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Biomedical subjects

E Decuypere

Publications and source records attributed to E Decuypere.

231 records · Page 13Linked to original sources
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

Effect of dehydration, haemorrhage and oviposition on serum concentrations of vasotocin, mesotocin and prolactin in the chicken.

Serum concentrations of arginine vasotocin (AVT), mesotocin and prolactin were determined by radioimmunoassay in Rhode Island Red chickens during and after dehydration, haemorrhage and oviposition. During dehydration increased circulating levels of AVT, mesotocin and prolactin were found. As water deprivation proceeded, marked differences were observed. After an initial rise in serum AVT, mesotocin and prolactin levels during mild and moderate dehydration, concentrations of both AVT and prolactin tended to normalize during continued water deprivation, while those of mesotocin remained high throughout the whole dehydration experiment with the highest at the end of the water-deprivation period. Removal of 5 ml blood at intervals of 10 min during six consecutive time-periods did not affect serum osmolality and circulating levels of AVT and prolactin, but slightly increased mesotocin. These results suggest an osmoregulatory role for AVT and prolactin, whereas mesotocin may be involved in volume control. Finally, 1 min after oviposition, control values of 19.5 +/- 3.4 pmol AVT/1 (n = 9) were raised more than sevenfold to 142.9 +/- 12.5 pmol/l (n = 11). Thereafter, a decline occurred with a half-life for AVT of 13 min with raised serum levels up to 31 min after oviposition. In contrast, the serum concentrations of mesotocin and prolactin remained unaffected by oviposition.

Animals↗
PubMed1983

The presence of vasotocin and mesotocin in serum and the hypothalamo-neurohypophyseal axis of chick embryos before hatching and in posthatch chicks.

Decreasing hematocrit values were observed in chick embryos, from Day 17 to 1 day posthatching. Arginine vasotocin (AVT) and mesotocin (MT) were determined radioimmunologically in serum, neural lobe, and hypothalamic tissue. Serum levels of AVT and MT were significantly increased on Day 18 of incubation compared to Day 17. Thereafter AVT levels decreased, reaching at hatching levels even below Day 17. Serum MT remained elevated on Day 19, but decreased thereafter to the concentration values of Day 17. The amount of AVT in the preoptic hypothalamus and infundibulum was maximal on Day 19, whereas in the neural lobe the maximum was attained on Day 20. The MT content of the infundibulum and neural lobe reached a maximum plateau on Day 18. These results suggest that a stimulation of the hypothalamo-neurohypophyseal axis in the chick embryo occurs at the end of incubation. A possible causal relation with the observed decreasing hematocrit values is discussed.

Animals↗
PubMed1983

Effects of glucocorticoids on circulating concentrations of thyroxine (T4) and triiodothyronine (T3) and on peripheral monodeiodination in pre- and post-hatching chickens.

The administration of either glucocorticoids (dexamethasone or corticosterone) or adrenocorticotropic hormone (ACTH) to chicken embryos was followed by increase in the circulating concentration of triiodothyronine (T3), the T3 to thyroxine (T4) ratio and the activity of liver T4-5' monodeiodinase. No consistent changes in plasma concentrations of T4 or GH were observed. In post-hatching chicks, corticosterone and dexamethasone depressed the circulating concentrations of both T4 and T3. Iopanoc acid, an inhibitor of liver T4-5' monodeiodinase, elevated plasma concentrations of T4 and depressed those of T3 in both chicken embryos and young chicks. It is suggested that glucocorticoids affect circulating concentrations of T4 and T3 both by affecting the activity of the liver T4-5' monodeiodinase and by influencing the hypothalamo-pituitary axis.

Adrenocorticotropic Hormone↗
PubMed1983

Variation in the release of thyroxine, triiodothyronine and growth hormone in response to thyrotrophin releasing hormone during development of the domestic fowl.

