghorn domestic fowl (Gallus domesticus).

Plasma concentrations of GH were high in young birds (2-12 weeks old) and low in older birds (15 and 18 weeks old) in the control Cornell K strain of White Leghorn fowl. There was little variation in the plasma concentrations of tri-iodothyronine (T3) and thyroxine (T4) with age in this strain. Similar patterns of plasma hormone concentrations with age were observed in autosomal recessive dwarf chickens. However, the plasma concentrations of T3 and T4 tended to be depressed while that of GH was raised. There was little age-related change in the plasma concentrations of GH, T3 and T4 in sex-linked recessive dwarf chickens. Throughout growth and maturation the plasma concentrations of T3 in the sex-linked dwarf birds were less 40% of those observed in the control strain. Plasma concentrations of T4 tended to be raised relative to the control in the sex-linked dwarf at each age examined. The plasma concentration of GH was raised only in older (12, 15 and 18 weeks old) sex-linked dwarfs. Liver T4-5' monodeiodinase activity was slightly depressed in autosomal dwarf chickens and very low in the sex-linked dwarf fowl. Neither autosomal nor sex-linked dwarfism appears to be due to hypopituitarism. It is probable that the depressed liver 5' monodeiodinase activity and the concomitant low plasma concentrations of T3 are a causative factor in the reduced growth and stature of the sex-linked dwarf chicken.

Animals↗
PubMed1983

Influences of growth hormone on glucose uptake by avian adipose tissue.

The uptake of glucose by chicken adipose tissue was determined in vitro using adipocytes or adipose explants using 14C orthomethyl glucose (OMG). The net uptake of 14C-OMG was enhanced by preparations of bovine and chicken GH and by insulin. Insulin and growth hormone (GH) (chicken or bovine) stimulated the uptake of 14C-OMG occurring in 1 hr by adipose tissue (both adipocytes and explants) from chicks hypophysectomized for 5 days but not from sham-operated birds. Tissue preincubated with GH became refractory to GH stimulation of 14C-OMG uptake. The short-term (2 to 15 min) uptake of 14C-OMG by explants was, however, stimulated by the bovine GH and insulin in tissue from sham-operated but not hypophysectomized chicks. Surprisingly, net decreases in 14C-OMG uptake, in the presence of bovine GH, were observed with adipose tissue (adipocytes and explants) from hypophysectomized birds, when incubated in the presence of epinephrine, and from hypophysectomized birds immediately following surgery.

3-O-Methylglucose↗
PubMed1980

Interrelationship between thyroid and gonadal function in female Japanese quail kept under short and long photoperiods.

The concentrations of progesterone, testosterone, oestrone, oestradiol, thyroxine (T4) and tri-iodothyronine (T3) in the plasma of 8-week-old female Japanese quail exposed to short (6 h light: 18 h darkness; 6L:18D) and long (18L:6D) photoperiods were determined by radioimmunoassay after ovariectomy, thyroidectomy and treatment with T4. In birds exposed to short days treatment with T4 slightly increased both the concentrations of progesterone, oestrone and oestradiol in plasma and the weight of the ovaries, while ovariectomy increased the testosterone and oestradiol concentrations in plasma. In birds exposed to a long photoperiod, treatment with T4 reduced the level of all the sex steroids measured, ovarian weight and egg production. Thyroidectomy increased the concentration of progesterone in plasma and decreased that of oestradiol. Photostimulation decreased the concentration of T4 in plasma of intact birds while it was ineffective in ovariectomized birds. Ovariectomy did not influence the concentration of T4 in the plasma of birds exposed to either long or short days but the level of T3 was slightly increased in the plasma of birds exposed to short days and markedly increased in the photostimulated group. It would seem, therefore, that whilst there is a distinct relationship between thyroid function and that of the ovary the relationship between ovarian and thyroid function is less marked.

Animals↗
PubMedDate not supplied

Rapid decrease of the peripheral deiodination of thyroxine in malabsorption syndrome in artificially inoculated broilers.

Thyroid function of broilers inoculated with the intestinal homogenate from birds from a field case of malabsorption syndrome was investigated during the first 2 days postinoculation. In one experiment, different amounts of the inoculum were applied to see if there exists a dose-response relationship. As early as 3 hours after inoculation, there was a significant drop in the serum level of triiodothyronine and in the activity of the liver 5'-deiodinase (type I). Type II deiodinase activity was less impaired. A minimum of 0.3 ml of inoculum was effective, whereas 0.05 ml of the same homogenate elicited a significant (P less than 0.01) drop in liver deiodinase activity. These findings underline the importance of thyroid impairment in the pathogenesis of malabsorption syndrome.

Animals↗
PubMedDate not supplied

Decreased thyroxine, triiodothyronine, and 5'-deiodination levels in malabsorption syndrome (runting or stunting syndrome) in artificially inoculated broilers.

The effect of malabsorption syndrome (stunting or runting syndrome) on the thyroid function of broilers was investigated in control and inoculated broilers from 1 to 29 days of age. The broilers were infected at 1 day of age with intestinal homogenates from chickens naturally suffering from this syndrome. The body weight of inoculated broilers was significantly (P less than 0.05) lower 1 week after inoculation than that of controls. The level of thyroxine in the serum of inoculated birds was lower (P less than 0.05) from day 6 through the remainder of the trial. The level of triiodothyronine of inoculated birds was depressed (P less than 0.05) on day 4, but 1 week later it returned to normal. The earliest phenomenon indicative of disturbance of thyroid function was the significant depression of 5'-deiodination in liver homogenates of inoculated broilers as early as day 2. It is concluded that thyroid function is one of the earliest targets of this syndrome.

Animals↗