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

Abstract

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.

Thyroid hormone does not induce maturation of embryonic chicken cardiomyocytes in vitro

“…Sharp rises in T 3 prior to hatching have been reported in chickens (Thommes and Hylka 1977;Christensen et al 1995) with a pattern very similar to that in sheep and humans (Polk 1995). In sheep, the T 3 surge prior to birth is driven by glucocorticoids during natural parturition (Klein et al 1978) or when exogenous cortisol is administered to induce parturition (Thomas et al 1978), which is similar to the corticosterone induced T 3 surge also seen in chickens (Decuypere et al 1983;Kuhn et al 1984).…”

Effect of Single or Combined Climatic and Hygienic Stress in Four Layer Lines: 2. Endocrine and Oxidative Stress Responses

“…and levels fall immediately after heat exposure (Uni et al, 2001). The importance of the thyroid gland in adaptation to heat stress is related to the central role that thyroid hormones play in regulation of metabolic rate of birds (Kü hn et al, 1984;Decuypere and Kü hn, 1988). A more common reaction to (different) stressors is the increase of free radicals in the body: oxidative stress.…”

Thyroid transcriptome analysis reveals different adaptive responses to cold environmental conditions between two chicken breeds

“…T3 and T4 are produced by the thyroid gland and are primarily responsible for the regulation of metabolism. Considerable evidence suggests that thyroid gland activity and/or serum TH concentrations increase when birds become acclimated to cold environments [ 8 , 9 , 15 – 17 ]. Previous studies [ 10 – 12 , 49 – 51 ] have also demonstrated that animals living in cold regions have higher T3 and/or T4 levels than their counterparts living in warmer regions.…”

“…THs are produced by the thyroid gland, which is organized into follicles filled with a secretory substance, colloid, and made up of cuboidal epithelial cells. Although investigations of avian thyroid function are less comprehensive than those on mammals, cold environments have been shown to enhance heat production and T3 concentrations in birds [ 8 – 11 ], dogs [ 12 ], and humans [ 13 , 14 ]. Thyroid size and activity were also shown to increase in birds acclimated to low temperatures [ 15 – 17 ].…”