In newly hatched chicks, TRH administration was followed by increased circulating concentrations of growth hormone (GH), thyroxine (T4) and 3,3',5-triiodothyronine (T3). Little change in the circulating concentration of 3,3',5'-triiodothyronine (rT3) was however observed. The effect of TRH on the circulating concentration of GH was not found in chick embryos at 17 or 19 days of incubation but was observed during pipping. The T4 response was maximal in newly hatched chicks and present in 17 and 19 days embryos. The magnitude of the T3 responses increased with age while that of T4 decreased.

Age Factors↗
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

Antagonism of serum tri-iodothyronine changes after injections of prolactin in the domestic fowl before and after hatching.

The influence of an intravenous injection of ovine prolactin on circulating levels of thyroid hormones was studied in Rhode Island Red embryos and chicks after hatching. In the chick embryo, 2 h after injection of 0.1 microgram prolactin (on incubation day 19), serum triiodothyronine (T3) increased threefold; after 10 or 100 micrograms prolactin (on incubation day 18) serum T3 increased 15- to 25-fold. These profound increases were not observed in chicks after hatching. Serum concentrations and thyroid content of thyroxine (T4) in embryos and chicks of all ages studied were not influenced by the prolactin injections. Maximal serum concentrations of reverse T3 (rT3) were found on incubation day 18 (110.25 +/- 23.36 pmol/l; 71.66 +/- 15.18 pg/ml; n = 8), whereas after hatching no rT3 could be detected. An injection of 10 micrograms prolactin on day 18 depressed serum rT3 after 2 h to 5.68 +/- 3.20 pmol/l (3.69 +/- 2.08 pg/ml; n = 8; P less than 0.001); the effect of 100 micrograms prolactin was less pronounced. After hatching, chronic administration of prolactin resulted in decreased serum levels of T3, but not of T4, and hypertrophy of the follicles in the thyroid gland. It is concluded that prolactin plays a major role in the maturation of embryonic thyroid metabolism by changing the T4-5-monodeiodination into a T4-5'-monodeiodination. The hypertrophy of the thyroid gland observed after hatching following prolonged prolactin administration may be due to decreased negative feedback of T3 on the hypophysis.

Animals↗
PubMed1982

Posthatch growth and development of a circadian rhythm for thyroid hormones in chicks incubated at different temperatures.

Rhode Island Red eggs were incubated at 33.8 and 376.8 C from day 17 until hatching under a photoperiod of 12L:12D. After hatching, the same light schedule was maintained, and all chicks were raised at 25 +/- 1 C and 50% relative humidity. Infrared lamps were used up to 7 days. Pipping and hatching occurred significantly later in chicks incubated at 33.8 C, and the interval between events was prolonged. Chicks of the 33.8 C group had a lower body weight on day 3 posthatch, but relative growth was accelerated from the 2nd week on, resulting in equal weights on day 36 for males and day 43 for females. Circadian mean serum levels of triiodothyronine (T3) during a 24-hr period (blood sampling every 4 hrs) were positively correlated with relative growth rate in both temperature groups, whereas thyroxine (T4) correlated with weight and age. Body weight of females remained lower from day 9 (33.8 C) and 22 (37.8 C) on. In the 37.8 C group, a significant fit of serum T4 to a sinusoidal curve (observed during a 24-hr cycle) was present for both sexes from day 16 on; this was true from day 32 on in the lower incubation temperature group. The acrophases of this rhythm occurred at about 0500 hr (1100 hr after onset of the dark period) and did not differ between temperature groups of sexes. A significant fit to a sinusoidal curve for the T3 data was only possible for both sexes and temperature groups on days 112 and 128 with an acrophase at about 1700 hr. Differences in growth rate between temperature groups can be related to differences in mean serum levels of T3. Differences in growth rate between sexes were not parallelled by differences in levels of thyroid hormones or acrophases, but males did not have a higher amplitude in the sinusoidal T4 rhythm compared to females. This difference was more pronounced in the 37.8 C group.

Animals↗
PubMed1982

Effect of blocking T4-monodeiodination on hatching in chickens.

Chick embryos were injected with iopanoic acid (IOP) on either day 17 or 18 of incubation, and radioimmunoassays of triiodothyronine (T3) and thyroxine (T4) in serum and thyroid glands were performed from day 19 on through pipping and hatching and 1 day after hatching. The IOP was able to block T4 to T3 conversion in chick embryos from day 19 of incubation. Blocking T4 conversion did not delay hatching significantly, nor did it affect embryonic mortality significantly. Yolk sac retraction was not affected at hatching. A rise in serum reverse T3 (rT3) and T4 was observed after IOP administration. The rise in T4 could not be explained solely by a decreased T4 conversion. The results indicated that peripheral monodeiodination occurs in the late chick embryo.

Animals↗
PubMed1981

[Effect of the length of egg storage on duration of incubation and serum thyroid hormone levels in the chick embryo].

After storage at 12 degrees C and 90 to 95 p. 100 humidity, for periods of 1, 5, 8, 11 and 14 days, Rhode Island Red eggs were incubated at 37.5 degrees C and 60 p. 100 humidity. Whatever the total duration of incubation within the experimental conditions, maximal serum levels of triiodothyronine (T3) and thyroxine (T4) were obtained the day of pipping. Embryos having perforated the air-space membrane the day before pipping showed elevated serum T3, but not T4, levels as compared to embryos without a perforation. The lower serum T3 levels, obtained at pipping, after longer periods of preincubation storage are discussed in relation to other experiments on perinatal changes in serum iodo-hormones.

Animals↗
PubMedDate not supplied

Alterations in thyroid hormone physiology induced by temperature and feeding in newly hatched chickens.

In the chicken the transition of a poikilotherm to a homeotherm reaction upon cold exposure takes place in the perinatal period between pipping and hatching. However, newly hatched chicks cannot maintain their body temperature within narrow limits after cold exposure. The fact that relatively little attention was payed on the role of thyroid hormones in the thermoregulatory reaction to cold of young chicks was probably due to the hypothetically long latention time that was thought to be necessary to bring about changes in secretory activity by cold stimulation. However, more recently, rapid changes (within hours) of thyroid hormone concentrations upon cold exposure were described in the chickens and the quail. In this study, changes in circulating T3 and T4 concentrations upon cold exposure of young chicks during the first two weeks were followed, that means during the period wherein NST (non-shivering thermogenesis), if it exists at all, should be progressively replaced by ST (shivering thermogenesis). Because of the importance of feeding condition on thyroid hormone levels, the experiments were carried out with and without a preceeding fasting period. In all experiments a short-term cold exposure of young chickens (1-11 days) fed ad lib decreased T3 but increased T4 levels while a reversed picture was found after short cold exposure of the fasted animals. However, after prolonged cold stimulus (15 degrees C) of young chickens fed ad lib, plasma T3 was also significantly elevated over that of controls whereas T4 levels returned to normal values. A prolonged warm treatment (37 degrees C) of young chickens fed ad lib resulted in significantly lower T3 and higher T4 concentrations. After a prolonged cold treatment no differences in T4 or T3 response upon TRH were found whereas the warm treatment abolished these responses upon TRH. However, a cold treatment at the stage of incubation during which the hypothalamo-hypophyseal control of thyroid function is established (dag 10-14) enhanced the T4 response to TRH with a long lasting effect extending to the posthatch period. Since T3 is thought to be the active form of thyroid hormones with regard to thermopoiesis we have studied more specifically the effect of blocking peripheral conversion of T4 on thermoregulatory abilities in young chicks and the influence of temperature treatment on monodeiodination capacity. The lower rectal temperatures following the interference with the peripheral monodeiodination of T4, the effect being more pronounced at the lower ambient temperature, are indicative for a preponderant role of T3 on thermogenesis.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